WIP

Nathan Sobo created

Change summary

Cargo.lock                             |  311 ++
gpui/Cargo.toml                        |    5 
gpui/src/app.rs                        | 3179 ++++++++++++++++++++++++++++
gpui/src/elements/align.rs             |   68 
gpui/src/elements/constrained_box.rs   |   67 
gpui/src/elements/container.rs         |  358 +++
gpui/src/elements/empty.rs             |   45 
gpui/src/elements/event_handler.rs     |   69 
gpui/src/elements/flex.rs              |  201 +
gpui/src/elements/label.rs             |  154 +
gpui/src/elements/line_box.rs          |   84 
gpui/src/elements/mod.rs               |   80 
gpui/src/elements/stack.rs             |   65 
gpui/src/elements/svg.rs               |   81 
gpui/src/elements/uniform_list.rs      |  226 +
gpui/src/fonts.rs                      |  298 ++
gpui/src/lib.rs                        |   11 
gpui/src/platform/mod.rs               |    2 
gpui/src/presenter.rs                  |  370 +++
gpui/src/scene.rs                      |    1 
gpui/src/util.rs                       |   77 
zed/Cargo.toml                         |   12 
zed/src/editor/buffer/anchor.rs        |   85 
zed/src/editor/buffer/mod.rs           | 2548 ++++++++++++++++++++++
zed/src/editor/buffer/point.rs         |  100 
zed/src/editor/buffer/text.rs          |  445 +++
zed/src/editor/buffer_element.rs       |  765 ++++++
zed/src/editor/buffer_view.rs          | 1521 +++++++++++++
zed/src/editor/display_map/fold_map.rs |  698 ++++++
zed/src/editor/display_map/mod.rs      |  375 +++
zed/src/editor/mod.rs                  |   25 
zed/src/editor/movement.rs             |   60 
zed/src/lib.rs                         |    3 
zed/src/sum_tree/cursor.rs             |  752 ++++++
zed/src/sum_tree/mod.rs                |  820 +++++++
zed/src/time.rs                        |  140 +
36 files changed, 14,097 insertions(+), 4 deletions(-)

Detailed changes

Cargo.lock 🔗

@@ -229,6 +229,12 @@ dependencies = [
  "once_cell",
 ]
 
+[[package]]
+name = "byteorder"
+version = "1.4.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ae44d1a3d5a19df61dd0c8beb138458ac2a53a7ac09eba97d55592540004306b"
+
 [[package]]
 name = "cache-padded"
 version = "1.1.1"
@@ -301,6 +307,15 @@ dependencies = [
  "vec_map",
 ]
 
+[[package]]
+name = "cmake"
+version = "0.1.45"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "eb6210b637171dfba4cda12e579ac6dc73f5165ad56133e5d72ef3131f320855"
+dependencies = [
+ "cc",
+]
+
 [[package]]
 name = "cocoa"
 version = "0.24.0"
@@ -431,6 +446,16 @@ dependencies = [
  "dirs-sys",
 ]
 
+[[package]]
+name = "dirs-next"
+version = "2.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b98cf8ebf19c3d1b223e151f99a4f9f0690dca41414773390fc824184ac833e1"
+dependencies = [
+ "cfg-if 1.0.0",
+ "dirs-sys-next",
+]
+
 [[package]]
 name = "dirs-sys"
 version = "0.3.5"
@@ -438,10 +463,33 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "8e93d7f5705de3e49895a2b5e0b8855a1c27f080192ae9c32a6432d50741a57a"
 dependencies = [
  "libc",
- "redox_users",
+ "redox_users 0.3.5",
+ "winapi",
+]
+
+[[package]]
+name = "dirs-sys-next"
+version = "0.1.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4ebda144c4fe02d1f7ea1a7d9641b6fc6b580adcfa024ae48797ecdeb6825b4d"
+dependencies = [
+ "libc",
+ "redox_users 0.4.0",
  "winapi",
 ]
 
+[[package]]
+name = "dwrote"
+version = "0.11.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "439a1c2ba5611ad3ed731280541d36d2e9c4ac5e7fb818a27b604bdc5a6aa65b"
+dependencies = [
+ "lazy_static",
+ "libc",
+ "winapi",
+ "wio",
+]
+
 [[package]]
 name = "env_logger"
 version = "0.8.3"
@@ -461,6 +509,16 @@ version = "2.5.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f7531096570974c3a9dcf9e4b8e1cede1ec26cf5046219fb3b9d897503b9be59"
 
+[[package]]
+name = "expat-sys"
+version = "2.1.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "658f19728920138342f68408b7cf7644d90d4784353d8ebc32e7e8663dbe45fa"
+dependencies = [
+ "cmake",
+ "pkg-config",
+]
+
 [[package]]
 name = "fastrand"
 version = "1.4.0"
@@ -470,6 +528,36 @@ dependencies = [
  "instant",
 ]
 
+[[package]]
+name = "float-ord"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7bad48618fdb549078c333a7a8528acb57af271d0433bdecd523eb620628364e"
+
+[[package]]
+name = "font-kit"
+version = "0.10.0"
+source = "git+https://github.com/zed-industries/font-kit?rev=8eaf7a918eafa28b0a37dc759e2e0e7683fa24f1#8eaf7a918eafa28b0a37dc759e2e0e7683fa24f1"
+dependencies = [
+ "bitflags",
+ "byteorder",
+ "core-foundation",
+ "core-graphics",
+ "core-text",
+ "dirs-next",
+ "dwrote",
+ "float-ord",
+ "freetype",
+ "lazy_static",
+ "libc",
+ "log",
+ "pathfinder_geometry",
+ "pathfinder_simd",
+ "servo-fontconfig",
+ "walkdir",
+ "winapi",
+]
+
 [[package]]
 name = "foreign-types"
 version = "0.3.2"
@@ -512,6 +600,27 @@ version = "0.3.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7684cf33bb7f28497939e8c7cf17e3e4e3b8d9a0080ffa4f8ae2f515442ee855"
 
+[[package]]
+name = "freetype"
+version = "0.7.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bee38378a9e3db1cc693b4f88d166ae375338a0ff75cb8263e1c601d51f35dc6"
+dependencies = [
+ "freetype-sys",
+ "libc",
+]
+
+[[package]]
+name = "freetype-sys"
+version = "0.13.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a37d4011c0cc628dfa766fcc195454f4b068d7afdc2adfd28861191d866e731a"
+dependencies = [
+ "cmake",
+ "libc",
+ "pkg-config",
+]
+
 [[package]]
 name = "futures-core"
 version = "0.3.12"
@@ -563,6 +672,17 @@ dependencies = [
  "wasi 0.9.0+wasi-snapshot-preview1",
 ]
 
+[[package]]
+name = "getrandom"
+version = "0.2.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c9495705279e7140bf035dde1f6e750c162df8b625267cd52cc44e0b156732c8"
+dependencies = [
+ "cfg-if 1.0.0",
+ "libc",
+ "wasi 0.10.0+wasi-snapshot-preview1",
+]
+
 [[package]]
 name = "glob"
 version = "0.3.0"
@@ -579,15 +699,20 @@ dependencies = [
  "cc",
  "cocoa",
  "core-foundation",
+ "core-graphics",
  "core-text",
  "ctor",
+ "font-kit",
  "foreign-types 0.5.0",
  "log",
  "metal",
  "num_cpus",
  "objc",
+ "ordered-float",
+ "parking_lot",
  "pathfinder_color",
  "pathfinder_geometry",
+ "rand",
  "smol",
  "tree-sitter",
 ]
@@ -644,6 +769,15 @@ dependencies = [
  "winapi",
 ]
 
+[[package]]
+name = "lock_api"
+version = "0.4.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dd96ffd135b2fd7b973ac026d28085defbe8983df057ced3eb4f2130b0831312"
+dependencies = [
+ "scopeguard",
+]
+
 [[package]]
 name = "log"
 version = "0.4.14"
@@ -767,12 +901,46 @@ version = "1.5.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "13bd41f508810a131401606d54ac32a467c97172d74ba7662562ebba5ad07fa0"
 
+[[package]]
+name = "ordered-float"
+version = "2.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "766f840da25490628d8e63e529cd21c014f6600c6b8517add12a6fa6167a6218"
+dependencies = [
+ "num-traits",
+]
+
 [[package]]
 name = "parking"
 version = "2.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "427c3892f9e783d91cc128285287e70a59e206ca452770ece88a76f7a3eddd72"
 
+[[package]]
+name = "parking_lot"
+version = "0.11.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6d7744ac029df22dca6284efe4e898991d28e3085c706c972bcd7da4a27a15eb"
+dependencies = [
+ "instant",
+ "lock_api",
+ "parking_lot_core",
+]
+
+[[package]]
+name = "parking_lot_core"
+version = "0.8.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "fa7a782938e745763fe6907fc6ba86946d72f49fe7e21de074e08128a99fb018"
+dependencies = [
+ "cfg-if 1.0.0",
+ "instant",
+ "libc",
+ "redox_syscall 0.2.5",
+ "smallvec",
+ "winapi",
+]
+
 [[package]]
 name = "pathfinder_color"
 version = "0.5.0"
@@ -813,6 +981,12 @@ version = "0.2.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "439697af366c49a6d0a010c56a0d97685bc140ce0d377b13a2ea2aa42d64a827"
 
+[[package]]
+name = "pkg-config"
+version = "0.3.19"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3831453b3449ceb48b6d9c7ad7c96d5ea673e9b470a1dc578c2ce6521230884c"
+
 [[package]]
 name = "polling"
 version = "2.0.2"
@@ -826,6 +1000,12 @@ dependencies = [
  "winapi",
 ]
 
+[[package]]
+name = "ppv-lite86"
+version = "0.2.10"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ac74c624d6b2d21f425f752262f42188365d7b8ff1aff74c82e45136510a4857"
+
 [[package]]
 name = "proc-macro2"
 version = "1.0.24"
@@ -844,23 +1024,82 @@ dependencies = [
  "proc-macro2",
 ]
 
+[[package]]
+name = "rand"
+version = "0.8.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0ef9e7e66b4468674bfcb0c81af8b7fa0bb154fa9f28eb840da5c447baeb8d7e"
+dependencies = [
+ "libc",
+ "rand_chacha",
+ "rand_core",
+ "rand_hc",
+]
+
+[[package]]
+name = "rand_chacha"
+version = "0.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e12735cf05c9e10bf21534da50a147b924d555dc7a547c42e6bb2d5b6017ae0d"
+dependencies = [
+ "ppv-lite86",
+ "rand_core",
+]
+
+[[package]]
+name = "rand_core"
+version = "0.6.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "34cf66eb183df1c5876e2dcf6b13d57340741e8dc255b48e40a26de954d06ae7"
+dependencies = [
+ "getrandom 0.2.2",
+]
+
+[[package]]
+name = "rand_hc"
+version = "0.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3190ef7066a446f2e7f42e239d161e905420ccab01eb967c9eb27d21b2322a73"
+dependencies = [
+ "rand_core",
+]
+
 [[package]]
 name = "redox_syscall"
 version = "0.1.57"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "41cc0f7e4d5d4544e8861606a285bb08d3e70712ccc7d2b84d7c0ccfaf4b05ce"
 
+[[package]]
+name = "redox_syscall"
+version = "0.2.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "94341e4e44e24f6b591b59e47a8a027df12e008d73fd5672dbea9cc22f4507d9"
+dependencies = [
+ "bitflags",
+]
+
 [[package]]
 name = "redox_users"
 version = "0.3.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "de0737333e7a9502c789a36d7c7fa6092a49895d4faa31ca5df163857ded2e9d"
 dependencies = [
- "getrandom",
- "redox_syscall",
+ "getrandom 0.1.16",
+ "redox_syscall 0.1.57",
  "rust-argon2",
 ]
 
+[[package]]
+name = "redox_users"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "528532f3d801c87aec9def2add9ca802fe569e44a544afe633765267840abe64"
+dependencies = [
+ "getrandom 0.2.2",
+ "redox_syscall 0.2.5",
+]
+
 [[package]]
 name = "regex"
 version = "1.4.3"
@@ -906,12 +1145,27 @@ dependencies = [
  "semver",
 ]
 
+[[package]]
+name = "same-file"
+version = "1.0.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "93fc1dc3aaa9bfed95e02e6eadabb4baf7e3078b0bd1b4d7b6b0b68378900502"
+dependencies = [
+ "winapi-util",
+]
+
 [[package]]
 name = "scoped-tls"
 version = "1.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "ea6a9290e3c9cf0f18145ef7ffa62d68ee0bf5fcd651017e586dc7fd5da448c2"
 
+[[package]]
+name = "scopeguard"
+version = "1.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d29ab0c6d3fc0ee92fe66e2d99f700eab17a8d57d1c1d3b748380fb20baa78cd"
+
 [[package]]
 name = "semver"
 version = "0.9.0"
@@ -927,6 +1181,27 @@ version = "0.7.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "388a1df253eca08550bef6c72392cfe7c30914bf41df5269b68cbd6ff8f570a3"
 
+[[package]]
+name = "servo-fontconfig"
+version = "0.5.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c7e3e22fe5fd73d04ebf0daa049d3efe3eae55369ce38ab16d07ddd9ac5c217c"
+dependencies = [
+ "libc",
+ "servo-fontconfig-sys",
+]
+
+[[package]]
+name = "servo-fontconfig-sys"
+version = "5.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e36b879db9892dfa40f95da1c38a835d41634b825fbd8c4c418093d53c24b388"
+dependencies = [
+ "expat-sys",
+ "freetype-sys",
+ "pkg-config",
+]
+
 [[package]]
 name = "shlex"
 version = "0.1.1"
@@ -963,6 +1238,12 @@ dependencies = [
  "termcolor",
 ]
 
+[[package]]
+name = "smallvec"
+version = "1.6.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "fe0f37c9e8f3c5a4a66ad655a93c74daac4ad00c441533bf5c6e7990bb42604e"
+
 [[package]]
 name = "smol"
 version = "1.2.5"
@@ -1093,6 +1374,17 @@ version = "1.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "9d5b2c62b4012a3e1eca5a7e077d13b3bf498c4073e33ccd58626607748ceeca"
 
+[[package]]
+name = "walkdir"
+version = "2.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "777182bc735b6424e1a57516d35ed72cb8019d85c8c9bf536dccb3445c1a2f7d"
+dependencies = [
+ "same-file",
+ "winapi",
+ "winapi-util",
+]
+
 [[package]]
 name = "wasi"
 version = "0.9.0+wasi-snapshot-preview1"
@@ -1154,13 +1446,26 @@ version = "0.4.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "712e227841d057c1ee1cd2fb22fa7e5a5461ae8e48fa2ca79ec42cfc1931183f"
 
+[[package]]
+name = "wio"
+version = "0.2.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5d129932f4644ac2396cb456385cbf9e63b5b30c6e8dc4820bdca4eb082037a5"
+dependencies = [
+ "winapi",
+]
+
 [[package]]
 name = "zed"
 version = "0.1.0"
 dependencies = [
+ "anyhow",
+ "arrayvec",
  "dirs",
  "gpui",
+ "lazy_static",
  "libc",
  "log",
+ "rand",
  "simplelog",
 ]

gpui/Cargo.toml 🔗

@@ -8,8 +8,11 @@ version = "0.1.0"
 async-task = {git = "https://github.com/zedit-io/async-task", rev = "341b57d6de98cdfd7b418567b8de2022ca993a6e"}
 ctor = "0.1"
 num_cpus = "1.13"
+ordered-float = "2.1.1"
+parking_lot = "0.11.1"
 pathfinder_color = "0.5"
 pathfinder_geometry = "0.5"
+rand = "0.8.3"
 smol = "1.2"
 tree-sitter = "0.17"
 
@@ -21,7 +24,9 @@ cc = "1.0.67"
 anyhow = "1"
 cocoa = "0.24"
 core-foundation = "0.9"
+core-graphics = "0.22.2"
 core-text = "19.2"
+font-kit = {git = "https://github.com/zed-industries/font-kit", rev = "8eaf7a918eafa28b0a37dc759e2e0e7683fa24f1"}
 foreign-types = "0.5"
 log = "0.4"
 metal = "0.21"

gpui/src/app.rs 🔗

@@ -0,0 +1,3179 @@
+use crate::{
+    elements::Element,
+    executor,
+    keymap::{self, Keystroke},
+    util::post_inc,
+};
+use anyhow::{anyhow, Result};
+use keymap::MatchResult;
+use parking_lot::Mutex;
+use smol::{channel, prelude::*};
+use std::{
+    any::{type_name, Any, TypeId},
+    borrow,
+    cell::RefCell,
+    collections::{HashMap, HashSet, VecDeque},
+    fmt::{self, Debug},
+    hash::{Hash, Hasher},
+    marker::PhantomData,
+    mem,
+    rc::{self, Rc},
+    sync::{Arc, Weak},
+};
+
+pub trait Entity: 'static + Send + Sync {
+    type Event;
+}
+
+pub trait View: Entity {
+    fn ui_name() -> &'static str;
+    fn render<'a>(&self, app: &AppContext) -> Box<dyn Element>;
+    fn on_focus(&mut self, _ctx: &mut ViewContext<Self>) {}
+    fn on_blur(&mut self, _ctx: &mut ViewContext<Self>) {}
+    fn keymap_context(&self, _: &AppContext) -> keymap::Context {
+        Self::default_keymap_context()
+    }
+    fn default_keymap_context() -> keymap::Context {
+        let mut ctx = keymap::Context::default();
+        ctx.set.insert(Self::ui_name().into());
+        ctx
+    }
+}
+
+pub trait ModelAsRef {
+    fn model<T: Entity>(&self, handle: &ModelHandle<T>) -> &T;
+}
+
+pub trait UpdateModel {
+    fn update_model<T, F, S>(&mut self, handle: &ModelHandle<T>, update: F) -> S
+    where
+        T: Entity,
+        F: FnOnce(&mut T, &mut ModelContext<T>) -> S;
+}
+
+pub trait ViewAsRef {
+    fn view<T: View>(&self, handle: &ViewHandle<T>) -> &T;
+}
+
+pub trait UpdateView {
+    fn update_view<T, F, S>(&mut self, handle: &ViewHandle<T>, update: F) -> S
+    where
+        T: View,
+        F: FnOnce(&mut T, &mut ViewContext<T>) -> S;
+}
+
+#[derive(Clone)]
+pub struct App(Rc<RefCell<MutableAppContext>>);
+
+impl App {
+    #[cfg(test)]
+    pub fn run<T, F: Future<Output = T>>(f: impl FnOnce(App) -> F) -> T {
+        let foreground = Rc::new(executor::Foreground::new().unwrap());
+        let app = Self(Rc::new(RefCell::new(
+            MutableAppContext::with_foreground_executor(foreground.clone()),
+        )));
+        app.0.borrow_mut().weak_self = Some(Rc::downgrade(&app.0));
+        smol::block_on(foreground.run(f(app)))
+    }
+
+    pub fn new() -> Result<Self> {
+        let app = Self(Rc::new(RefCell::new(MutableAppContext::new()?)));
+        app.0.borrow_mut().weak_self = Some(Rc::downgrade(&app.0));
+        Ok(app)
+    }
+
+    pub fn on_window_invalidated<F: 'static + FnMut(WindowInvalidation, &mut MutableAppContext)>(
+        &self,
+        window_id: usize,
+        callback: F,
+    ) {
+        self.0
+            .borrow_mut()
+            .on_window_invalidated(window_id, callback);
+    }
+
+    pub fn add_action<S, V, T, F>(&self, name: S, handler: F)
+    where
+        S: Into<String>,
+        V: View,
+        T: Any,
+        F: 'static + FnMut(&mut V, &T, &mut ViewContext<V>),
+    {
+        self.0.borrow_mut().add_action(name, handler);
+    }
+
+    pub fn add_global_action<S, T, F>(&self, name: S, handler: F)
+    where
+        S: Into<String>,
+        T: 'static + Any,
+        F: 'static + FnMut(&T, &mut MutableAppContext),
+    {
+        self.0.borrow_mut().add_global_action(name, handler);
+    }
+
+    pub fn dispatch_action<T: 'static + Any>(
+        &self,
+        window_id: usize,
+        responder_chain: Vec<usize>,
+        name: &str,
+        arg: T,
+    ) {
+        self.0.borrow_mut().dispatch_action(
+            window_id,
+            &responder_chain,
+            name,
+            Box::new(arg).as_ref(),
+        );
+    }
+
+    pub fn dispatch_global_action<T: 'static + Any>(&self, name: &str, arg: T) {
+        self.0
+            .borrow_mut()
+            .dispatch_global_action(name, Box::new(arg).as_ref());
+    }
+
+    pub fn add_bindings<T: IntoIterator<Item = keymap::Binding>>(&self, bindings: T) {
+        self.0.borrow_mut().add_bindings(bindings);
+    }
+
+    pub fn dispatch_keystroke(
+        &self,
+        window_id: usize,
+        responder_chain: Vec<usize>,
+        keystroke: &Keystroke,
+    ) -> Result<bool> {
+        let mut state = self.0.borrow_mut();
+        state.dispatch_keystroke(window_id, responder_chain, keystroke)
+    }
+
+    pub fn add_model<T, F>(&mut self, build_model: F) -> ModelHandle<T>
+    where
+        T: Entity,
+        F: FnOnce(&mut ModelContext<T>) -> T,
+    {
+        let mut state = self.0.borrow_mut();
+        state.pending_flushes += 1;
+        let handle = state.add_model(build_model);
+        state.flush_effects();
+        handle
+    }
+
+    fn read_model<T, F, S>(&self, handle: &ModelHandle<T>, read: F) -> S
+    where
+        T: Entity,
+        F: FnOnce(&T, &AppContext) -> S,
+    {
+        let state = self.0.borrow();
+        read(state.model(handle), &state.ctx)
+    }
+
+    pub fn add_window<T, F>(&mut self, build_root_view: F) -> (usize, ViewHandle<T>)
+    where
+        T: View,
+        F: FnOnce(&mut ViewContext<T>) -> T,
+    {
+        self.0.borrow_mut().add_window(build_root_view)
+    }
+
+    pub fn window_ids(&self) -> Vec<usize> {
+        self.0.borrow().window_ids().collect()
+    }
+
+    pub fn root_view<T: View>(&self, window_id: usize) -> Option<ViewHandle<T>> {
+        self.0.borrow().root_view(window_id)
+    }
+
+    pub fn add_view<T, F>(&mut self, window_id: usize, build_view: F) -> ViewHandle<T>
+    where
+        T: View,
+        F: FnOnce(&mut ViewContext<T>) -> T,
+    {
+        let mut state = self.0.borrow_mut();
+        state.pending_flushes += 1;
+        let handle = state.add_view(window_id, build_view);
+        state.flush_effects();
+        handle
+    }
+
+    pub fn add_option_view<T, F>(
+        &mut self,
+        window_id: usize,
+        build_view: F,
+    ) -> Option<ViewHandle<T>>
+    where
+        T: View,
+        F: FnOnce(&mut ViewContext<T>) -> Option<T>,
+    {
+        let mut state = self.0.borrow_mut();
+        state.pending_flushes += 1;
+        let handle = state.add_option_view(window_id, build_view);
+        state.flush_effects();
+        handle
+    }
+
+    pub fn read<T, F: FnOnce(&AppContext) -> T>(&mut self, callback: F) -> T {
+        callback(self.0.borrow().ctx())
+    }
+
+    pub fn update<T, F: FnOnce(&mut MutableAppContext) -> T>(&mut self, callback: F) -> T {
+        let mut state = self.0.borrow_mut();
+        state.pending_flushes += 1;
+        let result = callback(&mut *state);
+        state.flush_effects();
+        result
+    }
+
+    fn read_view<T, F, S>(&self, handle: &ViewHandle<T>, read: F) -> S
+    where
+        T: View,
+        F: FnOnce(&T, &AppContext) -> S,
+    {
+        let state = self.0.borrow();
+        read(state.view(handle), state.ctx())
+    }
+
+    #[cfg(test)]
+    pub fn finish_pending_tasks(&self) -> impl Future<Output = ()> {
+        self.0.borrow().finish_pending_tasks()
+    }
+}
+
+impl UpdateModel for App {
+    fn update_model<T, F, S>(&mut self, handle: &ModelHandle<T>, update: F) -> S
+    where
+        T: Entity,
+        F: FnOnce(&mut T, &mut ModelContext<T>) -> S,
+    {
+        let mut state = self.0.borrow_mut();
+        state.pending_flushes += 1;
+        let result = state.update_model(handle, update);
+        state.flush_effects();
+        result
+    }
+}
+
+impl UpdateView for App {
+    fn update_view<T, F, S>(&mut self, handle: &ViewHandle<T>, update: F) -> S
+    where
+        T: View,
+        F: FnOnce(&mut T, &mut ViewContext<T>) -> S,
+    {
+        let mut state = self.0.borrow_mut();
+        state.pending_flushes += 1;
+        let result = state.update_view(handle, update);
+        state.flush_effects();
+        result
+    }
+}
+
+type ActionCallback =
+    dyn FnMut(&mut dyn AnyView, &dyn Any, &mut MutableAppContext, usize, usize) -> bool;
+
+type GlobalActionCallback = dyn FnMut(&dyn Any, &mut MutableAppContext);
+
+pub struct MutableAppContext {
+    ctx: AppContext,
+    actions: HashMap<TypeId, HashMap<String, Vec<Box<ActionCallback>>>>,
+    global_actions: HashMap<String, Vec<Box<GlobalActionCallback>>>,
+    keystroke_matcher: keymap::Matcher,
+    next_entity_id: usize,
+    next_window_id: usize,
+    next_task_id: usize,
+    weak_self: Option<rc::Weak<RefCell<Self>>>,
+    subscriptions: HashMap<usize, Vec<Subscription>>,
+    observations: HashMap<usize, Vec<Observation>>,
+    window_invalidations: HashMap<usize, WindowInvalidation>,
+    invalidation_callbacks:
+        HashMap<usize, Box<dyn FnMut(WindowInvalidation, &mut MutableAppContext)>>,
+    foreground: Rc<executor::Foreground>,
+    background: Arc<executor::Background>,
+    task_callbacks: HashMap<usize, TaskCallback>,
+    task_done: (channel::Sender<usize>, channel::Receiver<usize>),
+    pending_effects: VecDeque<Effect>,
+    pending_flushes: usize,
+    flushing_effects: bool,
+}
+
+impl MutableAppContext {
+    pub fn new() -> Result<Self> {
+        Ok(Self::with_foreground_executor(Rc::new(
+            executor::Foreground::new()?,
+        )))
+    }
+
+    fn with_foreground_executor(foreground: Rc<executor::Foreground>) -> Self {
+        Self {
+            ctx: AppContext {
+                models: HashMap::new(),
+                windows: HashMap::new(),
+                ref_counts: Arc::new(Mutex::new(RefCounts::default())),
+            },
+            actions: HashMap::new(),
+            global_actions: HashMap::new(),
+            keystroke_matcher: keymap::Matcher::default(),
+            next_entity_id: 0,
+            next_window_id: 0,
+            next_task_id: 0,
+            weak_self: None,
+            subscriptions: HashMap::new(),
+            observations: HashMap::new(),
+            window_invalidations: HashMap::new(),
+            invalidation_callbacks: HashMap::new(),
+            foreground,
+            background: Arc::new(executor::Background::new()),
+            task_callbacks: HashMap::new(),
+            task_done: channel::unbounded(),
+            pending_effects: VecDeque::new(),
+            pending_flushes: 0,
+            flushing_effects: false,
+        }
+    }
+
+    pub fn ctx(&self) -> &AppContext {
+        &self.ctx
+    }
+
+    pub fn foreground_executor(&self) -> Rc<executor::Foreground> {
+        self.foreground.clone()
+    }
+
+    pub fn on_window_invalidated<F: 'static + FnMut(WindowInvalidation, &mut MutableAppContext)>(
+        &mut self,
+        window_id: usize,
+        callback: F,
+    ) {
+        self.invalidation_callbacks
+            .insert(window_id, Box::new(callback));
+    }
+
+    pub fn add_action<S, V, T, F>(&mut self, name: S, mut handler: F)
+    where
+        S: Into<String>,
+        V: View,
+        T: Any,
+        F: 'static + FnMut(&mut V, &T, &mut ViewContext<V>),
+    {
+        let name = name.into();
+        let name_clone = name.clone();
+        let handler = Box::new(
+            move |view: &mut dyn AnyView,
+                  arg: &dyn Any,
+                  app: &mut MutableAppContext,
+                  window_id: usize,
+                  view_id: usize| {
+                match arg.downcast_ref() {
+                    Some(arg) => {
+                        let mut ctx = ViewContext::new(app, window_id, view_id);
+                        handler(
+                            view.as_any_mut()
+                                .downcast_mut()
+                                .expect("downcast is type safe"),
+                            arg,
+                            &mut ctx,
+                        );
+                        ctx.halt_action_dispatch
+                    }
+                    None => {
+                        log::error!("Could not downcast argument for action {}", name_clone);
+                        false
+                    }
+                }
+            },
+        );
+
+        self.actions
+            .entry(TypeId::of::<V>())
+            .or_default()
+            .entry(name)
+            .or_default()
+            .push(handler);
+    }
+
+    pub fn add_global_action<S, T, F>(&mut self, name: S, mut handler: F)
+    where
+        S: Into<String>,
+        T: 'static + Any,
+        F: 'static + FnMut(&T, &mut MutableAppContext),
+    {
+        let name = name.into();
+        let name_clone = name.clone();
+        let handler = Box::new(move |arg: &dyn Any, app: &mut MutableAppContext| {
+            if let Some(arg) = arg.downcast_ref() {
+                handler(arg, app);
+            } else {
+                log::error!("Could not downcast argument for action {}", name_clone);
+            }
+        });
+
+        self.global_actions.entry(name).or_default().push(handler);
+    }
+
+    pub fn window_ids(&self) -> impl Iterator<Item = usize> + '_ {
+        self.ctx.windows.keys().cloned()
+    }
+
+    pub fn root_view<T: View>(&self, window_id: usize) -> Option<ViewHandle<T>> {
+        self.ctx
+            .windows
+            .get(&window_id)
+            .and_then(|window| window.root_view.as_ref().unwrap().clone().downcast::<T>())
+    }
+
+    pub fn root_view_id(&self, window_id: usize) -> Option<usize> {
+        self.ctx.root_view_id(window_id)
+    }
+
+    pub fn focused_view_id(&self, window_id: usize) -> Option<usize> {
+        self.ctx.focused_view_id(window_id)
+    }
+
+    pub fn render_view(&self, window_id: usize, view_id: usize) -> Result<Box<dyn Element>> {
+        self.ctx.render_view(window_id, view_id)
+    }
+
+    pub fn render_views(&self, window_id: usize) -> Result<HashMap<usize, Box<dyn Element>>> {
+        self.ctx.render_views(window_id)
+    }
+
+    pub fn dispatch_action(
+        &mut self,
+        window_id: usize,
+        responder_chain: &[usize],
+        name: &str,
+        arg: &dyn Any,
+    ) -> bool {
+        self.pending_flushes += 1;
+        let mut halted_dispatch = false;
+
+        for view_id in responder_chain.iter().rev() {
+            if let Some(mut view) = self
+                .ctx
+                .windows
+                .get_mut(&window_id)
+                .and_then(|w| w.views.remove(view_id))
+            {
+                let type_id = view.as_any().type_id();
+
+                if let Some((name, mut handlers)) = self
+                    .actions
+                    .get_mut(&type_id)
+                    .and_then(|h| h.remove_entry(name))
+                {
+                    for handler in handlers.iter_mut().rev() {
+                        let halt_dispatch = handler(view.as_mut(), arg, self, window_id, *view_id);
+                        if halt_dispatch {
+                            halted_dispatch = true;
+                            break;
+                        }
+                    }
+                    self.actions
+                        .get_mut(&type_id)
+                        .unwrap()
+                        .insert(name, handlers);
+                }
+
+                self.ctx
+                    .windows
+                    .get_mut(&window_id)
+                    .unwrap()
+                    .views
+                    .insert(*view_id, view);
+
+                if halted_dispatch {
+                    break;
+                }
+            }
+        }
+
+        if !halted_dispatch {
+            self.dispatch_global_action(name, arg);
+        }
+
+        self.flush_effects();
+        halted_dispatch
+    }
+
+    fn dispatch_global_action(&mut self, name: &str, arg: &dyn Any) {
+        if let Some((name, mut handlers)) = self.global_actions.remove_entry(name) {
+            self.pending_flushes += 1;
+            for handler in handlers.iter_mut().rev() {
+                handler(arg, self);
+            }
+            self.global_actions.insert(name, handlers);
+            self.flush_effects();
+        }
+    }
+
+    fn add_bindings<T: IntoIterator<Item = keymap::Binding>>(&mut self, bindings: T) {
+        self.keystroke_matcher.add_bindings(bindings);
+    }
+
+    pub fn dispatch_keystroke(
+        &mut self,
+        window_id: usize,
+        responder_chain: Vec<usize>,
+        keystroke: &Keystroke,
+    ) -> Result<bool> {
+        log::info!(
+            "dispatch_keystroke {} {:?} {:?}",
+            window_id,
+            responder_chain,
+            keystroke
+        );
+
+        let mut context_chain = Vec::new();
+        let mut context = keymap::Context::default();
+        for view_id in &responder_chain {
+            if let Some(view) = self
+                .ctx
+                .windows
+                .get(&window_id)
+                .and_then(|w| w.views.get(view_id))
+            {
+                context.extend(view.keymap_context(self.ctx()));
+                context_chain.push(context.clone());
+            } else {
+                return Err(anyhow!(
+                    "View {} in responder chain does not exist",
+                    view_id
+                ));
+            }
+        }
+
+        let mut pending = false;
+        for (i, ctx) in context_chain.iter().enumerate().rev() {
+            match self
+                .keystroke_matcher
+                .push_keystroke(keystroke.clone(), responder_chain[i], ctx)
+            {
+                MatchResult::None => {}
+                MatchResult::Pending => pending = true,
+                MatchResult::Action { name, arg } => {
+                    if self.dispatch_action(
+                        window_id,
+                        &responder_chain[0..=i],
+                        &name,
+                        arg.as_ref().map(|arg| arg.as_ref()).unwrap_or(&()),
+                    ) {
+                        return Ok(true);
+                    }
+                }
+            }
+        }
+
+        Ok(pending)
+    }
+
+    pub fn add_model<T, F>(&mut self, build_model: F) -> ModelHandle<T>
+    where
+        T: Entity,
+        F: FnOnce(&mut ModelContext<T>) -> T,
+    {
+        self.pending_flushes += 1;
+        let model_id = post_inc(&mut self.next_entity_id);
+        let mut ctx = ModelContext::new(self, model_id);
+        let model = build_model(&mut ctx);
+        self.ctx.models.insert(model_id, Box::new(model));
+        self.flush_effects();
+        ModelHandle::new(model_id, &self.ctx.ref_counts)
+    }
+
+    pub fn add_window<T, F>(&mut self, build_root_view: F) -> (usize, ViewHandle<T>)
+    where
+        T: View,
+        F: FnOnce(&mut ViewContext<T>) -> T,
+    {
+        let window_id = post_inc(&mut self.next_window_id);
+        self.ctx.windows.insert(window_id, Window::default());
+
+        let root_handle = self.add_view(window_id, build_root_view);
+        self.ctx.windows.get_mut(&window_id).unwrap().root_view = Some(root_handle.clone().into());
+        self.focus(window_id, root_handle.id());
+
+        self.emit_ui_update(UiUpdate::OpenWindow {
+            window_id,
+            width: 1024.0,
+            height: 768.0,
+        });
+
+        (window_id, root_handle)
+    }
+
+    pub fn add_view<T, F>(&mut self, window_id: usize, build_view: F) -> ViewHandle<T>
+    where
+        T: View,
+        F: FnOnce(&mut ViewContext<T>) -> T,
+    {
+        self.add_option_view(window_id, |ctx| Some(build_view(ctx)))
+            .unwrap()
+    }
+
+    pub fn add_option_view<T, F>(
+        &mut self,
+        window_id: usize,
+        build_view: F,
+    ) -> Option<ViewHandle<T>>
+    where
+        T: View,
+        F: FnOnce(&mut ViewContext<T>) -> Option<T>,
+    {
+        let view_id = post_inc(&mut self.next_entity_id);
+        self.pending_flushes += 1;
+        let mut ctx = ViewContext::new(self, window_id, view_id);
+        let handle = if let Some(view) = build_view(&mut ctx) {
+            if let Some(window) = self.ctx.windows.get_mut(&window_id) {
+                window.views.insert(view_id, Box::new(view));
+            } else {
+                panic!("Window does not exist");
+            }
+            self.window_invalidations
+                .entry(window_id)
+                .or_default()
+                .updated
+                .insert(view_id);
+            Some(ViewHandle::new(window_id, view_id, &self.ctx.ref_counts))
+        } else {
+            None
+        };
+        self.flush_effects();
+        handle
+    }
+
+    fn remove_dropped_entities(&mut self) {
+        loop {
+            let (dropped_models, dropped_views) = self.ctx.ref_counts.lock().take_dropped();
+            if dropped_models.is_empty() && dropped_views.is_empty() {
+                break;
+            }
+
+            for model_id in dropped_models {
+                self.ctx.models.remove(&model_id);
+                self.subscriptions.remove(&model_id);
+                self.observations.remove(&model_id);
+            }
+
+            for (window_id, view_id) in dropped_views {
+                self.subscriptions.remove(&view_id);
+                self.observations.remove(&view_id);
+                if let Some(window) = self.ctx.windows.get_mut(&window_id) {
+                    self.window_invalidations
+                        .entry(window_id)
+                        .or_default()
+                        .removed
+                        .push(view_id);
+                    window.views.remove(&view_id);
+                }
+            }
+        }
+    }
+
+    fn flush_effects(&mut self) {
+        self.pending_flushes -= 1;
+
+        if !self.flushing_effects && self.pending_flushes == 0 {
+            self.flushing_effects = true;
+
+            while let Some(effect) = self.pending_effects.pop_front() {
+                match effect {
+                    Effect::Event { entity_id, payload } => self.emit_event(entity_id, payload),
+                    Effect::ModelNotification { model_id } => self.notify_model_observers(model_id),
+                    Effect::ViewNotification { window_id, view_id } => {
+                        self.notify_view_observers(window_id, view_id)
+                    }
+                    Effect::Focus { window_id, view_id } => {
+                        self.focus(window_id, view_id);
+                    }
+                }
+            }
+
+            self.flushing_effects = false;
+            self.remove_dropped_entities();
+            self.update_windows();
+        }
+    }
+
+    fn update_windows(&mut self) {
+        let mut invalidations = HashMap::new();
+        std::mem::swap(&mut invalidations, &mut self.window_invalidations);
+
+        for (window_id, invalidation) in invalidations {
+            if let Some(mut callback) = self.invalidation_callbacks.remove(&window_id) {
+                callback(invalidation, self);
+                self.invalidation_callbacks.insert(window_id, callback);
+            }
+        }
+    }
+
+    fn emit_event(&mut self, entity_id: usize, payload: Box<dyn Any>) {
+        if let Some(subscriptions) = self.subscriptions.remove(&entity_id) {
+            for mut subscription in subscriptions {
+                let alive = match &mut subscription {
+                    Subscription::FromModel { model_id, callback } => {
+                        if let Some(mut model) = self.ctx.models.remove(model_id) {
+                            callback(model.as_any_mut(), payload.as_ref(), self, *model_id);
+                            self.ctx.models.insert(*model_id, model);
+                            true
+                        } else {
+                            false
+                        }
+                    }
+                    Subscription::FromView {
+                        window_id,
+                        view_id,
+                        callback,
+                    } => {
+                        if let Some(mut view) = self
+                            .ctx
+                            .windows
+                            .get_mut(&window_id)
+                            .and_then(|window| window.views.remove(view_id))
+                        {
+                            callback(
+                                view.as_any_mut(),
+                                payload.as_ref(),
+                                self,
+                                *window_id,
+                                *view_id,
+                            );
+                            self.ctx
+                                .windows
+                                .get_mut(&window_id)
+                                .unwrap()
+                                .views
+                                .insert(*view_id, view);
+                            true
+                        } else {
+                            false
+                        }
+                    }
+                };
+
+                if alive {
+                    self.subscriptions
+                        .entry(entity_id)
+                        .or_default()
+                        .push(subscription);
+                }
+            }
+        }
+    }
+
+    fn notify_model_observers(&mut self, observed_id: usize) {
+        if let Some(observations) = self.observations.remove(&observed_id) {
+            if self.ctx.models.contains_key(&observed_id) {
+                for mut observation in observations {
+                    let alive = match &mut observation {
+                        Observation::FromModel { model_id, callback } => {
+                            if let Some(mut model) = self.ctx.models.remove(model_id) {
+                                callback(model.as_any_mut(), observed_id, self, *model_id);
+                                self.ctx.models.insert(*model_id, model);
+                                true
+                            } else {
+                                false
+                            }
+                        }
+                        Observation::FromView {
+                            window_id,
+                            view_id,
+                            callback,
+                        } => {
+                            if let Some(mut view) = self
+                                .ctx
+                                .windows
+                                .get_mut(window_id)
+                                .and_then(|w| w.views.remove(view_id))
+                            {
+                                callback(
+                                    view.as_any_mut(),
+                                    observed_id,
+                                    self,
+                                    *window_id,
+                                    *view_id,
+                                );
+                                self.ctx
+                                    .windows
+                                    .get_mut(window_id)
+                                    .unwrap()
+                                    .views
+                                    .insert(*view_id, view);
+                                true
+                            } else {
+                                false
+                            }
+                        }
+                    };
+
+                    if alive {
+                        self.observations
+                            .entry(observed_id)
+                            .or_default()
+                            .push(observation);
+                    }
+                }
+            }
+        }
+    }
+
+    fn notify_view_observers(&mut self, window_id: usize, view_id: usize) {
+        self.window_invalidations
+            .entry(window_id)
+            .or_default()
+            .updated
+            .insert(view_id);
+    }
+
+    fn focus(&mut self, window_id: usize, focused_id: usize) {
+        if self
+            .ctx
+            .windows
+            .get(&window_id)
+            .and_then(|w| w.focused_view)
+            .map_or(false, |cur_focused| cur_focused == focused_id)
+        {
+            return;
+        }
+
+        self.pending_flushes += 1;
+
+        if let Some((blurred_id, mut blurred)) =
+            self.ctx.windows.get_mut(&window_id).and_then(|w| {
+                let blurred_view = w.focused_view;
+                w.focused_view = Some(focused_id);
+                blurred_view.and_then(|id| w.views.remove(&id).map(|view| (id, view)))
+            })
+        {
+            blurred.on_blur(self, window_id, blurred_id);
+            self.ctx
+                .windows
+                .get_mut(&window_id)
+                .unwrap()
+                .views
+                .insert(blurred_id, blurred);
+        }
+
+        if let Some(mut focused) = self
+            .ctx
+            .windows
+            .get_mut(&window_id)
+            .and_then(|w| w.views.remove(&focused_id))
+        {
+            focused.on_focus(self, window_id, focused_id);
+            self.ctx
+                .windows
+                .get_mut(&window_id)
+                .unwrap()
+                .views
+                .insert(focused_id, focused);
+        }
+
+        self.flush_effects();
+    }
+
+    fn spawn_local<F>(&mut self, future: F) -> usize
+    where
+        F: 'static + Future,
+    {
+        let task_id = post_inc(&mut self.next_task_id);
+        let app = self.weak_self.as_ref().unwrap().clone();
+        self.foreground
+            .spawn(async move {
+                let output = future.await;
+                if let Some(app) = app.upgrade() {
+                    app.borrow_mut()
+                        .relay_task_output(task_id, Box::new(output));
+                }
+            })
+            .detach();
+        task_id
+    }
+
+    fn spawn_stream_local<F>(&mut self, mut stream: F, done_tx: channel::Sender<()>) -> usize
+    where
+        F: 'static + Stream + Unpin,
+    {
+        let task_id = post_inc(&mut self.next_task_id);
+        let app = self.weak_self.as_ref().unwrap().clone();
+        self.foreground
+            .spawn(async move {
+                loop {
+                    match stream.next().await {
+                        item @ Some(_) => {
+                            if let Some(app) = app.upgrade() {
+                                let mut app = app.borrow_mut();
+                                if app.relay_task_output(task_id, Box::new(item)) {
+                                    app.stream_completed(task_id);
+                                    break;
+                                }
+                            } else {
+                                break;
+                            }
+                        }
+                        item @ None => {
+                            if let Some(app) = app.upgrade() {
+                                let mut app = app.borrow_mut();
+                                app.relay_task_output(task_id, Box::new(item));
+                                app.stream_completed(task_id);
+                            }
+                            let _ = done_tx.send(()).await;
+                            break;
+                        }
+                    }
+                }
+            })
+            .detach();
+        task_id
+    }
+
+    fn relay_task_output(&mut self, task_id: usize, output: Box<dyn Any>) -> bool {
+        self.pending_flushes += 1;
+        let task_callback = self.task_callbacks.remove(&task_id).unwrap();
+
+        let halt = match task_callback {
+            TaskCallback::OnModelFromFuture { model_id, callback } => {
+                if let Some(mut model) = self.ctx.models.remove(&model_id) {
+                    callback(
+                        model.as_any_mut(),
+                        output,
+                        self,
+                        model_id,
+                        self.foreground.clone(),
+                    );
+                    self.ctx.models.insert(model_id, model);
+                }
+                self.task_done(task_id);
+                true
+            }
+            TaskCallback::OnModelFromStream {
+                model_id,
+                mut callback,
+            } => {
+                if let Some(mut model) = self.ctx.models.remove(&model_id) {
+                    let halt = callback(model.as_any_mut(), output, self, model_id);
+                    self.ctx.models.insert(model_id, model);
+                    self.task_callbacks.insert(
+                        task_id,
+                        TaskCallback::OnModelFromStream { model_id, callback },
+                    );
+                    halt
+                } else {
+                    true
+                }
+            }
+            TaskCallback::OnViewFromFuture {
+                window_id,
+                view_id,
+                callback,
+            } => {
+                if let Some(mut view) = self
+                    .ctx
+                    .windows
+                    .get_mut(&window_id)
+                    .and_then(|w| w.views.remove(&view_id))
+                {
+                    callback(
+                        view.as_mut(),
+                        output,
+                        self,
+                        window_id,
+                        view_id,
+                        self.foreground.clone(),
+                    );
+                    self.ctx
+                        .windows
+                        .get_mut(&window_id)
+                        .unwrap()
+                        .views
+                        .insert(view_id, view);
+                }
+                self.task_done(task_id);
+                true
+            }
+            TaskCallback::OnViewFromStream {
+                window_id,
+                view_id,
+                mut callback,
+            } => {
+                if let Some(mut view) = self
+                    .ctx
+                    .windows
+                    .get_mut(&window_id)
+                    .and_then(|w| w.views.remove(&view_id))
+                {
+                    let halt = callback(view.as_mut(), output, self, window_id, view_id);
+                    self.ctx
+                        .windows
+                        .get_mut(&window_id)
+                        .unwrap()
+                        .views
+                        .insert(view_id, view);
+                    self.task_callbacks.insert(
+                        task_id,
+                        TaskCallback::OnViewFromStream {
+                            window_id,
+                            view_id,
+                            callback,
+                        },
+                    );
+                    halt
+                } else {
+                    true
+                }
+            }
+        };
+        self.flush_effects();
+        halt
+    }
+
+    fn stream_completed(&mut self, task_id: usize) {
+        self.task_callbacks.remove(&task_id);
+        self.task_done(task_id);
+    }
+
+    fn task_done(&self, task_id: usize) {
+        let task_done = self.task_done.0.clone();
+        self.foreground
+            .spawn(async move {
+                let _ = task_done.send(task_id).await;
+            })
+            .detach()
+    }
+
+    #[cfg(test)]
+    pub fn finish_pending_tasks(&self) -> impl Future<Output = ()> {
+        let mut pending_tasks = self.task_callbacks.keys().cloned().collect::<HashSet<_>>();
+        let task_done = self.task_done.1.clone();
+
+        async move {
+            while !pending_tasks.is_empty() {
+                if let Ok(task_id) = task_done.recv().await {
+                    pending_tasks.remove(&task_id);
+                } else {
+                    break;
+                }
+            }
+        }
+    }
+}
+
+impl ModelAsRef for MutableAppContext {
+    fn model<T: Entity>(&self, handle: &ModelHandle<T>) -> &T {
+        if let Some(model) = self.ctx.models.get(&handle.model_id) {
+            model
+                .as_any()
+                .downcast_ref()
+                .expect("Downcast is type safe")
+        } else {
+            panic!("Circular model reference");
+        }
+    }
+}
+
+impl UpdateModel for MutableAppContext {
+    fn update_model<T, F, S>(&mut self, handle: &ModelHandle<T>, update: F) -> S
+    where
+        T: Entity,
+        F: FnOnce(&mut T, &mut ModelContext<T>) -> S,
+    {
+        if let Some(mut model) = self.ctx.models.remove(&handle.model_id) {
+            self.pending_flushes += 1;
+            let mut ctx = ModelContext::new(self, handle.model_id);
+            let result = update(
+                model
+                    .as_any_mut()
+                    .downcast_mut()
+                    .expect("Downcast is type safe"),
+                &mut ctx,
+            );
+            self.ctx.models.insert(handle.model_id, model);
+            self.flush_effects();
+            result
+        } else {
+            panic!("Circular model update");
+        }
+    }
+}
+
+impl ViewAsRef for MutableAppContext {
+    fn view<T: View>(&self, handle: &ViewHandle<T>) -> &T {
+        if let Some(window) = self.ctx.windows.get(&handle.window_id) {
+            if let Some(view) = window.views.get(&handle.view_id) {
+                view.as_any().downcast_ref().expect("Downcast is type safe")
+            } else {
+                panic!("Circular view reference");
+            }
+        } else {
+            panic!("Window does not exist");
+        }
+    }
+}
+
+impl UpdateView for MutableAppContext {
+    fn update_view<T, F, S>(&mut self, handle: &ViewHandle<T>, update: F) -> S
+    where
+        T: View,
+        F: FnOnce(&mut T, &mut ViewContext<T>) -> S,
+    {
+        self.pending_flushes += 1;
+        let mut view = if let Some(window) = self.ctx.windows.get_mut(&handle.window_id) {
+            if let Some(view) = window.views.remove(&handle.view_id) {
+                view
+            } else {
+                panic!("Circular view update");
+            }
+        } else {
+            panic!("Window does not exist");
+        };
+
+        let mut ctx = ViewContext::new(self, handle.window_id, handle.view_id);
+        let result = update(
+            view.as_any_mut()
+                .downcast_mut()
+                .expect("Downcast is type safe"),
+            &mut ctx,
+        );
+        self.ctx
+            .windows
+            .get_mut(&handle.window_id)
+            .unwrap()
+            .views
+            .insert(handle.view_id, view);
+        self.flush_effects();
+        result
+    }
+}
+
+pub struct AppContext {
+    models: HashMap<usize, Box<dyn AnyModel>>,
+    windows: HashMap<usize, Window>,
+    ref_counts: Arc<Mutex<RefCounts>>,
+}
+
+impl AppContext {
+    pub fn root_view_id(&self, window_id: usize) -> Option<usize> {
+        self.windows
+            .get(&window_id)
+            .and_then(|window| window.root_view.as_ref().map(|v| v.id()))
+    }
+
+    pub fn focused_view_id(&self, window_id: usize) -> Option<usize> {
+        self.windows
+            .get(&window_id)
+            .and_then(|window| window.focused_view)
+    }
+
+    pub fn render_view(&self, window_id: usize, view_id: usize) -> Result<Box<dyn Element>> {
+        self.windows
+            .get(&window_id)
+            .and_then(|w| w.views.get(&view_id))
+            .map(|v| v.render(self))
+            .ok_or(anyhow!("view not found"))
+    }
+
+    pub fn render_views(&self, window_id: usize) -> Result<HashMap<usize, Box<dyn Element>>> {
+        self.windows
+            .get(&window_id)
+            .map(|w| {
+                w.views
+                    .iter()
+                    .map(|(id, view)| view.render(self))
+                    .collect::<HashMap<_, _>>()
+            })
+            .ok_or(anyhow!("window not found"))
+    }
+}
+
+impl ModelAsRef for AppContext {
+    fn model<T: Entity>(&self, handle: &ModelHandle<T>) -> &T {
+        if let Some(model) = self.models.get(&handle.model_id) {
+            model
+                .as_any()
+                .downcast_ref()
+                .expect("downcast should be type safe")
+        } else {
+            panic!("circular model reference");
+        }
+    }
+}
+
+impl ViewAsRef for AppContext {
+    fn view<T: View>(&self, handle: &ViewHandle<T>) -> &T {
+        if let Some(window) = self.windows.get(&handle.window_id) {
+            if let Some(view) = window.views.get(&handle.view_id) {
+                view.as_any()
+                    .downcast_ref()
+                    .expect("downcast should be type safe")
+            } else {
+                panic!("circular view reference");
+            }
+        } else {
+            panic!("window does not exist");
+        }
+    }
+}
+
+#[derive(Default)]
+struct Window {
+    views: HashMap<usize, Box<dyn AnyView>>,
+    root_view: Option<AnyViewHandle>,
+    focused_view: Option<usize>,
+}
+
+#[derive(Default, Clone)]
+pub struct WindowInvalidation {
+    pub updated: HashSet<usize>,
+    pub removed: Vec<usize>,
+}
+
+pub enum Effect {
+    Event {
+        entity_id: usize,
+        payload: Box<dyn Any>,
+    },
+    ModelNotification {
+        model_id: usize,
+    },
+    ViewNotification {
+        window_id: usize,
+        view_id: usize,
+    },
+    Focus {
+        window_id: usize,
+        view_id: usize,
+    },
+}
+
+pub trait AnyModel: Send + Sync {
+    fn as_any(&self) -> &dyn Any;
+    fn as_any_mut(&mut self) -> &mut dyn Any;
+}
+
+impl<T> AnyModel for T
+where
+    T: Entity,
+{
+    fn as_any(&self) -> &dyn Any {
+        self
+    }
+
+    fn as_any_mut(&mut self) -> &mut dyn Any {
+        self
+    }
+}
+
+pub trait AnyView: Send + Sync {
+    fn as_any(&self) -> &dyn Any;
+    fn as_any_mut(&mut self) -> &mut dyn Any;
+    fn ui_name(&self) -> &'static str;
+    fn render<'a>(&self, app: &AppContext) -> Box<dyn Element>;
+    fn on_focus(&mut self, app: &mut MutableAppContext, window_id: usize, view_id: usize);
+    fn on_blur(&mut self, app: &mut MutableAppContext, window_id: usize, view_id: usize);
+    fn keymap_context(&self, app: &AppContext) -> keymap::Context;
+}
+
+impl<T> AnyView for T
+where
+    T: View,
+{
+    fn as_any(&self) -> &dyn Any {
+        self
+    }
+
+    fn as_any_mut(&mut self) -> &mut dyn Any {
+        self
+    }
+
+    fn ui_name(&self) -> &'static str {
+        T::ui_name()
+    }
+
+    fn render<'a>(&self, app: &AppContext) -> Box<dyn Element> {
+        View::render(self, bump, app)
+    }
+
+    fn on_focus(&mut self, app: &mut MutableAppContext, window_id: usize, view_id: usize) {
+        let mut ctx = ViewContext::new(app, window_id, view_id);
+        View::on_focus(self, &mut ctx);
+    }
+
+    fn on_blur(&mut self, app: &mut MutableAppContext, window_id: usize, view_id: usize) {
+        let mut ctx = ViewContext::new(app, window_id, view_id);
+        View::on_blur(self, &mut ctx);
+    }
+
+    fn keymap_context(&self, app: &AppContext) -> keymap::Context {
+        View::keymap_context(self, app)
+    }
+}
+
+pub struct ModelContext<'a, T: ?Sized> {
+    app: &'a mut MutableAppContext,
+    model_id: usize,
+    model_type: PhantomData<T>,
+    halt_stream: bool,
+}
+
+impl<'a, T: Entity> ModelContext<'a, T> {
+    fn new(app: &'a mut MutableAppContext, model_id: usize) -> Self {
+        Self {
+            app,
+            model_id,
+            model_type: PhantomData,
+            halt_stream: false,
+        }
+    }
+
+    pub fn app(&self) -> &AppContext {
+        &self.app.ctx
+    }
+
+    pub fn app_mut(&mut self) -> &mut MutableAppContext {
+        self.app
+    }
+
+    pub fn background_executor(&self) -> Arc<executor::Background> {
+        self.app.background.clone()
+    }
+
+    pub fn halt_stream(&mut self) {
+        self.halt_stream = true;
+    }
+
+    pub fn model_id(&self) -> usize {
+        self.model_id
+    }
+
+    pub fn add_model<S, F>(&mut self, build_model: F) -> ModelHandle<S>
+    where
+        S: Entity,
+        F: FnOnce(&mut ModelContext<S>) -> S,
+    {
+        self.app.add_model(build_model)
+    }
+
+    pub fn subscribe<S: Entity, F>(&mut self, handle: &ModelHandle<S>, mut callback: F)
+    where
+        S::Event: 'static,
+        F: 'static + FnMut(&mut T, &S::Event, &mut ModelContext<T>),
+    {
+        self.app
+            .subscriptions
+            .entry(handle.model_id)
+            .or_default()
+            .push(Subscription::FromModel {
+                model_id: self.model_id,
+                callback: Box::new(move |model, payload, app, model_id| {
+                    let model = model.downcast_mut().expect("downcast is type safe");
+                    let payload = payload.downcast_ref().expect("downcast is type safe");
+                    let mut ctx = ModelContext::new(app, model_id);
+                    callback(model, payload, &mut ctx);
+                }),
+            });
+    }
+
+    pub fn emit(&mut self, payload: T::Event) {
+        self.app.pending_effects.push_back(Effect::Event {
+            entity_id: self.model_id,
+            payload: Box::new(payload),
+        });
+    }
+
+    pub fn observe<S, F>(&mut self, handle: &ModelHandle<S>, mut callback: F)
+    where
+        S: Entity,
+        F: 'static + FnMut(&mut T, ModelHandle<S>, &mut ModelContext<T>),
+    {
+        self.app
+            .observations
+            .entry(handle.model_id)
+            .or_default()
+            .push(Observation::FromModel {
+                model_id: self.model_id,
+                callback: Box::new(move |model, observed_id, app, model_id| {
+                    let model = model.downcast_mut().expect("downcast is type safe");
+                    let observed = ModelHandle::new(observed_id, &app.ctx.ref_counts);
+                    let mut ctx = ModelContext::new(app, model_id);
+                    callback(model, observed, &mut ctx);
+                }),
+            });
+    }
+
+    pub fn notify(&mut self) {
+        self.app
+            .pending_effects
+            .push_back(Effect::ModelNotification {
+                model_id: self.model_id,
+            });
+    }
+
+    pub fn spawn_local<S, F, U>(&mut self, future: S, callback: F) -> impl Future<Output = U>
+    where
+        S: 'static + Future,
+        F: 'static + FnOnce(&mut T, S::Output, &mut ModelContext<T>) -> U,
+        U: 'static,
+    {
+        let (tx, rx) = channel::bounded(1);
+
+        let task_id = self.app.spawn_local(future);
+
+        self.app.task_callbacks.insert(
+            task_id,
+            TaskCallback::OnModelFromFuture {
+                model_id: self.model_id,
+                callback: Box::new(move |model, output, app, model_id, executor| {
+                    let model = model.downcast_mut().unwrap();
+                    let output = *output.downcast().unwrap();
+                    let result = callback(model, output, &mut ModelContext::new(app, model_id));
+                    executor
+                        .spawn(async move { tx.send(result).await })
+                        .detach();
+                }),
+            },
+        );
+
+        async move { rx.recv().await.unwrap() }
+    }
+
+    pub fn spawn<S, F, U>(&mut self, future: S, callback: F) -> impl Future<Output = U>
+    where
+        S: 'static + Future + Send,
+        S::Output: Send,
+        F: 'static + FnOnce(&mut T, S::Output, &mut ModelContext<T>) -> U,
+        U: 'static,
+    {
+        let (tx, rx) = channel::bounded(1);
+
+        self.app
+            .background
+            .spawn(async move {
+                if let Err(_) = tx.send(future.await).await {
+                    log::error!("Error sending background task result to main thread",);
+                }
+            })
+            .detach();
+
+        self.spawn_local(async move { rx.recv().await.unwrap() }, callback)
+    }
+
+    pub fn spawn_stream_local<S, F>(
+        &mut self,
+        stream: S,
+        mut callback: F,
+    ) -> impl Future<Output = ()>
+    where
+        S: 'static + Stream + Unpin,
+        F: 'static + FnMut(&mut T, Option<S::Item>, &mut ModelContext<T>),
+    {
+        let (tx, rx) = channel::bounded(1);
+
+        let task_id = self.app.spawn_stream_local(stream, tx);
+        self.app.task_callbacks.insert(
+            task_id,
+            TaskCallback::OnModelFromStream {
+                model_id: self.model_id,
+                callback: Box::new(move |model, output, app, model_id| {
+                    let model = model.downcast_mut().unwrap();
+                    let output = *output.downcast().unwrap();
+                    let mut ctx = ModelContext::new(app, model_id);
+                    callback(model, output, &mut ctx);
+                    ctx.halt_stream
+                }),
+            },
+        );
+
+        async move { rx.recv().await.unwrap() }
+    }
+}
+
+impl<M> ModelAsRef for ModelContext<'_, M> {
+    fn model<T: Entity>(&self, handle: &ModelHandle<T>) -> &T {
+        self.app.model(handle)
+    }
+}
+
+impl<M> UpdateModel for ModelContext<'_, M> {
+    fn update_model<T, F, S>(&mut self, handle: &ModelHandle<T>, update: F) -> S
+    where
+        T: Entity,
+        F: FnOnce(&mut T, &mut ModelContext<T>) -> S,
+    {
+        self.app.update_model(handle, update)
+    }
+}
+
+pub struct ViewContext<'a, T: ?Sized> {
+    app: &'a mut MutableAppContext,
+    window_id: usize,
+    view_id: usize,
+    view_type: PhantomData<T>,
+    halt_action_dispatch: bool,
+    halt_stream: bool,
+}
+
+impl<'a, T: View> ViewContext<'a, T> {
+    fn new(app: &'a mut MutableAppContext, window_id: usize, view_id: usize) -> Self {
+        Self {
+            app,
+            window_id,
+            view_id,
+            view_type: PhantomData,
+            halt_action_dispatch: true,
+            halt_stream: false,
+        }
+    }
+
+    pub fn handle(&self) -> WeakViewHandle<T> {
+        WeakViewHandle::new(self.window_id, self.view_id)
+    }
+
+    pub fn window_id(&self) -> usize {
+        self.window_id
+    }
+
+    pub fn app(&self) -> &AppContext {
+        &self.app.ctx
+    }
+
+    pub fn app_mut(&mut self) -> &mut MutableAppContext {
+        self.app
+    }
+
+    pub fn focus<S>(&mut self, handle: S)
+    where
+        S: Into<AnyViewHandle>,
+    {
+        let handle = handle.into();
+        self.app.pending_effects.push_back(Effect::Focus {
+            window_id: handle.window_id,
+            view_id: handle.view_id,
+        });
+    }
+
+    pub fn focus_self(&mut self) {
+        self.app.pending_effects.push_back(Effect::Focus {
+            window_id: self.window_id,
+            view_id: self.view_id,
+        });
+    }
+
+    pub fn add_model<S, F>(&mut self, build_model: F) -> ModelHandle<S>
+    where
+        S: Entity,
+        F: FnOnce(&mut ModelContext<S>) -> S,
+    {
+        self.app.add_model(build_model)
+    }
+
+    pub fn add_view<S, F>(&mut self, build_view: F) -> ViewHandle<S>
+    where
+        S: View,
+        F: FnOnce(&mut ViewContext<S>) -> S,
+    {
+        self.app.add_view(self.window_id, build_view)
+    }
+
+    pub fn add_option_view<S, F>(&mut self, build_view: F) -> Option<ViewHandle<S>>
+    where
+        S: View,
+        F: FnOnce(&mut ViewContext<S>) -> Option<S>,
+    {
+        self.app.add_option_view(self.window_id, build_view)
+    }
+
+    pub fn subscribe_to_model<E, F>(&mut self, handle: &ModelHandle<E>, mut callback: F)
+    where
+        E: Entity,
+        E::Event: 'static,
+        F: 'static + FnMut(&mut T, ModelHandle<E>, &E::Event, &mut ViewContext<T>),
+    {
+        let emitter_handle = handle.downgrade();
+        self.app
+            .subscriptions
+            .entry(handle.id())
+            .or_default()
+            .push(Subscription::FromView {
+                window_id: self.window_id,
+                view_id: self.view_id,
+                callback: Box::new(move |view, payload, app, window_id, view_id| {
+                    if let Some(emitter_handle) = emitter_handle.upgrade(app.ctx()) {
+                        let model = view.downcast_mut().expect("downcast is type safe");
+                        let payload = payload.downcast_ref().expect("downcast is type safe");
+                        let mut ctx = ViewContext::new(app, window_id, view_id);
+                        callback(model, emitter_handle, payload, &mut ctx);
+                    }
+                }),
+            });
+    }
+
+    pub fn subscribe_to_view<V, F>(&mut self, handle: &ViewHandle<V>, mut callback: F)
+    where
+        V: View,
+        V::Event: 'static,
+        F: 'static + FnMut(&mut T, ViewHandle<V>, &V::Event, &mut ViewContext<T>),
+    {
+        let emitter_handle = handle.downgrade();
+
+        self.app
+            .subscriptions
+            .entry(handle.id())
+            .or_default()
+            .push(Subscription::FromView {
+                window_id: self.window_id,
+                view_id: self.view_id,
+                callback: Box::new(move |view, payload, app, window_id, view_id| {
+                    if let Some(emitter_handle) = emitter_handle.upgrade(app.ctx()) {
+                        let model = view.downcast_mut().expect("downcast is type safe");
+                        let payload = payload.downcast_ref().expect("downcast is type safe");
+                        let mut ctx = ViewContext::new(app, window_id, view_id);
+                        callback(model, emitter_handle, payload, &mut ctx);
+                    }
+                }),
+            });
+    }
+
+    pub fn emit(&mut self, payload: T::Event) {
+        self.app.pending_effects.push_back(Effect::Event {
+            entity_id: self.view_id,
+            payload: Box::new(payload),
+        });
+    }
+
+    pub fn observe<S, F>(&mut self, handle: &ModelHandle<S>, mut callback: F)
+    where
+        S: Entity,
+        F: 'static + FnMut(&mut T, ModelHandle<S>, &mut ViewContext<T>),
+    {
+        self.app
+            .observations
+            .entry(handle.id())
+            .or_default()
+            .push(Observation::FromView {
+                window_id: self.window_id,
+                view_id: self.view_id,
+                callback: Box::new(move |view, observed_id, app, window_id, view_id| {
+                    let view = view.downcast_mut().expect("downcast is type safe");
+                    let observed = ModelHandle::new(observed_id, &app.ctx.ref_counts);
+                    let mut ctx = ViewContext::new(app, window_id, view_id);
+                    callback(view, observed, &mut ctx);
+                }),
+            });
+    }
+
+    pub fn notify(&mut self) {
+        self.app
+            .pending_effects
+            .push_back(Effect::ViewNotification {
+                window_id: self.window_id,
+                view_id: self.view_id,
+            });
+    }
+
+    pub fn propagate_action(&mut self) {
+        self.halt_action_dispatch = false;
+    }
+
+    pub fn halt_stream(&mut self) {
+        self.halt_stream = true;
+    }
+
+    pub fn spawn_local<S, F, U>(&mut self, future: S, callback: F) -> impl Future<Output = U>
+    where
+        S: 'static + Future,
+        F: 'static + FnOnce(&mut T, S::Output, &mut ViewContext<T>) -> U,
+        U: 'static,
+    {
+        let (tx, rx) = channel::bounded(1);
+
+        let task_id = self.app.spawn_local(future);
+
+        self.app.task_callbacks.insert(
+            task_id,
+            TaskCallback::OnViewFromFuture {
+                window_id: self.window_id,
+                view_id: self.view_id,
+                callback: Box::new(move |view, output, app, window_id, view_id, executor| {
+                    let view = view.as_any_mut().downcast_mut().unwrap();
+                    let output = *output.downcast().unwrap();
+                    let result =
+                        callback(view, output, &mut ViewContext::new(app, window_id, view_id));
+                    executor
+                        .spawn(async move { tx.send(result).await })
+                        .detach();
+                }),
+            },
+        );
+
+        async move { rx.recv().await.unwrap() }
+    }
+
+    pub fn spawn<S, F, U>(&mut self, future: S, callback: F) -> impl Future<Output = U>
+    where
+        S: 'static + Future + Send,
+        S::Output: Send,
+        F: 'static + FnOnce(&mut T, S::Output, &mut ViewContext<T>) -> U,
+        U: 'static,
+    {
+        let (tx, rx) = channel::bounded(1);
+
+        self.app
+            .background
+            .spawn(async move {
+                if let Err(_) = tx.send(future.await).await {
+                    log::error!("Error sending background task result to main thread",);
+                }
+            })
+            .detach();
+
+        self.spawn_local(async move { rx.recv().await.unwrap() }, callback)
+    }
+
+    pub fn spawn_stream_local<S, F>(
+        &mut self,
+        stream: S,
+        mut callback: F,
+    ) -> impl Future<Output = ()>
+    where
+        S: 'static + Stream + Unpin,
+        F: 'static + FnMut(&mut T, Option<S::Item>, &mut ViewContext<T>),
+    {
+        let (tx, rx) = channel::bounded(1);
+
+        let task_id = self.app.spawn_stream_local(stream, tx);
+        self.app.task_callbacks.insert(
+            task_id,
+            TaskCallback::OnViewFromStream {
+                window_id: self.window_id,
+                view_id: self.view_id,
+                callback: Box::new(move |view, output, app, window_id, view_id| {
+                    let view = view.as_any_mut().downcast_mut().unwrap();
+                    let output = *output.downcast().unwrap();
+                    let mut ctx = ViewContext::new(app, window_id, view_id);
+                    callback(view, output, &mut ctx);
+                    ctx.halt_stream
+                }),
+            },
+        );
+
+        async move { rx.recv().await.unwrap() }
+    }
+}
+
+impl<V> ModelAsRef for ViewContext<'_, V> {
+    fn model<T: Entity>(&self, handle: &ModelHandle<T>) -> &T {
+        self.app.model(handle)
+    }
+}
+
+impl<V: View> UpdateModel for ViewContext<'_, V> {
+    fn update_model<T, F, S>(&mut self, handle: &ModelHandle<T>, update: F) -> S
+    where
+        T: Entity,
+        F: FnOnce(&mut T, &mut ModelContext<T>) -> S,
+    {
+        self.app.update_model(handle, update)
+    }
+}
+
+impl<V: View> ViewAsRef for ViewContext<'_, V> {
+    fn view<T: View>(&self, handle: &ViewHandle<T>) -> &T {
+        self.app.view(handle)
+    }
+}
+
+impl<V: View> UpdateView for ViewContext<'_, V> {
+    fn update_view<T, F, S>(&mut self, handle: &ViewHandle<T>, update: F) -> S
+    where
+        T: View,
+        F: FnOnce(&mut T, &mut ViewContext<T>) -> S,
+    {
+        self.app.update_view(handle, update)
+    }
+}
+
+pub trait Handle<T> {
+    fn id(&self) -> usize;
+    fn location(&self) -> EntityLocation;
+}
+
+#[derive(Clone, Copy, Debug, Eq, PartialEq, Hash)]
+pub enum EntityLocation {
+    Model(usize),
+    View(usize, usize),
+}
+
+pub struct ModelHandle<T> {
+    model_id: usize,
+    model_type: PhantomData<T>,
+    ref_counts: Weak<Mutex<RefCounts>>,
+}
+
+impl<T: Entity> ModelHandle<T> {
+    fn new(model_id: usize, ref_counts: &Arc<Mutex<RefCounts>>) -> Self {
+        ref_counts.lock().inc(model_id);
+        Self {
+            model_id,
+            model_type: PhantomData,
+            ref_counts: Arc::downgrade(ref_counts),
+        }
+    }
+
+    fn downgrade(&self) -> WeakModelHandle<T> {
+        WeakModelHandle::new(self.model_id)
+    }
+
+    pub fn id(&self) -> usize {
+        self.model_id
+    }
+
+    pub fn as_ref<'a, A: ModelAsRef>(&self, app: &'a A) -> &'a T {
+        app.model(self)
+    }
+
+    pub fn read<'a, S, F>(&self, app: &'a App, read: F) -> S
+    where
+        F: FnOnce(&T, &AppContext) -> S,
+    {
+        app.read_model(self, read)
+    }
+
+    pub fn update<A, F, S>(&self, app: &mut A, update: F) -> S
+    where
+        A: UpdateModel,
+        F: FnOnce(&mut T, &mut ModelContext<T>) -> S,
+    {
+        app.update_model(self, update)
+    }
+}
+
+impl<T> Clone for ModelHandle<T> {
+    fn clone(&self) -> Self {
+        if let Some(ref_counts) = self.ref_counts.upgrade() {
+            ref_counts.lock().inc(self.model_id);
+        }
+
+        Self {
+            model_id: self.model_id,
+            model_type: PhantomData,
+            ref_counts: self.ref_counts.clone(),
+        }
+    }
+}
+
+impl<T> PartialEq for ModelHandle<T> {
+    fn eq(&self, other: &Self) -> bool {
+        self.model_id == other.model_id
+    }
+}
+
+impl<T> Eq for ModelHandle<T> {}
+
+impl<T> Hash for ModelHandle<T> {
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        self.model_id.hash(state);
+    }
+}
+
+impl<T> borrow::Borrow<usize> for ModelHandle<T> {
+    fn borrow(&self) -> &usize {
+        &self.model_id
+    }
+}
+
+impl<T> Debug for ModelHandle<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_tuple(&format!("ModelHandle<{}>", type_name::<T>()))
+            .field(&self.model_id)
+            .finish()
+    }
+}
+
+unsafe impl<T> Send for ModelHandle<T> {}
+unsafe impl<T> Sync for ModelHandle<T> {}
+
+impl<T> Drop for ModelHandle<T> {
+    fn drop(&mut self) {
+        if let Some(ref_counts) = self.ref_counts.upgrade() {
+            ref_counts.lock().dec_model(self.model_id);
+        }
+    }
+}
+
+impl<T> Handle<T> for ModelHandle<T> {
+    fn id(&self) -> usize {
+        self.model_id
+    }
+
+    fn location(&self) -> EntityLocation {
+        EntityLocation::Model(self.model_id)
+    }
+}
+
+pub struct WeakModelHandle<T> {
+    model_id: usize,
+    model_type: PhantomData<T>,
+}
+
+impl<T: Entity> WeakModelHandle<T> {
+    fn new(model_id: usize) -> Self {
+        Self {
+            model_id,
+            model_type: PhantomData,
+        }
+    }
+
+    pub fn upgrade(&self, app: &AppContext) -> Option<ModelHandle<T>> {
+        if app.models.contains_key(&self.model_id) {
+            Some(ModelHandle::new(self.model_id, &app.ref_counts))
+        } else {
+            None
+        }
+    }
+}
+
+pub struct ViewHandle<T> {
+    window_id: usize,
+    view_id: usize,
+    view_type: PhantomData<T>,
+    ref_counts: Weak<Mutex<RefCounts>>,
+}
+
+impl<T: View> ViewHandle<T> {
+    fn new(window_id: usize, view_id: usize, ref_counts: &Arc<Mutex<RefCounts>>) -> Self {
+        ref_counts.lock().inc(view_id);
+        Self {
+            window_id,
+            view_id,
+            view_type: PhantomData,
+            ref_counts: Arc::downgrade(ref_counts),
+        }
+    }
+
+    fn downgrade(&self) -> WeakViewHandle<T> {
+        WeakViewHandle::new(self.window_id, self.view_id)
+    }
+
+    pub fn window_id(&self) -> usize {
+        self.window_id
+    }
+
+    pub fn id(&self) -> usize {
+        self.view_id
+    }
+
+    pub fn as_ref<'a, A: ViewAsRef>(&self, app: &'a A) -> &'a T {
+        app.view(self)
+    }
+
+    pub fn read<'a, F, S>(&self, app: &'a App, read: F) -> S
+    where
+        F: FnOnce(&T, &AppContext) -> S,
+    {
+        app.read_view(self, read)
+    }
+
+    pub fn update<A, F, S>(&self, app: &mut A, update: F) -> S
+    where
+        A: UpdateView,
+        F: FnOnce(&mut T, &mut ViewContext<T>) -> S,
+    {
+        app.update_view(self, update)
+    }
+
+    pub fn is_focused(&self, app: &AppContext) -> bool {
+        app.focused_view_id(self.window_id)
+            .map_or(false, |focused_id| focused_id == self.view_id)
+    }
+}
+
+impl<T> Clone for ViewHandle<T> {
+    fn clone(&self) -> Self {
+        if let Some(ref_counts) = self.ref_counts.upgrade() {
+            ref_counts.lock().inc(self.view_id);
+        }
+
+        Self {
+            window_id: self.window_id,
+            view_id: self.view_id,
+            view_type: PhantomData,
+            ref_counts: self.ref_counts.clone(),
+        }
+    }
+}
+
+impl<T> PartialEq for ViewHandle<T> {
+    fn eq(&self, other: &Self) -> bool {
+        self.window_id == other.window_id && self.view_id == other.view_id
+    }
+}
+
+impl<T> Eq for ViewHandle<T> {}
+
+impl<T> Debug for ViewHandle<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct(&format!("ViewHandle<{}>", type_name::<T>()))
+            .field("window_id", &self.window_id)
+            .field("view_id", &self.view_id)
+            .finish()
+    }
+}
+
+impl<T> Drop for ViewHandle<T> {
+    fn drop(&mut self) {
+        if let Some(ref_counts) = self.ref_counts.upgrade() {
+            ref_counts.lock().dec_view(self.window_id, self.view_id);
+        }
+    }
+}
+
+impl<T> Handle<T> for ViewHandle<T> {
+    fn id(&self) -> usize {
+        self.view_id
+    }
+
+    fn location(&self) -> EntityLocation {
+        EntityLocation::View(self.window_id, self.view_id)
+    }
+}
+
+#[derive(Clone)]
+pub struct AnyViewHandle {
+    window_id: usize,
+    view_id: usize,
+    view_type: TypeId,
+    ref_counts: Weak<Mutex<RefCounts>>,
+}
+
+impl AnyViewHandle {
+    pub fn id(&self) -> usize {
+        self.view_id
+    }
+
+    pub fn is<T: 'static>(&self) -> bool {
+        TypeId::of::<T>() == self.view_type
+    }
+
+    pub fn downcast<T: View>(self) -> Option<ViewHandle<T>> {
+        if self.is::<T>() {
+            if let Some(ref_counts) = self.ref_counts.upgrade() {
+                return Some(ViewHandle::new(self.window_id, self.view_id, &ref_counts));
+            }
+        }
+        None
+    }
+}
+
+impl<T: View> From<&ViewHandle<T>> for AnyViewHandle {
+    fn from(handle: &ViewHandle<T>) -> Self {
+        if let Some(ref_counts) = handle.ref_counts.upgrade() {
+            ref_counts.lock().inc(handle.view_id);
+        }
+        AnyViewHandle {
+            window_id: handle.window_id,
+            view_id: handle.view_id,
+            view_type: TypeId::of::<T>(),
+            ref_counts: handle.ref_counts.clone(),
+        }
+    }
+}
+
+impl<T: View> From<ViewHandle<T>> for AnyViewHandle {
+    fn from(handle: ViewHandle<T>) -> Self {
+        (&handle).into()
+    }
+}
+
+pub struct WeakViewHandle<T> {
+    window_id: usize,
+    view_id: usize,
+    view_type: PhantomData<T>,
+}
+
+impl<T: View> WeakViewHandle<T> {
+    fn new(window_id: usize, view_id: usize) -> Self {
+        Self {
+            window_id,
+            view_id,
+            view_type: PhantomData,
+        }
+    }
+
+    pub fn upgrade(&self, app: &AppContext) -> Option<ViewHandle<T>> {
+        if app
+            .windows
+            .get(&self.window_id)
+            .and_then(|w| w.views.get(&self.view_id))
+            .is_some()
+        {
+            Some(ViewHandle::new(
+                self.window_id,
+                self.view_id,
+                &app.ref_counts,
+            ))
+        } else {
+            None
+        }
+    }
+}
+
+impl<T> Clone for WeakViewHandle<T> {
+    fn clone(&self) -> Self {
+        Self {
+            window_id: self.window_id,
+            view_id: self.view_id,
+            view_type: PhantomData,
+        }
+    }
+}
+
+#[derive(Default)]
+struct RefCounts {
+    counts: HashMap<usize, usize>,
+    dropped_models: HashSet<usize>,
+    dropped_views: HashSet<(usize, usize)>,
+}
+
+impl RefCounts {
+    fn inc(&mut self, model_id: usize) {
+        *self.counts.entry(model_id).or_insert(0) += 1;
+    }
+
+    fn dec_model(&mut self, model_id: usize) {
+        if let Some(count) = self.counts.get_mut(&model_id) {
+            *count -= 1;
+            if *count == 0 {
+                self.counts.remove(&model_id);
+                self.dropped_models.insert(model_id);
+            }
+        } else {
+            panic!("Expected ref count to be positive")
+        }
+    }
+
+    fn dec_view(&mut self, window_id: usize, view_id: usize) {
+        if let Some(count) = self.counts.get_mut(&view_id) {
+            *count -= 1;
+            if *count == 0 {
+                self.counts.remove(&view_id);
+                self.dropped_views.insert((window_id, view_id));
+            }
+        } else {
+            panic!("Expected ref count to be positive")
+        }
+    }
+
+    fn take_dropped(&mut self) -> (HashSet<usize>, HashSet<(usize, usize)>) {
+        let mut dropped_models = HashSet::new();
+        let mut dropped_views = HashSet::new();
+        std::mem::swap(&mut self.dropped_models, &mut dropped_models);
+        std::mem::swap(&mut self.dropped_views, &mut dropped_views);
+        (dropped_models, dropped_views)
+    }
+}
+
+enum Subscription {
+    FromModel {
+        model_id: usize,
+        callback: Box<dyn FnMut(&mut dyn Any, &dyn Any, &mut MutableAppContext, usize)>,
+    },
+    FromView {
+        window_id: usize,
+        view_id: usize,
+        callback: Box<dyn FnMut(&mut dyn Any, &dyn Any, &mut MutableAppContext, usize, usize)>,
+    },
+}
+
+enum Observation {
+    FromModel {
+        model_id: usize,
+        callback: Box<dyn FnMut(&mut dyn Any, usize, &mut MutableAppContext, usize)>,
+    },
+    FromView {
+        window_id: usize,
+        view_id: usize,
+        callback: Box<dyn FnMut(&mut dyn Any, usize, &mut MutableAppContext, usize, usize)>,
+    },
+}
+
+enum TaskCallback {
+    OnModelFromFuture {
+        model_id: usize,
+        callback: Box<
+            dyn FnOnce(
+                &mut dyn Any,
+                Box<dyn Any>,
+                &mut MutableAppContext,
+                usize,
+                Rc<executor::Foreground>,
+            ),
+        >,
+    },
+    OnModelFromStream {
+        model_id: usize,
+        callback: Box<dyn FnMut(&mut dyn Any, Box<dyn Any>, &mut MutableAppContext, usize) -> bool>,
+    },
+    OnViewFromFuture {
+        window_id: usize,
+        view_id: usize,
+        callback: Box<
+            dyn FnOnce(
+                &mut dyn AnyView,
+                Box<dyn Any>,
+                &mut MutableAppContext,
+                usize,
+                usize,
+                Rc<executor::Foreground>,
+            ),
+        >,
+    },
+    OnViewFromStream {
+        window_id: usize,
+        view_id: usize,
+        callback: Box<
+            dyn FnMut(&mut dyn AnyView, Box<dyn Any>, &mut MutableAppContext, usize, usize) -> bool,
+        >,
+    },
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::elements::*;
+
+    #[test]
+    fn test_model_handles() {
+        struct Model {
+            other: Option<ModelHandle<Model>>,
+            events: Vec<String>,
+        }
+
+        impl Entity for Model {
+            type Event = usize;
+        }
+
+        impl Model {
+            fn new(other: Option<ModelHandle<Self>>, ctx: &mut ModelContext<Self>) -> Self {
+                if let Some(other) = other.as_ref() {
+                    ctx.observe(other, |me, _, _| {
+                        me.events.push("notified".into());
+                    });
+                    ctx.subscribe(other, |me, event, _| {
+                        me.events.push(format!("observed event {}", event));
+                    });
+                }
+
+                Self {
+                    other,
+                    events: Vec::new(),
+                }
+            }
+        }
+
+        let mut app = App::new().unwrap();
+        let app = &mut app;
+
+        let handle_1 = app.add_model(|ctx| Model::new(None, ctx));
+        let handle_2 = app.add_model(|ctx| Model::new(Some(handle_1.clone()), ctx));
+        assert_eq!(app.0.borrow().ctx.models.len(), 2);
+
+        handle_1.update(app, |model, ctx| {
+            model.events.push("updated".into());
+            ctx.emit(1);
+            ctx.notify();
+            ctx.emit(2);
+        });
+        handle_1.read(app, |model, _| {
+            assert_eq!(model.events, vec!["updated".to_string()]);
+        });
+        handle_2.read(app, |model, _| {
+            assert_eq!(
+                model.events,
+                vec![
+                    "observed event 1".to_string(),
+                    "notified".to_string(),
+                    "observed event 2".to_string(),
+                ]
+            );
+        });
+
+        handle_2.update(app, |model, _| {
+            drop(handle_1);
+            model.other.take();
+        });
+
+        let app_state = app.0.borrow();
+        assert_eq!(app_state.ctx.models.len(), 1);
+        assert!(app_state.subscriptions.is_empty());
+        assert!(app_state.observations.is_empty());
+    }
+
+    #[test]
+    fn test_subscribe_and_emit_from_model() {
+        #[derive(Default)]
+        struct Model {
+            events: Vec<usize>,
+        }
+
+        impl Entity for Model {
+            type Event = usize;
+        }
+
+        let mut app = App::new().unwrap();
+        let app = &mut app;
+
+        let handle_1 = app.add_model(|_| Model::default());
+        let handle_2 = app.add_model(|_| Model::default());
+        let handle_2b = handle_2.clone();
+
+        handle_1.update(app, |_, c| {
+            c.subscribe(&handle_2, move |model: &mut Model, event, c| {
+                model.events.push(*event);
+
+                c.subscribe(&handle_2b, |model, event, _| {
+                    model.events.push(*event * 2);
+                });
+            });
+        });
+
+        handle_2.update(app, |_, c| c.emit(7));
+        handle_1.read(app, |model, _| assert_eq!(model.events, vec![7]));
+
+        handle_2.update(app, |_, c| c.emit(5));
+        handle_1.read(app, |model, _| assert_eq!(model.events, vec![7, 10, 5]));
+    }
+
+    #[test]
+    fn test_observe_and_notify_from_model() {
+        #[derive(Default)]
+        struct Model {
+            count: usize,
+            events: Vec<usize>,
+        }
+
+        impl Entity for Model {
+            type Event = ();
+        }
+
+        let mut app = App::new().unwrap();
+
+        let app = &mut app;
+        let handle_1 = app.add_model(|_| Model::default());
+        let handle_2 = app.add_model(|_| Model::default());
+        let handle_2b = handle_2.clone();
+
+        handle_1.update(app, |_, c| {
+            c.observe(&handle_2, move |model, observed, c| {
+                model.events.push(observed.as_ref(c).count);
+                c.observe(&handle_2b, |model, observed, c| {
+                    model.events.push(observed.as_ref(c).count * 2);
+                });
+            });
+        });
+
+        handle_2.update(app, |model, c| {
+            model.count = 7;
+            c.notify()
+        });
+        handle_1.read(app, |model, _| assert_eq!(model.events, vec![7]));
+
+        handle_2.update(app, |model, c| {
+            model.count = 5;
+            c.notify()
+        });
+        handle_1.read(app, |model, _| assert_eq!(model.events, vec![7, 10, 5]))
+    }
+
+    #[test]
+    fn test_spawn_from_model() {
+        #[derive(Default)]
+        struct Model {
+            count: usize,
+        }
+
+        impl Entity for Model {
+            type Event = ();
+        }
+
+        App::run(|mut app| async move {
+            let handle = app.add_model(|_| Model::default());
+            handle
+                .update(&mut app, |_, c| {
+                    c.spawn_local(async { 7 }, |model, output, _| {
+                        model.count = output;
+                    })
+                })
+                .await;
+            handle.read(&app, |model, _| assert_eq!(model.count, 7));
+
+            handle
+                .update(&mut app, |_, c| {
+                    c.spawn(async { 14 }, |model, output, _| {
+                        model.count = output;
+                    })
+                })
+                .await;
+            handle.read(&app, |model, _| assert_eq!(model.count, 14));
+        });
+    }
+
+    #[test]
+    fn test_spawn_stream_local_from_model() {
+        #[derive(Default)]
+        struct Model {
+            events: Vec<Option<usize>>,
+        }
+
+        impl Entity for Model {
+            type Event = ();
+        }
+
+        App::run(|mut app| async move {
+            let handle = app.add_model(|_| Model::default());
+            handle
+                .update(&mut app, |_, c| {
+                    c.spawn_stream_local(smol::stream::iter(vec![1, 2, 3]), |model, output, _| {
+                        model.events.push(output);
+                    })
+                })
+                .await;
+
+            handle.read(&app, |model, _| {
+                assert_eq!(model.events, [Some(1), Some(2), Some(3), None])
+            });
+        })
+    }
+
+    #[test]
+    fn test_view_handles() {
+        struct View {
+            other: Option<ViewHandle<View>>,
+            events: Vec<String>,
+        }
+
+        impl Entity for View {
+            type Event = usize;
+        }
+
+        impl super::View for View {
+            fn render<'a>(&self, _: &AppContext) -> Box<dyn Element> {
+                Empty::new().finish(bump)
+            }
+
+            fn ui_name() -> &'static str {
+                "View"
+            }
+        }
+
+        impl View {
+            fn new(other: Option<ViewHandle<View>>, ctx: &mut ViewContext<Self>) -> Self {
+                if let Some(other) = other.as_ref() {
+                    ctx.subscribe_to_view(other, |me, _, event, _| {
+                        me.events.push(format!("observed event {}", event));
+                    });
+                }
+                Self {
+                    other,
+                    events: Vec::new(),
+                }
+            }
+        }
+
+        let mut app = App::new().unwrap();
+        let app = &mut app;
+
+        let (window_id, _) = app.add_window(|ctx| View::new(None, ctx));
+        let handle_1 = app.add_view(window_id, |ctx| View::new(None, ctx));
+        let handle_2 = app.add_view(window_id, |ctx| View::new(Some(handle_1.clone()), ctx));
+        assert_eq!(app.0.borrow().ctx.windows[&window_id].views.len(), 3);
+
+        handle_1.update(app, |view, ctx| {
+            view.events.push("updated".into());
+            ctx.emit(1);
+            ctx.emit(2);
+        });
+        handle_1.read(app, |view, _| {
+            assert_eq!(view.events, vec!["updated".to_string()]);
+        });
+        handle_2.read(app, |view, _| {
+            assert_eq!(
+                view.events,
+                vec![
+                    "observed event 1".to_string(),
+                    "observed event 2".to_string(),
+                ]
+            );
+        });
+
+        handle_2.update(app, |view, _| {
+            drop(handle_1);
+            view.other.take();
+        });
+
+        let app_state = app.0.borrow();
+        assert_eq!(app_state.ctx.windows[&window_id].views.len(), 2);
+        assert!(app_state.subscriptions.is_empty());
+        assert!(app_state.observations.is_empty());
+    }
+
+    #[test]
+    fn test_subscribe_and_emit_from_view() {
+        #[derive(Default)]
+        struct View {
+            events: Vec<usize>,
+        }
+
+        impl Entity for View {
+            type Event = usize;
+        }
+
+        impl super::View for View {
+            fn render<'a>(&self, bump: &'a Bump, _: &AppContext) -> Box<dyn Element> {
+                Empty::new().finish(bump)
+            }
+
+            fn ui_name() -> &'static str {
+                "View"
+            }
+        }
+
+        struct Model;
+
+        impl Entity for Model {
+            type Event = usize;
+        }
+
+        let mut app = App::new().unwrap();
+        let app = &mut app;
+
+        let (window_id, handle_1) = app.add_window(|_| View::default());
+        let handle_2 = app.add_view(window_id, |_| View::default());
+        let handle_2b = handle_2.clone();
+        let handle_3 = app.add_model(|_| Model);
+
+        handle_1.update(app, |_, c| {
+            c.subscribe_to_view(&handle_2, move |me, _, event, c| {
+                me.events.push(*event);
+
+                c.subscribe_to_view(&handle_2b, |me, _, event, _| {
+                    me.events.push(*event * 2);
+                });
+            });
+
+            c.subscribe_to_model(&handle_3, |me, _, event, _| {
+                me.events.push(*event);
+            })
+        });
+
+        handle_2.update(app, |_, c| c.emit(7));
+        handle_1.read(app, |view, _| assert_eq!(view.events, vec![7]));
+
+        handle_2.update(app, |_, c| c.emit(5));
+        handle_1.read(app, |view, _| assert_eq!(view.events, vec![7, 10, 5]));
+
+        handle_3.update(app, |_, c| c.emit(9));
+        handle_1.read(app, |view, _| assert_eq!(view.events, vec![7, 10, 5, 9]));
+    }
+
+    #[test]
+    fn test_dropping_subscribers() {
+        struct View;
+
+        impl Entity for View {
+            type Event = ();
+        }
+
+        impl super::View for View {
+            fn render<'a>(&self, bump: &'a Bump, _: &AppContext) -> Box<dyn Element> {
+                Empty::new().finish(bump)
+            }
+
+            fn ui_name() -> &'static str {
+                "View"
+            }
+        }
+
+        struct Model;
+
+        impl Entity for Model {
+            type Event = ();
+        }
+
+        let mut app = App::new().unwrap();
+        let app = &mut app;
+
+        let (window_id, _) = app.add_window(|_| View);
+        let observing_view = app.add_view(window_id, |_| View);
+        let emitting_view = app.add_view(window_id, |_| View);
+        let observing_model = app.add_model(|_| Model);
+        let observed_model = app.add_model(|_| Model);
+
+        observing_view.update(app, |_, ctx| {
+            ctx.subscribe_to_view(&emitting_view, |_, _, _, _| {});
+            ctx.subscribe_to_model(&observed_model, |_, _, _, _| {});
+        });
+        observing_model.update(app, |_, ctx| {
+            ctx.subscribe(&observed_model, |_, _, _| {});
+        });
+
+        app.update(|_| {
+            drop(observing_view);
+            drop(observing_model);
+        });
+
+        emitting_view.update(app, |_, ctx| ctx.emit(()));
+        observed_model.update(app, |_, ctx| ctx.emit(()));
+    }
+
+    #[test]
+    fn test_observe_and_notify_from_view() {
+        #[derive(Default)]
+        struct View {
+            events: Vec<usize>,
+        }
+
+        impl Entity for View {
+            type Event = usize;
+        }
+
+        impl super::View for View {
+            fn render<'a>(&self, bump: &'a Bump, _: &AppContext) -> Box<dyn Element> {
+                Empty::new().finish(bump)
+            }
+
+            fn ui_name() -> &'static str {
+                "View"
+            }
+        }
+
+        #[derive(Default)]
+        struct Model {
+            count: usize,
+        }
+
+        impl Entity for Model {
+            type Event = ();
+        }
+
+        let mut app = App::new().unwrap();
+        let app = &mut app;
+        let (_, view) = app.add_window(|_| View::default());
+        let model = app.add_model(|_| Model::default());
+
+        view.update(app, |_, c| {
+            c.observe(&model, |me, observed, c| {
+                me.events.push(observed.as_ref(c).count)
+            });
+        });
+
+        model.update(app, |model, c| {
+            model.count = 11;
+            c.notify();
+        });
+        view.read(app, |view, _| assert_eq!(view.events, vec![11]));
+    }
+
+    #[test]
+    fn test_dropping_observers() {
+        struct View;
+
+        impl Entity for View {
+            type Event = ();
+        }
+
+        impl super::View for View {
+            fn render<'a>(&self, bump: &'a Bump, _: &AppContext) -> Box<dyn Element> {
+                Empty::new().finish(bump)
+            }
+
+            fn ui_name() -> &'static str {
+                "View"
+            }
+        }
+
+        struct Model;
+
+        impl Entity for Model {
+            type Event = ();
+        }
+
+        let mut app = App::new().unwrap();
+        let app = &mut app;
+
+        let (window_id, _) = app.add_window(|_| View);
+        let observing_view = app.add_view(window_id, |_| View);
+        let observing_model = app.add_model(|_| Model);
+        let observed_model = app.add_model(|_| Model);
+
+        observing_view.update(app, |_, ctx| {
+            ctx.observe(&observed_model, |_, _, _| {});
+        });
+        observing_model.update(app, |_, ctx| {
+            ctx.observe(&observed_model, |_, _, _| {});
+        });
+
+        app.update(|_| {
+            drop(observing_view);
+            drop(observing_model);
+        });
+
+        observed_model.update(app, |_, ctx| ctx.notify());
+    }
+
+    #[test]
+    fn test_focus() {
+        #[derive(Default)]
+        struct View {
+            events: Vec<String>,
+        }
+
+        impl Entity for View {
+            type Event = String;
+        }
+
+        impl super::View for View {
+            fn render<'a>(&self, bump: &'a Bump, _: &AppContext) -> Box<dyn Element> {
+                Empty::new().finish(bump)
+            }
+
+            fn ui_name() -> &'static str {
+                "View"
+            }
+
+            fn on_focus(&mut self, ctx: &mut ViewContext<Self>) {
+                self.events.push("self focused".into());
+                ctx.emit("focused".into());
+            }
+
+            fn on_blur(&mut self, ctx: &mut ViewContext<Self>) {
+                self.events.push("self blurred".into());
+                ctx.emit("blurred".into());
+            }
+        }
+
+        let mut app = App::new().unwrap();
+        let app = &mut app;
+        let (window_id, view_1) = app.add_window(|_| View::default());
+        let view_2 = app.add_view(window_id, |_| View::default());
+
+        view_1.update(app, |_, ctx| {
+            ctx.subscribe_to_view(&view_2, |view_1, _, event, _| {
+                view_1.events.push(format!("view 2 {}", event));
+            });
+            ctx.focus(&view_2);
+        });
+
+        view_1.update(app, |_, ctx| {
+            ctx.focus(&view_1);
+        });
+
+        view_1.read(app, |view_1, _| {
+            assert_eq!(
+                view_1.events,
+                [
+                    "self focused".to_string(),
+                    "self blurred".to_string(),
+                    "view 2 focused".to_string(),
+                    "self focused".to_string(),
+                    "view 2 blurred".to_string(),
+                ],
+            );
+        });
+    }
+
+    #[test]
+    fn test_spawn_from_view() {
+        #[derive(Default)]
+        struct View {
+            count: usize,
+        }
+
+        impl Entity for View {
+            type Event = ();
+        }
+
+        impl super::View for View {
+            fn render<'a>(&self, bump: &'a Bump, _: &AppContext) -> Box<dyn Element> {
+                Empty::new().finish(bump)
+            }
+
+            fn ui_name() -> &'static str {
+                "View"
+            }
+        }
+
+        App::run(|mut app| async move {
+            let (_, handle) = app.add_window(|_| View::default());
+            handle
+                .update(&mut app, |_, c| {
+                    c.spawn_local(async { 7 }, |me, output, _| {
+                        me.count = output;
+                    })
+                })
+                .await;
+            handle.read(&app, |view, _| assert_eq!(view.count, 7));
+            handle
+                .update(&mut app, |_, c| {
+                    c.spawn(async { 14 }, |me, output, _| {
+                        me.count = output;
+                    })
+                })
+                .await;
+            handle.read(&app, |view, _| assert_eq!(view.count, 14));
+        });
+    }
+
+    #[test]
+    fn test_spawn_stream_local_from_view() {
+        #[derive(Default)]
+        struct View {
+            events: Vec<Option<usize>>,
+        }
+
+        impl Entity for View {
+            type Event = ();
+        }
+
+        impl super::View for View {
+            fn render<'a>(&self, bump: &'a Bump, _: &AppContext) -> Box<dyn Element> {
+                Empty::new().finish(bump)
+            }
+
+            fn ui_name() -> &'static str {
+                "View"
+            }
+        }
+
+        App::run(|mut app| async move {
+            let (_, handle) = app.add_window(|_| View::default());
+            handle
+                .update(&mut app, |_, c| {
+                    c.spawn_stream_local(stream::iter(vec![1, 2, 3]), |me, output, _| {
+                        me.events.push(output);
+                    })
+                })
+                .await;
+
+            handle.read(&app, |view, _| {
+                assert_eq!(view.events, [Some(1), Some(2), Some(3), None])
+            });
+        });
+    }
+
+    #[test]
+    fn test_dispatch_action() {
+        struct ViewA {
+            id: usize,
+        }
+
+        impl Entity for ViewA {
+            type Event = ();
+        }
+
+        impl View for ViewA {
+            fn render<'a>(&self, bump: &'a Bump, _: &AppContext) -> Box<dyn Element> {
+                Empty::new().finish(bump)
+            }
+
+            fn ui_name() -> &'static str {
+                "View"
+            }
+        }
+
+        struct ViewB {
+            id: usize,
+        }
+
+        impl Entity for ViewB {
+            type Event = ();
+        }
+
+        impl View for ViewB {
+            fn render<'a>(&self, bump: &'a Bump, _: &AppContext) -> Box<dyn Element> {
+                Empty::new().finish(bump)
+            }
+
+            fn ui_name() -> &'static str {
+                "View"
+            }
+        }
+
+        struct ActionArg {
+            foo: String,
+        }
+
+        let mut app = App::new().unwrap();
+        let actions = Rc::new(RefCell::new(Vec::new()));
+
+        let actions_clone = actions.clone();
+        app.add_global_action("action", move |_: &ActionArg, _: &mut MutableAppContext| {
+            actions_clone.borrow_mut().push("global a".to_string());
+        });
+
+        let actions_clone = actions.clone();
+        app.add_global_action("action", move |_: &ActionArg, _: &mut MutableAppContext| {
+            actions_clone.borrow_mut().push("global b".to_string());
+        });
+
+        let actions_clone = actions.clone();
+        app.add_action("action", move |view: &mut ViewA, arg: &ActionArg, ctx| {
+            assert_eq!(arg.foo, "bar");
+            ctx.propagate_action();
+            actions_clone.borrow_mut().push(format!("{} a", view.id));
+        });
+
+        let actions_clone = actions.clone();
+        app.add_action("action", move |view: &mut ViewA, _: &ActionArg, ctx| {
+            if view.id != 1 {
+                ctx.propagate_action();
+            }
+            actions_clone.borrow_mut().push(format!("{} b", view.id));
+        });
+
+        let actions_clone = actions.clone();
+        app.add_action("action", move |view: &mut ViewB, _: &ActionArg, ctx| {
+            ctx.propagate_action();
+            actions_clone.borrow_mut().push(format!("{} c", view.id));
+        });
+
+        let actions_clone = actions.clone();
+        app.add_action("action", move |view: &mut ViewB, _: &ActionArg, ctx| {
+            ctx.propagate_action();
+            actions_clone.borrow_mut().push(format!("{} d", view.id));
+        });
+
+        let (window_id, view_1) = app.add_window(|_| ViewA { id: 1 });
+        let view_2 = app.add_view(window_id, |_| ViewB { id: 2 });
+        let view_3 = app.add_view(window_id, |_| ViewA { id: 3 });
+        let view_4 = app.add_view(window_id, |_| ViewB { id: 4 });
+
+        app.dispatch_action(
+            window_id,
+            vec![view_1.id(), view_2.id(), view_3.id(), view_4.id()],
+            "action",
+            ActionArg { foo: "bar".into() },
+        );
+
+        assert_eq!(
+            *actions.borrow(),
+            vec!["4 d", "4 c", "3 b", "3 a", "2 d", "2 c", "1 b"]
+        );
+
+        // Remove view_1, which doesn't propagate the action
+        actions.borrow_mut().clear();
+        app.dispatch_action(
+            window_id,
+            vec![view_2.id(), view_3.id(), view_4.id()],
+            "action",
+            ActionArg { foo: "bar".into() },
+        );
+
+        assert_eq!(
+            *actions.borrow(),
+            vec!["4 d", "4 c", "3 b", "3 a", "2 d", "2 c", "global b", "global a"]
+        );
+    }
+
+    #[test]
+    fn test_dispatch_keystroke() -> Result<()> {
+        use std::cell::Cell;
+
+        #[derive(Clone)]
+        struct ActionArg {
+            key: String,
+        }
+
+        struct View {
+            id: usize,
+            keymap_context: keymap::Context,
+        }
+
+        impl Entity for View {
+            type Event = ();
+        }
+
+        impl super::View for View {
+            fn render<'a>(&self, bump: &'a Bump, _: &AppContext) -> Box<dyn Element> {
+                Empty::new().finish(bump)
+            }
+
+            fn ui_name() -> &'static str {
+                "View"
+            }
+
+            fn keymap_context(&self, _: &AppContext) -> keymap::Context {
+                self.keymap_context.clone()
+            }
+        }
+
+        impl View {
+            fn new(id: usize) -> Self {
+                View {
+                    id,
+                    keymap_context: keymap::Context::default(),
+                }
+            }
+        }
+
+        let mut app = App::new().unwrap();
+
+        let mut view_1 = View::new(1);
+        let mut view_2 = View::new(2);
+        let mut view_3 = View::new(3);
+        view_1.keymap_context.set.insert("a".into());
+        view_2.keymap_context.set.insert("b".into());
+        view_3.keymap_context.set.insert("c".into());
+
+        let (window_id, view_1) = app.add_window(|_| view_1);
+        let view_2 = app.add_view(window_id, |_| view_2);
+        let view_3 = app.add_view(window_id, |_| view_3);
+
+        // This keymap's only binding dispatches an action on view 2 because that view will have
+        // "a" and "b" in its context, but not "c".
+        let binding = keymap::Binding::new("a", "action", Some("a && b && !c"))
+            .with_arg(ActionArg { key: "a".into() });
+        app.add_bindings(vec![binding]);
+
+        let handled_action = Rc::new(Cell::new(false));
+        let handled_action_clone = handled_action.clone();
+        app.add_action("action", move |view: &mut View, arg: &ActionArg, _ctx| {
+            handled_action_clone.set(true);
+            assert_eq!(view.id, 2);
+            assert_eq!(arg.key, "a");
+        });
+
+        app.dispatch_keystroke(
+            window_id,
+            vec![view_1.id(), view_2.id(), view_3.id()],
+            &Keystroke::parse("a")?,
+        )?;
+
+        assert!(handled_action.get());
+        Ok(())
+    }
+
+    #[test]
+    fn test_ui_and_window_updates() {
+        struct View {
+            count: usize,
+        }
+
+        impl Entity for View {
+            type Event = ();
+        }
+
+        impl super::View for View {
+            fn render<'a>(&self, bump: &'a Bump, _: &AppContext) -> Box<dyn Element> {
+                Empty::new().finish(bump)
+            }
+
+            fn ui_name() -> &'static str {
+                "View"
+            }
+        }
+
+        App::run(|mut app| async move {
+            let (window_id, _) = app.add_window(|_| View { count: 3 });
+            let view_1 = app.add_view(window_id, |_| View { count: 1 });
+            let view_2 = app.add_view(window_id, |_| View { count: 2 });
+
+            // Ensure that registering for UI updates after mutating the app still gives us all the
+            // updates.
+            let ui_updates = Rc::new(RefCell::new(Vec::new()));
+            let ui_updates_ = ui_updates.clone();
+            app.on_ui_update(move |update, _| ui_updates_.borrow_mut().push(update));
+
+            assert_eq!(
+                ui_updates.borrow_mut().drain(..).collect::<Vec<_>>(),
+                vec![UiUpdate::OpenWindow {
+                    window_id,
+                    width: 1024.0,
+                    height: 768.0,
+                }]
+            );
+
+            let window_invalidations = Rc::new(RefCell::new(Vec::new()));
+            let window_invalidations_ = window_invalidations.clone();
+            app.on_window_invalidated(window_id, move |update, _| {
+                window_invalidations_.borrow_mut().push(update)
+            });
+
+            let view_2_id = view_2.id();
+            view_1.update(&mut app, |view, ctx| {
+                view.count = 7;
+                ctx.notify();
+                drop(view_2);
+            });
+
+            let invalidation = window_invalidations.borrow_mut().drain(..).next().unwrap();
+            assert_eq!(invalidation.updated.len(), 1);
+            assert!(invalidation.updated.contains(&view_1.id()));
+            assert_eq!(invalidation.removed, vec![view_2_id]);
+
+            let view_3 = view_1.update(&mut app, |_, ctx| ctx.add_view(|_| View { count: 8 }));
+
+            let invalidation = window_invalidations.borrow_mut().drain(..).next().unwrap();
+            assert_eq!(invalidation.updated.len(), 1);
+            assert!(invalidation.updated.contains(&view_3.id()));
+            assert!(invalidation.removed.is_empty());
+
+            view_3
+                .update(&mut app, |_, ctx| {
+                    ctx.spawn_local(async { 9 }, |me, output, ctx| {
+                        me.count = output;
+                        ctx.notify();
+                    })
+                })
+                .await;
+
+            let invalidation = window_invalidations.borrow_mut().drain(..).next().unwrap();
+            assert_eq!(invalidation.updated.len(), 1);
+            assert!(invalidation.updated.contains(&view_3.id()));
+            assert!(invalidation.removed.is_empty());
+        });
+    }
+
+    #[test]
+    fn test_finish_pending_tasks() {
+        struct View;
+
+        impl Entity for View {
+            type Event = ();
+        }
+
+        impl super::View for View {
+            fn render<'a>(&self, bump: &'a Bump, _: &AppContext) -> Box<dyn Element> {
+                Empty::new().finish(bump)
+            }
+
+            fn ui_name() -> &'static str {
+                "View"
+            }
+        }
+
+        struct Model;
+
+        impl Entity for Model {
+            type Event = ();
+        }
+
+        App::run(|mut app| async move {
+            let model = app.add_model(|_| Model);
+            let (_, view) = app.add_window(|_| View);
+
+            model.update(&mut app, |_, ctx| {
+                let _ = ctx.spawn(async {}, |_, _, _| {});
+                let _ = ctx.spawn_local(async {}, |_, _, _| {});
+                let _ = ctx.spawn_stream_local(futures::stream::iter(vec![1, 2, 3]), |_, _, _| {});
+            });
+
+            view.update(&mut app, |_, ctx| {
+                let _ = ctx.spawn(async {}, |_, _, _| {});
+                let _ = ctx.spawn_local(async {}, |_, _, _| {});
+                let _ = ctx.spawn_stream_local(futures::stream::iter(vec![1, 2, 3]), |_, _, _| {});
+            });
+
+            assert!(!app.0.borrow().task_callbacks.is_empty());
+            app.finish_pending_tasks().await;
+            assert!(app.0.borrow().task_callbacks.is_empty());
+            app.finish_pending_tasks().await; // Don't block if there are no tasks
+        });
+    }
+}

gpui/src/elements/align.rs 🔗

@@ -0,0 +1,68 @@
+use crate::{
+    AfterLayoutContext, AppContext, Element, Event, EventContext, LayoutContext, MutableAppContext,
+    PaintContext, SizeConstraint,
+};
+use pathfinder_geometry::vector::{vec2f, Vector2F};
+
+pub struct Align {
+    child: Box<dyn Element>,
+    alignment: Vector2F,
+    size: Option<Vector2F>,
+}
+
+impl Align {
+    pub fn new(child: Box<dyn Element>) -> Self {
+        Self {
+            child,
+            alignment: Vector2F::zero(),
+            size: None,
+        }
+    }
+
+    pub fn top_center(mut self) -> Self {
+        self.alignment = vec2f(0.0, -1.0);
+        self
+    }
+}
+
+impl Element for Align {
+    fn layout(
+        &mut self,
+        mut constraint: SizeConstraint,
+        ctx: &mut LayoutContext,
+        app: &AppContext,
+    ) -> Vector2F {
+        let mut size = constraint.max;
+        constraint.min = Vector2F::zero();
+        let child_size = self.child.layout(constraint, ctx, app);
+        if size.x().is_infinite() {
+            size.set_x(child_size.x());
+        }
+        if size.y().is_infinite() {
+            size.set_y(child_size.y());
+        }
+        self.size = Some(size);
+        size
+    }
+
+    fn after_layout(&mut self, ctx: &mut AfterLayoutContext, app: &mut MutableAppContext) {
+        self.child.after_layout(ctx, app);
+    }
+
+    fn paint(&mut self, origin: Vector2F, ctx: &mut PaintContext, app: &AppContext) {
+        let self_center = self.size.unwrap() / 2.0;
+        let self_target = self_center + self_center * self.alignment;
+        let child_center = self.child.size().unwrap() / 2.0;
+        let child_target = child_center + child_center * self.alignment;
+        let origin = origin - (child_target - self_target);
+        self.child.paint(origin, ctx, app);
+    }
+
+    fn dispatch_event(&self, event: &Event, ctx: &mut EventContext, app: &AppContext) -> bool {
+        self.child.dispatch_event(event, ctx, app)
+    }
+
+    fn size(&self) -> Option<Vector2F> {
+        self.size
+    }
+}

gpui/src/elements/constrained_box.rs 🔗

@@ -0,0 +1,67 @@
+use crate::{
+    AfterLayoutContext, AppContext, Element, Event, EventContext, LayoutContext, MutableAppContext,
+    PaintContext, SizeConstraint,
+};
+use pathfinder_geometry::vector::Vector2F;
+
+pub struct ConstrainedBox {
+    child: Box<dyn Element>,
+    constraint: SizeConstraint,
+}
+
+impl ConstrainedBox {
+    pub fn new(child: Box<dyn Element>) -> Self {
+        Self {
+            child,
+            constraint: SizeConstraint {
+                min: Vector2F::zero(),
+                max: Vector2F::splat(f32::INFINITY),
+            },
+        }
+    }
+
+    pub fn with_max_width(mut self, max_width: f32) -> Self {
+        self.constraint.max.set_x(max_width);
+        self
+    }
+
+    pub fn with_max_height(mut self, max_height: f32) -> Self {
+        self.constraint.max.set_y(max_height);
+        self
+    }
+
+    pub fn with_height(mut self, height: f32) -> Self {
+        self.constraint.min.set_y(height);
+        self.constraint.max.set_y(height);
+        self
+    }
+}
+
+impl Element for ConstrainedBox {
+    fn layout(
+        &mut self,
+        mut constraint: SizeConstraint,
+        ctx: &mut LayoutContext,
+        app: &AppContext,
+    ) -> Vector2F {
+        constraint.min = constraint.min.max(self.constraint.min);
+        constraint.max = constraint.max.min(self.constraint.max);
+        self.child.layout(constraint, ctx, app)
+    }
+
+    fn after_layout(&mut self, ctx: &mut AfterLayoutContext, app: &mut MutableAppContext) {
+        self.child.after_layout(ctx, app);
+    }
+
+    fn paint(&mut self, origin: Vector2F, ctx: &mut PaintContext, app: &AppContext) {
+        self.child.paint(origin, ctx, app);
+    }
+
+    fn dispatch_event(&self, event: &Event, ctx: &mut EventContext, app: &AppContext) -> bool {
+        self.child.dispatch_event(event, ctx, app)
+    }
+
+    fn size(&self) -> Option<Vector2F> {
+        self.child.size()
+    }
+}

gpui/src/elements/container.rs 🔗

@@ -0,0 +1,358 @@
+use crate::{
+    color::ColorU,
+    geometry::vector::{vec2f, Vector2F},
+    AfterLayoutContext, AppContext, Element, Event, EventContext, LayoutContext, MutableAppContext,
+    PaintContext, SizeConstraint,
+};
+
+pub struct Container {
+    margin: Margin,
+    padding: Padding,
+    overdraw: Overdraw,
+    background_color: Option<ColorU>,
+    border: Border,
+    corner_radius: f32,
+    shadow: Option<Shadow>,
+    child: Box<dyn Element>,
+    size: Option<Vector2F>,
+    origin: Option<Vector2F>,
+}
+
+impl Container {
+    pub fn new(child: Box<dyn Element>) -> Self {
+        Self {
+            margin: Margin::default(),
+            padding: Padding::default(),
+            overdraw: Overdraw::default(),
+            background_color: None,
+            border: Border::default(),
+            corner_radius: 0.0,
+            shadow: None,
+            child,
+            size: None,
+            origin: None,
+        }
+    }
+
+    pub fn with_margin_top(mut self, margin: f32) -> Self {
+        self.margin.top = margin;
+        self
+    }
+
+    pub fn with_uniform_padding(mut self, padding: f32) -> Self {
+        self.padding = Padding {
+            top: padding,
+            left: padding,
+            bottom: padding,
+            right: padding,
+        };
+        self
+    }
+
+    pub fn with_padding_right(mut self, padding: f32) -> Self {
+        self.padding.right = padding;
+        self
+    }
+
+    pub fn with_background_color(mut self, color: impl Into<ColorU>) -> Self {
+        self.background_color = Some(color.into());
+        self
+    }
+
+    pub fn with_border(mut self, border: Border) -> Self {
+        self.border = border;
+        self
+    }
+
+    pub fn with_overdraw_bottom(mut self, overdraw: f32) -> Self {
+        self.overdraw.bottom = overdraw;
+        self
+    }
+
+    pub fn with_corner_radius(mut self, radius: f32) -> Self {
+        self.corner_radius = radius;
+        self
+    }
+
+    pub fn with_shadow(mut self, offset: Vector2F, blur: f32, color: impl Into<ColorU>) -> Self {
+        self.shadow = Some(Shadow {
+            offset,
+            blur,
+            color: color.into(),
+        });
+        self
+    }
+
+    fn margin_size(&self) -> Vector2F {
+        vec2f(
+            self.margin.left + self.margin.right,
+            self.margin.top + self.margin.bottom,
+        )
+    }
+
+    fn padding_size(&self) -> Vector2F {
+        vec2f(
+            self.padding.left + self.padding.right,
+            self.padding.top + self.padding.bottom,
+        )
+    }
+
+    fn border_size(&self) -> Vector2F {
+        let mut x = 0.0;
+        if self.border.left {
+            x += self.border.width;
+        }
+        if self.border.right {
+            x += self.border.width;
+        }
+
+        let mut y = 0.0;
+        if self.border.top {
+            y += self.border.width;
+        }
+        if self.border.bottom {
+            y += self.border.width;
+        }
+
+        vec2f(x, y)
+    }
+}
+
+impl Element for Container {
+    fn layout(
+        &mut self,
+        constraint: SizeConstraint,
+        ctx: &mut LayoutContext,
+        app: &AppContext,
+    ) -> Vector2F {
+        let size_buffer = self.margin_size() + self.padding_size() + self.border_size();
+        let child_constraint = SizeConstraint {
+            min: (constraint.min - size_buffer).max(Vector2F::zero()),
+            max: (constraint.max - size_buffer).max(Vector2F::zero()),
+        };
+        let child_size = self.child.layout(child_constraint, ctx, app);
+        let size = child_size + size_buffer;
+        self.size = Some(size);
+        size
+    }
+
+    fn after_layout(&mut self, ctx: &mut AfterLayoutContext, app: &mut MutableAppContext) {
+        self.child.after_layout(ctx, app);
+    }
+
+    fn paint(&mut self, origin: Vector2F, ctx: &mut PaintContext, app: &AppContext) {
+        // self.origin = Some(origin);
+
+        // let canvas = &mut ctx.canvas;
+        // let size = self.size.unwrap() - self.margin_size()
+        //     + vec2f(self.overdraw.right, self.overdraw.bottom);
+        // let origin = origin + vec2f(self.margin.left, self.margin.top)
+        //     - vec2f(self.overdraw.left, self.overdraw.top);
+        // let rect = RectF::new(origin, size);
+
+        // let mut path = Path2D::new();
+        // if self.corner_radius > 0.0 {
+        //     path.move_to(rect.upper_right() - vec2f(self.corner_radius, 0.0));
+        //     path.arc_to(
+        //         rect.upper_right(),
+        //         rect.upper_right() + vec2f(0.0, self.corner_radius),
+        //         self.corner_radius,
+        //     );
+        //     path.line_to(rect.lower_right() - vec2f(0.0, self.corner_radius));
+        //     path.arc_to(
+        //         rect.lower_right(),
+        //         rect.lower_right() - vec2f(self.corner_radius, 0.0),
+        //         self.corner_radius,
+        //     );
+        //     path.line_to(rect.lower_left() + vec2f(self.corner_radius, 0.0));
+        //     path.arc_to(
+        //         rect.lower_left(),
+        //         rect.lower_left() - vec2f(0.0, self.corner_radius),
+        //         self.corner_radius,
+        //     );
+        //     path.line_to(origin + vec2f(0.0, self.corner_radius));
+        //     path.arc_to(
+        //         origin,
+        //         origin + vec2f(self.corner_radius, 0.0),
+        //         self.corner_radius,
+        //     );
+        //     path.close_path();
+        // } else {
+        //     path.rect(rect);
+        // }
+
+        // canvas.save();
+        // if let Some(shadow) = self.shadow.as_ref() {
+        //     canvas.set_shadow_offset(shadow.offset);
+        //     canvas.set_shadow_blur(shadow.blur);
+        //     canvas.set_shadow_color(shadow.color);
+        // }
+
+        // if let Some(background_color) = self.background_color {
+        //     canvas.set_fill_style(FillStyle::Color(background_color));
+        //     canvas.fill_path(path.clone(), FillRule::Winding);
+        // }
+
+        // canvas.set_line_width(self.border.width);
+        // canvas.set_stroke_style(FillStyle::Color(self.border.color));
+
+        // let border_rect = rect.contract(self.border.width / 2.0);
+
+        // // For now, we ignore the corner radius unless we draw a border on all sides.
+        // // This could be improved.
+        // if self.border.all_sides() {
+        //     let mut path = Path2D::new();
+        //     path.rect(border_rect);
+        //     canvas.stroke_path(path);
+        // } else {
+        //     canvas.set_line_cap(LineCap::Square);
+
+        //     if self.border.top {
+        //         let mut path = Path2D::new();
+        //         path.move_to(border_rect.origin());
+        //         path.line_to(border_rect.upper_right());
+        //         canvas.stroke_path(path);
+        //     }
+
+        //     if self.border.left {
+        //         let mut path = Path2D::new();
+        //         path.move_to(border_rect.origin());
+        //         path.line_to(border_rect.lower_left());
+        //         canvas.stroke_path(path);
+        //     }
+
+        //     if self.border.bottom {
+        //         let mut path = Path2D::new();
+        //         path.move_to(border_rect.lower_left());
+        //         path.line_to(border_rect.lower_right());
+        //         canvas.stroke_path(path);
+        //     }
+
+        //     if self.border.right {
+        //         let mut path = Path2D::new();
+        //         path.move_to(border_rect.upper_right());
+        //         path.line_to(border_rect.lower_right());
+        //         canvas.stroke_path(path);
+        //     }
+        // }
+        // canvas.restore();
+
+        // let mut child_origin = origin + vec2f(self.padding.left, self.padding.top);
+        // if self.border.left {
+        //     child_origin.set_x(child_origin.x() + self.border.width);
+        // }
+        // if self.border.top {
+        //     child_origin.set_y(child_origin.y() + self.border.width);
+        // }
+        // self.child.paint(child_origin, ctx, app);
+    }
+
+    fn dispatch_event(&self, event: &Event, ctx: &mut EventContext, app: &AppContext) -> bool {
+        self.child.dispatch_event(event, ctx, app)
+    }
+
+    fn size(&self) -> Option<Vector2F> {
+        self.size
+    }
+}
+
+#[derive(Default)]
+pub struct Margin {
+    top: f32,
+    left: f32,
+    bottom: f32,
+    right: f32,
+}
+
+#[derive(Default)]
+pub struct Padding {
+    top: f32,
+    left: f32,
+    bottom: f32,
+    right: f32,
+}
+
+#[derive(Default)]
+pub struct Overdraw {
+    top: f32,
+    left: f32,
+    bottom: f32,
+    right: f32,
+}
+
+#[derive(Default)]
+pub struct Border {
+    width: f32,
+    color: ColorU,
+    pub top: bool,
+    pub left: bool,
+    pub bottom: bool,
+    pub right: bool,
+}
+
+impl Border {
+    pub fn new(width: f32, color: impl Into<ColorU>) -> Self {
+        Self {
+            width,
+            color: color.into(),
+            top: false,
+            left: false,
+            bottom: false,
+            right: false,
+        }
+    }
+
+    pub fn all(width: f32, color: impl Into<ColorU>) -> Self {
+        Self {
+            width,
+            color: color.into(),
+            top: true,
+            left: true,
+            bottom: true,
+            right: true,
+        }
+    }
+
+    pub fn top(width: f32, color: impl Into<ColorU>) -> Self {
+        let mut border = Self::new(width, color);
+        border.top = true;
+        border
+    }
+
+    pub fn left(width: f32, color: impl Into<ColorU>) -> Self {
+        let mut border = Self::new(width, color);
+        border.left = true;
+        border
+    }
+
+    pub fn bottom(width: f32, color: impl Into<ColorU>) -> Self {
+        let mut border = Self::new(width, color);
+        border.bottom = true;
+        border
+    }
+
+    pub fn right(width: f32, color: impl Into<ColorU>) -> Self {
+        let mut border = Self::new(width, color);
+        border.right = true;
+        border
+    }
+
+    pub fn with_sides(mut self, top: bool, left: bool, bottom: bool, right: bool) -> Self {
+        self.top = top;
+        self.left = left;
+        self.bottom = bottom;
+        self.right = right;
+        self
+    }
+
+    fn all_sides(&self) -> bool {
+        self.top && self.left && self.bottom && self.right
+    }
+}
+
+#[derive(Default)]
+pub struct Shadow {
+    offset: Vector2F,
+    blur: f32,
+    color: ColorU,
+}

gpui/src/elements/empty.rs 🔗

@@ -0,0 +1,45 @@
+use crate::{
+    AfterLayoutContext, AppContext, Element, Event, EventContext, LayoutContext, MutableAppContext,
+    PaintContext, SizeConstraint,
+};
+use pathfinder_geometry::vector::Vector2F;
+
+pub struct Empty {
+    size: Option<Vector2F>,
+    origin: Option<Vector2F>,
+}
+
+impl Empty {
+    pub fn new() -> Self {
+        Self {
+            size: None,
+            origin: None,
+        }
+    }
+}
+
+impl Element for Empty {
+    fn layout(
+        &mut self,
+        constraint: SizeConstraint,
+        _: &mut LayoutContext,
+        _: &AppContext,
+    ) -> Vector2F {
+        self.size = Some(constraint.min);
+        constraint.max
+    }
+
+    fn after_layout(&mut self, _: &mut AfterLayoutContext, _: &mut MutableAppContext) {}
+
+    fn paint(&mut self, origin: Vector2F, _: &mut PaintContext, _: &AppContext) {
+        self.origin = Some(origin);
+    }
+
+    fn dispatch_event(&self, _: &Event, _: &mut EventContext, _: &AppContext) -> bool {
+        false
+    }
+
+    fn size(&self) -> Option<Vector2F> {
+        self.size
+    }
+}

gpui/src/elements/event_handler.rs 🔗

@@ -0,0 +1,69 @@
+use super::try_rect;
+use crate::{
+    geometry::vector::Vector2F, AfterLayoutContext, AppContext, Element, Event, EventContext,
+    LayoutContext, MutableAppContext, PaintContext, SizeConstraint,
+};
+use std::cell::RefCell;
+
+pub struct EventHandler {
+    child: Box<dyn Element>,
+    mouse_down: Option<RefCell<Box<dyn FnMut(&mut EventContext, &AppContext) -> bool>>>,
+    origin: Option<Vector2F>,
+}
+
+impl EventHandler {
+    pub fn new(child: Box<dyn Element>) -> Self {
+        Self {
+            child,
+            mouse_down: None,
+            origin: None,
+        }
+    }
+
+    pub fn on_mouse_down<F>(mut self, callback: F) -> Self
+    where
+        F: 'static + FnMut(&mut EventContext, &AppContext) -> bool,
+    {
+        self.mouse_down = Some(RefCell::new(Box::new(callback)));
+        self
+    }
+}
+
+impl Element for EventHandler {
+    fn layout(
+        &mut self,
+        constraint: SizeConstraint,
+        ctx: &mut LayoutContext,
+        app: &AppContext,
+    ) -> Vector2F {
+        self.child.layout(constraint, ctx, app)
+    }
+
+    fn after_layout(&mut self, ctx: &mut AfterLayoutContext, app: &mut MutableAppContext) {
+        self.child.after_layout(ctx, app);
+    }
+
+    fn paint(&mut self, origin: Vector2F, ctx: &mut PaintContext, app: &AppContext) {
+        self.origin = Some(origin);
+        self.child.paint(origin, ctx, app);
+    }
+
+    fn size(&self) -> Option<Vector2F> {
+        self.child.size()
+    }
+
+    fn dispatch_event(&self, event: &Event, ctx: &mut EventContext, app: &AppContext) -> bool {
+        match event {
+            Event::LeftMouseDown { position, .. } => {
+                if let Some(callback) = self.mouse_down.as_ref() {
+                    let rect = try_rect(self.origin, self.size()).unwrap();
+                    if rect.contains_point(*position) {
+                        return callback.borrow_mut()(ctx, app);
+                    }
+                }
+                false
+            }
+            _ => false,
+        }
+    }
+}

gpui/src/elements/flex.rs 🔗

@@ -0,0 +1,201 @@
+use crate::{
+    AfterLayoutContext, AppContext, Axis, Element, Event, EventContext, LayoutContext,
+    MutableAppContext, PaintContext, SizeConstraint, Vector2FExt,
+};
+use pathfinder_geometry::vector::{vec2f, Vector2F};
+use std::any::Any;
+
+pub struct Flex {
+    axis: Axis,
+    children: Vec<Box<dyn Element>>,
+    size: Option<Vector2F>,
+    origin: Option<Vector2F>,
+}
+
+impl Flex {
+    pub fn new(axis: Axis) -> Self {
+        Self {
+            axis,
+            children: Default::default(),
+            size: None,
+            origin: None,
+        }
+    }
+
+    pub fn row() -> Self {
+        Self::new(Axis::Horizontal)
+    }
+
+    pub fn column() -> Self {
+        Self::new(Axis::Vertical)
+    }
+
+    fn child_flex<'b>(child: &dyn Element) -> Option<f32> {
+        child
+            .parent_data()
+            .and_then(|d| d.downcast_ref::<FlexParentData>())
+            .map(|data| data.flex)
+    }
+}
+
+impl Extend<Box<dyn Element>> for Flex {
+    fn extend<T: IntoIterator<Item = Box<dyn Element>>>(&mut self, children: T) {
+        self.children.extend(children);
+    }
+}
+
+impl Element for Flex {
+    fn layout(
+        &mut self,
+        constraint: SizeConstraint,
+        ctx: &mut LayoutContext,
+        app: &AppContext,
+    ) -> Vector2F {
+        let mut total_flex = 0.0;
+        let mut fixed_space = 0.0;
+
+        let cross_axis = self.axis.invert();
+        let mut cross_axis_max: f32 = 0.0;
+        for child in &mut self.children {
+            if let Some(flex) = Self::child_flex(child.as_ref()) {
+                total_flex += flex;
+            } else {
+                let child_constraint =
+                    SizeConstraint::strict_along(cross_axis, constraint.max_along(cross_axis));
+                let size = child.layout(child_constraint, ctx, app);
+                fixed_space += size.along(self.axis);
+                cross_axis_max = cross_axis_max.max(size.along(cross_axis));
+            }
+        }
+
+        let mut size = if total_flex > 0.0 {
+            if constraint.max_along(self.axis).is_infinite() {
+                panic!("flex contains flexible children but has an infinite constraint along the flex axis");
+            }
+
+            let mut remaining_space = constraint.max_along(self.axis) - fixed_space;
+            let mut remaining_flex = total_flex;
+            for child in &mut self.children {
+                let space_per_flex = remaining_space / remaining_flex;
+                if let Some(flex) = Self::child_flex(child.as_ref()) {
+                    let child_max = space_per_flex * flex;
+                    let child_constraint = match self.axis {
+                        Axis::Horizontal => SizeConstraint::new(
+                            vec2f(0.0, constraint.max.y()),
+                            vec2f(child_max, constraint.max.y()),
+                        ),
+                        Axis::Vertical => SizeConstraint::new(
+                            vec2f(constraint.max.x(), 0.0),
+                            vec2f(constraint.max.x(), child_max),
+                        ),
+                    };
+                    let child_size = child.layout(child_constraint, ctx, app);
+                    remaining_space -= child_size.along(self.axis);
+                    remaining_flex -= flex;
+                    cross_axis_max = cross_axis_max.max(child_size.along(cross_axis));
+                }
+            }
+
+            match self.axis {
+                Axis::Horizontal => vec2f(constraint.max.x() - remaining_space, cross_axis_max),
+                Axis::Vertical => vec2f(cross_axis_max, constraint.max.y() - remaining_space),
+            }
+        } else {
+            match self.axis {
+                Axis::Horizontal => vec2f(fixed_space, cross_axis_max),
+                Axis::Vertical => vec2f(cross_axis_max, fixed_space),
+            }
+        };
+
+        if constraint.min.x().is_finite() {
+            size.set_x(size.x().max(constraint.min.x()));
+        }
+        if constraint.min.y().is_finite() {
+            size.set_y(size.y().max(constraint.min.y()));
+        }
+
+        self.size = Some(size);
+        size
+    }
+
+    fn after_layout(&mut self, ctx: &mut AfterLayoutContext, app: &mut MutableAppContext) {
+        for child in &mut self.children {
+            child.after_layout(ctx, app);
+        }
+    }
+
+    fn paint(&mut self, mut origin: Vector2F, ctx: &mut PaintContext, app: &AppContext) {
+        self.origin = Some(origin);
+
+        for child in &mut self.children {
+            child.paint(origin, ctx, app);
+            match self.axis {
+                Axis::Horizontal => origin += vec2f(child.size().unwrap().x(), 0.0),
+                Axis::Vertical => origin += vec2f(0.0, child.size().unwrap().y()),
+            }
+        }
+    }
+
+    fn dispatch_event(&self, event: &Event, ctx: &mut EventContext, app: &AppContext) -> bool {
+        let mut handled = false;
+        for child in &self.children {
+            if child.dispatch_event(event, ctx, app) {
+                handled = true;
+            }
+        }
+        handled
+    }
+
+    fn size(&self) -> Option<Vector2F> {
+        self.size
+    }
+}
+
+struct FlexParentData {
+    flex: f32,
+}
+
+pub struct Expanded {
+    parent_data: FlexParentData,
+    child: Box<dyn Element>,
+}
+
+impl Expanded {
+    pub fn new(flex: f32, child: Box<dyn Element>) -> Self {
+        Expanded {
+            parent_data: FlexParentData { flex },
+            child,
+        }
+    }
+}
+
+impl Element for Expanded {
+    fn layout(
+        &mut self,
+        constraint: SizeConstraint,
+        ctx: &mut LayoutContext,
+        app: &AppContext,
+    ) -> Vector2F {
+        self.child.layout(constraint, ctx, app)
+    }
+
+    fn after_layout(&mut self, ctx: &mut AfterLayoutContext, app: &mut MutableAppContext) {
+        self.child.after_layout(ctx, app);
+    }
+
+    fn paint(&mut self, origin: Vector2F, ctx: &mut PaintContext, app: &AppContext) {
+        self.child.paint(origin, ctx, app);
+    }
+
+    fn dispatch_event(&self, event: &Event, ctx: &mut EventContext, app: &AppContext) -> bool {
+        self.child.dispatch_event(event, ctx, app)
+    }
+
+    fn size(&self) -> Option<Vector2F> {
+        self.child.size()
+    }
+
+    fn parent_data(&self) -> Option<&dyn Any> {
+        Some(&self.parent_data)
+    }
+}

gpui/src/elements/label.rs 🔗

@@ -0,0 +1,154 @@
+use crate::{
+    color::ColorU,
+    fonts::{FamilyId, Properties},
+    geometry::vector::{vec2f, Vector2F},
+    AfterLayoutContext, AppContext, Element, Event, EventContext, LayoutContext, MutableAppContext,
+    PaintContext, SizeConstraint,
+};
+use std::{ops::Range, sync::Arc};
+
+pub struct Label {
+    text: String,
+    family_id: FamilyId,
+    font_properties: Properties,
+    font_size: f32,
+    highlights: Option<Highlights>,
+    layout_line: Option<Arc<Line>>,
+    colors: Option<Vec<(Range<usize>, ColorU)>>,
+    size: Option<Vector2F>,
+}
+
+pub struct Highlights {
+    color: ColorU,
+    indices: Vec<usize>,
+    font_properties: Properties,
+}
+
+impl Label {
+    pub fn new(text: String, family_id: FamilyId, font_size: f32) -> Self {
+        Self {
+            text,
+            family_id,
+            font_properties: Properties::new(),
+            font_size,
+            highlights: None,
+            layout_line: None,
+            colors: None,
+            size: None,
+        }
+    }
+
+    pub fn with_highlights(
+        mut self,
+        color: ColorU,
+        font_properties: Properties,
+        indices: Vec<usize>,
+    ) -> Self {
+        self.highlights = Some(Highlights {
+            color,
+            font_properties,
+            indices,
+        });
+        self
+    }
+}
+
+impl Element for Label {
+    fn layout(
+        &mut self,
+        constraint: SizeConstraint,
+        ctx: &mut LayoutContext,
+        _: &AppContext,
+    ) -> Vector2F {
+        let font_id = ctx
+            .font_cache
+            .select_font(self.family_id, &self.font_properties)
+            .unwrap();
+        let text_len = self.text.chars().count();
+        let mut styles;
+        let mut colors;
+        if let Some(highlights) = self.highlights.as_ref() {
+            styles = Vec::new();
+            colors = Vec::new();
+            let highlight_font_id = ctx
+                .font_cache
+                .select_font(self.family_id, &highlights.font_properties)
+                .unwrap_or(font_id);
+            let mut pending_highlight: Option<Range<usize>> = None;
+            for ix in &highlights.indices {
+                if let Some(pending_highlight) = pending_highlight.as_mut() {
+                    if *ix == pending_highlight.end {
+                        pending_highlight.end += 1;
+                    } else {
+                        styles.push((pending_highlight.clone(), highlight_font_id));
+                        colors.push((pending_highlight.clone(), highlights.color));
+                        styles.push((pending_highlight.end..*ix, font_id));
+                        colors.push((pending_highlight.end..*ix, ColorU::black()));
+                        *pending_highlight = *ix..*ix + 1;
+                    }
+                } else {
+                    styles.push((0..*ix, font_id));
+                    colors.push((0..*ix, ColorU::black()));
+                    pending_highlight = Some(*ix..*ix + 1);
+                }
+            }
+            if let Some(pending_highlight) = pending_highlight.as_mut() {
+                styles.push((pending_highlight.clone(), highlight_font_id));
+                colors.push((pending_highlight.clone(), highlights.color));
+                if text_len > pending_highlight.end {
+                    styles.push((pending_highlight.end..text_len, font_id));
+                    colors.push((pending_highlight.end..text_len, ColorU::black()));
+                }
+            } else {
+                styles.push((0..text_len, font_id));
+                colors.push((0..text_len, ColorU::black()));
+            }
+        } else {
+            styles = vec![(0..text_len, font_id)];
+            colors = vec![(0..text_len, ColorU::black())];
+        }
+
+        self.colors = Some(colors);
+
+        let layout_line = ctx.text_layout_cache.layout_str(
+            self.text.as_str(),
+            self.font_size,
+            styles.as_slice(),
+            ctx.font_cache,
+        );
+
+        let size = vec2f(
+            layout_line
+                .width
+                .max(constraint.min.x())
+                .min(constraint.max.x()),
+            ctx.font_cache.line_height(font_id, self.font_size).ceil(),
+        );
+
+        self.layout_line = Some(layout_line);
+        self.size = Some(size);
+
+        size
+    }
+
+    fn after_layout(&mut self, _: &mut AfterLayoutContext, _: &mut MutableAppContext) {}
+
+    fn paint(&mut self, origin: Vector2F, ctx: &mut PaintContext, _: &AppContext) {
+        // ctx.canvas.set_fill_style(FillStyle::Color(ColorU::black()));
+        // self.layout_line.as_ref().unwrap().paint(
+        //     origin,
+        //     RectF::new(origin, self.size.unwrap()),
+        //     self.colors.as_ref().unwrap(),
+        //     ctx.canvas,
+        //     ctx.font_cache,
+        // );
+    }
+
+    fn size(&self) -> Option<Vector2F> {
+        self.size
+    }
+
+    fn dispatch_event(&self, _: &Event, _: &mut EventContext, _: &AppContext) -> bool {
+        false
+    }
+}

gpui/src/elements/line_box.rs 🔗

@@ -0,0 +1,84 @@
+use super::{AppContext, Element, MutableAppContext};
+use crate::{
+    fonts::{FamilyId, FontId, Properties},
+    geometry::vector::{vec2f, Vector2F},
+    AfterLayoutContext, Event, EventContext, LayoutContext, PaintContext, SizeConstraint,
+};
+
+pub struct LineBox {
+    child: Box<dyn Element>,
+    family_id: FamilyId,
+    font_size: f32,
+    font_properties: Properties,
+    font_id: Option<FontId>,
+    size: Option<Vector2F>,
+}
+
+impl LineBox {
+    pub fn new(family_id: FamilyId, font_size: f32, child: Box<dyn Element>) -> Self {
+        Self {
+            child,
+            family_id,
+            font_size,
+            font_properties: Properties::default(),
+            font_id: None,
+            size: None,
+        }
+    }
+}
+
+impl Element for LineBox {
+    fn layout(
+        &mut self,
+        constraint: SizeConstraint,
+        ctx: &mut LayoutContext,
+        app: &AppContext,
+    ) -> Vector2F {
+        match ctx
+            .font_cache
+            .select_font(self.family_id, &self.font_properties)
+        {
+            Ok(font_id) => {
+                self.font_id = Some(font_id);
+                let line_height = ctx.font_cache.bounding_box(font_id, self.font_size).y();
+                let child_max = vec2f(
+                    constraint.max.x(),
+                    ctx.font_cache.ascent(font_id, self.font_size)
+                        - ctx.font_cache.descent(font_id, self.font_size),
+                );
+                let child_size = self.child.layout(
+                    SizeConstraint::new(constraint.min.min(child_max), child_max),
+                    ctx,
+                    app,
+                );
+                let size = vec2f(child_size.x(), line_height);
+                self.size = Some(size);
+                size
+            }
+            Err(error) => {
+                log::error!("can't layout LineBox: {}", error);
+                self.size = Some(constraint.min);
+                constraint.min
+            }
+        }
+    }
+
+    fn after_layout(&mut self, ctx: &mut AfterLayoutContext, app: &mut MutableAppContext) {
+        self.child.after_layout(ctx, app);
+    }
+
+    fn paint(&mut self, origin: Vector2F, ctx: &mut PaintContext, app: &AppContext) {
+        if let Some(font_id) = self.font_id {
+            let descent = ctx.font_cache.descent(font_id, self.font_size);
+            self.child.paint(origin + vec2f(0.0, -descent), ctx, app);
+        }
+    }
+
+    fn size(&self) -> Option<Vector2F> {
+        self.size
+    }
+
+    fn dispatch_event(&self, event: &Event, ctx: &mut EventContext, app: &AppContext) -> bool {
+        self.child.dispatch_event(event, ctx, app)
+    }
+}

gpui/src/elements/mod.rs 🔗

@@ -0,0 +1,80 @@
+mod align;
+mod constrained_box;
+mod container;
+mod empty;
+mod event_handler;
+mod flex;
+mod label;
+mod line_box;
+mod stack;
+mod svg;
+mod uniform_list;
+
+pub use align::*;
+pub use constrained_box::*;
+pub use container::*;
+pub use empty::*;
+pub use event_handler::*;
+pub use flex::*;
+pub use label::*;
+pub use line_box::*;
+pub use stack::*;
+pub use svg::*;
+pub use uniform_list::*;
+
+use crate::{
+    AfterLayoutContext, AppContext, Event, EventContext, LayoutContext, MutableAppContext,
+    PaintContext, SizeConstraint,
+};
+use pathfinder_geometry::{rect::RectF, vector::Vector2F};
+use std::any::Any;
+
+pub trait Element {
+    fn layout(
+        &mut self,
+        constraint: SizeConstraint,
+        ctx: &mut LayoutContext,
+        app: &AppContext,
+    ) -> Vector2F;
+
+    fn after_layout(&mut self, _: &mut AfterLayoutContext, _: &mut MutableAppContext) {}
+
+    fn paint(&mut self, origin: Vector2F, ctx: &mut PaintContext, app: &AppContext);
+
+    fn size(&self) -> Option<Vector2F>;
+
+    fn parent_data(&self) -> Option<&dyn Any> {
+        None
+    }
+
+    fn dispatch_event(&self, event: &Event, ctx: &mut EventContext, app: &AppContext) -> bool;
+
+    fn boxed(self) -> Box<dyn Element> {
+        Box::new(self)
+    }
+}
+
+pub trait ParentElement<'a>: Extend<Box<dyn Element>> + Sized {
+    fn add_children(&mut self, children: impl IntoIterator<Item = Box<dyn Element>>) {
+        self.extend(children);
+    }
+
+    fn add_child(&mut self, child: Box<dyn Element>) {
+        self.add_childen(Some(child));
+    }
+
+    fn with_children(mut self, children: impl IntoIterator<Item = Box<dyn Element>>) -> Self {
+        self.add_children(children);
+        self
+    }
+
+    fn with_child(self, child: Box<dyn Element>) -> Self {
+        self.with_children(Some(child))
+    }
+}
+
+impl<'a, T> ParentElement<'a> for T where T: Extend<Box<dyn Element>> {}
+
+pub fn try_rect(origin: Option<Vector2F>, size: Option<Vector2F>) -> Option<RectF> {
+    origin.and_then(|origin| size.map(|size| RectF::new(origin, size)))
+}

gpui/src/elements/stack.rs 🔗

@@ -0,0 +1,65 @@
+use crate::{
+    geometry::vector::Vector2F, AfterLayoutContext, AppContext, Element, Event, EventContext,
+    LayoutContext, MutableAppContext, PaintContext, SizeConstraint,
+};
+
+pub struct Stack {
+    children: Vec<Box<dyn Element>>,
+    size: Option<Vector2F>,
+}
+
+impl Stack {
+    pub fn new() -> Self {
+        Stack {
+            children: Vec::new(),
+            size: None,
+        }
+    }
+}
+
+impl Element for Stack {
+    fn layout(
+        &mut self,
+        constraint: SizeConstraint,
+        ctx: &mut LayoutContext,
+        app: &AppContext,
+    ) -> Vector2F {
+        let mut size = constraint.min;
+        for child in &mut self.children {
+            size = size.max(child.layout(constraint, ctx, app));
+        }
+        self.size = Some(size);
+        size
+    }
+
+    fn after_layout(&mut self, ctx: &mut AfterLayoutContext, app: &mut MutableAppContext) {
+        for child in &mut self.children {
+            child.after_layout(ctx, app);
+        }
+    }
+
+    fn paint(&mut self, origin: Vector2F, ctx: &mut PaintContext, app: &AppContext) {
+        for child in &mut self.children {
+            child.paint(origin, ctx, app);
+        }
+    }
+
+    fn dispatch_event(&self, event: &Event, ctx: &mut EventContext, app: &AppContext) -> bool {
+        for child in self.children.iter().rev() {
+            if child.dispatch_event(event, ctx, app) {
+                return true;
+            }
+        }
+        false
+    }
+
+    fn size(&self) -> Option<Vector2F> {
+        self.size
+    }
+}
+
+impl Extend<Box<dyn Element>> for Stack {
+    fn extend<T: IntoIterator<Item = Box<dyn Element>>>(&mut self, children: T) {
+        self.children.extend(children)
+    }
+}

gpui/src/elements/svg.rs 🔗

@@ -0,0 +1,81 @@
+use crate::{
+    geometry::{
+        rect::RectF,
+        vector::{vec2f, Vector2F},
+    },
+    AfterLayoutContext, AppContext, Element, Event, EventContext, LayoutContext, MutableAppContext,
+    PaintContext, SizeConstraint,
+};
+use std::rc::Rc;
+
+pub struct Svg {
+    path: String,
+    // tree: Option<Rc<usvg::Tree>>,
+    size: Option<Vector2F>,
+}
+
+impl Svg {
+    pub fn new(path: String) -> Self {
+        Self {
+            path,
+            // tree: None,
+            size: None,
+        }
+    }
+}
+
+impl Element for Svg {
+    fn layout(
+        &mut self,
+        constraint: SizeConstraint,
+        ctx: &mut LayoutContext,
+        _: &AppContext,
+    ) -> Vector2F {
+        // let size;
+        // match ctx.asset_cache.svg(&self.path) {
+        //     Ok(tree) => {
+        //         size = if constraint.max.x().is_infinite() && constraint.max.y().is_infinite() {
+        //             let rect = usvg_rect_to_euclid_rect(&tree.svg_node().view_box.rect);
+        //             rect.size()
+        //         } else {
+        //             let max_size = constraint.max;
+        //             let svg_size = usvg_rect_to_euclid_rect(&tree.svg_node().view_box.rect).size();
+
+        //             if max_size.x().is_infinite()
+        //                 || max_size.x() / max_size.y() > svg_size.x() / svg_size.y()
+        //             {
+        //                 vec2f(svg_size.x() * max_size.y() / svg_size.y(), max_size.y())
+        //             } else {
+        //                 vec2f(max_size.x(), svg_size.y() * max_size.x() / svg_size.x())
+        //             }
+        //         };
+        //         self.tree = Some(tree);
+        //     }
+        //     Err(error) => {
+        //         log::error!("{}", error);
+        //         size = constraint.min;
+        //     }
+        // };
+
+        // self.size = Some(size);
+        // size
+        todo!()
+    }
+
+    fn after_layout(&mut self, _: &mut AfterLayoutContext, _: &mut MutableAppContext) {}
+
+    fn paint(&mut self, origin: Vector2F, ctx: &mut PaintContext, _: &AppContext) {
+        if let Some(tree) = self.tree.as_ref() {
+            ctx.canvas
+                .draw_svg(tree, RectF::new(origin, self.size.unwrap()));
+        }
+    }
+
+    fn size(&self) -> Option<Vector2F> {
+        self.size
+    }
+
+    fn dispatch_event(&self, _: &Event, _: &mut EventContext, _: &AppContext) -> bool {
+        false
+    }
+}

gpui/src/elements/uniform_list.rs 🔗

@@ -0,0 +1,226 @@
+use super::{
+    try_rect, AfterLayoutContext, AppContext, Element, Event, EventContext, LayoutContext,
+    MutableAppContext, PaintContext, SizeConstraint,
+};
+use crate::geometry::{
+    rect::RectF,
+    vector::{vec2f, Vector2F},
+};
+use parking_lot::Mutex;
+use std::{cmp, ops::Range, sync::Arc};
+
+#[derive(Clone)]
+pub struct UniformListState(Arc<Mutex<StateInner>>);
+
+struct StateInner {
+    scroll_top: f32,
+    scroll_to: Option<usize>,
+}
+
+impl UniformListState {
+    pub fn new() -> Self {
+        Self(Arc::new(Mutex::new(StateInner {
+            scroll_top: 0.0,
+            scroll_to: None,
+        })))
+    }
+
+    pub fn scroll_to(&self, item_ix: usize) {
+        self.0.lock().scroll_to = Some(item_ix);
+    }
+}
+
+pub struct UniformList<F, G>
+where
+    F: Fn(Range<usize>, &AppContext) -> G,
+    G: Iterator<Item = Box<dyn Element>>,
+{
+    state: UniformListState,
+    item_count: usize,
+    build_items: F,
+    scroll_max: Option<f32>,
+    items: Vec<Box<dyn Element>>,
+    origin: Option<Vector2F>,
+    size: Option<Vector2F>,
+}
+
+impl<F, G> UniformList<F, G>
+where
+    F: Fn(Range<usize>, &AppContext) -> G,
+    G: Iterator<Item = Box<dyn Element>>,
+{
+    pub fn new(state: UniformListState, item_count: usize, build_items: F) -> Self {
+        Self {
+            state,
+            item_count,
+            build_items,
+            scroll_max: None,
+            items: Default::default(),
+            origin: None,
+            size: None,
+        }
+    }
+
+    fn scroll(
+        &self,
+        position: Vector2F,
+        delta: Vector2F,
+        precise: bool,
+        ctx: &mut EventContext,
+        _: &AppContext,
+    ) -> bool {
+        if !self.rect().unwrap().contains_point(position) {
+            return false;
+        }
+
+        if !precise {
+            todo!("still need to handle non-precise scroll events from a mouse wheel");
+        }
+
+        let mut state = self.state.0.lock();
+        state.scroll_top = (state.scroll_top - delta.y())
+            .max(0.0)
+            .min(self.scroll_max.unwrap());
+        ctx.dispatch_action("uniform_list:scroll", state.scroll_top);
+
+        true
+    }
+
+    fn autoscroll(&mut self, list_height: f32, item_height: f32) {
+        let mut state = self.state.0.lock();
+
+        let scroll_max = self.item_count as f32 * item_height - list_height;
+        if state.scroll_top > scroll_max {
+            state.scroll_top = scroll_max;
+        }
+
+        if let Some(item_ix) = state.scroll_to.take() {
+            let item_top = item_ix as f32 * item_height;
+            let item_bottom = item_top + item_height;
+
+            if item_top < state.scroll_top {
+                state.scroll_top = item_top;
+            } else if item_bottom > (state.scroll_top + list_height) {
+                state.scroll_top = item_bottom - list_height;
+            }
+        }
+    }
+
+    fn scroll_top(&self) -> f32 {
+        self.state.0.lock().scroll_top
+    }
+
+    fn rect(&self) -> Option<RectF> {
+        try_rect(self.origin, self.size)
+    }
+}
+
+impl<F, G> Element for UniformList<F, G>
+where
+    F: Fn(Range<usize>, &AppContext) -> G,
+    G: Iterator<Item = Box<dyn Element>>,
+{
+    fn layout(
+        &mut self,
+        constraint: SizeConstraint,
+        ctx: &mut LayoutContext,
+        app: &AppContext,
+    ) -> Vector2F {
+        if constraint.max.y().is_infinite() {
+            unimplemented!(
+                "UniformList does not support being rendered with an unconstrained height"
+            );
+        }
+        let mut size = constraint.max;
+        let mut item_constraint =
+            SizeConstraint::new(vec2f(size.x(), 0.0), vec2f(size.x(), f32::INFINITY));
+
+        let first_item = (self.build_items)(0..1, app).next();
+        if let Some(first_item) = first_item {
+            let mut item_size = first_item.layout(item_constraint, ctx, app);
+            item_size.set_x(size.x());
+            item_constraint.min = item_size;
+            item_constraint.max = item_size;
+
+            let scroll_height = self.item_count as f32 * item_size.y();
+            if scroll_height < size.y() {
+                size.set_y(size.y().min(scroll_height).max(constraint.min.y()));
+            }
+
+            self.autoscroll(size.y(), item_size.y());
+
+            let start = cmp::min(
+                (self.scroll_top() / item_size.y()) as usize,
+                self.item_count,
+            );
+            let end = cmp::min(
+                self.item_count,
+                start + (size.y() / item_size.y()).ceil() as usize + 1,
+            );
+            self.items.clear();
+            self.items.extend((self.build_items)(start..end, app));
+
+            self.scroll_max = Some(item_size.y() * self.item_count as f32 - size.y());
+
+            for item in &mut self.items {
+                item.layout(item_constraint, ctx, app);
+            }
+        }
+
+        self.size = Some(size);
+        size
+    }
+
+    fn after_layout(&mut self, ctx: &mut AfterLayoutContext, app: &mut MutableAppContext) {
+        for item in &mut self.items {
+            item.after_layout(ctx, app);
+        }
+    }
+
+    fn paint(&mut self, origin: Vector2F, ctx: &mut PaintContext, app: &AppContext) {
+        // self.origin = Some(origin);
+
+        // if let Some(item) = self.items.first() {
+        //     ctx.canvas.save();
+        //     let mut clip_path = Path2D::new();
+        //     clip_path.rect(RectF::new(origin, self.size.unwrap()));
+        //     ctx.canvas.clip_path(clip_path, FillRule::Winding);
+
+        //     let item_height = item.size().unwrap().y();
+        //     let mut item_origin = origin - vec2f(0.0, self.state.0.lock().scroll_top % item_height);
+        //     for item in &mut self.items {
+        //         item.paint(item_origin, ctx, app);
+        //         item_origin += vec2f(0.0, item_height);
+        //     }
+        //     ctx.canvas.restore();
+        // }
+    }
+
+    fn size(&self) -> Option<Vector2F> {
+        self.size
+    }
+
+    fn dispatch_event(&self, event: &Event, ctx: &mut EventContext, app: &AppContext) -> bool {
+        let mut handled = false;
+        for item in &self.items {
+            if item.dispatch_event(event, ctx, app) {
+                handled = true;
+            }
+        }
+
+        match event {
+            Event::ScrollWheel {
+                position,
+                delta,
+                precise,
+            } => {
+                if self.scroll(*position, *delta, *precise, ctx, app) {
+                    handled = true;
+                }
+            }
+            _ => {}
+        }
+
+        handled
+    }
+}

gpui/src/fonts.rs 🔗

@@ -0,0 +1,298 @@
+use crate::geometry::vector::{vec2f, Vector2F};
+use anyhow::{anyhow, Result};
+use parking_lot::{RwLock, RwLockUpgradableReadGuard};
+
+pub use font_kit::properties::{Properties, Weight};
+use font_kit::{
+    font::Font, loaders::core_text::NativeFont, metrics::Metrics, source::SystemSource,
+};
+use ordered_float::OrderedFloat;
+use std::{collections::HashMap, sync::Arc};
+
+pub type GlyphId = u32;
+
+#[derive(Copy, Clone, Debug, Eq, PartialEq, Hash)]
+pub struct FamilyId(usize);
+
+#[derive(Copy, Clone, Debug, Eq, PartialEq, Hash)]
+pub struct FontId(usize);
+
+pub struct FontCache(RwLock<FontCacheState>);
+
+pub struct FontCacheState {
+    source: SystemSource,
+    families: Vec<Family>,
+    fonts: Vec<Arc<Font>>,
+    font_names: Vec<Arc<String>>,
+    font_selections: HashMap<FamilyId, HashMap<Properties, FontId>>,
+    metrics: HashMap<FontId, Metrics>,
+    native_fonts: HashMap<(FontId, OrderedFloat<f32>), NativeFont>,
+    fonts_by_name: HashMap<Arc<String>, FontId>,
+    emoji_font_id: Option<FontId>,
+}
+
+unsafe impl Send for FontCache {}
+
+struct Family {
+    name: String,
+    font_ids: Vec<FontId>,
+}
+
+impl FontCache {
+    pub fn new() -> Self {
+        Self(RwLock::new(FontCacheState {
+            source: SystemSource::new(),
+            families: Vec::new(),
+            fonts: Vec::new(),
+            font_names: Vec::new(),
+            font_selections: HashMap::new(),
+            metrics: HashMap::new(),
+            native_fonts: HashMap::new(),
+            fonts_by_name: HashMap::new(),
+            emoji_font_id: None,
+        }))
+    }
+
+    pub fn load_family(&self, names: &[&str]) -> Result<FamilyId> {
+        for name in names {
+            let state = self.0.upgradable_read();
+
+            if let Some(ix) = state.families.iter().position(|f| f.name == *name) {
+                return Ok(FamilyId(ix));
+            }
+
+            let mut state = RwLockUpgradableReadGuard::upgrade(state);
+
+            if let Ok(handle) = state.source.select_family_by_name(name) {
+                if handle.is_empty() {
+                    continue;
+                }
+
+                let family_id = FamilyId(state.families.len());
+                let mut font_ids = Vec::new();
+                for font in handle.fonts() {
+                    let font = font.load()?;
+                    if font.glyph_for_char('m').is_none() {
+                        return Err(anyhow!("font must contain a glyph for the 'm' character"));
+                    }
+                    font_ids.push(push_font(&mut state, font));
+                }
+
+                state.families.push(Family {
+                    name: String::from(*name),
+                    font_ids,
+                });
+                return Ok(family_id);
+            }
+        }
+
+        Err(anyhow!(
+            "could not find a non-empty font family matching one of the given names"
+        ))
+    }
+
+    pub fn default_font(&self, family_id: FamilyId) -> FontId {
+        self.select_font(family_id, &Properties::default()).unwrap()
+    }
+
+    pub fn select_font(&self, family_id: FamilyId, properties: &Properties) -> Result<FontId> {
+        let inner = self.0.upgradable_read();
+        if let Some(font_id) = inner
+            .font_selections
+            .get(&family_id)
+            .and_then(|f| f.get(properties))
+        {
+            Ok(*font_id)
+        } else {
+            let mut inner = RwLockUpgradableReadGuard::upgrade(inner);
+            let family = &inner.families[family_id.0];
+            let candidates = family
+                .font_ids
+                .iter()
+                .map(|font_id| inner.fonts[font_id.0].properties())
+                .collect::<Vec<_>>();
+            let idx = font_kit::matching::find_best_match(&candidates, properties)?;
+            let font_id = family.font_ids[idx];
+
+            inner
+                .font_selections
+                .entry(family_id)
+                .or_default()
+                .insert(properties.clone(), font_id);
+            Ok(font_id)
+        }
+    }
+
+    pub fn font(&self, font_id: FontId) -> Arc<Font> {
+        self.0.read().fonts[font_id.0].clone()
+    }
+
+    pub fn font_name(&self, font_id: FontId) -> Arc<String> {
+        self.0.read().font_names[font_id.0].clone()
+    }
+
+    pub fn metric<F, T>(&self, font_id: FontId, f: F) -> T
+    where
+        F: FnOnce(&Metrics) -> T,
+        T: 'static,
+    {
+        let state = self.0.upgradable_read();
+        if let Some(metrics) = state.metrics.get(&font_id) {
+            f(metrics)
+        } else {
+            let metrics = state.fonts[font_id.0].metrics();
+            let metric = f(&metrics);
+            let mut state = RwLockUpgradableReadGuard::upgrade(state);
+            state.metrics.insert(font_id, metrics);
+            metric
+        }
+    }
+
+    pub fn is_emoji(&self, font_id: FontId) -> bool {
+        self.0
+            .read()
+            .emoji_font_id
+            .map_or(false, |emoji_font_id| emoji_font_id == font_id)
+    }
+
+    pub fn bounding_box(&self, font_id: FontId, font_size: f32) -> Vector2F {
+        let bounding_box = self.metric(font_id, |m| m.bounding_box);
+        let width = self.scale_metric(bounding_box.width(), font_id, font_size);
+        let height = self.scale_metric(bounding_box.height(), font_id, font_size);
+        vec2f(width, height)
+    }
+
+    pub fn line_height(&self, font_id: FontId, font_size: f32) -> f32 {
+        let bounding_box = self.metric(font_id, |m| m.bounding_box);
+        self.scale_metric(bounding_box.height(), font_id, font_size)
+    }
+
+    pub fn cap_height(&self, font_id: FontId, font_size: f32) -> f32 {
+        self.scale_metric(self.metric(font_id, |m| m.cap_height), font_id, font_size)
+    }
+
+    pub fn ascent(&self, font_id: FontId, font_size: f32) -> f32 {
+        self.scale_metric(self.metric(font_id, |m| m.ascent), font_id, font_size)
+    }
+
+    pub fn descent(&self, font_id: FontId, font_size: f32) -> f32 {
+        self.scale_metric(self.metric(font_id, |m| m.descent), font_id, font_size)
+    }
+
+    // pub fn render_emoji(&self, glyph_id: GlyphId, font_size: f32) -> Result<Pattern> {
+    //     let key = (glyph_id, OrderedFloat(font_size));
+
+    //     {
+    //         if let Some(image) = self.0.read().emoji_images.get(&key) {
+    //             return Ok(image.clone());
+    //         }
+    //     }
+
+    //     let font_id = self.emoji_font_id()?;
+    //     let bounding_box = self.bounding_box(font_id, font_size);
+    //     let width = (4.0 * bounding_box.x()) as usize;
+    //     let height = (4.0 * bounding_box.y()) as usize;
+    //     let mut ctx = CGContext::create_bitmap_context(
+    //         None,
+    //         width,
+    //         height,
+    //         8,
+    //         width * 4,
+    //         &CGColorSpace::create_device_rgb(),
+    //         kCGImageAlphaPremultipliedLast | kCGBitmapByteOrderDefault,
+    //     );
+    //     ctx.scale(4.0, 4.0);
+
+    //     let native_font = self.native_font(font_id, font_size);
+    //     let glyph = glyph_id.0 as CGGlyph;
+    //     let glyph_bounds = native_font.get_bounding_rects_for_glyphs(Default::default(), &[glyph]);
+    //     let position = CGPoint::new(glyph_bounds.origin.x, -glyph_bounds.origin.y);
+
+    //     native_font.draw_glyphs(&[glyph], &[position], ctx.clone());
+
+    //     ctx.flush();
+
+    //     let image = Pattern::from_image(Image::new(
+    //         vec2i(ctx.width() as i32, ctx.height() as i32),
+    //         Arc::new(u8_slice_to_color_slice(&ctx.data()).into()),
+    //     ));
+    //     self.0.write().emoji_images.insert(key, image.clone());
+
+    //     Ok(image)
+    // }
+
+    fn emoji_font_id(&self) -> Result<FontId> {
+        let state = self.0.upgradable_read();
+
+        if let Some(font_id) = state.emoji_font_id {
+            Ok(font_id)
+        } else {
+            let handle = state.source.select_family_by_name("Apple Color Emoji")?;
+            let font = handle
+                .fonts()
+                .first()
+                .ok_or(anyhow!("no fonts in Apple Color Emoji font family"))?
+                .load()?;
+            let mut state = RwLockUpgradableReadGuard::upgrade(state);
+            let font_id = push_font(&mut state, font);
+            state.emoji_font_id = Some(font_id);
+            Ok(font_id)
+        }
+    }
+
+    pub fn scale_metric(&self, metric: f32, font_id: FontId, font_size: f32) -> f32 {
+        metric * font_size / self.metric(font_id, |m| m.units_per_em as f32)
+    }
+
+    pub fn native_font(&self, font_id: FontId, size: f32) -> NativeFont {
+        let native_key = (font_id, OrderedFloat(size));
+
+        let state = self.0.upgradable_read();
+        if let Some(native_font) = state.native_fonts.get(&native_key).cloned() {
+            native_font
+        } else {
+            let native_font = state.fonts[font_id.0]
+                .native_font()
+                .clone_with_font_size(size as f64);
+            RwLockUpgradableReadGuard::upgrade(state)
+                .native_fonts
+                .insert(native_key, native_font.clone());
+            native_font
+        }
+    }
+
+    pub fn font_id_for_native_font(&self, native_font: NativeFont) -> FontId {
+        let postscript_name = native_font.postscript_name();
+        let state = self.0.upgradable_read();
+        if let Some(font_id) = state.fonts_by_name.get(&postscript_name) {
+            *font_id
+        } else {
+            push_font(&mut RwLockUpgradableReadGuard::upgrade(state), unsafe {
+                Font::from_native_font(native_font.clone())
+            })
+        }
+    }
+}
+
+fn push_font(state: &mut FontCacheState, font: Font) -> FontId {
+    let font_id = FontId(state.fonts.len());
+    let name = Arc::new(font.postscript_name().unwrap());
+    if *name == "AppleColorEmoji" {
+        state.emoji_font_id = Some(font_id);
+    }
+    state.fonts.push(Arc::new(font));
+    state.font_names.push(name.clone());
+    state.fonts_by_name.insert(name, font_id);
+    font_id
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_render_emoji() {
+        let ctx = FontCache::new();
+        let _ = ctx.render_emoji(0, 16.0);
+    }
+}

gpui/src/lib.rs 🔗

@@ -1,6 +1,17 @@
+mod app;
+pub mod elements;
 pub mod executor;
+mod fonts;
 pub mod keymap;
 pub mod platform;
+mod presenter;
+mod scene;
+mod util;
 
+pub use app::*;
+pub use elements::Element;
 pub use pathfinder_color as color;
 pub use pathfinder_geometry as geometry;
+pub use platform::Event;
+pub use presenter::*;
+use scene::Scene;

gpui/src/platform/mod.rs 🔗

@@ -9,7 +9,7 @@ pub mod current {
 use crate::{executor, geometry::rect::RectF};
 use anyhow::Result;
 use async_task::Runnable;
-use event::Event;
+pub use event::Event;
 use std::{path::PathBuf, rc::Rc, sync::Arc};
 
 pub trait Runner {

gpui/src/presenter.rs 🔗

@@ -0,0 +1,370 @@
+use crate::{
+    app::{AppContext, MutableAppContext, WindowInvalidation},
+    elements::Element,
+    platform::Event,
+    Scene,
+};
+use pathfinder_geometry::vector::{vec2f, Vector2F};
+use std::{any::Any, collections::HashMap, rc::Rc};
+
+pub struct Presenter {
+    window_id: usize,
+    rendered_views: HashMap<usize, Box<dyn Element>>,
+    parents: HashMap<usize, usize>,
+    font_cache: Rc<FontCache>,
+    text_layout_cache: LayoutCache,
+    asset_cache: Rc<AssetCache>,
+}
+
+impl Presenter {
+    pub fn new(
+        window_id: usize,
+        font_cache: Rc<FontCache>,
+        asset_cache: Rc<AssetCache>,
+        app: &MutableAppContext,
+    ) -> Self {
+        Self {
+            window_id,
+            rendered_views: app.render_views(window_id).unwrap(),
+            parents: HashMap::new(),
+            font_cache,
+            text_layout_cache: LayoutCache::new(),
+            asset_cache,
+        }
+    }
+
+    fn invalidate(&mut self, invalidation: WindowInvalidation, app: &AppContext) {
+        for view_id in invalidation.updated {
+            self.rendered_views
+                .insert(view_id, app.render_view(self.window_id, view_id).unwrap());
+        }
+        for view_id in invalidation.removed {
+            self.rendered_views.remove(&view_id);
+            self.parents.remove(&view_id);
+        }
+    }
+
+    pub fn build_scene(
+        &mut self,
+        window_size: Vector2F,
+        scale_factor: f32,
+        app: &mut MutableAppContext,
+    ) -> Scene {
+        self.layout(window_size, app.ctx());
+        self.after_layout(app);
+        let scene = self.paint(window_size, scale_factor, app.ctx());
+        self.text_layout_cache.finish_frame();
+        scene
+    }
+
+    fn layout(&mut self, size: Vector2F, app: &AppContext) {
+        if let Some(root_view_id) = app.root_view_id(self.window_id) {
+            let mut layout_ctx = LayoutContext {
+                rendered_views: &mut self.rendered_views,
+                parents: &mut self.parents,
+                font_cache: &self.font_cache,
+                text_layout_cache: &self.text_layout_cache,
+                asset_cache: &self.asset_cache,
+                view_stack: Vec::new(),
+            };
+            layout_ctx.layout(root_view_id, SizeConstraint::strict(size), app);
+        }
+    }
+
+    fn after_layout(&mut self, app: &mut MutableAppContext) {
+        if let Some(root_view_id) = app.root_view_id(self.window_id) {
+            let mut ctx = AfterLayoutContext {
+                rendered_views: &mut self.rendered_views,
+                font_cache: &self.font_cache,
+                text_layout_cache: &self.text_layout_cache,
+            };
+            ctx.after_layout(root_view_id, app);
+        }
+    }
+
+    fn paint(&mut self, size: Vector2F, scale_factor: f32, app: &AppContext) -> Scene {
+        // let mut canvas = Canvas::new(size * scale_factor).get_context_2d(self.font_context.clone());
+        // canvas.scale(scale_factor);
+
+        // if let Some(root_view_id) = app.root_view_id(self.window_id) {
+        //     let mut paint_ctx = PaintContext {
+        //         canvas: &mut canvas,
+        //         font_cache: &self.font_cache,
+        //         text_layout_cache: &self.text_layout_cache,
+        //         rendered_views: &mut self.rendered_views,
+        //     };
+        //     paint_ctx.paint(root_view_id, Vector2F::zero(), app);
+        // }
+
+        // canvas.into_canvas().into_scene()
+        todo!()
+    }
+
+    pub fn responder_chain(&self, app: &AppContext) -> Option<Vec<usize>> {
+        app.focused_view_id(self.window_id).map(|mut view_id| {
+            let mut chain = vec![view_id];
+            while let Some(parent_id) = self.parents.get(&view_id) {
+                view_id = *parent_id;
+                chain.push(view_id);
+            }
+            chain.reverse();
+            chain
+        })
+    }
+
+    pub fn dispatch_event(
+        &self,
+        event: Event,
+        app: &AppContext,
+    ) -> Vec<(usize, &'static str, Box<dyn Any>)> {
+        let mut event_ctx = EventContext {
+            rendered_views: &self.rendered_views,
+            actions: Vec::new(),
+            font_cache: &self.font_cache,
+            text_layout_cache: &self.text_layout_cache,
+            view_stack: Vec::new(),
+        };
+        if let Some(root_view_id) = app.root_view_id(self.window_id) {
+            event_ctx.dispatch_event_on_view(root_view_id, &event, app);
+        }
+        event_ctx.actions
+    }
+}
+
+pub struct LayoutContext<'a> {
+    rendered_views: &'a mut HashMap<usize, Box<dyn Element>>,
+    parents: &'a mut HashMap<usize, usize>,
+    pub font_cache: &'a FontCache,
+    pub text_layout_cache: &'a LayoutCache,
+    pub asset_cache: &'a AssetCache,
+    view_stack: Vec<usize>,
+}
+
+impl<'a> LayoutContext<'a> {
+    fn layout(&mut self, view_id: usize, constraint: SizeConstraint, app: &AppContext) -> Vector2F {
+        if let Some(parent_id) = self.view_stack.last() {
+            self.parents.insert(view_id, *parent_id);
+        }
+        self.view_stack.push(view_id);
+        let mut rendered_view = self.rendered_views.remove(&view_id).unwrap();
+        let size = rendered_view.layout(constraint, self, app);
+        self.rendered_views.insert(view_id, rendered_view);
+        self.view_stack.pop();
+        size
+    }
+}
+
+pub struct AfterLayoutContext<'a> {
+    rendered_views: &'a mut HashMap<usize, Box<dyn Element>>,
+    pub font_cache: &'a FontCache,
+    pub text_layout_cache: &'a LayoutCache,
+}
+
+impl<'a> AfterLayoutContext<'a> {
+    fn after_layout(&mut self, view_id: usize, app: &mut MutableAppContext) {
+        if let Some(mut view) = self.rendered_views.remove(&view_id) {
+            view.after_layout(self, app);
+            self.rendered_views.insert(view_id, view);
+        }
+    }
+}
+
+pub struct PaintContext<'a> {
+    rendered_views: &'a mut HashMap<usize, Box<dyn Element>>,
+    // pub canvas: &'a mut CanvasRenderingContext2D,
+    pub font_cache: &'a FontCache,
+    pub text_layout_cache: &'a LayoutCache,
+}
+
+impl<'a> PaintContext<'a> {
+    fn paint(&mut self, view_id: usize, origin: Vector2F, app: &AppContext) {
+        if let Some(mut tree) = self.rendered_views.remove(&view_id) {
+            tree.paint(origin, self, app);
+            self.rendered_views.insert(view_id, tree);
+        }
+    }
+}
+
+pub struct EventContext<'a> {
+    rendered_views: &'a HashMap<usize, Box<dyn Element>>,
+    actions: Vec<(usize, &'static str, Box<dyn Any>)>,
+    pub font_cache: &'a FontCache,
+    pub text_layout_cache: &'a LayoutCache,
+    view_stack: Vec<usize>,
+}
+
+impl<'a> EventContext<'a> {
+    pub fn dispatch_event_on_view(
+        &mut self,
+        view_id: usize,
+        event: &Event,
+        app: &AppContext,
+    ) -> bool {
+        if let Some(element) = self.rendered_views.get(&view_id) {
+            self.view_stack.push(view_id);
+            let result = element.dispatch_event(event, self, app);
+            self.view_stack.pop();
+            result
+        } else {
+            false
+        }
+    }
+
+    pub fn dispatch_action<A: 'static + Any>(&mut self, name: &'static str, arg: A) {
+        self.actions
+            .push((*self.view_stack.last().unwrap(), name, Box::new(arg)));
+    }
+}
+
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub enum Axis {
+    Horizontal,
+    Vertical,
+}
+
+impl Axis {
+    pub fn invert(self) -> Self {
+        match self {
+            Self::Horizontal => Self::Vertical,
+            Self::Vertical => Self::Horizontal,
+        }
+    }
+}
+
+pub trait Vector2FExt {
+    fn along(self, axis: Axis) -> f32;
+}
+
+impl Vector2FExt for Vector2F {
+    fn along(self, axis: Axis) -> f32 {
+        match axis {
+            Axis::Horizontal => self.x(),
+            Axis::Vertical => self.y(),
+        }
+    }
+}
+
+#[derive(Copy, Clone, Debug)]
+pub struct SizeConstraint {
+    pub min: Vector2F,
+    pub max: Vector2F,
+}
+
+impl SizeConstraint {
+    pub fn new(min: Vector2F, max: Vector2F) -> Self {
+        Self { min, max }
+    }
+
+    pub fn strict(size: Vector2F) -> Self {
+        Self {
+            min: size,
+            max: size,
+        }
+    }
+
+    pub fn strict_along(axis: Axis, max: f32) -> Self {
+        match axis {
+            Axis::Horizontal => Self {
+                min: vec2f(max, 0.0),
+                max: vec2f(max, f32::INFINITY),
+            },
+            Axis::Vertical => Self {
+                min: vec2f(0.0, max),
+                max: vec2f(f32::INFINITY, max),
+            },
+        }
+    }
+
+    pub fn max_along(&self, axis: Axis) -> f32 {
+        match axis {
+            Axis::Horizontal => self.max.x(),
+            Axis::Vertical => self.max.y(),
+        }
+    }
+}
+
+pub struct ChildView {
+    view_id: usize,
+    size: Option<Vector2F>,
+    origin: Option<Vector2F>,
+}
+
+impl ChildView {
+    pub fn new(view_id: usize) -> Self {
+        Self {
+            view_id,
+            size: None,
+            origin: None,
+        }
+    }
+}
+
+impl Element for ChildView {
+    fn layout(
+        &mut self,
+        constraint: SizeConstraint,
+        ctx: &mut LayoutContext,
+        app: &AppContext,
+    ) -> Vector2F {
+        let size = ctx.layout(self.view_id, constraint, app);
+        self.size = Some(size);
+        size
+    }
+
+    fn after_layout(&mut self, ctx: &mut AfterLayoutContext, app: &mut MutableAppContext) {
+        ctx.after_layout(self.view_id, app);
+    }
+
+    fn paint(&mut self, origin: Vector2F, ctx: &mut PaintContext, app: &AppContext) {
+        self.origin = Some(origin);
+        ctx.paint(self.view_id, origin, app);
+    }
+
+    fn dispatch_event(&self, event: &Event, ctx: &mut EventContext, app: &AppContext) -> bool {
+        ctx.dispatch_event_on_view(self.view_id, event, app)
+    }
+
+    fn size(&self) -> Option<Vector2F> {
+        self.size
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    // #[test]
+    // fn test_responder_chain() {
+    //     let settings = settings_rx(None);
+    //     let mut app = App::new().unwrap();
+    //     let workspace = app.add_model(|ctx| Workspace::new(Vec::new(), ctx));
+    //     let (window_id, workspace_view) =
+    //         app.add_window(|ctx| WorkspaceView::new(workspace.clone(), settings, ctx));
+
+    //     let invalidations = Rc::new(RefCell::new(Vec::new()));
+    //     let invalidations_ = invalidations.clone();
+    //     app.on_window_invalidated(window_id, move |invalidation, _| {
+    //         invalidations_.borrow_mut().push(invalidation)
+    //     });
+
+    //     let active_pane_id = workspace_view.update(&mut app, |view, ctx| {
+    //         ctx.focus(view.active_pane());
+    //         view.active_pane().id()
+    //     });
+
+    //     app.update(|app| {
+    //         let mut presenter = Presenter::new(
+    //             window_id,
+    //             Rc::new(FontCache::new()),
+    //             Rc::new(AssetCache::new()),
+    //             app,
+    //         );
+    //         for invalidation in invalidations.borrow().iter().cloned() {
+    //             presenter.update(vec2f(1024.0, 768.0), 2.0, Some(invalidation), app);
+    //         }
+
+    //         assert_eq!(
+    //             presenter.responder_chain(app.ctx()).unwrap(),
+    //             vec![workspace_view.id(), active_pane_id]
+    //         );
+    //     });
+    // }
+}

gpui/src/util.rs 🔗

@@ -0,0 +1,77 @@
+use rand::prelude::*;
+use std::cmp::Ordering;
+
+pub fn pre_inc(value: &mut usize) -> usize {
+    *value += 1;
+    *value
+}
+
+pub fn post_inc(value: &mut usize) -> usize {
+    let prev = *value;
+    *value += 1;
+    prev
+}
+
+pub fn find_insertion_index<'a, F, T, E>(slice: &'a [T], mut f: F) -> Result<usize, E>
+where
+    F: FnMut(&'a T) -> Result<Ordering, E>,
+{
+    use Ordering::*;
+
+    let s = slice;
+    let mut size = s.len();
+    if size == 0 {
+        return Ok(0);
+    }
+    let mut base = 0usize;
+    while size > 1 {
+        let half = size / 2;
+        let mid = base + half;
+        // mid is always in [0, size), that means mid is >= 0 and < size.
+        // mid >= 0: by definition
+        // mid < size: mid = size / 2 + size / 4 + size / 8 ...
+        let cmp = f(unsafe { s.get_unchecked(mid) })?;
+        base = if cmp == Greater { base } else { mid };
+        size -= half;
+    }
+    // base is always in [0, size) because base <= mid.
+    let cmp = f(unsafe { s.get_unchecked(base) })?;
+    if cmp == Equal {
+        Ok(base)
+    } else {
+        Ok(base + (cmp == Less) as usize)
+    }
+}
+
+pub struct RandomCharIter<T: Rng>(T);
+
+impl<T: Rng> RandomCharIter<T> {
+    pub fn new(rng: T) -> Self {
+        Self(rng)
+    }
+}
+
+impl<T: Rng> Iterator for RandomCharIter<T> {
+    type Item = char;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if self.0.gen_bool(1.0 / 5.0) {
+            Some('\n')
+        } else {
+            Some(self.0.gen_range(b'a', b'z' + 1).into())
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_find_insertion_index() {
+        assert_eq!(
+            find_insertion_index(&[0, 4, 8], |probe| Ok::<Ordering, ()>(probe.cmp(&2))),
+            Ok(1)
+        );
+    }
+}

zed/Cargo.toml 🔗

@@ -4,9 +4,21 @@ edition = "2018"
 name = "zed"
 version = "0.1.0"
 
+[lib]
+name = "zed"
+path = "src/lib.rs"
+
+[[bin]]
+name = "zed"
+path = "src/main.rs"
+
 [dependencies]
+anyhow = "1.0.38"
+arrayvec = "0.5.2"
 dirs = "3.0"
 gpui = {path = "../gpui"}
+lazy_static = "1.4.0"
 libc = "0.2"
 log = "0.4"
+rand = "0.8.3"
 simplelog = "0.9"

zed/src/editor/buffer/anchor.rs 🔗

@@ -0,0 +1,85 @@
+use super::Buffer;
+use crate::time;
+use anyhow::Result;
+use std::cmp::Ordering;
+use std::ops::Range;
+
+#[derive(Clone, Eq, PartialEq, Debug, Hash)]
+pub enum Anchor {
+    Start,
+    End,
+    Middle {
+        insertion_id: time::Local,
+        offset: usize,
+        bias: AnchorBias,
+    },
+}
+
+#[derive(Clone, Eq, PartialEq, Debug, Hash)]
+pub enum AnchorBias {
+    Left,
+    Right,
+}
+
+impl PartialOrd for AnchorBias {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
+impl Ord for AnchorBias {
+    fn cmp(&self, other: &Self) -> Ordering {
+        use AnchorBias::*;
+
+        if self == other {
+            return Ordering::Equal;
+        }
+
+        match (self, other) {
+            (Left, _) => Ordering::Less,
+            (Right, _) => Ordering::Greater,
+        }
+    }
+}
+
+impl Anchor {
+    pub fn cmp(&self, other: &Anchor, buffer: &Buffer) -> Result<Ordering> {
+        if self == other {
+            return Ok(Ordering::Equal);
+        }
+
+        Ok(match (self, other) {
+            (Anchor::Start, _) | (_, Anchor::End) => Ordering::Less,
+            (Anchor::End, _) | (_, Anchor::Start) => Ordering::Greater,
+            (
+                Anchor::Middle {
+                    offset: self_offset,
+                    bias: self_bias,
+                    ..
+                },
+                Anchor::Middle {
+                    offset: other_offset,
+                    bias: other_bias,
+                    ..
+                },
+            ) => buffer
+                .fragment_id_for_anchor(self)?
+                .cmp(buffer.fragment_id_for_anchor(other)?)
+                .then_with(|| self_offset.cmp(other_offset))
+                .then_with(|| self_bias.cmp(other_bias)),
+        })
+    }
+}
+
+pub trait AnchorRangeExt {
+    fn cmp(&self, b: &Range<Anchor>, buffer: &Buffer) -> Result<Ordering>;
+}
+
+impl AnchorRangeExt for Range<Anchor> {
+    fn cmp(&self, other: &Range<Anchor>, buffer: &Buffer) -> Result<Ordering> {
+        Ok(match self.start.cmp(&other.start, buffer)? {
+            Ordering::Equal => other.end.cmp(&self.end, buffer)?,
+            ord @ _ => ord,
+        })
+    }
+}

zed/src/editor/buffer/mod.rs 🔗

@@ -0,0 +1,2548 @@
+mod anchor;
+mod point;
+mod text;
+
+pub use anchor::*;
+pub use point::*;
+pub use text::*;
+
+use crate::{
+    app::{self as app, AppContext, ModelContext},
+    operation_queue::{self, OperationQueue},
+    sum_tree::{self, Cursor, FilterCursor, SeekBias, SumTree},
+    time,
+    util::RandomCharIter,
+    worktree::FileHandle,
+    ReplicaId,
+};
+use anyhow::{anyhow, Result};
+use lazy_static::lazy_static;
+use rand::prelude::*;
+use std::{
+    cmp::{self, Ordering},
+    collections::{HashMap, HashSet},
+    iter::{self, Iterator},
+    mem,
+    ops::{AddAssign, Range},
+    path::PathBuf,
+    str,
+    sync::Arc,
+};
+
+pub type SelectionSetId = time::Lamport;
+pub type SelectionsVersion = usize;
+
+pub struct Buffer {
+    file: Option<FileHandle>,
+    fragments: SumTree<Fragment>,
+    insertion_splits: HashMap<time::Local, SumTree<InsertionSplit>>,
+    pub version: time::Global,
+    last_edit: time::Local,
+    selections: HashMap<SelectionSetId, Vec<Selection>>,
+    pub selections_last_update: SelectionsVersion,
+    deferred_ops: OperationQueue<Operation>,
+    deferred_replicas: HashSet<ReplicaId>,
+    replica_id: ReplicaId,
+    local_clock: time::Local,
+    lamport_clock: time::Lamport,
+}
+
+#[derive(Clone)]
+pub struct History {
+    pub base_text: String,
+}
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct Selection {
+    pub start: Anchor,
+    pub end: Anchor,
+    pub reversed: bool,
+}
+
+#[derive(Clone)]
+pub struct Chars<'a> {
+    fragments_cursor: Cursor<'a, Fragment, usize, usize>,
+    fragment_chars: str::Chars<'a>,
+}
+
+struct Edits<'a, F: Fn(&FragmentSummary) -> bool> {
+    cursor: FilterCursor<'a, F, Fragment, usize>,
+    since: time::Global,
+    delta: isize,
+}
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct Edit {
+    pub old_range: Range<usize>,
+    pub new_range: Range<usize>,
+}
+
+impl Edit {
+    pub fn delta(&self) -> isize {
+        (self.new_range.end - self.new_range.start) as isize
+            - (self.old_range.end - self.old_range.start) as isize
+    }
+
+    pub fn old_extent(&self) -> usize {
+        self.old_range.end - self.old_range.start
+    }
+}
+
+#[derive(Clone, Eq, PartialEq, Debug)]
+pub struct Insertion {
+    id: time::Local,
+    parent_id: time::Local,
+    offset_in_parent: usize,
+    text: Text,
+    lamport_timestamp: time::Lamport,
+}
+
+#[derive(Eq, PartialEq, Clone, Debug)]
+struct Fragment {
+    id: FragmentId,
+    insertion: Insertion,
+    text: Text,
+    deletions: HashSet<time::Local>,
+}
+
+#[derive(Eq, PartialEq, Clone, Debug)]
+pub struct FragmentSummary {
+    text_summary: TextSummary,
+    max_fragment_id: FragmentId,
+    max_version: time::Global,
+}
+
+#[derive(Eq, PartialEq, Clone, Debug, Ord, PartialOrd)]
+struct FragmentExtent {
+    chars: usize,
+    lines: Point,
+}
+
+#[derive(Eq, PartialEq, Clone, Debug)]
+struct InsertionSplit {
+    extent: usize,
+    fragment_id: FragmentId,
+}
+
+#[derive(Eq, PartialEq, Clone, Debug)]
+struct InsertionSplitSummary {
+    extent: usize,
+}
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub enum Operation {
+    Edit {
+        start_id: time::Local,
+        start_offset: usize,
+        end_id: time::Local,
+        end_offset: usize,
+        version_in_range: time::Global,
+        new_text: Option<Text>,
+        local_timestamp: time::Local,
+        lamport_timestamp: time::Lamport,
+    },
+    UpdateSelections {
+        set_id: SelectionSetId,
+        selections: Option<Vec<Selection>>,
+        lamport_timestamp: time::Lamport,
+    },
+}
+
+impl Buffer {
+    pub fn new<T: Into<String>>(replica_id: ReplicaId, base_text: T) -> Self {
+        Self::build(replica_id, None, base_text.into())
+    }
+
+    pub fn from_history(replica_id: ReplicaId, file: FileHandle, history: History) -> Self {
+        Self::build(replica_id, Some(file), history.base_text)
+    }
+
+    fn build(replica_id: ReplicaId, file: Option<FileHandle>, base_text: String) -> Self {
+        let mut insertion_splits = HashMap::new();
+        let mut fragments = SumTree::new();
+
+        let base_insertion = Insertion {
+            id: time::Local::default(),
+            parent_id: time::Local::default(),
+            offset_in_parent: 0,
+            text: base_text.into(),
+            lamport_timestamp: time::Lamport::default(),
+        };
+
+        insertion_splits.insert(
+            base_insertion.id,
+            SumTree::from_item(InsertionSplit {
+                fragment_id: FragmentId::min_value().clone(),
+                extent: 0,
+            }),
+        );
+        fragments.push(Fragment {
+            id: FragmentId::min_value().clone(),
+            insertion: base_insertion.clone(),
+            text: base_insertion.text.slice(0..0),
+            deletions: HashSet::new(),
+        });
+
+        if base_insertion.text.len() > 0 {
+            let base_fragment_id =
+                FragmentId::between(&FragmentId::min_value(), &FragmentId::max_value());
+
+            insertion_splits
+                .get_mut(&base_insertion.id)
+                .unwrap()
+                .push(InsertionSplit {
+                    fragment_id: base_fragment_id.clone(),
+                    extent: base_insertion.text.len(),
+                });
+            fragments.push(Fragment {
+                id: base_fragment_id,
+                text: base_insertion.text.clone(),
+                insertion: base_insertion,
+                deletions: HashSet::new(),
+            });
+        }
+
+        Self {
+            file,
+            fragments,
+            insertion_splits,
+            version: time::Global::new(),
+            last_edit: time::Local::default(),
+            selections: HashMap::default(),
+            selections_last_update: 0,
+            deferred_ops: OperationQueue::new(),
+            deferred_replicas: HashSet::new(),
+            replica_id,
+            local_clock: time::Local::new(replica_id),
+            lamport_clock: time::Lamport::new(replica_id),
+        }
+    }
+
+    pub fn path(&self, app: &AppContext) -> Option<PathBuf> {
+        self.file.as_ref().map(|file| file.path(app))
+    }
+
+    pub fn entry_id(&self) -> Option<(usize, usize)> {
+        self.file.as_ref().map(|file| file.entry_id())
+    }
+
+    pub fn is_modified(&self) -> bool {
+        self.version != time::Global::new()
+    }
+
+    pub fn text_summary(&self) -> TextSummary {
+        self.fragments.extent::<TextSummary>()
+    }
+
+    pub fn text_summary_for_range(&self, range: Range<usize>) -> TextSummary {
+        let mut summary = TextSummary::default();
+
+        let mut cursor = self.fragments.cursor::<usize, usize>();
+        cursor.seek(&range.start, SeekBias::Right);
+
+        if let Some(fragment) = cursor.item() {
+            let summary_start = cmp::max(*cursor.start(), range.start) - cursor.start();
+            let summary_end = cmp::min(range.end - cursor.start(), fragment.len());
+            summary += &fragment.text.slice(summary_start..summary_end).summary();
+            cursor.next();
+        }
+
+        if range.end > *cursor.start() {
+            summary += &cursor.summary::<TextSummary>(&range.end, SeekBias::Right);
+
+            if let Some(fragment) = cursor.item() {
+                let summary_start = cmp::max(*cursor.start(), range.start) - cursor.start();
+                let summary_end = cmp::min(range.end - cursor.start(), fragment.len());
+                summary += &fragment.text.slice(summary_start..summary_end).summary();
+            }
+        }
+
+        summary
+    }
+
+    pub fn len(&self) -> usize {
+        self.fragments.extent::<usize>()
+    }
+
+    pub fn line_len(&self, row: u32) -> Result<u32> {
+        let row_start_offset = Point::new(row, 0).to_offset(self)?;
+        let row_end_offset = if row >= self.max_point().row {
+            self.len()
+        } else {
+            Point::new(row + 1, 0).to_offset(self)? - 1
+        };
+
+        Ok((row_end_offset - row_start_offset) as u32)
+    }
+
+    pub fn rightmost_point(&self) -> Point {
+        self.fragments.summary().text_summary.rightmost_point
+    }
+
+    pub fn rightmost_point_in_range(&self, range: Range<usize>) -> Point {
+        let mut summary = TextSummary::default();
+
+        let mut cursor = self.fragments.cursor::<usize, usize>();
+        cursor.seek(&range.start, SeekBias::Right);
+
+        if let Some(fragment) = cursor.item() {
+            let summary_start = cmp::max(*cursor.start(), range.start) - cursor.start();
+            let summary_end = cmp::min(range.end - cursor.start(), fragment.len());
+            summary += &fragment.text.slice(summary_start..summary_end).summary();
+            cursor.next();
+        }
+
+        if range.end > *cursor.start() {
+            summary += &cursor.summary::<TextSummary>(&range.end, SeekBias::Right);
+
+            if let Some(fragment) = cursor.item() {
+                let summary_start = cmp::max(*cursor.start(), range.start) - cursor.start();
+                let summary_end = cmp::min(range.end - cursor.start(), fragment.len());
+                summary += &fragment.text.slice(summary_start..summary_end).summary();
+            }
+        }
+
+        summary.rightmost_point
+    }
+
+    pub fn max_point(&self) -> Point {
+        self.fragments.extent()
+    }
+
+    pub fn line(&self, row: u32) -> Result<String> {
+        Ok(self
+            .chars_at(Point::new(row, 0))?
+            .take_while(|c| *c != '\n')
+            .collect())
+    }
+
+    pub fn text(&self) -> String {
+        self.chars().collect()
+    }
+
+    pub fn text_for_range<T: ToOffset>(&self, range: Range<T>) -> Result<String> {
+        let start = range.start.to_offset(self)?;
+        let end = range.end.to_offset(self)?;
+        Ok(self.chars_at(start)?.take(end - start).collect())
+    }
+
+    pub fn chars(&self) -> Chars {
+        self.chars_at(0).unwrap()
+    }
+
+    pub fn chars_at<T: ToOffset>(&self, position: T) -> Result<Chars> {
+        let offset = position.to_offset(self)?;
+
+        let mut fragments_cursor = self.fragments.cursor::<usize, usize>();
+        fragments_cursor.seek(&offset, SeekBias::Right);
+
+        let fragment_chars = fragments_cursor.item().map_or("".chars(), |fragment| {
+            let offset_in_fragment = offset - fragments_cursor.start();
+            fragment.text[offset_in_fragment..].chars()
+        });
+
+        Ok(Chars {
+            fragments_cursor,
+            fragment_chars,
+        })
+    }
+
+    pub fn selections_changed_since(&self, since: SelectionsVersion) -> bool {
+        self.selections_last_update != since
+    }
+
+    pub fn edits_since<'a>(&'a self, since: time::Global) -> impl 'a + Iterator<Item = Edit> {
+        let since_2 = since.clone();
+        let cursor = self
+            .fragments
+            .filter(move |summary| summary.max_version.changed_since(&since_2));
+
+        Edits {
+            cursor,
+            since,
+            delta: 0,
+        }
+    }
+
+    pub fn deferred_ops_len(&self) -> usize {
+        self.deferred_ops.len()
+    }
+
+    pub fn edit<I, S, T>(
+        &mut self,
+        old_ranges: I,
+        new_text: T,
+        ctx: Option<&mut ModelContext<Self>>,
+    ) -> Result<Vec<Operation>>
+    where
+        I: IntoIterator<Item = Range<S>>,
+        S: ToOffset,
+        T: Into<Text>,
+    {
+        let new_text = new_text.into();
+        let new_text = if new_text.len() > 0 {
+            Some(new_text)
+        } else {
+            None
+        };
+
+        let old_version = self.version.clone();
+        let old_ranges = old_ranges
+            .into_iter()
+            .map(|range| Ok(range.start.to_offset(self)?..range.end.to_offset(self)?))
+            .collect::<Result<Vec<Range<usize>>>>()?;
+
+        let ops = self.splice_fragments(
+            old_ranges
+                .into_iter()
+                .filter(|old_range| new_text.is_some() || old_range.end > old_range.start),
+            new_text.clone(),
+        );
+
+        if let Some(op) = ops.last() {
+            if let Some(ctx) = ctx {
+                ctx.notify();
+                let changes = self.edits_since(old_version).collect::<Vec<_>>();
+                if !changes.is_empty() {
+                    ctx.emit(Event::Edited(changes))
+                }
+            }
+
+            if let Operation::Edit {
+                local_timestamp, ..
+            } = op
+            {
+                self.last_edit = *local_timestamp;
+                self.version.observe(*local_timestamp);
+            } else {
+                unreachable!()
+            }
+        }
+
+        Ok(ops)
+    }
+
+    pub fn simulate_typing<T: Rng>(&mut self, rng: &mut T) {
+        let end = rng.gen_range(0, self.len() + 1);
+        let start = rng.gen_range(0, end + 1);
+        let mut range = start..end;
+
+        let new_text_len = rng.gen_range(0, 100);
+        let new_text: String = RandomCharIter::new(&mut *rng).take(new_text_len).collect();
+
+        for char in new_text.chars() {
+            self.edit(Some(range.clone()), char.to_string().as_str(), None)
+                .unwrap();
+            range = range.end + 1..range.end + 1;
+        }
+    }
+
+    pub fn randomly_edit<T>(
+        &mut self,
+        rng: &mut T,
+        old_range_count: usize,
+        ctx: Option<&mut ModelContext<Self>>,
+    ) -> (Vec<Range<usize>>, String, Vec<Operation>)
+    where
+        T: Rng,
+    {
+        let mut old_ranges: Vec<Range<usize>> = Vec::new();
+        for _ in 0..old_range_count {
+            let last_end = old_ranges.last().map_or(0, |last_range| last_range.end + 1);
+            if last_end > self.len() {
+                break;
+            }
+            let end = rng.gen_range(last_end, self.len() + 1);
+            let start = rng.gen_range(last_end, end + 1);
+            old_ranges.push(start..end);
+        }
+        let new_text_len = rng.gen_range(0, 10);
+        let new_text: String = RandomCharIter::new(&mut *rng).take(new_text_len).collect();
+
+        let operations = self
+            .edit(old_ranges.iter().cloned(), new_text.as_str(), ctx)
+            .unwrap();
+
+        (old_ranges, new_text, operations)
+    }
+
+    pub fn add_selection_set<I>(&mut self, ranges: I) -> Result<(SelectionSetId, Operation)>
+    where
+        I: IntoIterator<Item = Range<Point>>,
+    {
+        let selections = self.selections_from_ranges(ranges)?;
+        let lamport_timestamp = self.lamport_clock.tick();
+        self.selections
+            .insert(lamport_timestamp, selections.clone());
+        self.selections_last_update += 1;
+
+        Ok((
+            lamport_timestamp,
+            Operation::UpdateSelections {
+                set_id: lamport_timestamp,
+                selections: Some(selections),
+                lamport_timestamp,
+            },
+        ))
+    }
+
+    pub fn replace_selection_set<I>(
+        &mut self,
+        set_id: SelectionSetId,
+        ranges: I,
+    ) -> Result<Operation>
+    where
+        I: IntoIterator<Item = Range<Point>>,
+    {
+        self.selections
+            .remove(&set_id)
+            .ok_or_else(|| anyhow!("invalid selection set id {:?}", set_id))?;
+
+        let mut selections = self.selections_from_ranges(ranges)?;
+        self.merge_selections(&mut selections);
+        self.selections.insert(set_id, selections.clone());
+
+        let lamport_timestamp = self.lamport_clock.tick();
+        self.selections_last_update += 1;
+
+        Ok(Operation::UpdateSelections {
+            set_id,
+            selections: Some(selections),
+            lamport_timestamp,
+        })
+    }
+
+    pub fn remove_selection_set(&mut self, set_id: SelectionSetId) -> Result<Operation> {
+        self.selections
+            .remove(&set_id)
+            .ok_or_else(|| anyhow!("invalid selection set id {:?}", set_id))?;
+        let lamport_timestamp = self.lamport_clock.tick();
+        self.selections_last_update += 1;
+        Ok(Operation::UpdateSelections {
+            set_id,
+            selections: None,
+            lamport_timestamp,
+        })
+    }
+
+    pub fn selection_ranges<'a>(
+        &'a self,
+        set_id: SelectionSetId,
+    ) -> Result<impl Iterator<Item = Range<Point>> + 'a> {
+        let selections = self
+            .selections
+            .get(&set_id)
+            .ok_or_else(|| anyhow!("invalid selection set id {:?}", set_id))?;
+        Ok(selections.iter().map(move |selection| {
+            let start = selection.start.to_point(self).unwrap();
+            let end = selection.end.to_point(self).unwrap();
+            if selection.reversed {
+                end..start
+            } else {
+                start..end
+            }
+        }))
+    }
+
+    pub fn all_selections(&self) -> impl Iterator<Item = (&SelectionSetId, &Vec<Selection>)> {
+        self.selections.iter()
+    }
+
+    pub fn all_selection_ranges<'a>(
+        &'a self,
+    ) -> impl 'a + Iterator<Item = (SelectionSetId, Vec<Range<Point>>)> {
+        self.selections
+            .keys()
+            .map(move |set_id| (*set_id, self.selection_ranges(*set_id).unwrap().collect()))
+    }
+
+    fn merge_selections(&mut self, selections: &mut Vec<Selection>) {
+        let mut new_selections = Vec::with_capacity(selections.len());
+        {
+            let mut old_selections = selections.drain(..);
+            if let Some(mut prev_selection) = old_selections.next() {
+                for selection in old_selections {
+                    if prev_selection.end.cmp(&selection.start, self).unwrap() >= Ordering::Equal {
+                        if selection.end.cmp(&prev_selection.end, self).unwrap() > Ordering::Equal {
+                            prev_selection.end = selection.end;
+                        }
+                    } else {
+                        new_selections.push(mem::replace(&mut prev_selection, selection));
+                    }
+                }
+                new_selections.push(prev_selection);
+            }
+        }
+        *selections = new_selections;
+    }
+
+    fn selections_from_ranges<I>(&self, ranges: I) -> Result<Vec<Selection>>
+    where
+        I: IntoIterator<Item = Range<Point>>,
+    {
+        let mut ranges = ranges.into_iter().collect::<Vec<_>>();
+        ranges.sort_unstable_by_key(|range| range.start);
+
+        let mut selections = Vec::with_capacity(ranges.len());
+        for range in ranges {
+            if range.start > range.end {
+                selections.push(Selection {
+                    start: self.anchor_before(range.end)?,
+                    end: self.anchor_before(range.start)?,
+                    reversed: true,
+                });
+            } else {
+                selections.push(Selection {
+                    start: self.anchor_after(range.start)?,
+                    end: self.anchor_before(range.end)?,
+                    reversed: false,
+                });
+            }
+        }
+        Ok(selections)
+    }
+
+    pub fn apply_ops<I: IntoIterator<Item = Operation>>(
+        &mut self,
+        ops: I,
+        ctx: Option<&mut ModelContext<Self>>,
+    ) -> Result<()> {
+        let old_version = self.version.clone();
+
+        let mut deferred_ops = Vec::new();
+        for op in ops {
+            if self.can_apply_op(&op) {
+                self.apply_op(op)?;
+            } else {
+                self.deferred_replicas.insert(op.replica_id());
+                deferred_ops.push(op);
+            }
+        }
+        self.deferred_ops.insert(deferred_ops);
+        self.flush_deferred_ops()?;
+
+        if let Some(ctx) = ctx {
+            ctx.notify();
+            let changes = self.edits_since(old_version).collect::<Vec<_>>();
+            if !changes.is_empty() {
+                ctx.emit(Event::Edited(changes));
+            }
+        }
+
+        Ok(())
+    }
+
+    fn apply_op(&mut self, op: Operation) -> Result<()> {
+        match op {
+            Operation::Edit {
+                start_id,
+                start_offset,
+                end_id,
+                end_offset,
+                new_text,
+                version_in_range,
+                local_timestamp,
+                lamport_timestamp,
+            } => {
+                if !self.version.observed(local_timestamp) {
+                    self.apply_edit(
+                        start_id,
+                        start_offset,
+                        end_id,
+                        end_offset,
+                        new_text.as_ref().cloned(),
+                        &version_in_range,
+                        local_timestamp,
+                        lamport_timestamp,
+                    )?;
+                    self.version.observe(local_timestamp);
+                }
+            }
+            Operation::UpdateSelections {
+                set_id,
+                selections,
+                lamport_timestamp,
+            } => {
+                if let Some(selections) = selections {
+                    self.selections.insert(set_id, selections);
+                } else {
+                    self.selections.remove(&set_id);
+                }
+                self.lamport_clock.observe(lamport_timestamp);
+                self.selections_last_update += 1;
+            }
+        }
+        Ok(())
+    }
+
+    fn apply_edit(
+        &mut self,
+        start_id: time::Local,
+        start_offset: usize,
+        end_id: time::Local,
+        end_offset: usize,
+        new_text: Option<Text>,
+        version_in_range: &time::Global,
+        local_timestamp: time::Local,
+        lamport_timestamp: time::Lamport,
+    ) -> Result<()> {
+        let mut new_text = new_text.as_ref().cloned();
+        let start_fragment_id = self.resolve_fragment_id(start_id, start_offset)?;
+        let end_fragment_id = self.resolve_fragment_id(end_id, end_offset)?;
+
+        let old_fragments = self.fragments.clone();
+        let last_id = old_fragments.extent::<FragmentIdRef>().0.unwrap();
+        let last_id_ref = FragmentIdRef::new(&last_id);
+
+        let mut cursor = old_fragments.cursor::<FragmentIdRef, ()>();
+        let mut new_fragments =
+            cursor.slice(&FragmentIdRef::new(&start_fragment_id), SeekBias::Left);
+
+        if start_offset == cursor.item().unwrap().end_offset() {
+            new_fragments.push(cursor.item().unwrap().clone());
+            cursor.next();
+        }
+
+        while let Some(fragment) = cursor.item() {
+            if new_text.is_none() && fragment.id > end_fragment_id {
+                break;
+            }
+
+            let mut fragment = fragment.clone();
+
+            if fragment.id == start_fragment_id || fragment.id == end_fragment_id {
+                let split_start = if start_fragment_id == fragment.id {
+                    start_offset
+                } else {
+                    fragment.start_offset()
+                };
+                let split_end = if end_fragment_id == fragment.id {
+                    end_offset
+                } else {
+                    fragment.end_offset()
+                };
+                let (before_range, within_range, after_range) = self.split_fragment(
+                    cursor.prev_item().as_ref().unwrap(),
+                    &fragment,
+                    split_start..split_end,
+                );
+                let insertion = if let Some(new_text) = new_text.take() {
+                    Some(self.build_fragment_to_insert(
+                        before_range.as_ref().or(cursor.prev_item()).unwrap(),
+                        within_range.as_ref().or(after_range.as_ref()),
+                        new_text,
+                        local_timestamp,
+                        lamport_timestamp,
+                    ))
+                } else {
+                    None
+                };
+                if let Some(fragment) = before_range {
+                    new_fragments.push(fragment);
+                }
+                if let Some(fragment) = insertion {
+                    new_fragments.push(fragment);
+                }
+                if let Some(mut fragment) = within_range {
+                    if version_in_range.observed(fragment.insertion.id) {
+                        fragment.deletions.insert(local_timestamp);
+                    }
+                    new_fragments.push(fragment);
+                }
+                if let Some(fragment) = after_range {
+                    new_fragments.push(fragment);
+                }
+            } else {
+                if new_text.is_some() && lamport_timestamp > fragment.insertion.lamport_timestamp {
+                    new_fragments.push(self.build_fragment_to_insert(
+                        cursor.prev_item().as_ref().unwrap(),
+                        Some(&fragment),
+                        new_text.take().unwrap(),
+                        local_timestamp,
+                        lamport_timestamp,
+                    ));
+                }
+
+                if fragment.id < end_fragment_id && version_in_range.observed(fragment.insertion.id)
+                {
+                    fragment.deletions.insert(local_timestamp);
+                }
+                new_fragments.push(fragment);
+            }
+
+            cursor.next();
+        }
+
+        if let Some(new_text) = new_text {
+            new_fragments.push(self.build_fragment_to_insert(
+                cursor.prev_item().as_ref().unwrap(),
+                None,
+                new_text,
+                local_timestamp,
+                lamport_timestamp,
+            ));
+        }
+
+        new_fragments.push_tree(cursor.slice(&last_id_ref, SeekBias::Right));
+        self.fragments = new_fragments;
+        self.local_clock.observe(local_timestamp);
+        self.lamport_clock.observe(lamport_timestamp);
+        Ok(())
+    }
+
+    fn flush_deferred_ops(&mut self) -> Result<()> {
+        self.deferred_replicas.clear();
+        let mut deferred_ops = Vec::new();
+        for op in self.deferred_ops.drain().cursor().cloned() {
+            if self.can_apply_op(&op) {
+                self.apply_op(op)?;
+            } else {
+                self.deferred_replicas.insert(op.replica_id());
+                deferred_ops.push(op);
+            }
+        }
+        self.deferred_ops.insert(deferred_ops);
+        Ok(())
+    }
+
+    fn can_apply_op(&self, op: &Operation) -> bool {
+        if self.deferred_replicas.contains(&op.replica_id()) {
+            false
+        } else {
+            match op {
+                Operation::Edit {
+                    start_id,
+                    end_id,
+                    version_in_range,
+                    ..
+                } => {
+                    self.version.observed(*start_id)
+                        && self.version.observed(*end_id)
+                        && *version_in_range <= self.version
+                }
+                Operation::UpdateSelections { selections, .. } => {
+                    if let Some(selections) = selections {
+                        selections.iter().all(|selection| {
+                            let contains_start = match selection.start {
+                                Anchor::Middle { insertion_id, .. } => {
+                                    self.version.observed(insertion_id)
+                                }
+                                _ => true,
+                            };
+                            let contains_end = match selection.end {
+                                Anchor::Middle { insertion_id, .. } => {
+                                    self.version.observed(insertion_id)
+                                }
+                                _ => true,
+                            };
+                            contains_start && contains_end
+                        })
+                    } else {
+                        true
+                    }
+                }
+            }
+        }
+    }
+
+    fn resolve_fragment_id(&self, edit_id: time::Local, offset: usize) -> Result<FragmentId> {
+        let split_tree = self
+            .insertion_splits
+            .get(&edit_id)
+            .ok_or_else(|| anyhow!("invalid operation"))?;
+        let mut cursor = split_tree.cursor::<usize, ()>();
+        cursor.seek(&offset, SeekBias::Left);
+        Ok(cursor
+            .item()
+            .ok_or_else(|| anyhow!("invalid operation"))?
+            .fragment_id
+            .clone())
+    }
+
+    fn splice_fragments<I>(&mut self, mut old_ranges: I, new_text: Option<Text>) -> Vec<Operation>
+    where
+        I: Iterator<Item = Range<usize>>,
+    {
+        let mut cur_range = old_ranges.next();
+        if cur_range.is_none() {
+            return Vec::new();
+        }
+
+        let mut ops = Vec::with_capacity(old_ranges.size_hint().0);
+
+        let old_fragments = self.fragments.clone();
+        let mut cursor = old_fragments.cursor::<usize, usize>();
+        let mut new_fragments = SumTree::new();
+        new_fragments.push_tree(cursor.slice(&cur_range.as_ref().unwrap().start, SeekBias::Right));
+
+        let mut start_id = None;
+        let mut start_offset = None;
+        let mut end_id = None;
+        let mut end_offset = None;
+        let mut version_in_range = time::Global::new();
+
+        let mut local_timestamp = self.local_clock.tick();
+        let mut lamport_timestamp = self.lamport_clock.tick();
+
+        while cur_range.is_some() && cursor.item().is_some() {
+            let mut fragment = cursor.item().unwrap().clone();
+            let mut fragment_start = *cursor.start();
+            let mut fragment_end = fragment_start + fragment.visible_len();
+
+            let old_split_tree = self
+                .insertion_splits
+                .remove(&fragment.insertion.id)
+                .unwrap();
+            let mut splits_cursor = old_split_tree.cursor::<usize, ()>();
+            let mut new_split_tree = splits_cursor.slice(&fragment.start_offset(), SeekBias::Right);
+
+            // Find all splices that start or end within the current fragment. Then, split the
+            // fragment and reassemble it in both trees accounting for the deleted and the newly
+            // inserted text.
+            while cur_range.as_ref().map_or(false, |r| r.start < fragment_end) {
+                let range = cur_range.clone().unwrap();
+                if range.start > fragment_start {
+                    let mut prefix = fragment.clone();
+                    prefix.set_end_offset(prefix.start_offset() + (range.start - fragment_start));
+                    prefix.id =
+                        FragmentId::between(&new_fragments.last().unwrap().id, &fragment.id);
+                    fragment.set_start_offset(prefix.end_offset());
+                    new_fragments.push(prefix.clone());
+                    new_split_tree.push(InsertionSplit {
+                        extent: prefix.end_offset() - prefix.start_offset(),
+                        fragment_id: prefix.id,
+                    });
+                    fragment_start = range.start;
+                }
+
+                if range.end == fragment_start {
+                    end_id = Some(new_fragments.last().unwrap().insertion.id);
+                    end_offset = Some(new_fragments.last().unwrap().end_offset());
+                } else if range.end == fragment_end {
+                    end_id = Some(fragment.insertion.id);
+                    end_offset = Some(fragment.end_offset());
+                }
+
+                if range.start == fragment_start {
+                    start_id = Some(new_fragments.last().unwrap().insertion.id);
+                    start_offset = Some(new_fragments.last().unwrap().end_offset());
+
+                    if let Some(new_text) = new_text.clone() {
+                        let new_fragment = self.build_fragment_to_insert(
+                            &new_fragments.last().unwrap(),
+                            Some(&fragment),
+                            new_text,
+                            local_timestamp,
+                            lamport_timestamp,
+                        );
+                        new_fragments.push(new_fragment);
+                    }
+                }
+
+                if range.end < fragment_end {
+                    if range.end > fragment_start {
+                        let mut prefix = fragment.clone();
+                        prefix.set_end_offset(prefix.start_offset() + (range.end - fragment_start));
+                        prefix.id =
+                            FragmentId::between(&new_fragments.last().unwrap().id, &fragment.id);
+                        if fragment.is_visible() {
+                            prefix.deletions.insert(local_timestamp);
+                        }
+                        fragment.set_start_offset(prefix.end_offset());
+                        new_fragments.push(prefix.clone());
+                        new_split_tree.push(InsertionSplit {
+                            extent: prefix.end_offset() - prefix.start_offset(),
+                            fragment_id: prefix.id,
+                        });
+                        fragment_start = range.end;
+                        end_id = Some(fragment.insertion.id);
+                        end_offset = Some(fragment.start_offset());
+                        version_in_range.observe(fragment.insertion.id);
+                    }
+                } else {
+                    version_in_range.observe(fragment.insertion.id);
+                    if fragment.is_visible() {
+                        fragment.deletions.insert(local_timestamp);
+                    }
+                }
+
+                // If the splice ends inside this fragment, we can advance to the next splice and
+                // check if it also intersects the current fragment. Otherwise we break out of the
+                // loop and find the first fragment that the splice does not contain fully.
+                if range.end <= fragment_end {
+                    ops.push(Operation::Edit {
+                        start_id: start_id.unwrap(),
+                        start_offset: start_offset.unwrap(),
+                        end_id: end_id.unwrap(),
+                        end_offset: end_offset.unwrap(),
+                        version_in_range,
+                        new_text: new_text.clone(),
+                        local_timestamp,
+                        lamport_timestamp,
+                    });
+
+                    start_id = None;
+                    start_offset = None;
+                    end_id = None;
+                    end_offset = None;
+                    version_in_range = time::Global::new();
+                    cur_range = old_ranges.next();
+                    if cur_range.is_some() {
+                        local_timestamp = self.local_clock.tick();
+                        lamport_timestamp = self.lamport_clock.tick();
+                    }
+                } else {
+                    break;
+                }
+            }
+            new_split_tree.push(InsertionSplit {
+                extent: fragment.end_offset() - fragment.start_offset(),
+                fragment_id: fragment.id.clone(),
+            });
+            splits_cursor.next();
+            new_split_tree
+                .push_tree(splits_cursor.slice(&old_split_tree.extent::<usize>(), SeekBias::Right));
+            self.insertion_splits
+                .insert(fragment.insertion.id, new_split_tree);
+            new_fragments.push(fragment);
+
+            // Scan forward until we find a fragment that is not fully contained by the current splice.
+            cursor.next();
+            if let Some(range) = cur_range.clone() {
+                while let Some(fragment) = cursor.item() {
+                    fragment_start = *cursor.start();
+                    fragment_end = fragment_start + fragment.visible_len();
+                    if range.start < fragment_start && range.end >= fragment_end {
+                        let mut new_fragment = fragment.clone();
+                        if new_fragment.is_visible() {
+                            new_fragment.deletions.insert(local_timestamp);
+                        }
+                        version_in_range.observe(new_fragment.insertion.id);
+                        new_fragments.push(new_fragment);
+                        cursor.next();
+
+                        if range.end == fragment_end {
+                            end_id = Some(fragment.insertion.id);
+                            end_offset = Some(fragment.end_offset());
+                            ops.push(Operation::Edit {
+                                start_id: start_id.unwrap(),
+                                start_offset: start_offset.unwrap(),
+                                end_id: end_id.unwrap(),
+                                end_offset: end_offset.unwrap(),
+                                version_in_range,
+                                new_text: new_text.clone(),
+                                local_timestamp,
+                                lamport_timestamp,
+                            });
+
+                            start_id = None;
+                            start_offset = None;
+                            end_id = None;
+                            end_offset = None;
+                            version_in_range = time::Global::new();
+
+                            cur_range = old_ranges.next();
+                            if cur_range.is_some() {
+                                local_timestamp = self.local_clock.tick();
+                                lamport_timestamp = self.lamport_clock.tick();
+                            }
+                            break;
+                        }
+                    } else {
+                        break;
+                    }
+                }
+
+                // If the splice we are currently evaluating starts after the end of the fragment
+                // that the cursor is parked at, we should seek to the next splice's start range
+                // and push all the fragments in between into the new tree.
+                if cur_range.as_ref().map_or(false, |r| r.start > fragment_end) {
+                    new_fragments.push_tree(
+                        cursor.slice(&cur_range.as_ref().unwrap().start, SeekBias::Right),
+                    );
+                }
+            }
+        }
+
+        // Handle range that is at the end of the buffer if it exists. There should never be
+        // multiple because ranges must be disjoint.
+        if cur_range.is_some() {
+            debug_assert_eq!(old_ranges.next(), None);
+            let last_fragment = new_fragments.last().unwrap();
+            ops.push(Operation::Edit {
+                start_id: last_fragment.insertion.id,
+                start_offset: last_fragment.end_offset(),
+                end_id: last_fragment.insertion.id,
+                end_offset: last_fragment.end_offset(),
+                version_in_range: time::Global::new(),
+                new_text: new_text.clone(),
+                local_timestamp,
+                lamport_timestamp,
+            });
+
+            if let Some(new_text) = new_text {
+                let new_fragment = self.build_fragment_to_insert(
+                    &last_fragment,
+                    None,
+                    new_text,
+                    local_timestamp,
+                    lamport_timestamp,
+                );
+                new_fragments.push(new_fragment);
+            }
+        } else {
+            new_fragments
+                .push_tree(cursor.slice(&old_fragments.extent::<usize>(), SeekBias::Right));
+        }
+
+        self.fragments = new_fragments;
+        ops
+    }
+
+    fn split_fragment(
+        &mut self,
+        prev_fragment: &Fragment,
+        fragment: &Fragment,
+        range: Range<usize>,
+    ) -> (Option<Fragment>, Option<Fragment>, Option<Fragment>) {
+        debug_assert!(range.start >= fragment.start_offset());
+        debug_assert!(range.start <= fragment.end_offset());
+        debug_assert!(range.end <= fragment.end_offset());
+        debug_assert!(range.end >= fragment.start_offset());
+
+        if range.end == fragment.start_offset() {
+            (None, None, Some(fragment.clone()))
+        } else if range.start == fragment.end_offset() {
+            (Some(fragment.clone()), None, None)
+        } else if range.start == fragment.start_offset() && range.end == fragment.end_offset() {
+            (None, Some(fragment.clone()), None)
+        } else {
+            let mut prefix = fragment.clone();
+
+            let after_range = if range.end < fragment.end_offset() {
+                let mut suffix = prefix.clone();
+                suffix.set_start_offset(range.end);
+                prefix.set_end_offset(range.end);
+                prefix.id = FragmentId::between(&prev_fragment.id, &suffix.id);
+                Some(suffix)
+            } else {
+                None
+            };
+
+            let within_range = if range.start != range.end {
+                let mut suffix = prefix.clone();
+                suffix.set_start_offset(range.start);
+                prefix.set_end_offset(range.start);
+                prefix.id = FragmentId::between(&prev_fragment.id, &suffix.id);
+                Some(suffix)
+            } else {
+                None
+            };
+
+            let before_range = if range.start > fragment.start_offset() {
+                Some(prefix)
+            } else {
+                None
+            };
+
+            let old_split_tree = self
+                .insertion_splits
+                .remove(&fragment.insertion.id)
+                .unwrap();
+            let mut cursor = old_split_tree.cursor::<usize, ()>();
+            let mut new_split_tree = cursor.slice(&fragment.start_offset(), SeekBias::Right);
+
+            if let Some(ref fragment) = before_range {
+                new_split_tree.push(InsertionSplit {
+                    extent: range.start - fragment.start_offset(),
+                    fragment_id: fragment.id.clone(),
+                });
+            }
+
+            if let Some(ref fragment) = within_range {
+                new_split_tree.push(InsertionSplit {
+                    extent: range.end - range.start,
+                    fragment_id: fragment.id.clone(),
+                });
+            }
+
+            if let Some(ref fragment) = after_range {
+                new_split_tree.push(InsertionSplit {
+                    extent: fragment.end_offset() - range.end,
+                    fragment_id: fragment.id.clone(),
+                });
+            }
+
+            cursor.next();
+            new_split_tree
+                .push_tree(cursor.slice(&old_split_tree.extent::<usize>(), SeekBias::Right));
+
+            self.insertion_splits
+                .insert(fragment.insertion.id, new_split_tree);
+
+            (before_range, within_range, after_range)
+        }
+    }
+
+    fn build_fragment_to_insert(
+        &mut self,
+        prev_fragment: &Fragment,
+        next_fragment: Option<&Fragment>,
+        text: Text,
+        local_timestamp: time::Local,
+        lamport_timestamp: time::Lamport,
+    ) -> Fragment {
+        let new_fragment_id = FragmentId::between(
+            &prev_fragment.id,
+            next_fragment
+                .map(|f| &f.id)
+                .unwrap_or(&FragmentId::max_value()),
+        );
+
+        let mut split_tree = SumTree::new();
+        split_tree.push(InsertionSplit {
+            extent: text.len(),
+            fragment_id: new_fragment_id.clone(),
+        });
+        self.insertion_splits.insert(local_timestamp, split_tree);
+
+        Fragment::new(
+            new_fragment_id,
+            Insertion {
+                id: local_timestamp,
+                parent_id: prev_fragment.insertion.id,
+                offset_in_parent: prev_fragment.end_offset(),
+                text,
+                lamport_timestamp,
+            },
+        )
+    }
+
+    pub fn anchor_before<T: ToOffset>(&self, position: T) -> Result<Anchor> {
+        self.anchor_at(position, AnchorBias::Left)
+    }
+
+    pub fn anchor_after<T: ToOffset>(&self, position: T) -> Result<Anchor> {
+        self.anchor_at(position, AnchorBias::Right)
+    }
+
+    pub fn anchor_at<T: ToOffset>(&self, position: T, bias: AnchorBias) -> Result<Anchor> {
+        let offset = position.to_offset(self)?;
+        let max_offset = self.len();
+        if offset > max_offset {
+            return Err(anyhow!("offset is out of range"));
+        }
+
+        let seek_bias;
+        match bias {
+            AnchorBias::Left => {
+                if offset == 0 {
+                    return Ok(Anchor::Start);
+                } else {
+                    seek_bias = SeekBias::Left;
+                }
+            }
+            AnchorBias::Right => {
+                if offset == max_offset {
+                    return Ok(Anchor::End);
+                } else {
+                    seek_bias = SeekBias::Right;
+                }
+            }
+        };
+
+        let mut cursor = self.fragments.cursor::<usize, usize>();
+        cursor.seek(&offset, seek_bias);
+        let fragment = cursor.item().unwrap();
+        let offset_in_fragment = offset - cursor.start();
+        let offset_in_insertion = fragment.start_offset() + offset_in_fragment;
+        let anchor = Anchor::Middle {
+            insertion_id: fragment.insertion.id,
+            offset: offset_in_insertion,
+            bias,
+        };
+        Ok(anchor)
+    }
+
+    fn fragment_id_for_anchor(&self, anchor: &Anchor) -> Result<&FragmentId> {
+        match anchor {
+            Anchor::Start => Ok(FragmentId::max_value()),
+            Anchor::End => Ok(FragmentId::min_value()),
+            Anchor::Middle {
+                insertion_id,
+                offset,
+                bias,
+                ..
+            } => {
+                let seek_bias = match bias {
+                    AnchorBias::Left => SeekBias::Left,
+                    AnchorBias::Right => SeekBias::Right,
+                };
+
+                let splits = self
+                    .insertion_splits
+                    .get(&insertion_id)
+                    .ok_or_else(|| anyhow!("split does not exist for insertion id"))?;
+                let mut splits_cursor = splits.cursor::<usize, ()>();
+                splits_cursor.seek(offset, seek_bias);
+                splits_cursor
+                    .item()
+                    .ok_or_else(|| anyhow!("split offset is out of range"))
+                    .map(|split| &split.fragment_id)
+            }
+        }
+    }
+
+    fn summary_for_anchor(&self, anchor: &Anchor) -> Result<TextSummary> {
+        match anchor {
+            Anchor::Start => Ok(TextSummary::default()),
+            Anchor::End => Ok(self.fragments.summary().text_summary),
+            Anchor::Middle {
+                insertion_id,
+                offset,
+                bias,
+            } => {
+                let seek_bias = match bias {
+                    AnchorBias::Left => SeekBias::Left,
+                    AnchorBias::Right => SeekBias::Right,
+                };
+
+                let splits = self
+                    .insertion_splits
+                    .get(&insertion_id)
+                    .ok_or_else(|| anyhow!("split does not exist for insertion id"))?;
+                let mut splits_cursor = splits.cursor::<usize, ()>();
+                splits_cursor.seek(offset, seek_bias);
+                let split = splits_cursor
+                    .item()
+                    .ok_or_else(|| anyhow!("split offset is out of range"))?;
+
+                let mut fragments_cursor = self.fragments.cursor::<FragmentIdRef, TextSummary>();
+                fragments_cursor.seek(&FragmentIdRef::new(&split.fragment_id), SeekBias::Left);
+                let fragment = fragments_cursor
+                    .item()
+                    .ok_or_else(|| anyhow!("fragment id does not exist"))?;
+
+                let mut summary = fragments_cursor.start().clone();
+                if fragment.is_visible() {
+                    summary += fragment
+                        .text
+                        .slice(..offset - fragment.start_offset())
+                        .summary();
+                }
+                Ok(summary)
+            }
+        }
+    }
+
+    #[allow(dead_code)]
+    pub fn point_for_offset(&self, offset: usize) -> Result<Point> {
+        let mut fragments_cursor = self.fragments.cursor::<usize, TextSummary>();
+        fragments_cursor.seek(&offset, SeekBias::Left);
+        fragments_cursor
+            .item()
+            .ok_or_else(|| anyhow!("offset is out of range"))
+            .map(|fragment| {
+                let overshoot = fragment
+                    .point_for_offset(offset - &fragments_cursor.start().chars)
+                    .unwrap();
+                fragments_cursor.start().lines + &overshoot
+            })
+    }
+}
+
+impl Clone for Buffer {
+    fn clone(&self) -> Self {
+        Self {
+            file: self.file.clone(),
+            fragments: self.fragments.clone(),
+            insertion_splits: self.insertion_splits.clone(),
+            version: self.version.clone(),
+            last_edit: self.last_edit.clone(),
+            selections: self.selections.clone(),
+            selections_last_update: self.selections_last_update.clone(),
+            deferred_ops: self.deferred_ops.clone(),
+            deferred_replicas: self.deferred_replicas.clone(),
+            replica_id: self.replica_id,
+            local_clock: self.local_clock.clone(),
+            lamport_clock: self.lamport_clock.clone(),
+        }
+    }
+}
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub enum Event {
+    Edited(Vec<Edit>),
+}
+
+impl app::Entity for Buffer {
+    type Event = Event;
+}
+
+impl<'a> sum_tree::Dimension<'a, FragmentSummary> for Point {
+    fn add_summary(&mut self, summary: &FragmentSummary) {
+        *self += &summary.text_summary.lines;
+    }
+}
+
+impl<'a> Iterator for Chars<'a> {
+    type Item = char;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if let Some(char) = self.fragment_chars.next() {
+            Some(char)
+        } else {
+            loop {
+                self.fragments_cursor.next();
+                if let Some(fragment) = self.fragments_cursor.item() {
+                    if fragment.is_visible() {
+                        self.fragment_chars = fragment.text.as_str().chars();
+                        return self.fragment_chars.next();
+                    }
+                } else {
+                    return None;
+                }
+            }
+        }
+    }
+}
+
+impl<'a, F: Fn(&FragmentSummary) -> bool> Iterator for Edits<'a, F> {
+    type Item = Edit;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let mut change: Option<Edit> = None;
+
+        while let Some(fragment) = self.cursor.item() {
+            let new_offset = *self.cursor.start();
+            let old_offset = (new_offset as isize - self.delta) as usize;
+
+            if !fragment.was_visible(&self.since) && fragment.is_visible() {
+                if let Some(ref mut change) = change {
+                    if change.new_range.end == new_offset {
+                        change.new_range.end += fragment.len();
+                        self.delta += fragment.len() as isize;
+                    } else {
+                        break;
+                    }
+                } else {
+                    change = Some(Edit {
+                        old_range: old_offset..old_offset,
+                        new_range: new_offset..new_offset + fragment.len(),
+                    });
+                    self.delta += fragment.len() as isize;
+                }
+            } else if fragment.was_visible(&self.since) && !fragment.is_visible() {
+                if let Some(ref mut change) = change {
+                    if change.new_range.end == new_offset {
+                        change.old_range.end += fragment.len();
+                        self.delta -= fragment.len() as isize;
+                    } else {
+                        break;
+                    }
+                } else {
+                    change = Some(Edit {
+                        old_range: old_offset..old_offset + fragment.len(),
+                        new_range: new_offset..new_offset,
+                    });
+                    self.delta -= fragment.len() as isize;
+                }
+            }
+
+            self.cursor.next();
+        }
+
+        change
+    }
+}
+
+// pub fn diff(a: &[u16], b: &[u16]) -> Vec<Edit> {
+//     struct EditCollector<'a> {
+//         a: &'a [u16],
+//         b: &'a [u16],
+//         position: Point,
+//         changes: Vec<Edit>,
+//     }
+//
+//     impl<'a> diffs::Diff for EditCollector<'a> {
+//         type Error = ();
+//
+//         fn equal(&mut self, old: usize, _: usize, len: usize) -> Result<(), ()> {
+//             self.position += &Text::extent(&self.a[old..old + len]);
+//             Ok(())
+//         }
+//
+//         fn delete(&mut self, old: usize, len: usize) -> Result<(), ()> {
+//             self.changes.push(Edit {
+//                 range: self.position..self.position + &Text::extent(&self.a[old..old + len]),
+//                 chars: Vec::new(),
+//                 new_char_count: Point::zero(),
+//             });
+//             Ok(())
+//         }
+//
+//         fn insert(&mut self, _: usize, new: usize, new_len: usize) -> Result<(), ()> {
+//             let new_char_count = Text::extent(&self.b[new..new + new_len]);
+//             self.changes.push(Edit {
+//                 range: self.position..self.position,
+//                 chars: Vec::from(&self.b[new..new + new_len]),
+//                 new_char_count,
+//             });
+//             self.position += &new_char_count;
+//             Ok(())
+//         }
+//
+//         fn replace(
+//             &mut self,
+//             old: usize,
+//             old_len: usize,
+//             new: usize,
+//             new_len: usize,
+//         ) -> Result<(), ()> {
+//             let old_extent = text::extent(&self.a[old..old + old_len]);
+//             let new_char_count = text::extent(&self.b[new..new + new_len]);
+//             self.changes.push(Edit {
+//                 range: self.position..self.position + &old_extent,
+//                 chars: Vec::from(&self.b[new..new + new_len]),
+//                 new_char_count,
+//             });
+//             self.position += &new_char_count;
+//             Ok(())
+//         }
+//     }
+//
+//     let mut collector = diffs::Replace::new(EditCollector {
+//         a,
+//         b,
+//         position: Point::zero(),
+//         changes: Vec::new(),
+//     });
+//     diffs::myers::diff(&mut collector, a, 0, a.len(), b, 0, b.len()).unwrap();
+//     collector.into_inner().changes
+// }
+
+impl Selection {
+    pub fn head(&self) -> &Anchor {
+        if self.reversed {
+            &self.start
+        } else {
+            &self.end
+        }
+    }
+
+    pub fn set_head<S>(&mut self, buffer: &Buffer, cursor: Anchor) {
+        if cursor.cmp(self.tail(), buffer).unwrap() < Ordering::Equal {
+            if !self.reversed {
+                mem::swap(&mut self.start, &mut self.end);
+                self.reversed = true;
+            }
+            self.start = cursor;
+        } else {
+            if self.reversed {
+                mem::swap(&mut self.start, &mut self.end);
+                self.reversed = false;
+            }
+            self.end = cursor;
+        }
+    }
+
+    pub fn tail(&self) -> &Anchor {
+        if self.reversed {
+            &self.end
+        } else {
+            &self.start
+        }
+    }
+
+    pub fn is_empty(&self, buffer: &Buffer) -> bool {
+        self.start.to_offset(buffer).unwrap() == self.end.to_offset(buffer).unwrap()
+    }
+
+    pub fn anchor_range(&self) -> Range<Anchor> {
+        self.start.clone()..self.end.clone()
+    }
+}
+
+#[derive(Ord, PartialOrd, Eq, PartialEq, Clone, Debug)]
+struct FragmentId(Arc<[u16]>);
+
+lazy_static! {
+    static ref FRAGMENT_ID_EMPTY: FragmentId = FragmentId(Arc::from([]));
+    static ref FRAGMENT_ID_MIN_VALUE: FragmentId = FragmentId(Arc::from([0 as u16]));
+    static ref FRAGMENT_ID_MAX_VALUE: FragmentId = FragmentId(Arc::from([u16::max_value()]));
+}
+
+impl Default for FragmentId {
+    fn default() -> Self {
+        FRAGMENT_ID_EMPTY.clone()
+    }
+}
+
+impl FragmentId {
+    fn min_value() -> &'static Self {
+        &FRAGMENT_ID_MIN_VALUE
+    }
+
+    fn max_value() -> &'static Self {
+        &FRAGMENT_ID_MAX_VALUE
+    }
+
+    fn between(left: &Self, right: &Self) -> Self {
+        Self::between_with_max(left, right, u16::max_value())
+    }
+
+    fn between_with_max(left: &Self, right: &Self, max_value: u16) -> Self {
+        let mut new_entries = Vec::new();
+
+        let left_entries = left.0.iter().cloned().chain(iter::repeat(0));
+        let right_entries = right.0.iter().cloned().chain(iter::repeat(max_value));
+        for (l, r) in left_entries.zip(right_entries) {
+            let interval = r - l;
+            if interval > 1 {
+                new_entries.push(l + cmp::max(1, cmp::min(8, interval / 2)));
+                break;
+            } else {
+                new_entries.push(l);
+            }
+        }
+
+        FragmentId(Arc::from(new_entries))
+    }
+}
+
+#[derive(Ord, PartialOrd, Eq, PartialEq, Clone, Debug, Default)]
+struct FragmentIdRef<'a>(Option<&'a FragmentId>);
+
+impl<'a> FragmentIdRef<'a> {
+    fn new(id: &'a FragmentId) -> Self {
+        Self(Some(id))
+    }
+}
+
+impl<'a> sum_tree::Dimension<'a, FragmentSummary> for FragmentIdRef<'a> {
+    fn add_summary(&mut self, summary: &'a FragmentSummary) {
+        self.0 = Some(&summary.max_fragment_id)
+    }
+}
+
+impl Fragment {
+    fn new(id: FragmentId, insertion: Insertion) -> Self {
+        Self {
+            id,
+            text: insertion.text.clone(),
+            insertion,
+            deletions: HashSet::new(),
+        }
+    }
+
+    fn start_offset(&self) -> usize {
+        self.text.range().start
+    }
+
+    fn set_start_offset(&mut self, offset: usize) {
+        self.text = self.insertion.text.slice(offset..self.end_offset());
+    }
+
+    fn end_offset(&self) -> usize {
+        self.text.range().end
+    }
+
+    fn set_end_offset(&mut self, offset: usize) {
+        self.text = self.insertion.text.slice(self.start_offset()..offset);
+    }
+
+    fn as_str(&self) -> &str {
+        self.text.as_str()
+    }
+
+    fn visible_len(&self) -> usize {
+        if self.is_visible() {
+            self.len()
+        } else {
+            0
+        }
+    }
+
+    fn len(&self) -> usize {
+        self.text.len()
+    }
+
+    fn is_visible(&self) -> bool {
+        self.deletions.is_empty()
+    }
+
+    fn was_visible(&self, version: &time::Global) -> bool {
+        version.observed(self.insertion.id) && self.deletions.iter().all(|d| !version.observed(*d))
+    }
+
+    fn point_for_offset(&self, offset: usize) -> Result<Point> {
+        Ok(self.text.point_for_offset(offset))
+    }
+
+    fn offset_for_point(&self, point: Point) -> Result<usize> {
+        Ok(self.text.offset_for_point(point))
+    }
+}
+
+impl sum_tree::Item for Fragment {
+    type Summary = FragmentSummary;
+
+    fn summary(&self) -> Self::Summary {
+        let mut max_version = time::Global::new();
+        max_version.observe(self.insertion.id);
+        for deletion in &self.deletions {
+            max_version.observe(*deletion);
+        }
+
+        if self.is_visible() {
+            FragmentSummary {
+                text_summary: self.text.summary(),
+                max_fragment_id: self.id.clone(),
+                max_version,
+            }
+        } else {
+            FragmentSummary {
+                text_summary: TextSummary::default(),
+                max_fragment_id: self.id.clone(),
+                max_version,
+            }
+        }
+    }
+}
+
+impl<'a> AddAssign<&'a FragmentSummary> for FragmentSummary {
+    fn add_assign(&mut self, other: &Self) {
+        self.text_summary += &other.text_summary;
+        debug_assert!(self.max_fragment_id <= other.max_fragment_id);
+        self.max_fragment_id = other.max_fragment_id.clone();
+        self.max_version.observe_all(&other.max_version);
+    }
+}
+
+impl Default for FragmentSummary {
+    fn default() -> Self {
+        FragmentSummary {
+            text_summary: TextSummary::default(),
+            max_fragment_id: FragmentId::min_value().clone(),
+            max_version: time::Global::new(),
+        }
+    }
+}
+
+impl<'a> sum_tree::Dimension<'a, FragmentSummary> for TextSummary {
+    fn add_summary(&mut self, summary: &FragmentSummary) {
+        *self += &summary.text_summary;
+    }
+}
+
+impl<'a> AddAssign<&'a FragmentExtent> for FragmentExtent {
+    fn add_assign(&mut self, other: &Self) {
+        self.chars += other.chars;
+        self.lines += &other.lines;
+    }
+}
+
+impl Default for FragmentExtent {
+    fn default() -> Self {
+        FragmentExtent {
+            lines: Point::zero(),
+            chars: 0,
+        }
+    }
+}
+
+impl<'a> sum_tree::Dimension<'a, FragmentSummary> for FragmentExtent {
+    fn add_summary(&mut self, summary: &FragmentSummary) {
+        self.chars += summary.text_summary.chars;
+        self.lines += &summary.text_summary.lines;
+    }
+}
+
+impl<'a> sum_tree::Dimension<'a, FragmentSummary> for usize {
+    fn add_summary(&mut self, summary: &FragmentSummary) {
+        *self += summary.text_summary.chars;
+    }
+}
+
+impl sum_tree::Item for InsertionSplit {
+    type Summary = InsertionSplitSummary;
+
+    fn summary(&self) -> Self::Summary {
+        InsertionSplitSummary {
+            extent: self.extent,
+        }
+    }
+}
+
+impl<'a> AddAssign<&'a InsertionSplitSummary> for InsertionSplitSummary {
+    fn add_assign(&mut self, other: &Self) {
+        self.extent += other.extent;
+    }
+}
+
+impl Default for InsertionSplitSummary {
+    fn default() -> Self {
+        InsertionSplitSummary { extent: 0 }
+    }
+}
+
+impl<'a> sum_tree::Dimension<'a, InsertionSplitSummary> for usize {
+    fn add_summary(&mut self, summary: &InsertionSplitSummary) {
+        *self += &summary.extent;
+    }
+}
+
+impl Operation {
+    fn replica_id(&self) -> ReplicaId {
+        self.lamport_timestamp().replica_id
+    }
+
+    fn lamport_timestamp(&self) -> time::Lamport {
+        match self {
+            Operation::Edit {
+                lamport_timestamp, ..
+            } => *lamport_timestamp,
+            Operation::UpdateSelections {
+                lamport_timestamp, ..
+            } => *lamport_timestamp,
+        }
+    }
+
+    pub fn is_edit(&self) -> bool {
+        match self {
+            Operation::Edit { .. } => true,
+            _ => false,
+        }
+    }
+}
+
+impl operation_queue::Operation for Operation {
+    fn timestamp(&self) -> time::Lamport {
+        self.lamport_timestamp()
+    }
+}
+
+pub trait ToOffset {
+    fn to_offset(&self, buffer: &Buffer) -> Result<usize>;
+}
+
+impl ToOffset for Point {
+    fn to_offset(&self, buffer: &Buffer) -> Result<usize> {
+        let mut fragments_cursor = buffer.fragments.cursor::<Point, TextSummary>();
+        fragments_cursor.seek(self, SeekBias::Left);
+        fragments_cursor
+            .item()
+            .ok_or_else(|| anyhow!("point is out of range"))
+            .map(|fragment| {
+                let overshoot = fragment
+                    .offset_for_point(*self - fragments_cursor.start().lines)
+                    .unwrap();
+                fragments_cursor.start().chars + overshoot
+            })
+    }
+}
+
+impl ToOffset for usize {
+    fn to_offset(&self, _: &Buffer) -> Result<usize> {
+        Ok(*self)
+    }
+}
+
+impl ToOffset for Anchor {
+    fn to_offset(&self, buffer: &Buffer) -> Result<usize> {
+        Ok(buffer.summary_for_anchor(self)?.chars)
+    }
+}
+
+pub trait ToPoint {
+    fn to_point(&self, buffer: &Buffer) -> Result<Point>;
+}
+
+impl ToPoint for Anchor {
+    fn to_point(&self, buffer: &Buffer) -> Result<Point> {
+        Ok(buffer.summary_for_anchor(self)?.lines)
+    }
+}
+
+impl ToPoint for usize {
+    fn to_point(&self, buffer: &Buffer) -> Result<Point> {
+        let mut fragments_cursor = buffer.fragments.cursor::<usize, TextSummary>();
+        fragments_cursor.seek(&self, SeekBias::Left);
+        fragments_cursor
+            .item()
+            .ok_or_else(|| anyhow!("offset is out of range"))
+            .map(|fragment| {
+                let overshoot = fragment
+                    .point_for_offset(*self - &fragments_cursor.start().chars)
+                    .unwrap();
+                fragments_cursor.start().lines + overshoot
+            })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::collections::BTreeMap;
+
+    #[test]
+    fn test_edit() -> Result<()> {
+        let mut buffer = Buffer::new(0, "abc");
+        assert_eq!(buffer.text(), "abc");
+        buffer.edit(vec![3..3], "def", None)?;
+        assert_eq!(buffer.text(), "abcdef");
+        buffer.edit(vec![0..0], "ghi", None)?;
+        assert_eq!(buffer.text(), "ghiabcdef");
+        buffer.edit(vec![5..5], "jkl", None)?;
+        assert_eq!(buffer.text(), "ghiabjklcdef");
+        buffer.edit(vec![6..7], "", None)?;
+        assert_eq!(buffer.text(), "ghiabjlcdef");
+        buffer.edit(vec![4..9], "mno", None)?;
+        assert_eq!(buffer.text(), "ghiamnoef");
+
+        Ok(())
+    }
+
+    #[test]
+    fn test_edit_events() {
+        use crate::app::App;
+        use std::{cell::RefCell, rc::Rc};
+
+        let mut app = App::new().unwrap();
+
+        let buffer_1_events = Rc::new(RefCell::new(Vec::new()));
+        let buffer_2_events = Rc::new(RefCell::new(Vec::new()));
+
+        let buffer1 = app.add_model(|_| Buffer::new(0, "abcdef"));
+        let buffer2 = app.add_model(|_| Buffer::new(1, "abcdef"));
+        let ops = buffer1.update(&mut app, |buffer, ctx| {
+            let buffer_1_events = buffer_1_events.clone();
+            ctx.subscribe(&buffer1, move |_, event, _| {
+                buffer_1_events.borrow_mut().push(event.clone())
+            });
+            let buffer_2_events = buffer_2_events.clone();
+            ctx.subscribe(&buffer2, move |_, event, _| {
+                buffer_2_events.borrow_mut().push(event.clone())
+            });
+
+            buffer.edit(Some(2..4), "XYZ", Some(ctx)).unwrap()
+        });
+        buffer2.update(&mut app, |buffer, ctx| {
+            buffer.apply_ops(ops, Some(ctx)).unwrap();
+        });
+
+        let buffer_1_events = buffer_1_events.borrow();
+        assert_eq!(
+            *buffer_1_events,
+            vec![Event::Edited(vec![Edit {
+                old_range: 2..4,
+                new_range: 2..5
+            }])]
+        );
+
+        let buffer_2_events = buffer_2_events.borrow();
+        assert_eq!(
+            *buffer_2_events,
+            vec![Event::Edited(vec![Edit {
+                old_range: 2..4,
+                new_range: 2..5
+            }])]
+        );
+    }
+
+    #[test]
+    fn test_random_edits() {
+        for seed in 0..100 {
+            println!("{:?}", seed);
+            let mut rng = &mut StdRng::seed_from_u64(seed);
+
+            let reference_string_len = rng.gen_range(0, 3);
+            let mut reference_string = RandomCharIter::new(&mut rng)
+                .take(reference_string_len)
+                .collect::<String>();
+            let mut buffer = Buffer::new(0, reference_string.as_str());
+            let mut buffer_versions = Vec::new();
+
+            for _i in 0..10 {
+                let (old_ranges, new_text, _) = buffer.randomly_mutate(rng, None);
+                for old_range in old_ranges.iter().rev() {
+                    reference_string = [
+                        &reference_string[0..old_range.start],
+                        new_text.as_str(),
+                        &reference_string[old_range.end..],
+                    ]
+                    .concat();
+                }
+                assert_eq!(buffer.text(), reference_string);
+
+                {
+                    let line_lengths = line_lengths_in_range(&buffer, 0..buffer.len());
+
+                    for (len, rows) in &line_lengths {
+                        for row in rows {
+                            assert_eq!(buffer.line_len(*row).unwrap(), *len);
+                        }
+                    }
+
+                    let (longest_column, longest_rows) = line_lengths.iter().next_back().unwrap();
+                    let rightmost_point = buffer.rightmost_point();
+                    assert_eq!(rightmost_point.column, *longest_column);
+                    assert!(longest_rows.contains(&rightmost_point.row));
+                }
+
+                for _ in 0..5 {
+                    let end = rng.gen_range(0, buffer.len() + 1);
+                    let start = rng.gen_range(0, end + 1);
+
+                    let line_lengths = line_lengths_in_range(&buffer, start..end);
+                    let (longest_column, longest_rows) = line_lengths.iter().next_back().unwrap();
+                    let range_sum = buffer.text_summary_for_range(start..end);
+                    assert_eq!(range_sum.rightmost_point.column, *longest_column);
+                    assert!(longest_rows.contains(&range_sum.rightmost_point.row));
+                    let range_text = &buffer.text()[start..end];
+                    assert_eq!(range_sum.chars, range_text.chars().count());
+                    assert_eq!(range_sum.bytes, range_text.len());
+                }
+
+                if rng.gen_bool(0.3) {
+                    buffer_versions.push(buffer.clone());
+                }
+            }
+
+            for mut old_buffer in buffer_versions {
+                let mut delta = 0_isize;
+                for Edit {
+                    old_range,
+                    new_range,
+                } in buffer.edits_since(old_buffer.version.clone())
+                {
+                    let old_len = old_range.end - old_range.start;
+                    let new_len = new_range.end - new_range.start;
+                    let old_start = (old_range.start as isize + delta) as usize;
+
+                    old_buffer
+                        .edit(
+                            Some(old_start..old_start + old_len),
+                            buffer.text_for_range(new_range).unwrap(),
+                            None,
+                        )
+                        .unwrap();
+
+                    delta += new_len as isize - old_len as isize;
+                }
+                assert_eq!(old_buffer.text(), buffer.text());
+            }
+        }
+    }
+
+    #[test]
+    fn test_line_len() -> Result<()> {
+        let mut buffer = Buffer::new(0, "");
+        buffer.edit(vec![0..0], "abcd\nefg\nhij", None)?;
+        buffer.edit(vec![12..12], "kl\nmno", None)?;
+        buffer.edit(vec![18..18], "\npqrs\n", None)?;
+        buffer.edit(vec![18..21], "\nPQ", None)?;
+
+        assert_eq!(buffer.line_len(0)?, 4);
+        assert_eq!(buffer.line_len(1)?, 3);
+        assert_eq!(buffer.line_len(2)?, 5);
+        assert_eq!(buffer.line_len(3)?, 3);
+        assert_eq!(buffer.line_len(4)?, 4);
+        assert_eq!(buffer.line_len(5)?, 0);
+        assert!(buffer.line_len(6).is_err());
+
+        Ok(())
+    }
+
+    #[test]
+    fn test_rightmost_point() -> Result<()> {
+        let mut buffer = Buffer::new(0, "");
+        assert_eq!(buffer.rightmost_point().row, 0);
+        buffer.edit(vec![0..0], "abcd\nefg\nhij", None)?;
+        assert_eq!(buffer.rightmost_point().row, 0);
+        buffer.edit(vec![12..12], "kl\nmno", None)?;
+        assert_eq!(buffer.rightmost_point().row, 2);
+        buffer.edit(vec![18..18], "\npqrs", None)?;
+        assert_eq!(buffer.rightmost_point().row, 2);
+        buffer.edit(vec![10..12], "", None)?;
+        assert_eq!(buffer.rightmost_point().row, 0);
+        buffer.edit(vec![24..24], "tuv", None)?;
+        assert_eq!(buffer.rightmost_point().row, 4);
+
+        println!("{:?}", buffer.text());
+
+        Ok(())
+    }
+
+    #[test]
+    fn test_text_summary_for_range() {
+        let buffer = Buffer::new(0, "ab\nefg\nhklm\nnopqrs\ntuvwxyz");
+        let text = Text::from(buffer.text());
+
+        assert_eq!(
+            buffer.text_summary_for_range(1..3),
+            text.slice(1..3).summary()
+        );
+        assert_eq!(
+            buffer.text_summary_for_range(1..12),
+            text.slice(1..12).summary()
+        );
+        assert_eq!(
+            buffer.text_summary_for_range(0..20),
+            text.slice(0..20).summary()
+        );
+        assert_eq!(
+            buffer.text_summary_for_range(0..22),
+            text.slice(0..22).summary()
+        );
+        assert_eq!(
+            buffer.text_summary_for_range(7..22),
+            text.slice(7..22).summary()
+        );
+    }
+
+    #[test]
+    fn test_chars_at() -> Result<()> {
+        let mut buffer = Buffer::new(0, "");
+        buffer.edit(vec![0..0], "abcd\nefgh\nij", None)?;
+        buffer.edit(vec![12..12], "kl\nmno", None)?;
+        buffer.edit(vec![18..18], "\npqrs", None)?;
+        buffer.edit(vec![18..21], "\nPQ", None)?;
+
+        let chars = buffer.chars_at(Point::new(0, 0))?;
+        assert_eq!(chars.collect::<String>(), "abcd\nefgh\nijkl\nmno\nPQrs");
+
+        let chars = buffer.chars_at(Point::new(1, 0))?;
+        assert_eq!(chars.collect::<String>(), "efgh\nijkl\nmno\nPQrs");
+
+        let chars = buffer.chars_at(Point::new(2, 0))?;
+        assert_eq!(chars.collect::<String>(), "ijkl\nmno\nPQrs");
+
+        let chars = buffer.chars_at(Point::new(3, 0))?;
+        assert_eq!(chars.collect::<String>(), "mno\nPQrs");
+
+        let chars = buffer.chars_at(Point::new(4, 0))?;
+        assert_eq!(chars.collect::<String>(), "PQrs");
+
+        // Regression test:
+        let mut buffer = Buffer::new(0, "");
+        buffer.edit(vec![0..0], "[workspace]\nmembers = [\n    \"xray_core\",\n    \"xray_server\",\n    \"xray_cli\",\n    \"xray_wasm\",\n]\n", None)?;
+        buffer.edit(vec![60..60], "\n", None)?;
+
+        let chars = buffer.chars_at(Point::new(6, 0))?;
+        assert_eq!(chars.collect::<String>(), "    \"xray_wasm\",\n]\n");
+
+        Ok(())
+    }
+
+    // #[test]
+    // fn test_point_for_offset() -> Result<()> {
+    //     let text = Text::from("abc\ndefgh\nijklm\nopq");
+    //     assert_eq!(text.point_for_offset(0)?, Point { row: 0, column: 0 });
+    //     assert_eq!(text.point_for_offset(1)?, Point { row: 0, column: 1 });
+    //     assert_eq!(text.point_for_offset(2)?, Point { row: 0, column: 2 });
+    //     assert_eq!(text.point_for_offset(3)?, Point { row: 0, column: 3 });
+    //     assert_eq!(text.point_for_offset(4)?, Point { row: 1, column: 0 });
+    //     assert_eq!(text.point_for_offset(5)?, Point { row: 1, column: 1 });
+    //     assert_eq!(text.point_for_offset(9)?, Point { row: 1, column: 5 });
+    //     assert_eq!(text.point_for_offset(10)?, Point { row: 2, column: 0 });
+    //     assert_eq!(text.point_for_offset(14)?, Point { row: 2, column: 4 });
+    //     assert_eq!(text.point_for_offset(15)?, Point { row: 2, column: 5 });
+    //     assert_eq!(text.point_for_offset(16)?, Point { row: 3, column: 0 });
+    //     assert_eq!(text.point_for_offset(17)?, Point { row: 3, column: 1 });
+    //     assert_eq!(text.point_for_offset(19)?, Point { row: 3, column: 3 });
+    //     assert!(text.point_for_offset(20).is_err());
+    //
+    //     let text = Text::from("abc");
+    //     assert_eq!(text.point_for_offset(0)?, Point { row: 0, column: 0 });
+    //     assert_eq!(text.point_for_offset(1)?, Point { row: 0, column: 1 });
+    //     assert_eq!(text.point_for_offset(2)?, Point { row: 0, column: 2 });
+    //     assert_eq!(text.point_for_offset(3)?, Point { row: 0, column: 3 });
+    //     assert!(text.point_for_offset(4).is_err());
+    //     Ok(())
+    // }
+
+    // #[test]
+    // fn test_offset_for_point() -> Result<()> {
+    //     let text = Text::from("abc\ndefgh");
+    //     assert_eq!(text.offset_for_point(Point { row: 0, column: 0 })?, 0);
+    //     assert_eq!(text.offset_for_point(Point { row: 0, column: 1 })?, 1);
+    //     assert_eq!(text.offset_for_point(Point { row: 0, column: 2 })?, 2);
+    //     assert_eq!(text.offset_for_point(Point { row: 0, column: 3 })?, 3);
+    //     assert!(text.offset_for_point(Point { row: 0, column: 4 }).is_err());
+    //     assert_eq!(text.offset_for_point(Point { row: 1, column: 0 })?, 4);
+    //     assert_eq!(text.offset_for_point(Point { row: 1, column: 1 })?, 5);
+    //     assert_eq!(text.offset_for_point(Point { row: 1, column: 5 })?, 9);
+    //     assert!(text.offset_for_point(Point { row: 1, column: 6 }).is_err());
+    //
+    //     let text = Text::from("abc");
+    //     assert_eq!(text.offset_for_point(Point { row: 0, column: 0 })?, 0);
+    //     assert_eq!(text.offset_for_point(Point { row: 0, column: 1 })?, 1);
+    //     assert_eq!(text.offset_for_point(Point { row: 0, column: 2 })?, 2);
+    //     assert_eq!(text.offset_for_point(Point { row: 0, column: 3 })?, 3);
+    //     assert!(text.offset_for_point(Point { row: 0, column: 4 }).is_err());
+    //     Ok(())
+    // }
+
+    // #[test]
+    // fn test_longest_row_in_range() -> Result<()> {
+    //     for seed in 0..100 {
+    //         println!("{:?}", seed);
+    //         let mut rng = &mut StdRng::seed_from_u64(seed);
+    //         let string_len = rng.gen_range(1, 10);
+    //         let string = RandomCharIter(&mut rng)
+    //             .take(string_len)
+    //             .collect::<String>();
+    //         let text = Text::from(string.as_ref());
+    //
+    //         for _i in 0..10 {
+    //             let end = rng.gen_range(1, string.len() + 1);
+    //             let start = rng.gen_range(0, end);
+    //
+    //             let mut cur_row = string[0..start].chars().filter(|c| *c == '\n').count() as u32;
+    //             let mut cur_row_len = 0;
+    //             let mut expected_longest_row = cur_row;
+    //             let mut expected_longest_row_len = cur_row_len;
+    //             for ch in string[start..end].chars() {
+    //                 if ch == '\n' {
+    //                     if cur_row_len > expected_longest_row_len {
+    //                         expected_longest_row = cur_row;
+    //                         expected_longest_row_len = cur_row_len;
+    //                     }
+    //                     cur_row += 1;
+    //                     cur_row_len = 0;
+    //                 } else {
+    //                     cur_row_len += 1;
+    //                 }
+    //             }
+    //             if cur_row_len > expected_longest_row_len {
+    //                 expected_longest_row = cur_row;
+    //                 expected_longest_row_len = cur_row_len;
+    //             }
+    //
+    //             assert_eq!(
+    //                 text.longest_row_in_range(start..end)?,
+    //                 (expected_longest_row, expected_longest_row_len)
+    //             );
+    //         }
+    //     }
+    //     Ok(())
+    // }
+
+    #[test]
+    fn test_fragment_ids() {
+        for seed in 0..10 {
+            let rng = &mut StdRng::seed_from_u64(seed);
+
+            let mut ids = vec![FragmentId(Arc::from([0])), FragmentId(Arc::from([4]))];
+            for _i in 0..100 {
+                let index = rng.gen_range(1, ids.len());
+
+                let left = ids[index - 1].clone();
+                let right = ids[index].clone();
+                ids.insert(index, FragmentId::between_with_max(&left, &right, 4));
+
+                let mut sorted_ids = ids.clone();
+                sorted_ids.sort();
+                assert_eq!(ids, sorted_ids);
+            }
+        }
+    }
+
+    #[test]
+    fn test_anchors() -> Result<()> {
+        let mut buffer = Buffer::new(0, "");
+        buffer.edit(vec![0..0], "abc", None)?;
+        let left_anchor = buffer.anchor_before(2).unwrap();
+        let right_anchor = buffer.anchor_after(2).unwrap();
+
+        buffer.edit(vec![1..1], "def\n", None)?;
+        assert_eq!(buffer.text(), "adef\nbc");
+        assert_eq!(left_anchor.to_offset(&buffer).unwrap(), 6);
+        assert_eq!(right_anchor.to_offset(&buffer).unwrap(), 6);
+        assert_eq!(
+            left_anchor.to_point(&buffer).unwrap(),
+            Point { row: 1, column: 1 }
+        );
+        assert_eq!(
+            right_anchor.to_point(&buffer).unwrap(),
+            Point { row: 1, column: 1 }
+        );
+
+        buffer.edit(vec![2..3], "", None)?;
+        assert_eq!(buffer.text(), "adf\nbc");
+        assert_eq!(left_anchor.to_offset(&buffer).unwrap(), 5);
+        assert_eq!(right_anchor.to_offset(&buffer).unwrap(), 5);
+        assert_eq!(
+            left_anchor.to_point(&buffer).unwrap(),
+            Point { row: 1, column: 1 }
+        );
+        assert_eq!(
+            right_anchor.to_point(&buffer).unwrap(),
+            Point { row: 1, column: 1 }
+        );
+
+        buffer.edit(vec![5..5], "ghi\n", None)?;
+        assert_eq!(buffer.text(), "adf\nbghi\nc");
+        assert_eq!(left_anchor.to_offset(&buffer).unwrap(), 5);
+        assert_eq!(right_anchor.to_offset(&buffer).unwrap(), 9);
+        assert_eq!(
+            left_anchor.to_point(&buffer).unwrap(),
+            Point { row: 1, column: 1 }
+        );
+        assert_eq!(
+            right_anchor.to_point(&buffer).unwrap(),
+            Point { row: 2, column: 0 }
+        );
+
+        buffer.edit(vec![7..9], "", None)?;
+        assert_eq!(buffer.text(), "adf\nbghc");
+        assert_eq!(left_anchor.to_offset(&buffer).unwrap(), 5);
+        assert_eq!(right_anchor.to_offset(&buffer).unwrap(), 7);
+        assert_eq!(
+            left_anchor.to_point(&buffer).unwrap(),
+            Point { row: 1, column: 1 },
+        );
+        assert_eq!(
+            right_anchor.to_point(&buffer).unwrap(),
+            Point { row: 1, column: 3 }
+        );
+
+        // Ensure anchoring to a point is equivalent to anchoring to an offset.
+        assert_eq!(
+            buffer.anchor_before(Point { row: 0, column: 0 })?,
+            buffer.anchor_before(0)?
+        );
+        assert_eq!(
+            buffer.anchor_before(Point { row: 0, column: 1 })?,
+            buffer.anchor_before(1)?
+        );
+        assert_eq!(
+            buffer.anchor_before(Point { row: 0, column: 2 })?,
+            buffer.anchor_before(2)?
+        );
+        assert_eq!(
+            buffer.anchor_before(Point { row: 0, column: 3 })?,
+            buffer.anchor_before(3)?
+        );
+        assert_eq!(
+            buffer.anchor_before(Point { row: 1, column: 0 })?,
+            buffer.anchor_before(4)?
+        );
+        assert_eq!(
+            buffer.anchor_before(Point { row: 1, column: 1 })?,
+            buffer.anchor_before(5)?
+        );
+        assert_eq!(
+            buffer.anchor_before(Point { row: 1, column: 2 })?,
+            buffer.anchor_before(6)?
+        );
+        assert_eq!(
+            buffer.anchor_before(Point { row: 1, column: 3 })?,
+            buffer.anchor_before(7)?
+        );
+        assert_eq!(
+            buffer.anchor_before(Point { row: 1, column: 4 })?,
+            buffer.anchor_before(8)?
+        );
+
+        // Comparison between anchors.
+        let anchor_at_offset_0 = buffer.anchor_before(0).unwrap();
+        let anchor_at_offset_1 = buffer.anchor_before(1).unwrap();
+        let anchor_at_offset_2 = buffer.anchor_before(2).unwrap();
+
+        assert_eq!(
+            anchor_at_offset_0.cmp(&anchor_at_offset_0, &buffer)?,
+            Ordering::Equal
+        );
+        assert_eq!(
+            anchor_at_offset_1.cmp(&anchor_at_offset_1, &buffer)?,
+            Ordering::Equal
+        );
+        assert_eq!(
+            anchor_at_offset_2.cmp(&anchor_at_offset_2, &buffer)?,
+            Ordering::Equal
+        );
+
+        assert_eq!(
+            anchor_at_offset_0.cmp(&anchor_at_offset_1, &buffer)?,
+            Ordering::Less
+        );
+        assert_eq!(
+            anchor_at_offset_1.cmp(&anchor_at_offset_2, &buffer)?,
+            Ordering::Less
+        );
+        assert_eq!(
+            anchor_at_offset_0.cmp(&anchor_at_offset_2, &buffer)?,
+            Ordering::Less
+        );
+
+        assert_eq!(
+            anchor_at_offset_1.cmp(&anchor_at_offset_0, &buffer)?,
+            Ordering::Greater
+        );
+        assert_eq!(
+            anchor_at_offset_2.cmp(&anchor_at_offset_1, &buffer)?,
+            Ordering::Greater
+        );
+        assert_eq!(
+            anchor_at_offset_2.cmp(&anchor_at_offset_0, &buffer)?,
+            Ordering::Greater
+        );
+        Ok(())
+    }
+
+    #[test]
+    fn test_anchors_at_start_and_end() -> Result<()> {
+        let mut buffer = Buffer::new(0, "");
+        let before_start_anchor = buffer.anchor_before(0).unwrap();
+        let after_end_anchor = buffer.anchor_after(0).unwrap();
+
+        buffer.edit(vec![0..0], "abc", None)?;
+        assert_eq!(buffer.text(), "abc");
+        assert_eq!(before_start_anchor.to_offset(&buffer).unwrap(), 0);
+        assert_eq!(after_end_anchor.to_offset(&buffer).unwrap(), 3);
+
+        let after_start_anchor = buffer.anchor_after(0).unwrap();
+        let before_end_anchor = buffer.anchor_before(3).unwrap();
+
+        buffer.edit(vec![3..3], "def", None)?;
+        buffer.edit(vec![0..0], "ghi", None)?;
+        assert_eq!(buffer.text(), "ghiabcdef");
+        assert_eq!(before_start_anchor.to_offset(&buffer).unwrap(), 0);
+        assert_eq!(after_start_anchor.to_offset(&buffer).unwrap(), 3);
+        assert_eq!(before_end_anchor.to_offset(&buffer).unwrap(), 6);
+        assert_eq!(after_end_anchor.to_offset(&buffer).unwrap(), 9);
+
+        Ok(())
+    }
+
+    #[test]
+    fn test_is_modified() -> Result<()> {
+        let mut buffer = Buffer::new(0, "abc");
+        assert!(!buffer.is_modified());
+        buffer.edit(vec![1..2], "", None)?;
+        assert!(buffer.is_modified());
+
+        Ok(())
+    }
+
+    #[test]
+    fn test_random_concurrent_edits() {
+        use crate::tests::Network;
+
+        const PEERS: usize = 3;
+
+        for seed in 0..50 {
+            println!("{:?}", seed);
+            let mut rng = &mut StdRng::seed_from_u64(seed);
+
+            let base_text_len = rng.gen_range(0, 10);
+            let base_text = RandomCharIter::new(&mut rng)
+                .take(base_text_len)
+                .collect::<String>();
+            let mut replica_ids = Vec::new();
+            let mut buffers = Vec::new();
+            let mut network = Network::new();
+            for i in 0..PEERS {
+                let buffer = Buffer::new(i as ReplicaId, base_text.as_str());
+                buffers.push(buffer);
+                replica_ids.push(i as u16);
+                network.add_peer(i as u16);
+            }
+
+            let mut mutation_count = 10;
+            loop {
+                let replica_index = rng.gen_range(0, PEERS);
+                let replica_id = replica_ids[replica_index];
+                let buffer = &mut buffers[replica_index];
+                if mutation_count > 0 && rng.gen() {
+                    let (_, _, ops) = buffer.randomly_mutate(&mut rng, None);
+                    network.broadcast(replica_id, ops, &mut rng);
+                    mutation_count -= 1;
+                } else if network.has_unreceived(replica_id) {
+                    buffer
+                        .apply_ops(network.receive(replica_id, &mut rng), None)
+                        .unwrap();
+                }
+
+                if mutation_count == 0 && network.is_idle() {
+                    break;
+                }
+            }
+
+            for buffer in &buffers[1..] {
+                assert_eq!(buffer.text(), buffers[0].text());
+                assert_eq!(
+                    buffer.all_selections().collect::<HashMap<_, _>>(),
+                    buffers[0].all_selections().collect::<HashMap<_, _>>()
+                );
+                assert_eq!(
+                    buffer.all_selection_ranges().collect::<HashMap<_, _>>(),
+                    buffers[0].all_selection_ranges().collect::<HashMap<_, _>>()
+                );
+            }
+        }
+    }
+
+    impl Buffer {
+        pub fn randomly_mutate<T>(
+            &mut self,
+            rng: &mut T,
+            ctx: Option<&mut ModelContext<Self>>,
+        ) -> (Vec<Range<usize>>, String, Vec<Operation>)
+        where
+            T: Rng,
+        {
+            // Randomly edit
+            let (old_ranges, new_text, mut operations) = self.randomly_edit(rng, 5, ctx);
+
+            // Randomly add, remove or mutate selection sets.
+            let replica_selection_sets = &self
+                .all_selections()
+                .map(|(set_id, _)| *set_id)
+                .filter(|set_id| self.replica_id == set_id.replica_id)
+                .collect::<Vec<_>>();
+            let set_id = replica_selection_sets.choose(rng);
+            if set_id.is_some() && rng.gen_bool(1.0 / 6.0) {
+                let op = self.remove_selection_set(*set_id.unwrap()).unwrap();
+                operations.push(op);
+            } else {
+                let mut ranges = Vec::new();
+                for _ in 0..5 {
+                    let start = rng.gen_range(0, self.len() + 1);
+                    let start_point = self.point_for_offset(start).unwrap();
+                    let end = rng.gen_range(0, self.len() + 1);
+                    let end_point = self.point_for_offset(end).unwrap();
+                    ranges.push(start_point..end_point);
+                }
+
+                let op = if set_id.is_none() || rng.gen_bool(1.0 / 5.0) {
+                    self.add_selection_set(ranges).unwrap().1
+                } else {
+                    self.replace_selection_set(*set_id.unwrap(), ranges)
+                        .unwrap()
+                };
+                operations.push(op);
+            }
+
+            (old_ranges, new_text, operations)
+        }
+    }
+
+    fn line_lengths_in_range(buffer: &Buffer, range: Range<usize>) -> BTreeMap<u32, HashSet<u32>> {
+        let mut lengths = BTreeMap::new();
+        for (row, line) in buffer.text()[range].lines().enumerate() {
+            lengths
+                .entry(line.len() as u32)
+                .or_insert(HashSet::new())
+                .insert(row as u32);
+        }
+        if lengths.is_empty() {
+            let mut rows = HashSet::new();
+            rows.insert(0);
+            lengths.insert(0, rows);
+        }
+        lengths
+    }
+}

zed/src/editor/buffer/point.rs 🔗

@@ -0,0 +1,100 @@
+use std::{
+    cmp::Ordering,
+    ops::{Add, AddAssign, Sub},
+};
+
+#[derive(Clone, Copy, Default, Eq, PartialEq, Debug, Hash)]
+pub struct Point {
+    pub row: u32,
+    pub column: u32,
+}
+
+impl Point {
+    pub fn new(row: u32, column: u32) -> Self {
+        Point { row, column }
+    }
+
+    pub fn zero() -> Self {
+        Point::new(0, 0)
+    }
+
+    pub fn is_zero(&self) -> bool {
+        self.row == 0 && self.column == 0
+    }
+}
+
+impl<'a> Add<&'a Self> for Point {
+    type Output = Point;
+
+    fn add(self, other: &'a Self) -> Self::Output {
+        if other.row == 0 {
+            Point::new(self.row, self.column + other.column)
+        } else {
+            Point::new(self.row + other.row, other.column)
+        }
+    }
+}
+
+impl Add for Point {
+    type Output = Point;
+
+    fn add(self, other: Self) -> Self::Output {
+        self + &other
+    }
+}
+
+impl<'a> Sub<&'a Self> for Point {
+    type Output = Point;
+
+    fn sub(self, other: &'a Self) -> Self::Output {
+        debug_assert!(*other <= self);
+
+        if self.row == other.row {
+            Point::new(0, self.column - other.column)
+        } else {
+            Point::new(self.row - other.row, self.column)
+        }
+    }
+}
+
+impl Sub for Point {
+    type Output = Point;
+
+    fn sub(self, other: Self) -> Self::Output {
+        self - &other
+    }
+}
+
+impl<'a> AddAssign<&'a Self> for Point {
+    fn add_assign(&mut self, other: &'a Self) {
+        if other.row == 0 {
+            self.column += other.column;
+        } else {
+            self.row += other.row;
+            self.column = other.column;
+        }
+    }
+}
+
+impl PartialOrd for Point {
+    fn partial_cmp(&self, other: &Point) -> Option<Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
+impl Ord for Point {
+    #[cfg(target_pointer_width = "64")]
+    fn cmp(&self, other: &Point) -> Ordering {
+        let a = (self.row as usize) << 32 | self.column as usize;
+        let b = (other.row as usize) << 32 | other.column as usize;
+        a.cmp(&b)
+    }
+
+    #[cfg(target_pointer_width = "32")]
+    fn cmp(&self, other: &Point) -> Ordering {
+        match self.row.cmp(&other.row) {
+            Ordering::Equal => self.column.cmp(&other.column),
+            comparison @ _ => comparison,
+        }
+    }
+}

zed/src/editor/buffer/text.rs 🔗

@@ -0,0 +1,445 @@
+use super::Point;
+use crate::sum_tree::{self, SeekBias, SumTree};
+use arrayvec::ArrayVec;
+use std::{
+    cmp,
+    fmt::{self, Debug},
+    ops::{Bound, Index, Range, RangeBounds},
+    sync::Arc,
+};
+
+#[derive(Copy, Clone, Debug, Eq, PartialEq)]
+enum Run {
+    Newline,
+    Chars { len: usize, char_size: u8 },
+}
+
+#[derive(Clone, Copy, Debug, Default, Eq, Ord, PartialEq, PartialOrd)]
+struct ByteOffset(usize);
+
+impl sum_tree::Item for Run {
+    type Summary = TextSummary;
+
+    fn summary(&self) -> Self::Summary {
+        match *self {
+            Run::Newline => TextSummary {
+                chars: 1,
+                bytes: 1,
+                lines: Point::new(1, 0),
+                first_line_len: 0,
+                rightmost_point: Point::new(0, 0),
+            },
+            Run::Chars { len, char_size } => TextSummary {
+                chars: len,
+                bytes: len * char_size as usize,
+                lines: Point::new(0, len as u32),
+                first_line_len: len as u32,
+                rightmost_point: Point::new(0, len as u32),
+            },
+        }
+    }
+}
+
+impl Run {
+    fn char_size(&self) -> u8 {
+        match self {
+            Run::Newline => 1,
+            Run::Chars { char_size, .. } => *char_size,
+        }
+    }
+}
+
+#[derive(Clone, Debug, Default, Eq, PartialEq)]
+pub struct TextSummary {
+    pub chars: usize,
+    pub bytes: usize,
+    pub lines: Point,
+    pub first_line_len: u32,
+    pub rightmost_point: Point,
+}
+
+impl<'a> std::ops::AddAssign<&'a Self> for TextSummary {
+    fn add_assign(&mut self, other: &'a Self) {
+        let joined_line_len = self.lines.column + other.first_line_len;
+        if joined_line_len > self.rightmost_point.column {
+            self.rightmost_point = Point::new(self.lines.row, joined_line_len);
+        }
+        if other.rightmost_point.column > self.rightmost_point.column {
+            self.rightmost_point = self.lines + &other.rightmost_point;
+        }
+
+        if self.lines.row == 0 {
+            self.first_line_len += other.first_line_len;
+        }
+
+        self.chars += other.chars;
+        self.bytes += other.bytes;
+        self.lines += &other.lines;
+    }
+}
+
+impl std::ops::AddAssign<Self> for TextSummary {
+    fn add_assign(&mut self, other: Self) {
+        *self += &other;
+    }
+}
+
+impl<'a> sum_tree::Dimension<'a, TextSummary> for TextSummary {
+    fn add_summary(&mut self, summary: &TextSummary) {
+        *self += summary;
+    }
+}
+
+impl<'a> sum_tree::Dimension<'a, TextSummary> for Point {
+    fn add_summary(&mut self, summary: &TextSummary) {
+        *self += &summary.lines;
+    }
+}
+
+impl<'a> sum_tree::Dimension<'a, TextSummary> for ByteOffset {
+    fn add_summary(&mut self, summary: &TextSummary) {
+        self.0 += summary.bytes
+    }
+}
+
+impl<'a> sum_tree::Dimension<'a, TextSummary> for usize {
+    fn add_summary(&mut self, summary: &TextSummary) {
+        *self += summary.chars;
+    }
+}
+
+#[derive(Clone)]
+pub struct Text {
+    text: Arc<str>,
+    runs: SumTree<Run>,
+    range: Range<usize>,
+}
+
+impl From<String> for Text {
+    fn from(text: String) -> Self {
+        let mut runs = Vec::new();
+
+        let mut chars_len = 0;
+        let mut run_char_size = 0;
+        let mut run_chars = 0;
+
+        let mut chars = text.chars();
+        loop {
+            let ch = chars.next();
+            let ch_size = ch.map_or(0, |ch| ch.len_utf8());
+            if run_chars != 0 && (ch.is_none() || ch == Some('\n') || run_char_size != ch_size) {
+                runs.push(Run::Chars {
+                    len: run_chars,
+                    char_size: run_char_size as u8,
+                });
+                run_chars = 0;
+            }
+            run_char_size = ch_size;
+
+            match ch {
+                Some('\n') => runs.push(Run::Newline),
+                Some(_) => run_chars += 1,
+                None => break,
+            }
+            chars_len += 1;
+        }
+
+        let mut tree = SumTree::new();
+        tree.extend(runs);
+        Text {
+            text: text.into(),
+            runs: tree,
+            range: 0..chars_len,
+        }
+    }
+}
+
+impl<'a> From<&'a str> for Text {
+    fn from(text: &'a str) -> Self {
+        Self::from(String::from(text))
+    }
+}
+
+impl Debug for Text {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_tuple("Text").field(&self.text).finish()
+    }
+}
+
+impl PartialEq for Text {
+    fn eq(&self, other: &Self) -> bool {
+        self.text == other.text
+    }
+}
+
+impl Eq for Text {}
+
+impl<T: RangeBounds<usize>> Index<T> for Text {
+    type Output = str;
+
+    fn index(&self, range: T) -> &Self::Output {
+        let start = match range.start_bound() {
+            Bound::Included(start) => cmp::min(self.range.start + start, self.range.end),
+            Bound::Excluded(_) => unimplemented!(),
+            Bound::Unbounded => self.range.start,
+        };
+        let end = match range.end_bound() {
+            Bound::Included(end) => cmp::min(self.range.start + end + 1, self.range.end),
+            Bound::Excluded(end) => cmp::min(self.range.start + end, self.range.end),
+            Bound::Unbounded => self.range.end,
+        };
+
+        let byte_start = self.abs_byte_offset_for_offset(start);
+        let byte_end = self.abs_byte_offset_for_offset(end);
+        &self.text[byte_start..byte_end]
+    }
+}
+
+impl Text {
+    pub fn range(&self) -> Range<usize> {
+        self.range.clone()
+    }
+
+    pub fn as_str(&self) -> &str {
+        &self[..]
+    }
+
+    pub fn slice<T: RangeBounds<usize>>(&self, range: T) -> Text {
+        let start = match range.start_bound() {
+            Bound::Included(start) => cmp::min(self.range.start + start, self.range.end),
+            Bound::Excluded(_) => unimplemented!(),
+            Bound::Unbounded => self.range.start,
+        };
+        let end = match range.end_bound() {
+            Bound::Included(end) => cmp::min(self.range.start + end + 1, self.range.end),
+            Bound::Excluded(end) => cmp::min(self.range.start + end, self.range.end),
+            Bound::Unbounded => self.range.end,
+        };
+
+        Text {
+            text: self.text.clone(),
+            runs: self.runs.clone(),
+            range: start..end,
+        }
+    }
+
+    pub fn line_len(&self, row: u32) -> u32 {
+        let mut cursor = self.runs.cursor::<usize, Point>();
+        cursor.seek(&self.range.start, SeekBias::Right);
+        let absolute_row = cursor.start().row + row;
+
+        let mut cursor = self.runs.cursor::<Point, usize>();
+        cursor.seek(&Point::new(absolute_row, 0), SeekBias::Right);
+        let prefix_len = self.range.start.saturating_sub(*cursor.start());
+        let line_len = cursor.summary::<usize>(&Point::new(absolute_row + 1, 0), SeekBias::Left);
+        let suffix_len = cursor.start().saturating_sub(self.range.end);
+
+        line_len
+            .saturating_sub(prefix_len)
+            .saturating_sub(suffix_len) as u32
+    }
+
+    pub fn len(&self) -> usize {
+        self.range.end - self.range.start
+    }
+
+    pub fn lines(&self) -> Point {
+        self.abs_point_for_offset(self.range.end) - &self.abs_point_for_offset(self.range.start)
+    }
+
+    pub fn rightmost_point(&self) -> Point {
+        let lines = self.lines();
+
+        let mut candidates = ArrayVec::<[Point; 3]>::new();
+        candidates.push(lines);
+        if lines.row > 0 {
+            candidates.push(Point::new(0, self.line_len(0)));
+            if lines.row > 1 {
+                let mut cursor = self.runs.cursor::<usize, Point>();
+                cursor.seek(&self.range.start, SeekBias::Right);
+                let absolute_start_row = cursor.start().row;
+
+                let mut cursor = self.runs.cursor::<Point, usize>();
+                cursor.seek(&Point::new(absolute_start_row + 1, 0), SeekBias::Right);
+                let summary = cursor.summary::<TextSummary>(
+                    &Point::new(absolute_start_row + lines.row, 0),
+                    SeekBias::Left,
+                );
+
+                candidates.push(Point::new(1, 0) + &summary.rightmost_point);
+            }
+        }
+
+        candidates.into_iter().max_by_key(|p| p.column).unwrap()
+    }
+
+    pub fn point_for_offset(&self, offset: usize) -> Point {
+        self.abs_point_for_offset(self.range.start + offset)
+            - &self.abs_point_for_offset(self.range.start)
+    }
+
+    pub fn offset_for_point(&self, point: Point) -> usize {
+        let mut cursor = self.runs.cursor::<Point, TextSummary>();
+        let abs_point = self.abs_point_for_offset(self.range.start) + &point;
+        cursor.seek(&abs_point, SeekBias::Right);
+        let overshoot = abs_point - &cursor.start().lines;
+        let abs_offset = cursor.start().chars + overshoot.column as usize;
+        abs_offset - self.range.start
+    }
+
+    pub fn summary(&self) -> TextSummary {
+        TextSummary {
+            chars: self.range.end - self.range.start,
+            bytes: self.abs_byte_offset_for_offset(self.range.end)
+                - self.abs_byte_offset_for_offset(self.range.start),
+            lines: self.abs_point_for_offset(self.range.end)
+                - &self.abs_point_for_offset(self.range.start),
+            first_line_len: self.line_len(0),
+            rightmost_point: self.rightmost_point(),
+        }
+    }
+
+    fn abs_point_for_offset(&self, offset: usize) -> Point {
+        let mut cursor = self.runs.cursor::<usize, TextSummary>();
+        cursor.seek(&offset, SeekBias::Right);
+        let overshoot = (offset - cursor.start().chars) as u32;
+        cursor.start().lines + &Point::new(0, overshoot)
+    }
+
+    fn abs_byte_offset_for_offset(&self, offset: usize) -> usize {
+        let mut cursor = self.runs.cursor::<usize, TextSummary>();
+        cursor.seek(&offset, SeekBias::Right);
+        let overshoot = offset - cursor.start().chars;
+        cursor.start().bytes + overshoot * cursor.item().map_or(0, |run| run.char_size()) as usize
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::collections::HashSet;
+    use std::iter::FromIterator;
+
+    #[test]
+    fn test_basic() {
+        let text = Text::from(String::from("ab\ncd€\nfghij\nkl¢m"));
+        assert_eq!(text.len(), 17);
+        assert_eq!(text.as_str(), "ab\ncd€\nfghij\nkl¢m");
+        assert_eq!(text.lines(), Point::new(3, 4));
+        assert_eq!(text.line_len(0), 2);
+        assert_eq!(text.line_len(1), 3);
+        assert_eq!(text.line_len(2), 5);
+        assert_eq!(text.line_len(3), 4);
+        assert_eq!(text.rightmost_point(), Point::new(2, 5));
+
+        let b_to_g = text.slice(1..9);
+        assert_eq!(b_to_g.as_str(), "b\ncd€\nfg");
+        assert_eq!(b_to_g.len(), 8);
+        assert_eq!(b_to_g.lines(), Point::new(2, 2));
+        assert_eq!(b_to_g.line_len(0), 1);
+        assert_eq!(b_to_g.line_len(1), 3);
+        assert_eq!(b_to_g.line_len(2), 2);
+        assert_eq!(b_to_g.line_len(3), 0);
+        assert_eq!(b_to_g.rightmost_point(), Point::new(1, 3));
+
+        let d_to_i = text.slice(4..11);
+        assert_eq!(d_to_i.as_str(), "d€\nfghi");
+        assert_eq!(&d_to_i[1..5], "€\nfg");
+        assert_eq!(d_to_i.len(), 7);
+        assert_eq!(d_to_i.lines(), Point::new(1, 4));
+        assert_eq!(d_to_i.line_len(0), 2);
+        assert_eq!(d_to_i.line_len(1), 4);
+        assert_eq!(d_to_i.line_len(2), 0);
+        assert_eq!(d_to_i.rightmost_point(), Point::new(1, 4));
+
+        let d_to_j = text.slice(4..=11);
+        assert_eq!(d_to_j.as_str(), "d€\nfghij");
+        assert_eq!(&d_to_j[1..], "€\nfghij");
+        assert_eq!(d_to_j.len(), 8);
+    }
+
+    #[test]
+    fn test_random() {
+        use rand::prelude::*;
+
+        for seed in 0..100 {
+            println!("buffer::text seed: {}", seed);
+            let rng = &mut StdRng::seed_from_u64(seed);
+
+            let len = rng.gen_range(0, 50);
+            let mut string = String::new();
+            for _ in 0..len {
+                if rng.gen_ratio(1, 5) {
+                    string.push('\n');
+                } else {
+                    string.push(rng.gen());
+                }
+            }
+            let text = Text::from(string.clone());
+
+            for _ in 0..10 {
+                let start = rng.gen_range(0, text.len() + 1);
+                let end = rng.gen_range(start, text.len() + 2);
+
+                let string_slice = string
+                    .chars()
+                    .skip(start)
+                    .take(end - start)
+                    .collect::<String>();
+                let expected_line_endpoints = string_slice
+                    .split('\n')
+                    .enumerate()
+                    .map(|(row, line)| Point::new(row as u32, line.chars().count() as u32))
+                    .collect::<Vec<_>>();
+                let text_slice = text.slice(start..end);
+
+                assert_eq!(text_slice.lines(), lines(&string_slice));
+
+                let mut rightmost_points: HashSet<Point> = HashSet::new();
+                for endpoint in &expected_line_endpoints {
+                    if let Some(rightmost_point) = rightmost_points.iter().next().cloned() {
+                        if endpoint.column > rightmost_point.column {
+                            rightmost_points.clear();
+                        }
+                        if endpoint.column >= rightmost_point.column {
+                            rightmost_points.insert(*endpoint);
+                        }
+                    } else {
+                        rightmost_points.insert(*endpoint);
+                    }
+
+                    assert_eq!(text_slice.line_len(endpoint.row as u32), endpoint.column);
+                }
+
+                assert!(rightmost_points.contains(&text_slice.rightmost_point()));
+
+                for _ in 0..10 {
+                    let offset = rng.gen_range(0, string_slice.chars().count() + 1);
+                    let point = lines(&string_slice.chars().take(offset).collect::<String>());
+                    assert_eq!(text_slice.point_for_offset(offset), point);
+                    assert_eq!(text_slice.offset_for_point(point), offset);
+                    if offset < string_slice.chars().count() {
+                        assert_eq!(
+                            &text_slice[offset..offset + 1],
+                            String::from_iter(string_slice.chars().nth(offset)).as_str()
+                        );
+                    }
+                }
+            }
+        }
+    }
+
+    pub fn lines(s: &str) -> Point {
+        let mut row = 0;
+        let mut column = 0;
+        for ch in s.chars() {
+            if ch == '\n' {
+                row += 1;
+                column = 0;
+            } else {
+                column += 1;
+            }
+        }
+        Point::new(row, column)
+    }
+}

zed/src/editor/buffer_element.rs 🔗

@@ -0,0 +1,765 @@
+use super::{BufferView, DisplayPoint, SelectAction};
+use crate::{
+    app::{AppContext, MutableAppContext, ViewHandle},
+    fonts::FontCache,
+    text_layout::{self, LayoutCache},
+    ui::{
+        AfterLayoutContext, Bump, Element, Event, EventContext, LayoutContext, PaintContext,
+        SizeConstraint,
+    },
+};
+use pathfinder_canvas::{
+    ArcDirection, CanvasRenderingContext2D, ColorF, FillRule, FillStyle, Path2D,
+};
+use pathfinder_color::ColorU;
+use pathfinder_geometry::{
+    rect::RectF,
+    vector::{vec2f, Vector2F},
+};
+use smallvec::SmallVec;
+use std::{
+    cmp::{self, Ordering},
+    sync::Arc,
+};
+
+pub struct BufferElement {
+    view: ViewHandle<BufferView>,
+    layout: Option<LayoutState>,
+    paint: Option<PaintState>,
+}
+
+impl BufferElement {
+    pub fn new(view: ViewHandle<BufferView>) -> Self {
+        Self {
+            view,
+            layout: None,
+            paint: None,
+        }
+    }
+
+    fn mouse_down(
+        &self,
+        position: Vector2F,
+        cmd: bool,
+        ctx: &mut EventContext,
+        app: &AppContext,
+    ) -> bool {
+        let layout = self.layout.as_ref().unwrap();
+        let paint = self.paint.as_ref().unwrap();
+        if paint.text_rect.contains_point(position) {
+            let view = self.view.as_ref(app);
+            let position = paint.point_for_position(view, layout, position, ctx.font_cache, app);
+            ctx.dispatch_action("buffer:select", SelectAction::Begin { position, add: cmd });
+            true
+        } else {
+            false
+        }
+    }
+
+    fn mouse_up(&self, _position: Vector2F, ctx: &mut EventContext, app: &AppContext) -> bool {
+        if self.view.as_ref(app).is_selecting() {
+            ctx.dispatch_action("buffer:select", SelectAction::End);
+            true
+        } else {
+            false
+        }
+    }
+
+    fn mouse_dragged(&self, position: Vector2F, ctx: &mut EventContext, app: &AppContext) -> bool {
+        let view = self.view.as_ref(app);
+        let layout = self.layout.as_ref().unwrap();
+        let paint = self.paint.as_ref().unwrap();
+
+        if view.is_selecting() {
+            let rect = self.paint.as_ref().unwrap().text_rect;
+            let mut scroll_delta = Vector2F::zero();
+
+            let vertical_margin = view.line_height(ctx.font_cache).min(rect.height() / 3.0);
+            let top = rect.origin_y() + vertical_margin;
+            let bottom = rect.lower_left().y() - vertical_margin;
+            if position.y() < top {
+                scroll_delta.set_y(-scale_vertical_mouse_autoscroll_delta(top - position.y()))
+            }
+            if position.y() > bottom {
+                scroll_delta.set_y(scale_vertical_mouse_autoscroll_delta(position.y() - bottom))
+            }
+
+            let horizontal_margin = view.line_height(ctx.font_cache).min(rect.width() / 3.0);
+            let left = rect.origin_x() + horizontal_margin;
+            let right = rect.upper_right().x() - horizontal_margin;
+            if position.x() < left {
+                scroll_delta.set_x(-scale_horizontal_mouse_autoscroll_delta(
+                    left - position.x(),
+                ))
+            }
+            if position.x() > right {
+                scroll_delta.set_x(scale_horizontal_mouse_autoscroll_delta(
+                    position.x() - right,
+                ))
+            }
+
+            ctx.dispatch_action(
+                "buffer:select",
+                SelectAction::Update {
+                    position: paint.point_for_position(view, layout, position, ctx.font_cache, app),
+                    scroll_position: (view.scroll_position() + scroll_delta).clamp(
+                        Vector2F::zero(),
+                        self.layout.as_ref().unwrap().scroll_max(
+                            view,
+                            ctx.font_cache,
+                            ctx.text_layout_cache,
+                            app,
+                        ),
+                    ),
+                },
+            );
+            true
+        } else {
+            false
+        }
+    }
+
+    fn key_down(&self, chars: &str, ctx: &mut EventContext, app: &AppContext) -> bool {
+        if self.view.is_focused(app) {
+            if chars.is_empty() {
+                false
+            } else {
+                if chars.chars().any(|c| c.is_control()) {
+                    false
+                } else {
+                    ctx.dispatch_action("buffer:insert", chars.to_string());
+                    true
+                }
+            }
+        } else {
+            false
+        }
+    }
+
+    fn scroll(
+        &self,
+        position: Vector2F,
+        delta: Vector2F,
+        precise: bool,
+        ctx: &mut EventContext,
+        app: &AppContext,
+    ) -> bool {
+        let paint = self.paint.as_ref().unwrap();
+
+        if !paint.rect.contains_point(position) {
+            return false;
+        }
+
+        if !precise {
+            todo!("still need to handle non-precise scroll events from a mouse wheel");
+        }
+
+        let view = self.view.as_ref(app);
+        let font_cache = &ctx.font_cache;
+        let layout_cache = &ctx.text_layout_cache;
+        let max_glyph_width = view.em_width(font_cache);
+        let line_height = view.line_height(font_cache);
+
+        let x = (view.scroll_position().x() * max_glyph_width - delta.x()) / max_glyph_width;
+        let y = (view.scroll_position().y() * line_height - delta.y()) / line_height;
+        let scroll_position = vec2f(x, y).clamp(
+            Vector2F::zero(),
+            self.layout
+                .as_ref()
+                .unwrap()
+                .scroll_max(view, font_cache, layout_cache, app),
+        );
+
+        ctx.dispatch_action("buffer:scroll", scroll_position);
+
+        true
+    }
+
+    fn paint_gutter(&mut self, rect: RectF, ctx: &mut PaintContext, app: &AppContext) {
+        if let Some(layout) = self.layout.as_ref() {
+            let view = self.view.as_ref(app);
+            let canvas = &mut ctx.canvas;
+            let font_cache = &ctx.font_cache;
+            let line_height = view.line_height(font_cache);
+            let scroll_top = view.scroll_position().y() * line_height;
+
+            canvas.save();
+            canvas.translate(rect.origin());
+            canvas.set_fill_style(FillStyle::Color(ColorU::white()));
+
+            let rect = RectF::new(Vector2F::zero(), rect.size());
+            let mut rect_path = Path2D::new();
+            rect_path.rect(rect);
+            canvas.clip_path(rect_path, FillRule::EvenOdd);
+            canvas.fill_rect(rect);
+
+            for (ix, line) in layout.line_number_layouts.iter().enumerate() {
+                let line_origin = vec2f(
+                    rect.width() - line.width - layout.gutter_padding,
+                    ix as f32 * line_height - (scroll_top % line_height),
+                );
+                line.paint(
+                    line_origin,
+                    rect,
+                    &[(0..line.len, ColorU::black())],
+                    canvas,
+                    font_cache,
+                );
+            }
+
+            canvas.restore();
+        }
+    }
+
+    fn paint_text(&mut self, rect: RectF, ctx: &mut PaintContext, app: &AppContext) {
+        if let Some(layout) = self.layout.as_ref() {
+            let canvas = &mut ctx.canvas;
+            let font_cache = &ctx.font_cache;
+
+            canvas.save();
+            canvas.translate(rect.origin());
+            canvas.set_fill_style(FillStyle::Color(ColorU::white()));
+            let rect = RectF::new(Vector2F::zero(), rect.size());
+            let mut rect_path = Path2D::new();
+            rect_path.rect(rect);
+            canvas.clip_path(rect_path, FillRule::EvenOdd);
+            canvas.fill_rect(rect);
+
+            let view = self.view.as_ref(app);
+            let line_height = view.line_height(font_cache);
+            let descent = view.font_descent(font_cache);
+            let start_row = view.scroll_position().y() as u32;
+            let scroll_top = view.scroll_position().y() * line_height;
+            let end_row = ((scroll_top + rect.height()) / line_height).ceil() as u32 + 1; // Add 1 to ensure selections bleed off screen
+            let max_glyph_width = view.em_width(font_cache);
+            let scroll_left = view.scroll_position().x() * max_glyph_width;
+
+            // Draw selections
+            canvas.save();
+            let corner_radius = 2.5;
+            let mut cursors = SmallVec::<[Cursor; 32]>::new();
+
+            for selection in view.selections_in_range(
+                DisplayPoint::new(start_row, 0)..DisplayPoint::new(end_row, 0),
+                app,
+            ) {
+                if selection.start != selection.end {
+                    let range_start = cmp::min(selection.start, selection.end);
+                    let range_end = cmp::max(selection.start, selection.end);
+                    let row_range = if range_end.column() == 0 {
+                        cmp::max(range_start.row(), start_row)..cmp::min(range_end.row(), end_row)
+                    } else {
+                        cmp::max(range_start.row(), start_row)
+                            ..cmp::min(range_end.row() + 1, end_row)
+                    };
+
+                    let selection = Selection {
+                        line_height,
+                        start_y: row_range.start as f32 * line_height - scroll_top,
+                        lines: row_range
+                            .into_iter()
+                            .map(|row| {
+                                let line_layout = &layout.line_layouts[(row - start_row) as usize];
+                                SelectionLine {
+                                    start_x: if row == range_start.row() {
+                                        line_layout.x_for_index(range_start.column() as usize)
+                                            - scroll_left
+                                            - descent
+                                    } else {
+                                        -scroll_left
+                                    },
+                                    end_x: if row == range_end.row() {
+                                        line_layout.x_for_index(range_end.column() as usize)
+                                            - scroll_left
+                                            - descent
+                                    } else {
+                                        line_layout.width + corner_radius * 2.0
+                                            - scroll_left
+                                            - descent
+                                    },
+                                }
+                            })
+                            .collect(),
+                    };
+
+                    selection.paint(canvas);
+                }
+
+                if view.cursors_visible() {
+                    let cursor_position = selection.end;
+                    if (start_row..end_row).contains(&cursor_position.row()) {
+                        let cursor_row_layout =
+                            &layout.line_layouts[(selection.end.row() - start_row) as usize];
+                        cursors.push(Cursor {
+                            x: cursor_row_layout.x_for_index(selection.end.column() as usize)
+                                - scroll_left
+                                - descent,
+                            y: selection.end.row() as f32 * line_height - scroll_top,
+                            line_height,
+                        });
+                    }
+                }
+            }
+            canvas.restore();
+
+            // Draw glyphs
+
+            canvas.set_fill_style(FillStyle::Color(ColorU::black()));
+
+            for (ix, line) in layout.line_layouts.iter().enumerate() {
+                let row = start_row + ix as u32;
+                let line_origin = vec2f(
+                    -scroll_left - descent,
+                    row as f32 * line_height - scroll_top,
+                );
+
+                line.paint(
+                    line_origin,
+                    rect,
+                    &[(0..line.len, ColorU::black())],
+                    canvas,
+                    font_cache,
+                );
+            }
+
+            for cursor in cursors {
+                cursor.paint(canvas);
+            }
+
+            canvas.restore()
+        }
+    }
+}
+
+impl<'a> Element<'a> for BufferElement {
+    fn layout(
+        &mut self,
+        constraint: SizeConstraint,
+        _: &'a Bump,
+        ctx: &mut LayoutContext,
+        app: &AppContext,
+    ) -> Vector2F {
+        let mut size = constraint.max;
+        if size.y().is_infinite() {
+            let view = self.view.as_ref(app);
+            size.set_y((view.max_point(app).row() + 1) as f32 * view.line_height(ctx.font_cache));
+        }
+        if size.x().is_infinite() {
+            unimplemented!("we don't yet handle an infinite width constraint on buffer elements");
+        }
+
+        let view = self.view.as_ref(app);
+        let font_cache = &ctx.font_cache;
+        let layout_cache = &ctx.text_layout_cache;
+        let line_height = view.line_height(font_cache);
+
+        let gutter_padding;
+        let gutter_width;
+        if view.is_gutter_visible() {
+            gutter_padding = view.em_width(ctx.font_cache);
+            match view.max_line_number_width(ctx.font_cache, ctx.text_layout_cache, app) {
+                Err(error) => {
+                    log::error!("error computing max line number width: {}", error);
+                    return size;
+                }
+                Ok(width) => gutter_width = width + gutter_padding * 2.0,
+            }
+        } else {
+            gutter_padding = 0.0;
+            gutter_width = 0.0
+        };
+
+        let gutter_size = vec2f(gutter_width, size.y());
+        let text_size = size - vec2f(gutter_width, 0.0);
+
+        let autoscroll_horizontally = view.autoscroll_vertically(size.y(), line_height, app);
+
+        let line_number_layouts = if view.is_gutter_visible() {
+            match view.layout_line_numbers(size.y(), ctx.font_cache, ctx.text_layout_cache, app) {
+                Err(error) => {
+                    log::error!("error laying out line numbers: {}", error);
+                    return size;
+                }
+                Ok(layouts) => layouts,
+            }
+        } else {
+            Vec::new()
+        };
+
+        let start_row = view.scroll_position().y() as u32;
+        let scroll_top = view.scroll_position().y() * line_height;
+        let end_row = ((scroll_top + size.y()) / line_height).ceil() as u32 + 1; // Add 1 to ensure selections bleed off screen
+
+        let mut max_visible_line_width = 0.0;
+        let line_layouts =
+            match view.layout_lines(start_row..end_row, font_cache, layout_cache, app) {
+                Err(error) => {
+                    log::error!("error laying out lines: {}", error);
+                    return size;
+                }
+                Ok(layouts) => {
+                    for line in &layouts {
+                        if line.width > max_visible_line_width {
+                            max_visible_line_width = line.width;
+                        }
+                    }
+
+                    layouts
+                }
+            };
+
+        self.layout = Some(LayoutState {
+            size,
+            gutter_size,
+            gutter_padding,
+            text_size,
+            line_layouts,
+            line_number_layouts,
+            max_visible_line_width,
+            autoscroll_horizontally,
+        });
+
+        size
+    }
+
+    fn after_layout(&mut self, ctx: &mut AfterLayoutContext, app: &mut MutableAppContext) {
+        let layout = self.layout.as_ref().unwrap();
+
+        let view = self.view.as_ref(app);
+        view.clamp_scroll_left(
+            layout
+                .scroll_max(view, ctx.font_cache, ctx.text_layout_cache, app.ctx())
+                .x(),
+        );
+
+        if layout.autoscroll_horizontally {
+            view.autoscroll_horizontally(
+                view.scroll_position().y() as u32,
+                layout.text_size.x(),
+                layout.scroll_width(view, ctx.font_cache, ctx.text_layout_cache, app.ctx()),
+                view.em_width(ctx.font_cache),
+                &layout.line_layouts,
+                app.ctx(),
+            );
+        }
+    }
+
+    fn paint(&mut self, origin: Vector2F, ctx: &mut PaintContext, app: &AppContext) {
+        let rect;
+        let gutter_rect;
+        let text_rect;
+        {
+            let layout = self.layout.as_ref().unwrap();
+            rect = RectF::new(origin, layout.size);
+            gutter_rect = RectF::new(origin, layout.gutter_size);
+            text_rect = RectF::new(
+                origin + vec2f(layout.gutter_size.x(), 0.0),
+                layout.text_size,
+            );
+        }
+
+        if self.view.as_ref(app).is_gutter_visible() {
+            self.paint_gutter(gutter_rect, ctx, app);
+        }
+        self.paint_text(text_rect, ctx, app);
+
+        self.paint = Some(PaintState { rect, text_rect });
+    }
+
+    fn dispatch_event(&self, event: &Event, ctx: &mut EventContext, app: &AppContext) -> bool {
+        match event {
+            Event::LeftMouseDown { position, cmd } => self.mouse_down(*position, *cmd, ctx, app),
+            Event::LeftMouseUp { position } => self.mouse_up(*position, ctx, app),
+            Event::LeftMouseDragged { position } => self.mouse_dragged(*position, ctx, app),
+            Event::ScrollWheel {
+                position,
+                delta,
+                precise,
+            } => self.scroll(*position, *delta, *precise, ctx, app),
+            Event::KeyDown { chars, .. } => self.key_down(chars, ctx, app),
+        }
+    }
+
+    fn size(&self) -> Option<pathfinder_canvas::Vector2F> {
+        self.layout.as_ref().map(|layout| layout.size)
+    }
+}
+
+struct LayoutState {
+    size: Vector2F,
+    gutter_size: Vector2F,
+    gutter_padding: f32,
+    text_size: Vector2F,
+    line_layouts: Vec<Arc<text_layout::Line>>,
+    line_number_layouts: Vec<Arc<text_layout::Line>>,
+    max_visible_line_width: f32,
+    autoscroll_horizontally: bool,
+}
+
+impl LayoutState {
+    fn scroll_width(
+        &self,
+        view: &BufferView,
+        font_cache: &FontCache,
+        layout_cache: &LayoutCache,
+        app: &AppContext,
+    ) -> f32 {
+        let row = view.rightmost_point(app).row();
+        let longest_line_width = view
+            .layout_line(row, font_cache, layout_cache, app)
+            .unwrap()
+            .width;
+        longest_line_width.max(self.max_visible_line_width) + view.em_width(font_cache)
+    }
+
+    fn scroll_max(
+        &self,
+        view: &BufferView,
+        font_cache: &FontCache,
+        layout_cache: &LayoutCache,
+        app: &AppContext,
+    ) -> Vector2F {
+        vec2f(
+            ((self.scroll_width(view, font_cache, layout_cache, app) - self.text_size.x())
+                / view.em_width(font_cache))
+            .max(0.0),
+            view.max_point(app).row().saturating_sub(1) as f32,
+        )
+    }
+}
+
+struct PaintState {
+    rect: RectF,
+    text_rect: RectF,
+}
+
+impl PaintState {
+    fn point_for_position(
+        &self,
+        view: &BufferView,
+        layout: &LayoutState,
+        position: Vector2F,
+        font_cache: &FontCache,
+        app: &AppContext,
+    ) -> DisplayPoint {
+        let scroll_position = view.scroll_position();
+        let position = position - self.text_rect.origin();
+        let y = position.y().max(0.0).min(layout.size.y());
+        let row = ((y / view.line_height(font_cache)) + scroll_position.y()) as u32;
+        let row = cmp::min(row, view.max_point(app).row());
+        let line = &layout.line_layouts[(row - scroll_position.y() as u32) as usize];
+        let x = position.x() + (scroll_position.x() * view.em_width(font_cache));
+
+        let column = if x >= 0.0 {
+            line.index_for_x(x)
+                .map(|ix| ix as u32)
+                .unwrap_or(view.line_len(row, app).unwrap())
+        } else {
+            0
+        };
+
+        DisplayPoint::new(row, column)
+    }
+}
+
+struct Cursor {
+    x: f32,
+    y: f32,
+    line_height: f32,
+}
+
+impl Cursor {
+    fn paint(&self, canvas: &mut CanvasRenderingContext2D) {
+        canvas.set_fill_style(FillStyle::Color(ColorU::black()));
+        canvas.fill_rect(RectF::new(
+            vec2f(self.x, self.y),
+            vec2f(2.0, self.line_height),
+        ));
+    }
+}
+
+#[derive(Debug)]
+struct Selection {
+    start_y: f32,
+    line_height: f32,
+    lines: Vec<SelectionLine>,
+}
+
+#[derive(Debug)]
+struct SelectionLine {
+    start_x: f32,
+    end_x: f32,
+}
+
+impl Selection {
+    fn paint(&self, canvas: &mut CanvasRenderingContext2D) {
+        if self.lines.len() >= 2 && self.lines[0].start_x > self.lines[1].end_x {
+            self.paint_lines(self.start_y, &self.lines[0..1], canvas);
+            self.paint_lines(self.start_y + self.line_height, &self.lines[1..], canvas);
+        } else {
+            self.paint_lines(self.start_y, &self.lines, canvas);
+        }
+    }
+
+    fn paint_lines(
+        &self,
+        start_y: f32,
+        lines: &[SelectionLine],
+        canvas: &mut CanvasRenderingContext2D,
+    ) {
+        use Direction::*;
+
+        if lines.is_empty() {
+            return;
+        }
+
+        let mut path = Path2D::new();
+        let corner_radius = 0.08 * self.line_height;
+
+        let first_line = lines.first().unwrap();
+        let last_line = lines.last().unwrap();
+
+        let corner = vec2f(first_line.end_x, start_y);
+        path.move_to(corner - vec2f(corner_radius, 0.0));
+        rounded_corner(&mut path, corner, corner_radius, Right, Down);
+
+        let mut iter = lines.iter().enumerate().peekable();
+        while let Some((ix, line)) = iter.next() {
+            let corner = vec2f(line.end_x, start_y + (ix + 1) as f32 * self.line_height);
+
+            if let Some((_, next_line)) = iter.peek() {
+                let next_corner = vec2f(next_line.end_x, corner.y());
+
+                match next_corner.x().partial_cmp(&corner.x()).unwrap() {
+                    Ordering::Equal => {
+                        path.line_to(corner);
+                    }
+                    Ordering::Less => {
+                        path.line_to(corner - vec2f(0.0, corner_radius));
+                        rounded_corner(&mut path, corner, corner_radius, Down, Left);
+                        path.line_to(next_corner + vec2f(corner_radius, 0.0));
+                        rounded_corner(&mut path, next_corner, corner_radius, Left, Down);
+                    }
+                    Ordering::Greater => {
+                        path.line_to(corner - vec2f(0.0, corner_radius));
+                        rounded_corner(&mut path, corner, corner_radius, Down, Right);
+                        path.line_to(next_corner - vec2f(corner_radius, 0.0));
+                        rounded_corner(&mut path, next_corner, corner_radius, Right, Down);
+                    }
+                }
+            } else {
+                path.line_to(corner - vec2f(0.0, corner_radius));
+                rounded_corner(&mut path, corner, corner_radius, Down, Left);
+
+                let corner = vec2f(line.start_x, corner.y());
+                path.line_to(corner + vec2f(corner_radius, 0.0));
+                rounded_corner(&mut path, corner, corner_radius, Left, Up);
+            }
+        }
+
+        if first_line.start_x > last_line.start_x {
+            let corner = vec2f(last_line.start_x, start_y + self.line_height);
+            path.line_to(corner + vec2f(0.0, corner_radius));
+            rounded_corner(&mut path, corner, corner_radius, Up, Right);
+            let corner = vec2f(first_line.start_x, corner.y());
+            path.line_to(corner - vec2f(corner_radius, 0.0));
+            rounded_corner(&mut path, corner, corner_radius, Right, Up);
+        }
+
+        let corner = vec2f(first_line.start_x, start_y);
+        path.line_to(corner + vec2f(0.0, corner_radius));
+        rounded_corner(&mut path, corner, corner_radius, Up, Right);
+        path.close_path();
+
+        canvas.set_fill_style(FillStyle::Color(
+            ColorF::new(0.639, 0.839, 1.0, 1.0).to_u8(),
+        ));
+        canvas.fill_path(path, FillRule::Winding);
+    }
+}
+
+enum Direction {
+    Up,
+    Down,
+    Left,
+    Right,
+}
+
+fn rounded_corner(
+    path: &mut Path2D,
+    corner: Vector2F,
+    radius: f32,
+    incoming: Direction,
+    outgoing: Direction,
+) {
+    use std::f32::consts::PI;
+    use Direction::*;
+
+    match (incoming, outgoing) {
+        (Down, Right) => path.arc(
+            corner + vec2f(radius, -radius),
+            radius,
+            1.0 * PI,
+            0.5 * PI,
+            ArcDirection::CCW,
+        ),
+        (Down, Left) => path.arc(
+            corner + vec2f(-radius, -radius),
+            radius,
+            0.0,
+            0.5 * PI,
+            ArcDirection::CW,
+        ),
+        (Up, Right) => path.arc(
+            corner + vec2f(radius, radius),
+            radius,
+            1.0 * PI,
+            1.5 * PI,
+            ArcDirection::CW,
+        ),
+        (Up, Left) => path.arc(
+            corner + vec2f(-radius, radius),
+            radius,
+            0.0,
+            1.5 * PI,
+            ArcDirection::CCW,
+        ),
+        (Right, Up) => path.arc(
+            corner + vec2f(-radius, -radius),
+            radius,
+            0.5 * PI,
+            0.0,
+            ArcDirection::CCW,
+        ),
+        (Right, Down) => path.arc(
+            corner + vec2f(-radius, radius),
+            radius,
+            1.5 * PI,
+            2.0 * PI,
+            ArcDirection::CW,
+        ),
+        (Left, Up) => path.arc(
+            corner + vec2f(radius, -radius),
+            radius,
+            0.5 * PI,
+            PI,
+            ArcDirection::CW,
+        ),
+        (Left, Down) => path.arc(
+            corner + vec2f(radius, radius),
+            radius,
+            1.5 * PI,
+            PI,
+            ArcDirection::CCW,
+        ),
+        _ => panic!("invalid incoming and outgoing directions for a corner"),
+    }
+}
+
+fn scale_vertical_mouse_autoscroll_delta(delta: f32) -> f32 {
+    delta.powf(1.5) / 100.0
+}
+
+fn scale_horizontal_mouse_autoscroll_delta(delta: f32) -> f32 {
+    delta.powf(1.2) / 300.0
+}

zed/src/editor/buffer_view.rs 🔗

@@ -0,0 +1,1521 @@
+use super::{
+    buffer, movement, Anchor, Bias, Buffer, BufferElement, DisplayMap, DisplayPoint, Point,
+    ToOffset, ToPoint,
+};
+use crate::{
+    app::{self as app, App, AppContext, ModelHandle, ViewContext, WeakViewHandle},
+    fonts::FontCache,
+    keymap::Binding,
+    settings::Settings,
+    text_layout,
+    ui::elements::*,
+    watch, workspace,
+};
+use anyhow::Result;
+use easy_parallel::Parallel;
+use font_kit::properties::Properties as FontProperties;
+use parking_lot::Mutex;
+use pathfinder_geometry::vector::Vector2F;
+use smallvec::SmallVec;
+use smol::Timer;
+use std::{
+    cmp::{self, Ordering},
+    fmt::Write,
+    mem,
+    ops::Range,
+    sync::Arc,
+    time::Duration,
+};
+use text_layout::LayoutCache;
+
+const CURSOR_BLINK_INTERVAL: Duration = Duration::from_millis(500);
+
+pub fn init(app: &mut App) {
+    app.add_bindings(vec![
+        Binding::new("backspace", "buffer:backspace", Some("BufferView")),
+        Binding::new("enter", "buffer:newline", Some("BufferView")),
+        Binding::new("up", "buffer:move_up", Some("BufferView")),
+        Binding::new("down", "buffer:move_down", Some("BufferView")),
+        Binding::new("left", "buffer:move_left", Some("BufferView")),
+        Binding::new("right", "buffer:move_right", Some("BufferView")),
+        Binding::new("shift-up", "buffer:select_up", Some("BufferView")),
+        Binding::new("shift-down", "buffer:select_down", Some("BufferView")),
+        Binding::new("shift-left", "buffer:select_left", Some("BufferView")),
+        Binding::new("shift-right", "buffer:select_right", Some("BufferView")),
+        Binding::new("pageup", "buffer:page_up", Some("BufferView")),
+        Binding::new("pagedown", "buffer:page_down", Some("BufferView")),
+        Binding::new("alt-cmd-[", "buffer:fold", Some("BufferView")),
+        Binding::new("alt-cmd-]", "buffer:unfold", Some("BufferView")),
+        Binding::new(
+            "alt-cmd-f",
+            "buffer:fold_selected_ranges",
+            Some("BufferView"),
+        ),
+    ]);
+
+    app.add_action("buffer:scroll", BufferView::scroll);
+    app.add_action("buffer:select", BufferView::select);
+    app.add_action("buffer:insert", BufferView::insert);
+    app.add_action("buffer:newline", BufferView::newline);
+    app.add_action("buffer:backspace", BufferView::backspace);
+    app.add_action("buffer:move_up", BufferView::move_up);
+    app.add_action("buffer:move_down", BufferView::move_down);
+    app.add_action("buffer:move_left", BufferView::move_left);
+    app.add_action("buffer:move_right", BufferView::move_right);
+    app.add_action("buffer:select_up", BufferView::select_up);
+    app.add_action("buffer:select_down", BufferView::select_down);
+    app.add_action("buffer:select_left", BufferView::select_left);
+    app.add_action("buffer:select_right", BufferView::select_right);
+    app.add_action("buffer:page_up", BufferView::page_up);
+    app.add_action("buffer:page_down", BufferView::page_down);
+    app.add_action("buffer:fold", BufferView::fold);
+    app.add_action("buffer:unfold", BufferView::unfold);
+    app.add_action(
+        "buffer:fold_selected_ranges",
+        BufferView::fold_selected_ranges,
+    );
+}
+
+pub enum SelectAction {
+    Begin {
+        position: DisplayPoint,
+        add: bool,
+    },
+    Update {
+        position: DisplayPoint,
+        scroll_position: Vector2F,
+    },
+    End,
+}
+
+impl workspace::Item for Buffer {
+    type View = BufferView;
+
+    fn build_view(
+        buffer: ModelHandle<Self>,
+        settings: watch::Receiver<Settings>,
+        ctx: &mut ViewContext<Self::View>,
+    ) -> Self::View {
+        BufferView::for_buffer(buffer, settings, ctx)
+    }
+}
+
+pub struct BufferView {
+    handle: WeakViewHandle<Self>,
+    buffer: ModelHandle<Buffer>,
+    display_map: ModelHandle<DisplayMap>,
+    selections: Vec<Selection>,
+    pending_selection: Option<Selection>,
+    scroll_position: Mutex<Vector2F>,
+    autoscroll_requested: Mutex<bool>,
+    settings: watch::Receiver<Settings>,
+    focused: bool,
+    cursors_visible: bool,
+    blink_epoch: usize,
+    blinking_paused: bool,
+    single_line: bool,
+}
+
+impl BufferView {
+    pub fn single_line(settings: watch::Receiver<Settings>, ctx: &mut ViewContext<Self>) -> Self {
+        let buffer = ctx.add_model(|_| Buffer::new(0, String::new()));
+        let mut view = Self::for_buffer(buffer, settings, ctx);
+        view.single_line = true;
+        view
+    }
+
+    pub fn for_buffer(
+        buffer: ModelHandle<Buffer>,
+        settings: watch::Receiver<Settings>,
+        ctx: &mut ViewContext<Self>,
+    ) -> Self {
+        settings.notify_view_on_change(ctx);
+
+        ctx.observe(&buffer, Self::on_buffer_changed);
+        ctx.subscribe_to_model(&buffer, Self::on_buffer_event);
+        let display_map = ctx.add_model(|ctx| {
+            DisplayMap::new(
+                buffer.clone(),
+                smol::block_on(settings.read()).tab_size,
+                ctx,
+            )
+        });
+        ctx.observe(&display_map, Self::on_display_map_changed);
+
+        let buffer_ref = buffer.as_ref(ctx);
+        Self {
+            handle: ctx.handle(),
+            buffer,
+            display_map,
+            selections: vec![Selection {
+                start: buffer_ref.anchor_before(0).unwrap(),
+                end: buffer_ref.anchor_before(0).unwrap(),
+                reversed: false,
+                goal_column: None,
+            }],
+            pending_selection: None,
+            scroll_position: Mutex::new(Vector2F::zero()),
+            autoscroll_requested: Mutex::new(false),
+            settings,
+            focused: false,
+            cursors_visible: false,
+            blink_epoch: 0,
+            blinking_paused: false,
+            single_line: false,
+        }
+    }
+
+    pub fn buffer(&self) -> &ModelHandle<Buffer> {
+        &self.buffer
+    }
+
+    pub fn is_gutter_visible(&self) -> bool {
+        !self.single_line
+    }
+
+    fn scroll(&mut self, scroll_position: &Vector2F, ctx: &mut ViewContext<Self>) {
+        *self.scroll_position.lock() = *scroll_position;
+        ctx.notify();
+    }
+
+    pub fn scroll_position(&self) -> Vector2F {
+        *self.scroll_position.lock()
+    }
+
+    pub fn clamp_scroll_left(&self, max: f32) {
+        let mut scroll_position = self.scroll_position.lock();
+        let scroll_left = scroll_position.x();
+        scroll_position.set_x(scroll_left.min(max));
+    }
+
+    pub fn autoscroll_vertically(
+        &self,
+        viewport_height: f32,
+        line_height: f32,
+        app: &AppContext,
+    ) -> bool {
+        let mut scroll_position = self.scroll_position.lock();
+        let scroll_top = scroll_position.y();
+        scroll_position.set_y(scroll_top.min(self.max_point(app).row().saturating_sub(1) as f32));
+
+        let mut autoscroll_requested = self.autoscroll_requested.lock();
+        if *autoscroll_requested {
+            *autoscroll_requested = false;
+        } else {
+            return false;
+        }
+
+        let map = self.display_map.as_ref(app);
+        let visible_lines = viewport_height / line_height;
+        let first_cursor_top = self
+            .selections
+            .first()
+            .unwrap()
+            .head()
+            .to_display_point(map, app)
+            .unwrap()
+            .row() as f32;
+        let last_cursor_bottom = self
+            .selections
+            .last()
+            .unwrap()
+            .head()
+            .to_display_point(map, app)
+            .unwrap()
+            .row() as f32
+            + 1.0;
+
+        let margin = ((visible_lines - (last_cursor_bottom - first_cursor_top)) / 2.0)
+            .floor()
+            .min(3.0);
+        if margin < 0.0 {
+            return false;
+        }
+
+        let target_top = (first_cursor_top - margin).max(0.0);
+        let target_bottom = last_cursor_bottom + margin;
+        let start_row = scroll_position.y();
+        let end_row = start_row + visible_lines;
+
+        if target_top < start_row {
+            scroll_position.set_y(target_top);
+        } else if target_bottom >= end_row {
+            scroll_position.set_y(target_bottom - visible_lines);
+        }
+
+        true
+    }
+
+    pub fn autoscroll_horizontally(
+        &self,
+        start_row: u32,
+        viewport_width: f32,
+        scroll_width: f32,
+        max_glyph_width: f32,
+        layouts: &[Arc<text_layout::Line>],
+        app: &AppContext,
+    ) {
+        let map = self.display_map.as_ref(app);
+
+        let mut target_left = std::f32::INFINITY;
+        let mut target_right = 0.0_f32;
+        for selection in &self.selections {
+            let head = selection.head().to_display_point(map, app).unwrap();
+            let start_column = head.column().saturating_sub(3);
+            let end_column = cmp::min(map.line_len(head.row(), app).unwrap(), head.column() + 3);
+            target_left = target_left
+                .min(layouts[(head.row() - start_row) as usize].x_for_index(start_column as usize));
+            target_right = target_right.max(
+                layouts[(head.row() - start_row) as usize].x_for_index(end_column as usize)
+                    + max_glyph_width,
+            );
+        }
+        target_right = target_right.min(scroll_width);
+
+        if target_right - target_left > viewport_width {
+            return;
+        }
+
+        let mut scroll_position = self.scroll_position.lock();
+        let scroll_left = scroll_position.x() * max_glyph_width;
+        let scroll_right = scroll_left + viewport_width;
+
+        if target_left < scroll_left {
+            scroll_position.set_x(target_left / max_glyph_width);
+        } else if target_right > scroll_right {
+            scroll_position.set_x((target_right - viewport_width) / max_glyph_width);
+        }
+    }
+
+    fn select(&mut self, arg: &SelectAction, ctx: &mut ViewContext<Self>) {
+        match arg {
+            SelectAction::Begin { position, add } => self.begin_selection(*position, *add, ctx),
+            SelectAction::Update {
+                position,
+                scroll_position,
+            } => self.update_selection(*position, *scroll_position, ctx),
+            SelectAction::End => self.end_selection(ctx),
+        }
+    }
+
+    fn begin_selection(&mut self, position: DisplayPoint, add: bool, ctx: &mut ViewContext<Self>) {
+        if !self.focused {
+            ctx.focus_self();
+            ctx.emit(Event::Activate);
+        }
+
+        let display_map = self.display_map.as_ref(ctx);
+        let cursor = display_map
+            .anchor_before(position, Bias::Left, ctx.app())
+            .unwrap();
+        let selection = Selection {
+            start: cursor.clone(),
+            end: cursor,
+            reversed: false,
+            goal_column: None,
+        };
+
+        if !add {
+            self.selections.clear();
+        }
+        self.pending_selection = Some(selection);
+
+        ctx.notify();
+    }
+
+    fn update_selection(
+        &mut self,
+        position: DisplayPoint,
+        scroll_position: Vector2F,
+        ctx: &mut ViewContext<Self>,
+    ) {
+        let buffer = self.buffer.as_ref(ctx);
+        let map = self.display_map.as_ref(ctx);
+        let cursor = map.anchor_before(position, Bias::Left, ctx.app()).unwrap();
+        if let Some(selection) = self.pending_selection.as_mut() {
+            selection.set_head(buffer, cursor);
+        } else {
+            log::error!("update_selection dispatched with no pending selection");
+            return;
+        }
+
+        *self.scroll_position.lock() = scroll_position;
+
+        ctx.notify();
+    }
+
+    fn end_selection(&mut self, ctx: &mut ViewContext<Self>) {
+        if let Some(selection) = self.pending_selection.take() {
+            let ix = self.selection_insertion_index(&selection.start, ctx.app());
+            self.selections.insert(ix, selection);
+            self.merge_selections(ctx);
+            ctx.notify();
+        } else {
+            log::error!("end_selection dispatched with no pending selection");
+        }
+    }
+
+    pub fn is_selecting(&self) -> bool {
+        self.pending_selection.is_some()
+    }
+
+    #[cfg(test)]
+    fn select_ranges<T>(&mut self, ranges: T, ctx: &mut ViewContext<Self>) -> Result<()>
+    where
+        T: IntoIterator<Item = Range<DisplayPoint>>,
+    {
+        let buffer = self.buffer.as_ref(ctx);
+        let map = self.display_map.as_ref(ctx);
+        let mut selections = Vec::new();
+        for range in ranges {
+            selections.push(Selection {
+                start: map.anchor_after(range.start, Bias::Left, ctx.app())?,
+                end: map.anchor_before(range.end, Bias::Left, ctx.app())?,
+                reversed: false,
+                goal_column: None,
+            });
+        }
+        selections.sort_unstable_by(|a, b| a.start.cmp(&b.start, buffer).unwrap());
+        self.selections = selections;
+        self.merge_selections(ctx);
+        ctx.notify();
+        Ok(())
+    }
+
+    fn insert(&mut self, text: &String, ctx: &mut ViewContext<Self>) {
+        let buffer = self.buffer.as_ref(ctx);
+        let mut offset_ranges = SmallVec::<[Range<usize>; 32]>::new();
+        for selection in &self.selections {
+            let start = selection.start.to_offset(buffer).unwrap();
+            let end = selection.end.to_offset(buffer).unwrap();
+            offset_ranges.push(start..end);
+        }
+
+        self.buffer.update(ctx, |buffer, ctx| {
+            if let Err(error) = buffer.edit(offset_ranges.iter().cloned(), text.as_str(), Some(ctx))
+            {
+                log::error!("error inserting text: {}", error);
+            };
+        });
+
+        let buffer = self.buffer.as_ref(ctx);
+        let char_count = text.chars().count() as isize;
+        let mut delta = 0_isize;
+        self.selections = offset_ranges
+            .into_iter()
+            .map(|range| {
+                let start = range.start as isize;
+                let end = range.end as isize;
+                let anchor = buffer
+                    .anchor_before((start + delta + char_count) as usize)
+                    .unwrap();
+                let deleted_count = end - start;
+                delta += char_count - deleted_count;
+                Selection {
+                    start: anchor.clone(),
+                    end: anchor,
+                    reversed: false,
+                    goal_column: None,
+                }
+            })
+            .collect();
+
+        self.pause_cursor_blinking(ctx);
+        *self.autoscroll_requested.lock() = true;
+    }
+
+    fn newline(&mut self, _: &(), ctx: &mut ViewContext<Self>) {
+        if self.single_line {
+            ctx.propagate_action();
+        } else {
+            self.insert(&"\n".into(), ctx);
+        }
+    }
+
+    pub fn backspace(&mut self, _: &(), ctx: &mut ViewContext<Self>) {
+        self.select_left(&(), ctx);
+        self.insert(&String::new(), ctx);
+    }
+
+    pub fn move_left(&mut self, _: &(), ctx: &mut ViewContext<Self>) {
+        {
+            let app = ctx.app();
+            let map = self.display_map.as_ref(ctx);
+            for selection in &mut self.selections {
+                let start = selection.start.to_display_point(map, app).unwrap();
+                let end = selection.end.to_display_point(map, app).unwrap();
+
+                if start != end {
+                    selection.end = selection.start.clone();
+                } else {
+                    let cursor = map
+                        .anchor_before(movement::left(map, start, app).unwrap(), Bias::Left, app)
+                        .unwrap();
+                    selection.start = cursor.clone();
+                    selection.end = cursor;
+                }
+                selection.reversed = false;
+                selection.goal_column = None;
+            }
+        }
+        self.changed_selections(ctx);
+    }
+
+    pub fn select_left(&mut self, _: &(), ctx: &mut ViewContext<Self>) {
+        {
+            let buffer = self.buffer.as_ref(ctx);
+            let map = self.display_map.as_ref(ctx);
+            for selection in &mut self.selections {
+                let head = selection.head().to_display_point(map, ctx.app()).unwrap();
+                let cursor = map
+                    .anchor_before(
+                        movement::left(map, head, ctx.app()).unwrap(),
+                        Bias::Left,
+                        ctx.app(),
+                    )
+                    .unwrap();
+                selection.set_head(&buffer, cursor);
+                selection.goal_column = None;
+            }
+        }
+        self.changed_selections(ctx);
+    }
+
+    pub fn move_right(&mut self, _: &(), ctx: &mut ViewContext<Self>) {
+        {
+            let app = ctx.app();
+            let map = self.display_map.as_ref(app);
+            for selection in &mut self.selections {
+                let start = selection.start.to_display_point(map, app).unwrap();
+                let end = selection.end.to_display_point(map, app).unwrap();
+
+                if start != end {
+                    selection.start = selection.end.clone();
+                } else {
+                    let cursor = map
+                        .anchor_before(movement::right(map, end, app).unwrap(), Bias::Right, app)
+                        .unwrap();
+                    selection.start = cursor.clone();
+                    selection.end = cursor;
+                }
+                selection.reversed = false;
+                selection.goal_column = None;
+            }
+        }
+        self.changed_selections(ctx);
+    }
+
+    pub fn select_right(&mut self, _: &(), ctx: &mut ViewContext<Self>) {
+        {
+            let buffer = self.buffer.as_ref(ctx);
+            let app = ctx.app();
+            let map = self.display_map.as_ref(app);
+            for selection in &mut self.selections {
+                let head = selection.head().to_display_point(map, ctx.app()).unwrap();
+                let cursor = map
+                    .anchor_before(movement::right(map, head, app).unwrap(), Bias::Right, app)
+                    .unwrap();
+                selection.set_head(&buffer, cursor);
+                selection.goal_column = None;
+            }
+        }
+        self.changed_selections(ctx);
+    }
+
+    pub fn move_up(&mut self, _: &(), ctx: &mut ViewContext<Self>) {
+        if self.single_line {
+            ctx.propagate_action();
+        } else {
+            let app = ctx.app();
+            let map = self.display_map.as_ref(app);
+            for selection in &mut self.selections {
+                let start = selection.start.to_display_point(map, app).unwrap();
+                let end = selection.end.to_display_point(map, app).unwrap();
+                if start != end {
+                    selection.goal_column = None;
+                }
+
+                let (start, goal_column) =
+                    movement::up(map, start, selection.goal_column, app).unwrap();
+                let cursor = map.anchor_before(start, Bias::Left, app).unwrap();
+                selection.start = cursor.clone();
+                selection.end = cursor;
+                selection.goal_column = goal_column;
+                selection.reversed = false;
+            }
+            self.changed_selections(ctx);
+        }
+    }
+
+    pub fn select_up(&mut self, _: &(), ctx: &mut ViewContext<Self>) {
+        if self.single_line {
+            ctx.propagate_action();
+        } else {
+            let app = ctx.app();
+            let buffer = self.buffer.as_ref(app);
+            let map = self.display_map.as_ref(app);
+            for selection in &mut self.selections {
+                let head = selection.head().to_display_point(map, app).unwrap();
+                let (head, goal_column) =
+                    movement::up(map, head, selection.goal_column, app).unwrap();
+                selection.set_head(&buffer, map.anchor_before(head, Bias::Left, app).unwrap());
+                selection.goal_column = goal_column;
+            }
+            self.changed_selections(ctx);
+        }
+    }
+
+    pub fn move_down(&mut self, _: &(), ctx: &mut ViewContext<Self>) {
+        if self.single_line {
+            ctx.propagate_action();
+        } else {
+            let app = ctx.app();
+            let map = self.display_map.as_ref(app);
+            for selection in &mut self.selections {
+                let start = selection.start.to_display_point(map, app).unwrap();
+                let end = selection.end.to_display_point(map, app).unwrap();
+                if start != end {
+                    selection.goal_column = None;
+                }
+
+                let (start, goal_column) =
+                    movement::down(map, end, selection.goal_column, app).unwrap();
+                let cursor = map.anchor_before(start, Bias::Right, app).unwrap();
+                selection.start = cursor.clone();
+                selection.end = cursor;
+                selection.goal_column = goal_column;
+                selection.reversed = false;
+            }
+            self.changed_selections(ctx);
+        }
+    }
+
+    pub fn select_down(&mut self, _: &(), ctx: &mut ViewContext<Self>) {
+        if self.single_line {
+            ctx.propagate_action();
+        } else {
+            let app = ctx.app();
+            let buffer = self.buffer.as_ref(ctx);
+            let map = self.display_map.as_ref(ctx);
+            for selection in &mut self.selections {
+                let head = selection.head().to_display_point(map, app).unwrap();
+                let (head, goal_column) =
+                    movement::down(map, head, selection.goal_column, app).unwrap();
+                selection.set_head(&buffer, map.anchor_before(head, Bias::Right, app).unwrap());
+                selection.goal_column = goal_column;
+            }
+            self.changed_selections(ctx);
+        }
+    }
+
+    pub fn changed_selections(&mut self, ctx: &mut ViewContext<Self>) {
+        self.merge_selections(ctx);
+        self.pause_cursor_blinking(ctx);
+        *self.autoscroll_requested.lock() = true;
+        ctx.notify();
+    }
+
+    fn merge_selections<A: app::ModelAsRef>(&mut self, ctx: &A) {
+        let buffer = self.buffer.as_ref(ctx);
+        let mut i = 1;
+        while i < self.selections.len() {
+            if self.selections[i - 1]
+                .end
+                .cmp(&self.selections[i].start, buffer)
+                .unwrap()
+                >= Ordering::Equal
+            {
+                let removed = self.selections.remove(i);
+                if removed
+                    .start
+                    .cmp(&self.selections[i - 1].start, buffer)
+                    .unwrap()
+                    < Ordering::Equal
+                {
+                    self.selections[i - 1].start = removed.start;
+                }
+                if removed
+                    .end
+                    .cmp(&self.selections[i - 1].end, buffer)
+                    .unwrap()
+                    > Ordering::Equal
+                {
+                    self.selections[i - 1].end = removed.end;
+                }
+            } else {
+                i += 1;
+            }
+        }
+    }
+
+    pub fn first_selection(&self, app: &AppContext) -> Range<DisplayPoint> {
+        self.selections
+            .first()
+            .unwrap()
+            .display_range(self.display_map.as_ref(app), app)
+    }
+
+    pub fn last_selection(&self, app: &AppContext) -> Range<DisplayPoint> {
+        self.selections
+            .last()
+            .unwrap()
+            .display_range(self.display_map.as_ref(app), app)
+    }
+
+    pub fn selections_in_range<'a>(
+        &'a self,
+        range: Range<DisplayPoint>,
+        app: &'a AppContext,
+    ) -> impl 'a + Iterator<Item = Range<DisplayPoint>> {
+        let map = self.display_map.as_ref(app);
+
+        let start = map.anchor_before(range.start, Bias::Left, app).unwrap();
+        let start_index = self.selection_insertion_index(&start, app);
+        let pending_selection = self.pending_selection.as_ref().and_then(|s| {
+            let selection_range = s.display_range(map, app);
+            if selection_range.start <= range.end || selection_range.end <= range.end {
+                Some(selection_range)
+            } else {
+                None
+            }
+        });
+        self.selections[start_index..]
+            .iter()
+            .map(move |s| s.display_range(map, app))
+            .take_while(move |r| r.start <= range.end || r.end <= range.end)
+            .chain(pending_selection)
+    }
+
+    fn selection_insertion_index(&self, start: &Anchor, app: &AppContext) -> usize {
+        let buffer = self.buffer.as_ref(app);
+
+        match self
+            .selections
+            .binary_search_by(|probe| probe.start.cmp(&start, buffer).unwrap())
+        {
+            Ok(index) => index,
+            Err(index) => {
+                if index > 0
+                    && self.selections[index - 1].end.cmp(&start, buffer).unwrap()
+                        == Ordering::Greater
+                {
+                    index - 1
+                } else {
+                    index
+                }
+            }
+        }
+    }
+
+    pub fn page_up(&mut self, _: &(), _: &mut ViewContext<Self>) {
+        log::info!("BufferView::page_up");
+    }
+
+    pub fn page_down(&mut self, _: &(), _: &mut ViewContext<Self>) {
+        log::info!("BufferView::page_down");
+    }
+
+    pub fn fold(&mut self, _: &(), ctx: &mut ViewContext<Self>) {
+        use super::RangeExt;
+
+        let mut fold_ranges = Vec::new();
+
+        let app = ctx.app();
+        let map = self.display_map.as_ref(app);
+        for selection in &self.selections {
+            let (start, end) = selection.display_range(map, app).sorted();
+            let buffer_start_row = start.to_buffer_point(map, Bias::Left, app).unwrap().row;
+
+            for row in (0..=end.row()).rev() {
+                if self.is_line_foldable(row, app) && !map.is_line_folded(row) {
+                    let fold_range = self.foldable_range_for_line(row, app).unwrap();
+                    if fold_range.end.row >= buffer_start_row {
+                        fold_ranges.push(fold_range);
+                        if row <= start.row() {
+                            break;
+                        }
+                    }
+                }
+            }
+        }
+
+        if !fold_ranges.is_empty() {
+            self.display_map.update(ctx, |map, ctx| {
+                map.fold(fold_ranges, ctx).unwrap();
+            });
+            *self.autoscroll_requested.lock() = true;
+        }
+    }
+
+    pub fn unfold(&mut self, _: &(), ctx: &mut ViewContext<Self>) {
+        use super::RangeExt;
+
+        let app = ctx.app();
+        let map = self.display_map.as_ref(app);
+        let buffer = self.buffer.as_ref(app);
+        let ranges = self
+            .selections
+            .iter()
+            .map(|s| {
+                let (start, end) = s.display_range(map, app).sorted();
+                let mut start = start.to_buffer_point(map, Bias::Left, app).unwrap();
+                let mut end = end.to_buffer_point(map, Bias::Left, app).unwrap();
+                start.column = 0;
+                end.column = buffer.line_len(end.row).unwrap();
+                start..end
+            })
+            .collect::<Vec<_>>();
+
+        self.display_map.update(ctx, |map, ctx| {
+            map.unfold(ranges, ctx).unwrap();
+        });
+        *self.autoscroll_requested.lock() = true;
+    }
+
+    fn is_line_foldable(&self, display_row: u32, app: &AppContext) -> bool {
+        let max_point = self.max_point(app);
+        if display_row >= max_point.row() {
+            false
+        } else {
+            let (start_indent, is_blank) = self.line_indent(display_row, app).unwrap();
+            if is_blank {
+                false
+            } else {
+                for display_row in display_row + 1..=max_point.row() {
+                    let (indent, is_blank) = self.line_indent(display_row, app).unwrap();
+                    if !is_blank {
+                        return indent > start_indent;
+                    }
+                }
+                false
+            }
+        }
+    }
+
+    fn line_indent(&self, display_row: u32, app: &AppContext) -> Result<(usize, bool)> {
+        let mut indent = 0;
+        let mut is_blank = true;
+        for c in self
+            .display_map
+            .as_ref(app)
+            .chars_at(DisplayPoint::new(display_row, 0), app)?
+        {
+            if c == ' ' {
+                indent += 1;
+            } else {
+                is_blank = c == '\n';
+                break;
+            }
+        }
+        Ok((indent, is_blank))
+    }
+
+    fn foldable_range_for_line(&self, start_row: u32, app: &AppContext) -> Result<Range<Point>> {
+        let map = self.display_map.as_ref(app);
+        let max_point = self.max_point(app);
+
+        let (start_indent, _) = self.line_indent(start_row, app)?;
+        let start = DisplayPoint::new(start_row, self.line_len(start_row, app)?);
+        let mut end = None;
+        for row in start_row + 1..=max_point.row() {
+            let (indent, is_blank) = self.line_indent(row, app)?;
+            if !is_blank && indent <= start_indent {
+                end = Some(DisplayPoint::new(row - 1, self.line_len(row - 1, app)?));
+                break;
+            }
+        }
+
+        let end = end.unwrap_or(max_point);
+        return Ok(start.to_buffer_point(map, Bias::Left, app)?
+            ..end.to_buffer_point(map, Bias::Left, app)?);
+    }
+
+    pub fn fold_selected_ranges(&mut self, _: &(), ctx: &mut ViewContext<Self>) {
+        self.display_map.update(ctx, |map, ctx| {
+            let buffer = self.buffer.as_ref(ctx);
+            let ranges = self
+                .selections
+                .iter()
+                .map(|s| s.range(buffer))
+                .collect::<Vec<_>>();
+            map.fold(ranges, ctx).unwrap();
+        });
+    }
+
+    pub fn line(&self, display_row: u32, app: &AppContext) -> Result<String> {
+        self.display_map.as_ref(app).line(display_row, app)
+    }
+
+    pub fn line_len(&self, display_row: u32, app: &AppContext) -> Result<u32> {
+        self.display_map.as_ref(app).line_len(display_row, app)
+    }
+
+    pub fn rightmost_point(&self, app: &AppContext) -> DisplayPoint {
+        self.display_map.as_ref(app).rightmost_point()
+    }
+
+    pub fn max_point(&self, app: &AppContext) -> DisplayPoint {
+        self.display_map.as_ref(app).max_point(app)
+    }
+
+    pub fn text(&self, app: &AppContext) -> String {
+        self.display_map.as_ref(app).text(app)
+    }
+
+    pub fn font_size(&self) -> f32 {
+        smol::block_on(self.settings.read()).buffer_font_size
+    }
+
+    pub fn font_ascent(&self, font_cache: &FontCache) -> f32 {
+        let settings = smol::block_on(self.settings.read());
+        let font_id = font_cache.default_font(settings.buffer_font_family);
+        let ascent = font_cache.metric(font_id, |m| m.ascent);
+        font_cache.scale_metric(ascent, font_id, settings.buffer_font_size)
+    }
+
+    pub fn font_descent(&self, font_cache: &FontCache) -> f32 {
+        let settings = smol::block_on(self.settings.read());
+        let font_id = font_cache.default_font(settings.buffer_font_family);
+        let ascent = font_cache.metric(font_id, |m| m.descent);
+        font_cache.scale_metric(ascent, font_id, settings.buffer_font_size)
+    }
+
+    pub fn line_height(&self, font_cache: &FontCache) -> f32 {
+        let settings = smol::block_on(self.settings.read());
+        let font_id = font_cache.default_font(settings.buffer_font_family);
+        font_cache
+            .bounding_box(font_id, settings.buffer_font_size)
+            .y()
+    }
+
+    pub fn em_width(&self, font_cache: &FontCache) -> f32 {
+        let settings = smol::block_on(self.settings.read());
+        let font_id = font_cache.default_font(settings.buffer_font_family);
+        let font = font_cache.font(font_id);
+        let glyph_id = font.glyph_for_char('m').unwrap();
+        let bounds = font.typographic_bounds(glyph_id).unwrap();
+        font_cache.scale_metric(bounds.width(), font_id, settings.buffer_font_size)
+    }
+
+    pub fn max_line_number_width(
+        &self,
+        font_cache: &FontCache,
+        layout_cache: &LayoutCache,
+        app: &AppContext,
+    ) -> Result<f32> {
+        let settings = smol::block_on(self.settings.read());
+        let font_size = settings.buffer_font_size;
+        let font_id =
+            font_cache.select_font(settings.buffer_font_family, &FontProperties::new())?;
+        let digit_count = ((self.buffer.as_ref(app).max_point().row + 1) as f32)
+            .log10()
+            .floor() as usize
+            + 1;
+
+        Ok(layout_cache
+            .layout_str(
+                "1".repeat(digit_count).as_str(),
+                font_size,
+                &[(0..digit_count, font_id)],
+                font_cache,
+            )
+            .width)
+    }
+
+    pub fn layout_line_numbers(
+        &self,
+        viewport_height: f32,
+        font_cache: &FontCache,
+        layout_cache: &LayoutCache,
+        app: &AppContext,
+    ) -> Result<Vec<Arc<text_layout::Line>>> {
+        let display_map = self.display_map.as_ref(app);
+
+        let settings = smol::block_on(self.settings.read());
+        let font_size = settings.buffer_font_size;
+        let font_id =
+            font_cache.select_font(settings.buffer_font_family, &FontProperties::new())?;
+
+        let start_row = self.scroll_position().y() as usize;
+        let end_row = cmp::min(
+            self.max_point(app).row() as usize,
+            start_row + (viewport_height / self.line_height(font_cache)).ceil() as usize,
+        );
+        let line_count = end_row - start_row + 1;
+        let cpus = num_cpus::get();
+        let chunk_size = (line_count + cpus - 1) / cpus;
+
+        let mut layouts = Vec::new();
+        layouts.resize_with(line_count, Default::default);
+
+        Parallel::<Result<()>>::new()
+            .each(
+                layouts.chunks_mut(chunk_size).enumerate(),
+                |(i, layouts)| {
+                    let mut line_number = String::new();
+                    let start = start_row + i * chunk_size;
+                    let line_numbers = display_map.buffer_rows(start as u32)?.take(layouts.len());
+                    for (j, buffer_row) in line_numbers.enumerate() {
+                        line_number.clear();
+                        write!(&mut line_number, "{}", buffer_row + 1).unwrap();
+                        layouts[j] = layout_cache.layout_str(
+                            &line_number,
+                            font_size,
+                            &[(0..line_number.len(), font_id)],
+                            font_cache,
+                        );
+                    }
+                    Ok(())
+                },
+            )
+            .run()
+            .into_iter()
+            .collect::<Result<()>>()?;
+
+        Ok(layouts)
+    }
+
+    pub fn layout_lines(
+        &self,
+        mut rows: Range<u32>,
+        font_cache: &FontCache,
+        layout_cache: &LayoutCache,
+        app: &AppContext,
+    ) -> Result<Vec<Arc<text_layout::Line>>> {
+        let display_map = self.display_map.as_ref(app);
+
+        rows.end = cmp::min(rows.end, display_map.max_point(app).row() + 1);
+        if rows.start >= rows.end {
+            return Ok(Vec::new());
+        }
+
+        let settings = smol::block_on(self.settings.read());
+        let font_id =
+            font_cache.select_font(settings.buffer_font_family, &FontProperties::new())?;
+        let font_size = settings.buffer_font_size;
+
+        let cpus = num_cpus::get();
+        let chunk_size = (rows.len() + cpus - 1) / cpus;
+
+        let mut layouts = Vec::new();
+        layouts.resize_with(rows.len(), Default::default);
+
+        crossbeam::thread::scope(|s| {
+            for (ix, chunk) in layouts.chunks_mut(chunk_size as usize).enumerate() {
+                let font_cache = &font_cache;
+                let chunk_start = rows.start as usize + ix * chunk_size;
+                let chunk_end = cmp::min(chunk_start + chunk_size, rows.end as usize);
+
+                s.spawn(move |_| {
+                    let mut row = chunk_start;
+                    let mut line = String::new();
+                    let mut line_len = 0;
+                    let chars = display_map
+                        .chars_at(DisplayPoint::new(chunk_start as u32, 0), app)
+                        .unwrap();
+                    for char in chars.chain(Some('\n')) {
+                        if char == '\n' {
+                            chunk[(row - chunk_start) as usize] = layout_cache.layout_str(
+                                &line,
+                                font_size,
+                                &[(0..line_len, font_id)],
+                                font_cache,
+                            );
+                            line.clear();
+                            line_len = 0;
+                            row += 1;
+                            if row == chunk_end {
+                                break;
+                            }
+                        } else {
+                            line_len += 1;
+                            line.push(char);
+                        }
+                    }
+                });
+            }
+        })
+        .unwrap();
+
+        Ok(layouts)
+    }
+
+    pub fn layout_line(
+        &self,
+        row: u32,
+        font_cache: &FontCache,
+        layout_cache: &LayoutCache,
+        app: &AppContext,
+    ) -> Result<Arc<text_layout::Line>> {
+        let settings = smol::block_on(self.settings.read());
+        let font_id =
+            font_cache.select_font(settings.buffer_font_family, &FontProperties::new())?;
+
+        let line = self.line(row, app)?;
+
+        Ok(layout_cache.layout_str(
+            &line,
+            settings.buffer_font_size,
+            &[(0..self.line_len(row, app)? as usize, font_id)],
+            font_cache,
+        ))
+    }
+
+    fn next_blink_epoch(&mut self) -> usize {
+        self.blink_epoch += 1;
+        self.blink_epoch
+    }
+
+    fn pause_cursor_blinking(&mut self, ctx: &mut ViewContext<Self>) {
+        self.cursors_visible = true;
+        ctx.notify();
+
+        let epoch = self.next_blink_epoch();
+        let _ = ctx.spawn_local(
+            async move {
+                Timer::after(CURSOR_BLINK_INTERVAL).await;
+                epoch
+            },
+            Self::resume_cursor_blinking,
+        );
+    }
+
+    fn resume_cursor_blinking(&mut self, epoch: usize, ctx: &mut ViewContext<Self>) {
+        if epoch == self.blink_epoch {
+            self.blinking_paused = false;
+            self.blink_cursors(epoch, ctx);
+        }
+    }
+
+    fn blink_cursors(&mut self, epoch: usize, ctx: &mut ViewContext<Self>) {
+        if epoch == self.blink_epoch && self.focused && !self.blinking_paused {
+            self.cursors_visible = !self.cursors_visible;
+            ctx.notify();
+
+            let epoch = self.next_blink_epoch();
+            let _ = ctx.spawn_local(
+                async move {
+                    Timer::after(CURSOR_BLINK_INTERVAL).await;
+                    epoch
+                },
+                Self::blink_cursors,
+            );
+        }
+    }
+
+    pub fn cursors_visible(&self) -> bool {
+        self.cursors_visible
+    }
+
+    fn on_buffer_changed(&mut self, _: ModelHandle<Buffer>, ctx: &mut ViewContext<Self>) {
+        ctx.notify();
+    }
+
+    fn on_display_map_changed(&mut self, _: ModelHandle<DisplayMap>, ctx: &mut ViewContext<Self>) {
+        ctx.notify();
+    }
+
+    fn on_buffer_event(
+        &mut self,
+        _: ModelHandle<Buffer>,
+        event: &buffer::Event,
+        ctx: &mut ViewContext<Self>,
+    ) {
+        match event {
+            buffer::Event::Edited(_) => ctx.emit(Event::Edited),
+        }
+    }
+}
+
+struct Selection {
+    start: Anchor,
+    end: Anchor,
+    reversed: bool,
+    goal_column: Option<u32>,
+}
+
+pub enum Event {
+    Activate,
+    Edited,
+    Blurred,
+}
+
+impl app::Entity for BufferView {
+    type Event = Event;
+}
+
+impl app::View for BufferView {
+    fn render<'a>(&self, bump: &'a Bump, app: &AppContext) -> &'a mut dyn Element<'a> {
+        BufferElement::new(self.handle.upgrade(app).unwrap()).finish(bump)
+    }
+
+    fn ui_name() -> &'static str {
+        "BufferView"
+    }
+
+    fn on_focus(&mut self, ctx: &mut ViewContext<Self>) {
+        self.focused = true;
+        self.blink_cursors(self.blink_epoch, ctx);
+    }
+
+    fn on_blur(&mut self, ctx: &mut ViewContext<Self>) {
+        self.focused = false;
+        self.cursors_visible = false;
+        ctx.emit(Event::Blurred);
+        ctx.notify();
+    }
+}
+
+impl workspace::ItemView for BufferView {
+    fn is_activate_event(event: &Self::Event) -> bool {
+        match event {
+            Event::Activate => true,
+            _ => false,
+        }
+    }
+
+    fn title(&self, app: &AppContext) -> std::string::String {
+        if let Some(path) = self.buffer.as_ref(app).path(app) {
+            path.file_name()
+                .expect("buffer's path is always to a file")
+                .to_string_lossy()
+                .into()
+        } else {
+            "untitled".into()
+        }
+    }
+
+    fn entry_id(&self, app: &AppContext) -> Option<(usize, usize)> {
+        self.buffer.as_ref(app).entry_id()
+    }
+
+    fn clone_on_split(&self, ctx: &mut ViewContext<Self>) -> Option<Self>
+    where
+        Self: Sized,
+    {
+        let clone = BufferView::for_buffer(self.buffer.clone(), self.settings.clone(), ctx);
+        *clone.scroll_position.lock() = *self.scroll_position.lock();
+        Some(clone)
+    }
+}
+
+impl Selection {
+    fn head(&self) -> &Anchor {
+        if self.reversed {
+            &self.start
+        } else {
+            &self.end
+        }
+    }
+
+    fn set_head(&mut self, buffer: &Buffer, cursor: Anchor) {
+        if cursor.cmp(self.tail(), buffer).unwrap() < Ordering::Equal {
+            if !self.reversed {
+                mem::swap(&mut self.start, &mut self.end);
+                self.reversed = true;
+            }
+            self.start = cursor;
+        } else {
+            if self.reversed {
+                mem::swap(&mut self.start, &mut self.end);
+                self.reversed = false;
+            }
+            self.end = cursor;
+        }
+    }
+
+    fn tail(&self) -> &Anchor {
+        if self.reversed {
+            &self.end
+        } else {
+            &self.start
+        }
+    }
+
+    fn range(&self, buffer: &Buffer) -> Range<Point> {
+        let start = self.start.to_point(buffer).unwrap();
+        let end = self.end.to_point(buffer).unwrap();
+        if self.reversed {
+            end..start
+        } else {
+            start..end
+        }
+    }
+
+    fn display_range(&self, map: &DisplayMap, app: &AppContext) -> Range<DisplayPoint> {
+        let start = self.start.to_display_point(map, app).unwrap();
+        let end = self.end.to_display_point(map, app).unwrap();
+        if self.reversed {
+            end..start
+        } else {
+            start..end
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::buffer::Point;
+    use crate::test_utils::*;
+    use anyhow::Error;
+    use unindent::Unindent;
+
+    #[test]
+    fn test_selection_with_mouse() {
+        App::run(|mut app| async move {
+            let buffer = app.add_model(|_| Buffer::new(0, "aaaaaa\nbbbbbb\ncccccc\ndddddd\n"));
+            let settings = settings_rx(None);
+            let (_, buffer_view) =
+                app.add_window(|ctx| BufferView::for_buffer(buffer, settings, ctx));
+
+            buffer_view.update(&mut app, |view, ctx| {
+                view.begin_selection(DisplayPoint::new(2, 2), false, ctx);
+            });
+
+            buffer_view.read(&app, |view, app| {
+                let selections = view
+                    .selections_in_range(DisplayPoint::zero()..view.max_point(app), app)
+                    .collect::<Vec<_>>();
+                assert_eq!(
+                    selections,
+                    [DisplayPoint::new(2, 2)..DisplayPoint::new(2, 2)]
+                );
+            });
+
+            buffer_view.update(&mut app, |view, ctx| {
+                view.update_selection(DisplayPoint::new(3, 3), Vector2F::zero(), ctx);
+            });
+
+            buffer_view.read(&app, |view, app| {
+                let selections = view
+                    .selections_in_range(DisplayPoint::zero()..view.max_point(app), app)
+                    .collect::<Vec<_>>();
+                assert_eq!(
+                    selections,
+                    [DisplayPoint::new(2, 2)..DisplayPoint::new(3, 3)]
+                );
+            });
+
+            buffer_view.update(&mut app, |view, ctx| {
+                view.update_selection(DisplayPoint::new(1, 1), Vector2F::zero(), ctx);
+            });
+
+            buffer_view.read(&app, |view, app| {
+                let selections = view
+                    .selections_in_range(DisplayPoint::zero()..view.max_point(app), app)
+                    .collect::<Vec<_>>();
+                assert_eq!(
+                    selections,
+                    [DisplayPoint::new(2, 2)..DisplayPoint::new(1, 1)]
+                );
+            });
+
+            buffer_view.update(&mut app, |view, ctx| {
+                view.end_selection(ctx);
+                view.update_selection(DisplayPoint::new(3, 3), Vector2F::zero(), ctx);
+            });
+
+            buffer_view.read(&app, |view, app| {
+                let selections = view
+                    .selections_in_range(DisplayPoint::zero()..view.max_point(app), app)
+                    .collect::<Vec<_>>();
+                assert_eq!(
+                    selections,
+                    [DisplayPoint::new(2, 2)..DisplayPoint::new(1, 1)]
+                );
+            });
+
+            buffer_view.update(&mut app, |view, ctx| {
+                view.begin_selection(DisplayPoint::new(3, 3), true, ctx);
+                view.update_selection(DisplayPoint::new(0, 0), Vector2F::zero(), ctx);
+            });
+
+            buffer_view.read(&app, |view, app| {
+                let selections = view
+                    .selections_in_range(DisplayPoint::zero()..view.max_point(app), app)
+                    .collect::<Vec<_>>();
+                assert_eq!(
+                    selections,
+                    [
+                        DisplayPoint::new(2, 2)..DisplayPoint::new(1, 1),
+                        DisplayPoint::new(3, 3)..DisplayPoint::new(0, 0)
+                    ]
+                );
+            });
+
+            buffer_view.update(&mut app, |view, ctx| {
+                view.end_selection(ctx);
+            });
+
+            buffer_view.read(&app, |view, app| {
+                let selections = view
+                    .selections_in_range(DisplayPoint::zero()..view.max_point(app), app)
+                    .collect::<Vec<_>>();
+                assert_eq!(
+                    selections,
+                    [DisplayPoint::new(3, 3)..DisplayPoint::new(0, 0)]
+                );
+            });
+        });
+    }
+
+    #[test]
+    fn test_layout_line_numbers() -> Result<()> {
+        use crate::fonts::FontCache;
+        use crate::text_layout::LayoutCache;
+
+        let font_cache = FontCache::new();
+        let layout_cache = LayoutCache::new();
+
+        let mut app = App::new().unwrap();
+        let buffer = app.add_model(|_| Buffer::new(0, sample_text(6, 6)));
+
+        let settings = settings_rx(Some(&font_cache));
+        let (_, view) = app.add_window(|ctx| BufferView::for_buffer(buffer.clone(), settings, ctx));
+
+        view.read(&app, |view, app| {
+            let layouts = view.layout_line_numbers(1000.0, &font_cache, &layout_cache, app)?;
+            assert_eq!(layouts.len(), 6);
+            Result::<()>::Ok(())
+        })?;
+
+        Ok(())
+    }
+
+    #[test]
+    fn test_fold() -> Result<()> {
+        init_logger();
+
+        let mut app = App::new().unwrap();
+        let buffer = app.add_model(|_| {
+            Buffer::new(
+                0,
+                "
+                    impl Foo {
+                        // Hello!
+
+                        fn a() {
+                            1
+                        }
+
+                        fn b() {
+                            2
+                        }
+
+                        fn c() {
+                            3
+                        }
+                    }
+                "
+                .unindent(),
+            )
+        });
+        let settings = settings_rx(None);
+        let (_, view) = app.add_window(|ctx| BufferView::for_buffer(buffer.clone(), settings, ctx));
+
+        view.update(&mut app, |view, ctx| {
+            view.select_ranges(Some(DisplayPoint::new(8, 0)..DisplayPoint::new(12, 0)), ctx)?;
+            view.fold(&(), ctx);
+            assert_eq!(
+                view.text(ctx.app()),
+                "
+                    impl Foo {
+                        // Hello!
+
+                        fn a() {
+                            1
+                        }
+
+                        fn b() {…
+                        }
+
+                        fn c() {…
+                        }
+                    }
+                "
+                .unindent(),
+            );
+
+            view.fold(&(), ctx);
+            assert_eq!(
+                view.text(ctx.app()),
+                "
+                    impl Foo {…
+                    }
+                "
+                .unindent(),
+            );
+
+            view.unfold(&(), ctx);
+            assert_eq!(
+                view.text(ctx.app()),
+                "
+                    impl Foo {
+                        // Hello!
+
+                        fn a() {
+                            1
+                        }
+
+                        fn b() {…
+                        }
+
+                        fn c() {…
+                        }
+                    }
+                "
+                .unindent(),
+            );
+
+            view.unfold(&(), ctx);
+            assert_eq!(view.text(ctx.app()), buffer.as_ref(ctx).text());
+
+            Ok::<(), Error>(())
+        })?;
+
+        Ok(())
+    }
+
+    #[test]
+    fn test_move_cursor() -> Result<()> {
+        let mut app = App::new().unwrap();
+        let buffer = app.add_model(|_| Buffer::new(0, sample_text(6, 6)));
+        let settings = settings_rx(None);
+        let (_, view) = app.add_window(|ctx| BufferView::for_buffer(buffer.clone(), settings, ctx));
+
+        buffer.update(&mut app, |buffer, ctx| {
+            buffer.edit(
+                vec![
+                    Point::new(1, 0)..Point::new(1, 0),
+                    Point::new(1, 1)..Point::new(1, 1),
+                ],
+                "\t",
+                Some(ctx),
+            )
+        })?;
+
+        view.update(&mut app, |view, ctx| {
+            view.move_down(&(), ctx);
+            assert_eq!(
+                view.selections(ctx.app()),
+                &[DisplayPoint::new(1, 0)..DisplayPoint::new(1, 0)]
+            );
+            view.move_right(&(), ctx);
+            assert_eq!(
+                view.selections(ctx.app()),
+                &[DisplayPoint::new(1, 4)..DisplayPoint::new(1, 4)]
+            );
+            Ok::<(), Error>(())
+        })?;
+
+        Ok(())
+    }
+
+    impl BufferView {
+        fn selections(&self, app: &AppContext) -> Vec<Range<DisplayPoint>> {
+            self.selections_in_range(DisplayPoint::zero()..self.max_point(app), app)
+                .collect::<Vec<_>>()
+        }
+    }
+}

zed/src/editor/display_map/fold_map.rs 🔗

@@ -0,0 +1,698 @@
+use super::{
+    buffer, Anchor, AnchorRangeExt, Buffer, DisplayPoint, Edit, Point, TextSummary, ToOffset,
+};
+use crate::{
+    app::{AppContext, ModelHandle},
+    sum_tree::{self, Cursor, SumTree},
+    util::find_insertion_index,
+};
+use anyhow::{anyhow, Result};
+use std::{
+    cmp::{self, Ordering},
+    iter::Take,
+    ops::Range,
+};
+use sum_tree::{Dimension, SeekBias};
+
+pub struct FoldMap {
+    buffer: ModelHandle<Buffer>,
+    transforms: SumTree<Transform>,
+    folds: Vec<Range<Anchor>>,
+}
+
+impl FoldMap {
+    pub fn new(buffer: ModelHandle<Buffer>, app: &AppContext) -> Self {
+        let text_summary = buffer.as_ref(app).text_summary();
+        Self {
+            buffer,
+            folds: Vec::new(),
+            transforms: SumTree::from_item(Transform {
+                summary: TransformSummary {
+                    buffer: text_summary.clone(),
+                    display: text_summary,
+                },
+                display_text: None,
+            }),
+        }
+    }
+
+    pub fn buffer_rows(&self, start_row: u32) -> Result<BufferRows> {
+        if start_row > self.transforms.summary().display.lines.row {
+            return Err(anyhow!("invalid display row {}", start_row));
+        }
+
+        let display_point = Point::new(start_row, 0);
+        let mut cursor = self.transforms.cursor();
+        cursor.seek(&DisplayPoint(display_point), SeekBias::Left);
+
+        Ok(BufferRows {
+            display_point,
+            cursor,
+        })
+    }
+
+    pub fn len(&self) -> usize {
+        self.transforms.summary().display.chars
+    }
+
+    pub fn line_len(&self, row: u32, ctx: &AppContext) -> Result<u32> {
+        let line_start = self.to_display_offset(DisplayPoint::new(row, 0), ctx)?.0;
+        let line_end = if row >= self.max_point().row() {
+            self.len()
+        } else {
+            self.to_display_offset(DisplayPoint::new(row + 1, 0), ctx)?
+                .0
+                - 1
+        };
+
+        Ok((line_end - line_start) as u32)
+    }
+
+    pub fn chars_at<'a>(&'a self, point: DisplayPoint, app: &'a AppContext) -> Result<Chars<'a>> {
+        let offset = self.to_display_offset(point, app)?;
+        let mut cursor = self.transforms.cursor();
+        cursor.seek(&offset, SeekBias::Right);
+        let buffer = self.buffer.as_ref(app);
+        Ok(Chars {
+            cursor,
+            offset: offset.0,
+            buffer,
+            buffer_chars: None,
+        })
+    }
+
+    pub fn max_point(&self) -> DisplayPoint {
+        DisplayPoint(self.transforms.summary().display.lines)
+    }
+
+    pub fn rightmost_point(&self) -> DisplayPoint {
+        DisplayPoint(self.transforms.summary().display.rightmost_point)
+    }
+
+    pub fn fold<T: ToOffset>(
+        &mut self,
+        ranges: impl IntoIterator<Item = Range<T>>,
+        app: &AppContext,
+    ) -> Result<()> {
+        let mut edits = Vec::new();
+        let buffer = self.buffer.as_ref(app);
+        for range in ranges.into_iter() {
+            let start = range.start.to_offset(buffer)?;
+            let end = range.end.to_offset(buffer)?;
+            edits.push(Edit {
+                old_range: start..end,
+                new_range: start..end,
+            });
+
+            let fold = buffer.anchor_after(start)?..buffer.anchor_before(end)?;
+            let ix = find_insertion_index(&self.folds, |probe| probe.cmp(&fold, buffer))?;
+            self.folds.insert(ix, fold);
+        }
+        edits.sort_unstable_by(|a, b| {
+            a.old_range
+                .start
+                .cmp(&b.old_range.start)
+                .then_with(|| b.old_range.end.cmp(&a.old_range.end))
+        });
+
+        self.apply_edits(&edits, app)?;
+        Ok(())
+    }
+
+    pub fn unfold<T: ToOffset>(
+        &mut self,
+        ranges: impl IntoIterator<Item = Range<T>>,
+        app: &AppContext,
+    ) -> Result<()> {
+        let buffer = self.buffer.as_ref(app);
+
+        let mut edits = Vec::new();
+        for range in ranges.into_iter() {
+            let start = buffer.anchor_before(range.start.to_offset(buffer)?)?;
+            let end = buffer.anchor_after(range.end.to_offset(buffer)?)?;
+
+            // Remove intersecting folds and add their ranges to edits that are passed to apply_edits
+            self.folds.retain(|fold| {
+                if fold.start.cmp(&end, buffer).unwrap() > Ordering::Equal
+                    || fold.end.cmp(&start, buffer).unwrap() < Ordering::Equal
+                {
+                    true
+                } else {
+                    let offset_range =
+                        fold.start.to_offset(buffer).unwrap()..fold.end.to_offset(buffer).unwrap();
+                    edits.push(Edit {
+                        old_range: offset_range.clone(),
+                        new_range: offset_range,
+                    });
+                    false
+                }
+            });
+        }
+
+        self.apply_edits(&edits, app)?;
+        Ok(())
+    }
+
+    pub fn is_line_folded(&self, display_row: u32) -> bool {
+        let mut cursor = self.transforms.cursor::<DisplayPoint, DisplayPoint>();
+        cursor.seek(&DisplayPoint::new(display_row, 0), SeekBias::Right);
+        while let Some(transform) = cursor.item() {
+            if transform.display_text.is_some() {
+                return true;
+            }
+            if cursor.end().row() == display_row {
+                cursor.next()
+            } else {
+                break;
+            }
+        }
+        false
+    }
+
+    pub fn to_display_offset(
+        &self,
+        point: DisplayPoint,
+        app: &AppContext,
+    ) -> Result<DisplayOffset> {
+        let mut cursor = self.transforms.cursor::<DisplayPoint, TransformSummary>();
+        cursor.seek(&point, SeekBias::Right);
+        let overshoot = point.0 - cursor.start().display.lines;
+        let mut offset = cursor.start().display.chars;
+        if !overshoot.is_zero() {
+            let transform = cursor
+                .item()
+                .ok_or_else(|| anyhow!("display point {:?} is out of range", point))?;
+            assert!(transform.display_text.is_none());
+            let end_buffer_offset =
+                (cursor.start().buffer.lines + overshoot).to_offset(self.buffer.as_ref(app))?;
+            offset += end_buffer_offset - cursor.start().buffer.chars;
+        }
+        Ok(DisplayOffset(offset))
+    }
+
+    pub fn to_buffer_point(&self, display_point: DisplayPoint) -> Point {
+        let mut cursor = self.transforms.cursor::<DisplayPoint, TransformSummary>();
+        cursor.seek(&display_point, SeekBias::Right);
+        let overshoot = display_point.0 - cursor.start().display.lines;
+        cursor.start().buffer.lines + overshoot
+    }
+
+    pub fn to_display_point(&self, point: Point) -> DisplayPoint {
+        let mut cursor = self.transforms.cursor::<Point, TransformSummary>();
+        cursor.seek(&point, SeekBias::Right);
+        let overshoot = point - cursor.start().buffer.lines;
+        DisplayPoint(cmp::min(
+            cursor.start().display.lines + overshoot,
+            cursor.end().display.lines,
+        ))
+    }
+
+    pub fn apply_edits(&mut self, edits: &[Edit], app: &AppContext) -> Result<()> {
+        let buffer = self.buffer.as_ref(app);
+        let mut edits = edits.iter().cloned().peekable();
+
+        let mut new_transforms = SumTree::new();
+        let mut cursor = self.transforms.cursor::<usize, usize>();
+        cursor.seek(&0, SeekBias::Right);
+
+        while let Some(mut edit) = edits.next() {
+            new_transforms.push_tree(cursor.slice(&edit.old_range.start, SeekBias::Left));
+            edit.new_range.start -= edit.old_range.start - cursor.start();
+            edit.old_range.start = *cursor.start();
+
+            cursor.seek(&edit.old_range.end, SeekBias::Right);
+            cursor.next();
+
+            let mut delta = edit.delta();
+            loop {
+                edit.old_range.end = *cursor.start();
+
+                if let Some(next_edit) = edits.peek() {
+                    if next_edit.old_range.start > edit.old_range.end {
+                        break;
+                    }
+
+                    let next_edit = edits.next().unwrap();
+                    delta += next_edit.delta();
+
+                    if next_edit.old_range.end > edit.old_range.end {
+                        edit.old_range.end = next_edit.old_range.end;
+                        cursor.seek(&edit.old_range.end, SeekBias::Right);
+                        cursor.next();
+                    }
+                } else {
+                    break;
+                }
+            }
+
+            edit.new_range.end =
+                ((edit.new_range.start + edit.old_extent()) as isize + delta) as usize;
+
+            let anchor = buffer.anchor_before(edit.new_range.start)?;
+            let folds_start =
+                find_insertion_index(&self.folds, |probe| probe.start.cmp(&anchor, buffer))?;
+            let mut folds = self.folds[folds_start..]
+                .iter()
+                .map(|fold| {
+                    fold.start.to_offset(buffer).unwrap()..fold.end.to_offset(buffer).unwrap()
+                })
+                .peekable();
+
+            while folds
+                .peek()
+                .map_or(false, |fold| fold.start < edit.new_range.end)
+            {
+                let mut fold = folds.next().unwrap();
+                let sum = new_transforms.summary();
+
+                assert!(fold.start >= sum.buffer.chars);
+
+                while folds
+                    .peek()
+                    .map_or(false, |next_fold| next_fold.start <= fold.end)
+                {
+                    let next_fold = folds.next().unwrap();
+                    if next_fold.end > fold.end {
+                        fold.end = next_fold.end;
+                    }
+                }
+
+                if fold.start > sum.buffer.chars {
+                    let text_summary = buffer.text_summary_for_range(sum.buffer.chars..fold.start);
+                    new_transforms.push(Transform {
+                        summary: TransformSummary {
+                            display: text_summary.clone(),
+                            buffer: text_summary,
+                        },
+                        display_text: None,
+                    });
+                }
+
+                if fold.end > fold.start {
+                    new_transforms.push(Transform {
+                        summary: TransformSummary {
+                            display: TextSummary {
+                                chars: 1,
+                                bytes: '…'.len_utf8(),
+                                lines: Point::new(0, 1),
+                                first_line_len: 1,
+                                rightmost_point: Point::new(0, 1),
+                            },
+                            buffer: buffer.text_summary_for_range(fold.start..fold.end),
+                        },
+                        display_text: Some('…'),
+                    });
+                }
+            }
+
+            let sum = new_transforms.summary();
+            if sum.buffer.chars < edit.new_range.end {
+                let text_summary =
+                    buffer.text_summary_for_range(sum.buffer.chars..edit.new_range.end);
+                new_transforms.push(Transform {
+                    summary: TransformSummary {
+                        display: text_summary.clone(),
+                        buffer: text_summary,
+                    },
+                    display_text: None,
+                });
+            }
+        }
+
+        new_transforms.push_tree(cursor.suffix());
+
+        drop(cursor);
+        self.transforms = new_transforms;
+
+        Ok(())
+    }
+}
+
+#[derive(Clone, Debug, Default, Eq, PartialEq)]
+struct Transform {
+    summary: TransformSummary,
+    display_text: Option<char>,
+}
+
+#[derive(Clone, Debug, Default, Eq, PartialEq)]
+struct TransformSummary {
+    display: TextSummary,
+    buffer: TextSummary,
+}
+
+impl sum_tree::Item for Transform {
+    type Summary = TransformSummary;
+
+    fn summary(&self) -> Self::Summary {
+        self.summary.clone()
+    }
+}
+
+impl<'a> std::ops::AddAssign<&'a Self> for TransformSummary {
+    fn add_assign(&mut self, other: &'a Self) {
+        self.buffer += &other.buffer;
+        self.display += &other.display;
+    }
+}
+
+impl<'a> Dimension<'a, TransformSummary> for TransformSummary {
+    fn add_summary(&mut self, summary: &'a TransformSummary) {
+        *self += summary;
+    }
+}
+
+pub struct BufferRows<'a> {
+    cursor: Cursor<'a, Transform, DisplayPoint, TransformSummary>,
+    display_point: Point,
+}
+
+impl<'a> Iterator for BufferRows<'a> {
+    type Item = u32;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        while self.display_point > self.cursor.end().display.lines {
+            self.cursor.next();
+            if self.cursor.item().is_none() {
+                // TODO: Return a bool from next?
+                break;
+            }
+        }
+
+        if self.cursor.item().is_some() {
+            let overshoot = self.display_point - self.cursor.start().display.lines;
+            let buffer_point = self.cursor.start().buffer.lines + overshoot;
+            self.display_point.row += 1;
+            Some(buffer_point.row)
+        } else {
+            None
+        }
+    }
+}
+
+pub struct Chars<'a> {
+    cursor: Cursor<'a, Transform, DisplayOffset, TransformSummary>,
+    offset: usize,
+    buffer: &'a Buffer,
+    buffer_chars: Option<Take<buffer::Chars<'a>>>,
+}
+
+impl<'a> Iterator for Chars<'a> {
+    type Item = char;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if let Some(c) = self.buffer_chars.as_mut().and_then(|chars| chars.next()) {
+            self.offset += 1;
+            return Some(c);
+        }
+
+        if self.offset == self.cursor.end().display.chars {
+            self.cursor.next();
+        }
+
+        self.cursor.item().and_then(|transform| {
+            if let Some(c) = transform.display_text {
+                self.offset += 1;
+                Some(c)
+            } else {
+                let overshoot = self.offset - self.cursor.start().display.chars;
+                let buffer_start = self.cursor.start().buffer.chars + overshoot;
+                let char_count = self.cursor.end().buffer.chars - buffer_start;
+                self.buffer_chars =
+                    Some(self.buffer.chars_at(buffer_start).unwrap().take(char_count));
+                self.next()
+            }
+        })
+    }
+}
+
+impl<'a> Dimension<'a, TransformSummary> for DisplayPoint {
+    fn add_summary(&mut self, summary: &'a TransformSummary) {
+        self.0 += &summary.display.lines;
+    }
+}
+
+#[derive(Copy, Clone, Debug, Default, Eq, Ord, PartialOrd, PartialEq)]
+pub struct DisplayOffset(usize);
+
+impl<'a> Dimension<'a, TransformSummary> for DisplayOffset {
+    fn add_summary(&mut self, summary: &'a TransformSummary) {
+        self.0 += &summary.display.chars;
+    }
+}
+
+impl<'a> Dimension<'a, TransformSummary> for Point {
+    fn add_summary(&mut self, summary: &'a TransformSummary) {
+        *self += &summary.buffer.lines;
+    }
+}
+
+impl<'a> Dimension<'a, TransformSummary> for usize {
+    fn add_summary(&mut self, summary: &'a TransformSummary) {
+        *self += &summary.buffer.chars;
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::app::App;
+    use crate::test_utils::sample_text;
+
+    #[test]
+    fn test_basic_folds() -> Result<()> {
+        let mut app = App::new()?;
+        let buffer = app.add_model(|_| Buffer::new(0, sample_text(5, 6)));
+        let mut map = app.read(|app| FoldMap::new(buffer.clone(), app));
+
+        app.read(|app| {
+            map.fold(
+                vec![
+                    Point::new(0, 2)..Point::new(2, 2),
+                    Point::new(2, 4)..Point::new(4, 1),
+                ],
+                app,
+            )?;
+            assert_eq!(map.text(app), "aa…cc…eeeee");
+            Ok::<(), anyhow::Error>(())
+        })?;
+
+        let edits = buffer.update(&mut app, |buffer, ctx| {
+            let start_version = buffer.version.clone();
+            buffer.edit(
+                vec![
+                    Point::new(0, 0)..Point::new(0, 1),
+                    Point::new(2, 3)..Point::new(2, 3),
+                ],
+                "123",
+                Some(ctx),
+            )?;
+            Ok::<_, anyhow::Error>(buffer.edits_since(start_version).collect::<Vec<_>>())
+        })?;
+
+        app.read(|app| {
+            map.apply_edits(&edits, app)?;
+            assert_eq!(map.text(app), "123a…c123c…eeeee");
+            Ok::<(), anyhow::Error>(())
+        })?;
+
+        let edits = buffer.update(&mut app, |buffer, ctx| {
+            let start_version = buffer.version.clone();
+            buffer.edit(Some(Point::new(2, 6)..Point::new(4, 3)), "456", Some(ctx))?;
+            Ok::<_, anyhow::Error>(buffer.edits_since(start_version).collect::<Vec<_>>())
+        })?;
+
+        app.read(|app| {
+            map.apply_edits(&edits, app)?;
+            assert_eq!(map.text(app), "123a…c123456eee");
+
+            map.unfold(Some(Point::new(0, 4)..Point::new(0, 4)), app)?;
+            assert_eq!(map.text(app), "123aaaaa\nbbbbbb\nccc123456eee");
+
+            Ok(())
+        })
+    }
+
+    #[test]
+    fn test_overlapping_folds() -> Result<()> {
+        let mut app = App::new()?;
+        let buffer = app.add_model(|_| Buffer::new(0, sample_text(5, 6)));
+        app.read(|app| {
+            let mut map = FoldMap::new(buffer.clone(), app);
+            map.fold(
+                vec![
+                    Point::new(0, 2)..Point::new(2, 2),
+                    Point::new(0, 4)..Point::new(1, 0),
+                    Point::new(1, 2)..Point::new(3, 2),
+                    Point::new(3, 1)..Point::new(4, 1),
+                ],
+                app,
+            )?;
+            assert_eq!(map.text(app), "aa…eeeee");
+            Ok(())
+        })
+    }
+
+    #[test]
+    fn test_merging_folds_via_edit() -> Result<()> {
+        let mut app = App::new()?;
+        let buffer = app.add_model(|_| Buffer::new(0, sample_text(5, 6)));
+        let mut map = app.read(|app| FoldMap::new(buffer.clone(), app));
+
+        app.read(|app| {
+            map.fold(
+                vec![
+                    Point::new(0, 2)..Point::new(2, 2),
+                    Point::new(3, 1)..Point::new(4, 1),
+                ],
+                app,
+            )?;
+            assert_eq!(map.text(app), "aa…cccc\nd…eeeee");
+            Ok::<(), anyhow::Error>(())
+        })?;
+
+        let edits = buffer.update(&mut app, |buffer, ctx| {
+            let start_version = buffer.version.clone();
+            buffer.edit(Some(Point::new(2, 2)..Point::new(3, 1)), "", Some(ctx))?;
+            Ok::<_, anyhow::Error>(buffer.edits_since(start_version).collect::<Vec<_>>())
+        })?;
+
+        app.read(|app| {
+            map.apply_edits(&edits, app)?;
+            assert_eq!(map.text(app), "aa…eeeee");
+            Ok(())
+        })
+    }
+
+    #[test]
+    fn test_random_folds() -> Result<()> {
+        use crate::buffer::ToPoint;
+        use crate::util::RandomCharIter;
+        use rand::prelude::*;
+
+        for seed in 0..100 {
+            println!("{:?}", seed);
+            let mut rng = StdRng::seed_from_u64(seed);
+
+            let mut app = App::new()?;
+            let buffer = app.add_model(|_| {
+                let len = rng.gen_range(0, 10);
+                let text = RandomCharIter::new(&mut rng).take(len).collect::<String>();
+                Buffer::new(0, text)
+            });
+            let mut map = app.read(|app| FoldMap::new(buffer.clone(), app));
+
+            app.read(|app| {
+                let buffer = buffer.as_ref(app);
+
+                let fold_count = rng.gen_range(0, 10);
+                let mut fold_ranges: Vec<Range<usize>> = Vec::new();
+                for _ in 0..fold_count {
+                    let end = rng.gen_range(0, buffer.len() + 1);
+                    let start = rng.gen_range(0, end + 1);
+                    fold_ranges.push(start..end);
+                }
+
+                map.fold(fold_ranges, app)?;
+
+                let mut expected_text = buffer.text();
+                for fold_range in map.merged_fold_ranges(app).into_iter().rev() {
+                    expected_text.replace_range(fold_range.start..fold_range.end, "…");
+                }
+
+                assert_eq!(map.text(app), expected_text);
+
+                for fold_range in map.merged_fold_ranges(app) {
+                    let display_point =
+                        map.to_display_point(fold_range.start.to_point(buffer).unwrap());
+                    assert!(map.is_line_folded(display_point.row()));
+                }
+
+                Ok::<(), anyhow::Error>(())
+            })?;
+
+            let edits = buffer.update(&mut app, |buffer, ctx| {
+                let start_version = buffer.version.clone();
+                let edit_count = rng.gen_range(1, 10);
+                buffer.randomly_edit(&mut rng, edit_count, Some(ctx));
+                Ok::<_, anyhow::Error>(buffer.edits_since(start_version).collect::<Vec<_>>())
+            })?;
+
+            app.read(|app| {
+                map.apply_edits(&edits, app)?;
+
+                let buffer = map.buffer.as_ref(app);
+                let mut expected_text = buffer.text();
+                for fold_range in map.merged_fold_ranges(app).into_iter().rev() {
+                    expected_text.replace_range(fold_range.start..fold_range.end, "…");
+                }
+                assert_eq!(map.text(app), expected_text);
+
+                Ok::<(), anyhow::Error>(())
+            })?;
+        }
+
+        Ok(())
+    }
+
+    #[test]
+    fn test_buffer_rows() -> Result<()> {
+        let mut app = App::new()?;
+        let text = sample_text(6, 6) + "\n";
+        let buffer = app.add_model(|_| Buffer::new(0, text));
+
+        app.read(|app| {
+            let mut map = FoldMap::new(buffer.clone(), app);
+
+            map.fold(
+                vec![
+                    Point::new(0, 2)..Point::new(2, 2),
+                    Point::new(3, 1)..Point::new(4, 1),
+                ],
+                app,
+            )?;
+
+            assert_eq!(map.text(app), "aa…cccc\nd…eeeee\nffffff\n");
+            assert_eq!(map.buffer_rows(0)?.collect::<Vec<_>>(), vec![0, 3, 5, 6]);
+            assert_eq!(map.buffer_rows(3)?.collect::<Vec<_>>(), vec![6]);
+
+            Ok(())
+        })
+    }
+
+    impl FoldMap {
+        fn text(&self, app: &AppContext) -> String {
+            self.chars_at(DisplayPoint(Point::zero()), app)
+                .unwrap()
+                .collect()
+        }
+
+        fn merged_fold_ranges(&self, app: &AppContext) -> Vec<Range<usize>> {
+            let buffer = self.buffer.as_ref(app);
+            let mut fold_ranges = self
+                .folds
+                .iter()
+                .map(|fold| {
+                    fold.start.to_offset(buffer).unwrap()..fold.end.to_offset(buffer).unwrap()
+                })
+                .peekable();
+
+            let mut merged_ranges = Vec::new();
+            while let Some(mut fold_range) = fold_ranges.next() {
+                while let Some(next_range) = fold_ranges.peek() {
+                    if fold_range.end >= next_range.start {
+                        if next_range.end > fold_range.end {
+                            fold_range.end = next_range.end;
+                        }
+                        fold_ranges.next();
+                    } else {
+                        break;
+                    }
+                }
+                if fold_range.end > fold_range.start {
+                    merged_ranges.push(fold_range);
+                }
+            }
+            merged_ranges
+        }
+    }
+}

zed/src/editor/display_map/mod.rs 🔗

@@ -0,0 +1,375 @@
+mod fold_map;
+
+use super::ToPoint;
+use super::{buffer, Anchor, AnchorRangeExt, Buffer, Edit, Point, TextSummary, ToOffset};
+use crate::app::{AppContext, Entity, ModelContext, ModelHandle};
+use anyhow::Result;
+pub use fold_map::BufferRows;
+use fold_map::FoldMap;
+use std::ops::Range;
+
+#[derive(Copy, Clone)]
+pub enum Bias {
+    Left,
+    Right,
+}
+
+pub struct DisplayMap {
+    buffer: ModelHandle<Buffer>,
+    fold_map: FoldMap,
+    tab_size: usize,
+}
+
+impl Entity for DisplayMap {
+    type Event = ();
+}
+
+impl DisplayMap {
+    pub fn new(buffer: ModelHandle<Buffer>, tab_size: usize, ctx: &mut ModelContext<Self>) -> Self {
+        ctx.subscribe(&buffer, Self::handle_buffer_event);
+
+        DisplayMap {
+            buffer: buffer.clone(),
+            fold_map: FoldMap::new(buffer, ctx.app()),
+            tab_size,
+        }
+    }
+
+    pub fn fold<T: ToOffset>(
+        &mut self,
+        ranges: impl IntoIterator<Item = Range<T>>,
+        ctx: &mut ModelContext<Self>,
+    ) -> Result<()> {
+        self.fold_map.fold(ranges, ctx.app())?;
+        ctx.notify();
+        Ok(())
+    }
+
+    pub fn unfold<T: ToOffset>(
+        &mut self,
+        ranges: impl IntoIterator<Item = Range<T>>,
+        ctx: &mut ModelContext<Self>,
+    ) -> Result<()> {
+        self.fold_map.unfold(ranges, ctx.app())?;
+        ctx.notify();
+        Ok(())
+    }
+
+    pub fn is_line_folded(&self, display_row: u32) -> bool {
+        self.fold_map.is_line_folded(display_row)
+    }
+
+    pub fn text(&self, app: &AppContext) -> String {
+        self.chars_at(DisplayPoint::zero(), app).unwrap().collect()
+    }
+
+    pub fn line(&self, display_row: u32, app: &AppContext) -> Result<String> {
+        let chars = self.chars_at(DisplayPoint::new(display_row, 0), app)?;
+        Ok(chars.take_while(|c| *c != '\n').collect())
+    }
+
+    pub fn chars_at<'a>(&'a self, point: DisplayPoint, app: &'a AppContext) -> Result<Chars<'a>> {
+        let column = point.column() as usize;
+        let (point, to_next_stop) = point.collapse_tabs(self, Bias::Left, app)?;
+        let mut fold_chars = self.fold_map.chars_at(point, app)?;
+        if to_next_stop > 0 {
+            fold_chars.next();
+        }
+
+        Ok(Chars {
+            fold_chars,
+            column,
+            to_next_stop,
+            tab_size: self.tab_size,
+        })
+    }
+
+    pub fn buffer_rows(&self, start_row: u32) -> Result<BufferRows> {
+        self.fold_map.buffer_rows(start_row)
+    }
+
+    pub fn line_len(&self, row: u32, ctx: &AppContext) -> Result<u32> {
+        DisplayPoint::new(row, self.fold_map.line_len(row, ctx)?)
+            .expand_tabs(self, ctx)
+            .map(|point| point.column())
+    }
+
+    pub fn max_point(&self, app: &AppContext) -> DisplayPoint {
+        self.fold_map.max_point().expand_tabs(self, app).unwrap()
+    }
+
+    pub fn rightmost_point(&self) -> DisplayPoint {
+        self.fold_map.rightmost_point()
+    }
+
+    pub fn anchor_before(
+        &self,
+        point: DisplayPoint,
+        bias: Bias,
+        app: &AppContext,
+    ) -> Result<Anchor> {
+        self.buffer
+            .as_ref(app)
+            .anchor_before(point.to_buffer_point(self, bias, app)?)
+    }
+
+    pub fn anchor_after(
+        &self,
+        point: DisplayPoint,
+        bias: Bias,
+        app: &AppContext,
+    ) -> Result<Anchor> {
+        self.buffer
+            .as_ref(app)
+            .anchor_after(point.to_buffer_point(self, bias, app)?)
+    }
+
+    fn handle_buffer_event(&mut self, event: &buffer::Event, ctx: &mut ModelContext<Self>) {
+        match event {
+            buffer::Event::Edited(edits) => self.fold_map.apply_edits(edits, ctx.app()).unwrap(),
+        }
+    }
+}
+
+#[derive(Copy, Clone, Debug, Default, Eq, Ord, PartialOrd, PartialEq)]
+pub struct DisplayPoint(Point);
+
+impl DisplayPoint {
+    pub fn new(row: u32, column: u32) -> Self {
+        Self(Point::new(row, column))
+    }
+
+    pub fn zero() -> Self {
+        Self::new(0, 0)
+    }
+
+    pub fn row(self) -> u32 {
+        self.0.row
+    }
+
+    pub fn column(self) -> u32 {
+        self.0.column
+    }
+
+    pub fn row_mut(&mut self) -> &mut u32 {
+        &mut self.0.row
+    }
+
+    pub fn column_mut(&mut self) -> &mut u32 {
+        &mut self.0.column
+    }
+
+    pub fn to_buffer_point(self, map: &DisplayMap, bias: Bias, app: &AppContext) -> Result<Point> {
+        Ok(map
+            .fold_map
+            .to_buffer_point(self.collapse_tabs(map, bias, app)?.0))
+    }
+
+    fn expand_tabs(mut self, map: &DisplayMap, app: &AppContext) -> Result<Self> {
+        let chars = map
+            .fold_map
+            .chars_at(DisplayPoint(Point::new(self.row(), 0)), app)?;
+        let expanded = expand_tabs(chars, self.column() as usize, map.tab_size);
+        *self.column_mut() = expanded as u32;
+
+        Ok(self)
+    }
+
+    fn collapse_tabs(
+        mut self,
+        map: &DisplayMap,
+        bias: Bias,
+        app: &AppContext,
+    ) -> Result<(Self, usize)> {
+        let chars = map
+            .fold_map
+            .chars_at(DisplayPoint(Point::new(self.0.row, 0)), app)?;
+        let expanded = self.column() as usize;
+        let (collapsed, to_next_stop) = collapse_tabs(chars, expanded, bias, map.tab_size);
+        *self.column_mut() = collapsed as u32;
+
+        Ok((self, to_next_stop))
+    }
+}
+
+impl Point {
+    pub fn to_display_point(self, map: &DisplayMap, app: &AppContext) -> Result<DisplayPoint> {
+        let mut display_point = map.fold_map.to_display_point(self);
+        let chars = map
+            .fold_map
+            .chars_at(DisplayPoint::new(display_point.row(), 0), app)?;
+        *display_point.column_mut() =
+            expand_tabs(chars, display_point.column() as usize, map.tab_size) as u32;
+        Ok(display_point)
+    }
+}
+
+impl Anchor {
+    pub fn to_display_point(&self, map: &DisplayMap, app: &AppContext) -> Result<DisplayPoint> {
+        self.to_point(map.buffer.as_ref(app))?
+            .to_display_point(map, app)
+    }
+}
+
+pub struct Chars<'a> {
+    fold_chars: fold_map::Chars<'a>,
+    column: usize,
+    to_next_stop: usize,
+    tab_size: usize,
+}
+
+impl<'a> Iterator for Chars<'a> {
+    type Item = char;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if self.to_next_stop > 0 {
+            self.to_next_stop -= 1;
+            self.column += 1;
+            Some(' ')
+        } else {
+            self.fold_chars.next().map(|c| match c {
+                '\t' => {
+                    self.to_next_stop = self.tab_size - self.column % self.tab_size - 1;
+                    self.column += 1;
+                    ' '
+                }
+                '\n' => {
+                    self.column = 0;
+                    c
+                }
+                _ => {
+                    self.column += 1;
+                    c
+                }
+            })
+        }
+    }
+}
+
+pub fn expand_tabs(chars: impl Iterator<Item = char>, column: usize, tab_size: usize) -> usize {
+    let mut expanded = 0;
+    for c in chars.take(column) {
+        if c == '\t' {
+            expanded += tab_size - expanded % tab_size;
+        } else {
+            expanded += 1;
+        }
+    }
+    expanded
+}
+
+pub fn collapse_tabs(
+    mut chars: impl Iterator<Item = char>,
+    column: usize,
+    bias: Bias,
+    tab_size: usize,
+) -> (usize, usize) {
+    let mut expanded = 0;
+    let mut collapsed = 0;
+    while let Some(c) = chars.next() {
+        if expanded == column {
+            break;
+        }
+
+        if c == '\t' {
+            expanded += tab_size - (expanded % tab_size);
+            if expanded > column {
+                return match bias {
+                    Bias::Left => (collapsed, expanded - column),
+                    Bias::Right => (collapsed + 1, 0),
+                };
+            }
+            collapsed += 1;
+        } else {
+            expanded += 1;
+            collapsed += 1;
+        }
+    }
+    (collapsed, 0)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::app::App;
+    use crate::test_utils::*;
+    use anyhow::Error;
+
+    #[test]
+    fn test_chars_at() -> Result<()> {
+        let mut app = App::new()?;
+        let text = sample_text(6, 6);
+        let buffer = app.add_model(|_| Buffer::new(0, text));
+        let map = app.add_model(|ctx| DisplayMap::new(buffer.clone(), 4, ctx));
+        buffer.update(&mut app, |buffer, ctx| {
+            buffer.edit(
+                vec![
+                    Point::new(1, 0)..Point::new(1, 0),
+                    Point::new(1, 1)..Point::new(1, 1),
+                    Point::new(2, 1)..Point::new(2, 1),
+                ],
+                "\t",
+                Some(ctx),
+            )
+        })?;
+
+        map.read(&app, |map, ctx| {
+            assert_eq!(
+                map.chars_at(DisplayPoint::new(1, 0), ctx)?
+                    .take(10)
+                    .collect::<String>(),
+                "    b   bb"
+            );
+            assert_eq!(
+                map.chars_at(DisplayPoint::new(1, 2), ctx)?
+                    .take(10)
+                    .collect::<String>(),
+                "  b   bbbb"
+            );
+            assert_eq!(
+                map.chars_at(DisplayPoint::new(1, 6), ctx)?
+                    .take(13)
+                    .collect::<String>(),
+                "  bbbbb\nc   c"
+            );
+
+            Ok::<(), Error>(())
+        })?;
+
+        Ok(())
+    }
+
+    #[test]
+    fn test_expand_tabs() {
+        assert_eq!(expand_tabs("\t".chars(), 0, 4), 0);
+        assert_eq!(expand_tabs("\t".chars(), 1, 4), 4);
+        assert_eq!(expand_tabs("\ta".chars(), 2, 4), 5);
+    }
+
+    #[test]
+    fn test_collapse_tabs() {
+        assert_eq!(collapse_tabs("\t".chars(), 0, Bias::Left, 4), (0, 0));
+        assert_eq!(collapse_tabs("\t".chars(), 0, Bias::Right, 4), (0, 0));
+        assert_eq!(collapse_tabs("\t".chars(), 1, Bias::Left, 4), (0, 3));
+        assert_eq!(collapse_tabs("\t".chars(), 1, Bias::Right, 4), (1, 0));
+        assert_eq!(collapse_tabs("\t".chars(), 2, Bias::Left, 4), (0, 2));
+        assert_eq!(collapse_tabs("\t".chars(), 2, Bias::Right, 4), (1, 0));
+        assert_eq!(collapse_tabs("\t".chars(), 3, Bias::Left, 4), (0, 1));
+        assert_eq!(collapse_tabs("\t".chars(), 3, Bias::Right, 4), (1, 0));
+        assert_eq!(collapse_tabs("\t".chars(), 4, Bias::Left, 4), (1, 0));
+        assert_eq!(collapse_tabs("\t".chars(), 4, Bias::Right, 4), (1, 0));
+        assert_eq!(collapse_tabs("\ta".chars(), 5, Bias::Left, 4), (2, 0));
+        assert_eq!(collapse_tabs("\ta".chars(), 5, Bias::Right, 4), (2, 0));
+    }
+
+    #[test]
+    fn test_max_point() -> Result<()> {
+        let mut app = App::new()?;
+        let buffer = app.add_model(|_| Buffer::new(0, "aaa\n\t\tbbb"));
+        let map = app.add_model(|ctx| DisplayMap::new(buffer.clone(), 4, ctx));
+        map.read(&app, |map, app| {
+            assert_eq!(map.max_point(app), DisplayPoint::new(1, 11))
+        });
+        Ok(())
+    }
+}

zed/src/editor/mod.rs 🔗

@@ -0,0 +1,25 @@
+mod buffer;
+mod buffer_element;
+pub mod buffer_view;
+pub mod display_map;
+pub mod movement;
+
+pub use buffer::*;
+pub use buffer_element::*;
+pub use buffer_view::*;
+pub use display_map::DisplayPoint;
+use display_map::*;
+use std::{cmp, ops::Range};
+
+trait RangeExt<T> {
+    fn sorted(&self) -> (T, T);
+}
+
+impl<T: Ord + Clone> RangeExt<T> for Range<T> {
+    fn sorted(&self) -> (T, T) {
+        (
+            cmp::min(&self.start, &self.end).clone(),
+            cmp::max(&self.start, &self.end).clone(),
+        )
+    }
+}

zed/src/editor/movement.rs 🔗

@@ -0,0 +1,60 @@
+use super::{DisplayMap, DisplayPoint};
+use crate::app::AppContext;
+use anyhow::Result;
+use std::cmp;
+
+pub fn left(map: &DisplayMap, mut point: DisplayPoint, app: &AppContext) -> Result<DisplayPoint> {
+    if point.column() > 0 {
+        *point.column_mut() -= 1;
+    } else if point.row() > 0 {
+        *point.row_mut() -= 1;
+        *point.column_mut() = map.line_len(point.row(), app)?;
+    }
+    Ok(point)
+}
+
+pub fn right(map: &DisplayMap, mut point: DisplayPoint, app: &AppContext) -> Result<DisplayPoint> {
+    let max_column = map.line_len(point.row(), app).unwrap();
+    if point.column() < max_column {
+        *point.column_mut() += 1;
+    } else if point.row() < map.max_point(app).row() {
+        *point.row_mut() += 1;
+        *point.column_mut() = 0;
+    }
+    Ok(point)
+}
+
+pub fn up(
+    map: &DisplayMap,
+    mut point: DisplayPoint,
+    goal_column: Option<u32>,
+    app: &AppContext,
+) -> Result<(DisplayPoint, Option<u32>)> {
+    let goal_column = goal_column.or(Some(point.column()));
+    if point.row() > 0 {
+        *point.row_mut() -= 1;
+        *point.column_mut() = cmp::min(goal_column.unwrap(), map.line_len(point.row(), app)?);
+    } else {
+        point = DisplayPoint::new(0, 0);
+    }
+
+    Ok((point, goal_column))
+}
+
+pub fn down(
+    map: &DisplayMap,
+    mut point: DisplayPoint,
+    goal_column: Option<u32>,
+    app: &AppContext,
+) -> Result<(DisplayPoint, Option<u32>)> {
+    let goal_column = goal_column.or(Some(point.column()));
+    let max_point = map.max_point(app);
+    if point.row() < max_point.row() {
+        *point.row_mut() += 1;
+        *point.column_mut() = cmp::min(goal_column.unwrap(), map.line_len(point.row(), app)?)
+    } else {
+        point = max_point;
+    }
+
+    Ok((point, goal_column))
+}

zed/src/sum_tree/cursor.rs 🔗

@@ -0,0 +1,752 @@
+use super::*;
+use arrayvec::ArrayVec;
+use std::{cmp::Ordering, sync::Arc};
+
+#[derive(Clone)]
+struct StackEntry<'a, T: Item, S, U> {
+    tree: &'a SumTree<T>,
+    index: usize,
+    seek_dimension: S,
+    sum_dimension: U,
+}
+
+#[derive(Clone)]
+pub struct Cursor<'a, T: Item, S, U> {
+    tree: &'a SumTree<T>,
+    stack: ArrayVec<[StackEntry<'a, T, S, U>; 16]>,
+    seek_dimension: S,
+    sum_dimension: U,
+    did_seek: bool,
+    at_end: bool,
+}
+
+impl<'a, T, S, U> Cursor<'a, T, S, U>
+where
+    T: Item,
+    S: Dimension<'a, T::Summary>,
+    U: Dimension<'a, T::Summary>,
+{
+    pub fn new(tree: &'a SumTree<T>) -> Self {
+        Self {
+            tree,
+            stack: ArrayVec::new(),
+            seek_dimension: S::default(),
+            sum_dimension: U::default(),
+            did_seek: false,
+            at_end: false,
+        }
+    }
+
+    fn reset(&mut self) {
+        self.did_seek = false;
+        self.at_end = false;
+        self.stack.truncate(0);
+        self.seek_dimension = S::default();
+        self.sum_dimension = U::default();
+    }
+
+    pub fn start(&self) -> &U {
+        &self.sum_dimension
+    }
+
+    pub fn end(&self) -> U {
+        if let Some(item_summary) = self.item_summary() {
+            let mut end = self.start().clone();
+            end.add_summary(item_summary);
+            end
+        } else {
+            self.start().clone()
+        }
+    }
+
+    pub fn item(&self) -> Option<&'a T> {
+        assert!(self.did_seek, "Must seek before calling this method");
+        if let Some(entry) = self.stack.last() {
+            match *entry.tree.0 {
+                Node::Leaf { ref items, .. } => {
+                    if entry.index == items.len() {
+                        None
+                    } else {
+                        Some(&items[entry.index])
+                    }
+                }
+                _ => unreachable!(),
+            }
+        } else {
+            None
+        }
+    }
+
+    fn item_summary(&self) -> Option<&'a T::Summary> {
+        assert!(self.did_seek, "Must seek before calling this method");
+        if let Some(entry) = self.stack.last() {
+            match *entry.tree.0 {
+                Node::Leaf {
+                    ref item_summaries, ..
+                } => {
+                    if entry.index == item_summaries.len() {
+                        None
+                    } else {
+                        Some(&item_summaries[entry.index])
+                    }
+                }
+                _ => unreachable!(),
+            }
+        } else {
+            None
+        }
+    }
+
+    pub fn prev_item(&self) -> Option<&'a T> {
+        assert!(self.did_seek, "Must seek before calling this method");
+        if let Some(entry) = self.stack.last() {
+            if entry.index == 0 {
+                if let Some(prev_leaf) = self.prev_leaf() {
+                    Some(prev_leaf.0.items().last().unwrap())
+                } else {
+                    None
+                }
+            } else {
+                match *entry.tree.0 {
+                    Node::Leaf { ref items, .. } => Some(&items[entry.index - 1]),
+                    _ => unreachable!(),
+                }
+            }
+        } else if self.at_end {
+            self.tree.last()
+        } else {
+            None
+        }
+    }
+
+    fn prev_leaf(&self) -> Option<&'a SumTree<T>> {
+        for entry in self.stack.iter().rev().skip(1) {
+            if entry.index != 0 {
+                match *entry.tree.0 {
+                    Node::Internal {
+                        ref child_trees, ..
+                    } => return Some(child_trees[entry.index - 1].rightmost_leaf()),
+                    Node::Leaf { .. } => unreachable!(),
+                };
+            }
+        }
+        None
+    }
+
+    pub fn prev(&mut self) {
+        assert!(self.did_seek, "Must seek before calling this method");
+
+        if self.at_end {
+            self.seek_dimension = S::default();
+            self.sum_dimension = U::default();
+            self.descend_to_last_item(self.tree);
+            self.at_end = false;
+        } else {
+            while let Some(entry) = self.stack.pop() {
+                if entry.index > 0 {
+                    let new_index = entry.index - 1;
+
+                    if let Some(StackEntry {
+                        seek_dimension,
+                        sum_dimension,
+                        ..
+                    }) = self.stack.last()
+                    {
+                        self.seek_dimension = seek_dimension.clone();
+                        self.sum_dimension = sum_dimension.clone();
+                    } else {
+                        self.seek_dimension = S::default();
+                        self.sum_dimension = U::default();
+                    }
+
+                    match entry.tree.0.as_ref() {
+                        Node::Internal {
+                            child_trees,
+                            child_summaries,
+                            ..
+                        } => {
+                            for summary in &child_summaries[0..new_index] {
+                                self.seek_dimension.add_summary(summary);
+                                self.sum_dimension.add_summary(summary);
+                            }
+                            self.stack.push(StackEntry {
+                                tree: entry.tree,
+                                index: new_index,
+                                seek_dimension: self.seek_dimension.clone(),
+                                sum_dimension: self.sum_dimension.clone(),
+                            });
+                            self.descend_to_last_item(&child_trees[new_index]);
+                        }
+                        Node::Leaf { item_summaries, .. } => {
+                            for item_summary in &item_summaries[0..new_index] {
+                                self.seek_dimension.add_summary(item_summary);
+                                self.sum_dimension.add_summary(item_summary);
+                            }
+                            self.stack.push(StackEntry {
+                                tree: entry.tree,
+                                index: new_index,
+                                seek_dimension: self.seek_dimension.clone(),
+                                sum_dimension: self.sum_dimension.clone(),
+                            });
+                        }
+                    }
+
+                    break;
+                }
+            }
+        }
+    }
+
+    pub fn next(&mut self) {
+        self.next_internal(|_| true)
+    }
+
+    fn next_internal<F>(&mut self, filter_node: F)
+    where
+        F: Fn(&T::Summary) -> bool,
+    {
+        assert!(self.did_seek, "Must seek before calling this method");
+
+        if self.stack.is_empty() {
+            if !self.at_end {
+                self.descend_to_first_item(self.tree, filter_node);
+            }
+        } else {
+            while self.stack.len() > 0 {
+                let new_subtree = {
+                    let entry = self.stack.last_mut().unwrap();
+                    match entry.tree.0.as_ref() {
+                        Node::Internal {
+                            child_trees,
+                            child_summaries,
+                            ..
+                        } => {
+                            while entry.index < child_summaries.len() {
+                                entry
+                                    .seek_dimension
+                                    .add_summary(&child_summaries[entry.index]);
+                                entry
+                                    .sum_dimension
+                                    .add_summary(&child_summaries[entry.index]);
+
+                                entry.index += 1;
+                                if let Some(next_summary) = child_summaries.get(entry.index) {
+                                    if filter_node(next_summary) {
+                                        break;
+                                    } else {
+                                        self.seek_dimension.add_summary(next_summary);
+                                        self.sum_dimension.add_summary(next_summary);
+                                    }
+                                }
+                            }
+
+                            child_trees.get(entry.index)
+                        }
+                        Node::Leaf { item_summaries, .. } => loop {
+                            let item_summary = &item_summaries[entry.index];
+                            self.seek_dimension.add_summary(item_summary);
+                            entry.seek_dimension.add_summary(item_summary);
+                            self.sum_dimension.add_summary(item_summary);
+                            entry.sum_dimension.add_summary(item_summary);
+                            entry.index += 1;
+                            if let Some(next_item_summary) = item_summaries.get(entry.index) {
+                                if filter_node(next_item_summary) {
+                                    return;
+                                }
+                            } else {
+                                break None;
+                            }
+                        },
+                    }
+                };
+
+                if let Some(subtree) = new_subtree {
+                    self.descend_to_first_item(subtree, filter_node);
+                    break;
+                } else {
+                    self.stack.pop();
+                }
+            }
+        }
+
+        self.at_end = self.stack.is_empty();
+    }
+
+    pub fn descend_to_first_item<F>(&mut self, mut subtree: &'a SumTree<T>, filter_node: F)
+    where
+        F: Fn(&T::Summary) -> bool,
+    {
+        self.did_seek = true;
+        loop {
+            subtree = match *subtree.0 {
+                Node::Internal {
+                    ref child_trees,
+                    ref child_summaries,
+                    ..
+                } => {
+                    let mut new_index = None;
+                    for (index, summary) in child_summaries.iter().enumerate() {
+                        if filter_node(summary) {
+                            new_index = Some(index);
+                            break;
+                        }
+                        self.seek_dimension.add_summary(summary);
+                        self.sum_dimension.add_summary(summary);
+                    }
+
+                    if let Some(new_index) = new_index {
+                        self.stack.push(StackEntry {
+                            tree: subtree,
+                            index: new_index,
+                            seek_dimension: self.seek_dimension.clone(),
+                            sum_dimension: self.sum_dimension.clone(),
+                        });
+                        &child_trees[new_index]
+                    } else {
+                        break;
+                    }
+                }
+                Node::Leaf {
+                    ref item_summaries, ..
+                } => {
+                    let mut new_index = None;
+                    for (index, item_summary) in item_summaries.iter().enumerate() {
+                        if filter_node(item_summary) {
+                            new_index = Some(index);
+                            break;
+                        }
+                        self.seek_dimension.add_summary(item_summary);
+                        self.sum_dimension.add_summary(item_summary);
+                    }
+
+                    if let Some(new_index) = new_index {
+                        self.stack.push(StackEntry {
+                            tree: subtree,
+                            index: new_index,
+                            seek_dimension: self.seek_dimension.clone(),
+                            sum_dimension: self.sum_dimension.clone(),
+                        });
+                    }
+                    break;
+                }
+            }
+        }
+    }
+
+    fn descend_to_last_item(&mut self, mut subtree: &'a SumTree<T>) {
+        self.did_seek = true;
+        loop {
+            match subtree.0.as_ref() {
+                Node::Internal {
+                    child_trees,
+                    child_summaries,
+                    ..
+                } => {
+                    for summary in &child_summaries[0..child_summaries.len() - 1] {
+                        self.seek_dimension.add_summary(summary);
+                        self.sum_dimension.add_summary(summary);
+                    }
+
+                    self.stack.push(StackEntry {
+                        tree: subtree,
+                        index: child_trees.len() - 1,
+                        seek_dimension: self.seek_dimension.clone(),
+                        sum_dimension: self.sum_dimension.clone(),
+                    });
+                    subtree = child_trees.last().unwrap();
+                }
+                Node::Leaf { item_summaries, .. } => {
+                    let last_index = item_summaries.len().saturating_sub(1);
+                    for item_summary in &item_summaries[0..last_index] {
+                        self.seek_dimension.add_summary(item_summary);
+                        self.sum_dimension.add_summary(item_summary);
+                    }
+                    self.stack.push(StackEntry {
+                        tree: subtree,
+                        index: last_index,
+                        seek_dimension: self.seek_dimension.clone(),
+                        sum_dimension: self.sum_dimension.clone(),
+                    });
+                    break;
+                }
+            }
+        }
+    }
+}
+
+impl<'a, T, S, U> Cursor<'a, T, S, U>
+where
+    T: Item,
+    S: Dimension<'a, T::Summary> + Ord,
+    U: Dimension<'a, T::Summary>,
+{
+    pub fn seek(&mut self, pos: &S, bias: SeekBias) -> bool {
+        self.reset();
+        self.seek_internal::<()>(pos, bias, &mut SeekAggregate::None)
+    }
+
+    pub fn seek_forward(&mut self, pos: &S, bias: SeekBias) -> bool {
+        self.seek_internal::<()>(pos, bias, &mut SeekAggregate::None)
+    }
+
+    pub fn slice(&mut self, end: &S, bias: SeekBias) -> SumTree<T> {
+        let mut slice = SeekAggregate::Slice(SumTree::new());
+        self.seek_internal::<()>(end, bias, &mut slice);
+        if let SeekAggregate::Slice(slice) = slice {
+            slice
+        } else {
+            unreachable!()
+        }
+    }
+
+    pub fn suffix(&mut self) -> SumTree<T> {
+        let extent = self.tree.extent::<S>();
+        let mut slice = SeekAggregate::Slice(SumTree::new());
+        self.seek_internal::<()>(&extent, SeekBias::Right, &mut slice);
+        if let SeekAggregate::Slice(slice) = slice {
+            slice
+        } else {
+            unreachable!()
+        }
+    }
+
+    pub fn summary<D>(&mut self, end: &S, bias: SeekBias) -> D
+    where
+        D: Dimension<'a, T::Summary>,
+    {
+        let mut summary = SeekAggregate::Summary(D::default());
+        self.seek_internal(end, bias, &mut summary);
+        if let SeekAggregate::Summary(summary) = summary {
+            summary
+        } else {
+            unreachable!()
+        }
+    }
+
+    fn seek_internal<D>(
+        &mut self,
+        target: &S,
+        bias: SeekBias,
+        aggregate: &mut SeekAggregate<T, D>,
+    ) -> bool
+    where
+        D: Dimension<'a, T::Summary>,
+    {
+        debug_assert!(target >= &self.seek_dimension);
+        let mut containing_subtree = None;
+
+        if self.did_seek {
+            'outer: while let Some(entry) = self.stack.last_mut() {
+                {
+                    match *entry.tree.0 {
+                        Node::Internal {
+                            ref child_summaries,
+                            ref child_trees,
+                            ..
+                        } => {
+                            entry.index += 1;
+                            for (child_tree, child_summary) in child_trees[entry.index..]
+                                .iter()
+                                .zip(&child_summaries[entry.index..])
+                            {
+                                let mut child_end = self.seek_dimension.clone();
+                                child_end.add_summary(&child_summary);
+
+                                let comparison = target.cmp(&child_end);
+                                if comparison == Ordering::Greater
+                                    || (comparison == Ordering::Equal && bias == SeekBias::Right)
+                                {
+                                    self.seek_dimension.add_summary(child_summary);
+                                    self.sum_dimension.add_summary(child_summary);
+                                    match aggregate {
+                                        SeekAggregate::None => {}
+                                        SeekAggregate::Slice(slice) => {
+                                            slice.push_tree(child_tree.clone());
+                                        }
+                                        SeekAggregate::Summary(summary) => {
+                                            summary.add_summary(child_summary);
+                                        }
+                                    }
+                                    entry.index += 1;
+                                } else {
+                                    containing_subtree = Some(child_tree);
+                                    break 'outer;
+                                }
+                            }
+                        }
+                        Node::Leaf {
+                            ref items,
+                            ref item_summaries,
+                            ..
+                        } => {
+                            let mut slice_items = ArrayVec::<[T; 2 * TREE_BASE]>::new();
+                            let mut slice_item_summaries =
+                                ArrayVec::<[T::Summary; 2 * TREE_BASE]>::new();
+                            let mut slice_items_summary = match aggregate {
+                                SeekAggregate::Slice(_) => Some(T::Summary::default()),
+                                _ => None,
+                            };
+
+                            for (item, item_summary) in items[entry.index..]
+                                .iter()
+                                .zip(&item_summaries[entry.index..])
+                            {
+                                let mut item_end = self.seek_dimension.clone();
+                                item_end.add_summary(item_summary);
+
+                                let comparison = target.cmp(&item_end);
+                                if comparison == Ordering::Greater
+                                    || (comparison == Ordering::Equal && bias == SeekBias::Right)
+                                {
+                                    self.seek_dimension.add_summary(item_summary);
+                                    self.sum_dimension.add_summary(item_summary);
+                                    match aggregate {
+                                        SeekAggregate::None => {}
+                                        SeekAggregate::Slice(_) => {
+                                            slice_items.push(item.clone());
+                                            slice_item_summaries.push(item_summary.clone());
+                                            *slice_items_summary.as_mut().unwrap() += item_summary;
+                                        }
+                                        SeekAggregate::Summary(summary) => {
+                                            summary.add_summary(item_summary);
+                                        }
+                                    }
+                                    entry.index += 1;
+                                } else {
+                                    if let SeekAggregate::Slice(slice) = aggregate {
+                                        slice.push_tree(SumTree(Arc::new(Node::Leaf {
+                                            summary: slice_items_summary.unwrap(),
+                                            items: slice_items,
+                                            item_summaries: slice_item_summaries,
+                                        })));
+                                    }
+                                    break 'outer;
+                                }
+                            }
+
+                            if let SeekAggregate::Slice(slice) = aggregate {
+                                if !slice_items.is_empty() {
+                                    slice.push_tree(SumTree(Arc::new(Node::Leaf {
+                                        summary: slice_items_summary.unwrap(),
+                                        items: slice_items,
+                                        item_summaries: slice_item_summaries,
+                                    })));
+                                }
+                            }
+                        }
+                    }
+                }
+
+                self.stack.pop();
+            }
+        } else {
+            self.did_seek = true;
+            containing_subtree = Some(self.tree);
+        }
+
+        if let Some(mut subtree) = containing_subtree {
+            loop {
+                let mut next_subtree = None;
+                match *subtree.0 {
+                    Node::Internal {
+                        ref child_summaries,
+                        ref child_trees,
+                        ..
+                    } => {
+                        for (index, (child_tree, child_summary)) in
+                            child_trees.iter().zip(child_summaries).enumerate()
+                        {
+                            let mut child_end = self.seek_dimension.clone();
+                            child_end.add_summary(child_summary);
+
+                            let comparison = target.cmp(&child_end);
+                            if comparison == Ordering::Greater
+                                || (comparison == Ordering::Equal && bias == SeekBias::Right)
+                            {
+                                self.seek_dimension.add_summary(child_summary);
+                                self.sum_dimension.add_summary(child_summary);
+                                match aggregate {
+                                    SeekAggregate::None => {}
+                                    SeekAggregate::Slice(slice) => {
+                                        slice.push_tree(child_trees[index].clone());
+                                    }
+                                    SeekAggregate::Summary(summary) => {
+                                        summary.add_summary(child_summary);
+                                    }
+                                }
+                            } else {
+                                self.stack.push(StackEntry {
+                                    tree: subtree,
+                                    index,
+                                    seek_dimension: self.seek_dimension.clone(),
+                                    sum_dimension: self.sum_dimension.clone(),
+                                });
+                                next_subtree = Some(child_tree);
+                                break;
+                            }
+                        }
+                    }
+                    Node::Leaf {
+                        ref items,
+                        ref item_summaries,
+                        ..
+                    } => {
+                        let mut slice_items = ArrayVec::<[T; 2 * TREE_BASE]>::new();
+                        let mut slice_item_summaries =
+                            ArrayVec::<[T::Summary; 2 * TREE_BASE]>::new();
+                        let mut slice_items_summary = match aggregate {
+                            SeekAggregate::Slice(_) => Some(T::Summary::default()),
+                            _ => None,
+                        };
+
+                        for (index, (item, item_summary)) in
+                            items.iter().zip(item_summaries).enumerate()
+                        {
+                            let mut child_end = self.seek_dimension.clone();
+                            child_end.add_summary(item_summary);
+
+                            let comparison = target.cmp(&child_end);
+                            if comparison == Ordering::Greater
+                                || (comparison == Ordering::Equal && bias == SeekBias::Right)
+                            {
+                                self.seek_dimension.add_summary(item_summary);
+                                self.sum_dimension.add_summary(item_summary);
+                                match aggregate {
+                                    SeekAggregate::None => {}
+                                    SeekAggregate::Slice(_) => {
+                                        slice_items.push(item.clone());
+                                        *slice_items_summary.as_mut().unwrap() += item_summary;
+                                        slice_item_summaries.push(item_summary.clone());
+                                    }
+                                    SeekAggregate::Summary(summary) => {
+                                        summary.add_summary(item_summary);
+                                    }
+                                }
+                            } else {
+                                self.stack.push(StackEntry {
+                                    tree: subtree,
+                                    index,
+                                    seek_dimension: self.seek_dimension.clone(),
+                                    sum_dimension: self.sum_dimension.clone(),
+                                });
+                                break;
+                            }
+                        }
+
+                        if let SeekAggregate::Slice(slice) = aggregate {
+                            if !slice_items.is_empty() {
+                                slice.push_tree(SumTree(Arc::new(Node::Leaf {
+                                    summary: slice_items_summary.unwrap(),
+                                    items: slice_items,
+                                    item_summaries: slice_item_summaries,
+                                })));
+                            }
+                        }
+                    }
+                };
+
+                if let Some(next_subtree) = next_subtree {
+                    subtree = next_subtree;
+                } else {
+                    break;
+                }
+            }
+        }
+
+        self.at_end = self.stack.is_empty();
+        if bias == SeekBias::Left {
+            let mut end = self.seek_dimension.clone();
+            if let Some(summary) = self.item_summary() {
+                end.add_summary(summary);
+            }
+            *target == end
+        } else {
+            *target == self.seek_dimension
+        }
+    }
+}
+
+impl<'a, T, S, U> Iterator for Cursor<'a, T, S, U>
+where
+    T: Item,
+    S: Dimension<'a, T::Summary>,
+    U: Dimension<'a, T::Summary>,
+{
+    type Item = &'a T;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if !self.did_seek {
+            self.descend_to_first_item(self.tree, |_| true);
+        }
+
+        if let Some(item) = self.item() {
+            self.next();
+            Some(item)
+        } else {
+            None
+        }
+    }
+}
+
+pub struct FilterCursor<'a, F: Fn(&T::Summary) -> bool, T: Item, U> {
+    cursor: Cursor<'a, T, (), U>,
+    filter_node: F,
+}
+
+impl<'a, F, T, U> FilterCursor<'a, F, T, U>
+where
+    F: Fn(&T::Summary) -> bool,
+    T: Item,
+    U: Dimension<'a, T::Summary>,
+{
+    pub fn new(tree: &'a SumTree<T>, filter_node: F) -> Self {
+        let mut cursor = tree.cursor::<(), U>();
+        if filter_node(&tree.summary()) {
+            cursor.descend_to_first_item(tree, &filter_node);
+        } else {
+            cursor.did_seek = true;
+            cursor.at_end = true;
+        }
+
+        Self {
+            cursor,
+            filter_node,
+        }
+    }
+
+    pub fn start(&self) -> &U {
+        self.cursor.start()
+    }
+
+    pub fn item(&self) -> Option<&'a T> {
+        self.cursor.item()
+    }
+
+    pub fn next(&mut self) {
+        self.cursor.next_internal(&self.filter_node);
+    }
+}
+
+impl<'a, F, T, U> Iterator for FilterCursor<'a, F, T, U>
+where
+    F: Fn(&T::Summary) -> bool,
+    T: Item,
+    U: Dimension<'a, T::Summary>,
+{
+    type Item = &'a T;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if let Some(item) = self.item() {
+            self.cursor.next_internal(&self.filter_node);
+            Some(item)
+        } else {
+            None
+        }
+    }
+}
+
+enum SeekAggregate<T: Item, D> {
+    None,
+    Slice(SumTree<T>),
+    Summary(D),
+}

zed/src/sum_tree/mod.rs 🔗

@@ -0,0 +1,820 @@
+mod cursor;
+
+use arrayvec::ArrayVec;
+pub use cursor::Cursor;
+pub use cursor::FilterCursor;
+use std::{fmt, iter::FromIterator, ops::AddAssign, sync::Arc};
+
+#[cfg(test)]
+const TREE_BASE: usize = 2;
+#[cfg(not(test))]
+const TREE_BASE: usize = 6;
+
+pub trait Item: Clone + Eq + fmt::Debug {
+    type Summary: for<'a> AddAssign<&'a Self::Summary> + Default + Clone + fmt::Debug;
+
+    fn summary(&self) -> Self::Summary;
+}
+
+pub trait KeyedItem: Item {
+    type Key: for<'a> Dimension<'a, Self::Summary> + Ord;
+
+    fn key(&self) -> Self::Key;
+}
+
+pub trait Dimension<'a, Summary: Default>: 'a + Clone + fmt::Debug + Default {
+    fn add_summary(&mut self, summary: &'a Summary);
+}
+
+impl<'a, T: Default> Dimension<'a, T> for () {
+    fn add_summary(&mut self, _: &'a T) {}
+}
+
+#[derive(Copy, Clone, Eq, PartialEq)]
+pub enum SeekBias {
+    Left,
+    Right,
+}
+
+#[derive(Debug, Clone)]
+pub struct SumTree<T: Item>(Arc<Node<T>>);
+
+impl<T: Item> SumTree<T> {
+    pub fn new() -> Self {
+        SumTree(Arc::new(Node::Leaf {
+            summary: T::Summary::default(),
+            items: ArrayVec::new(),
+            item_summaries: ArrayVec::new(),
+        }))
+    }
+
+    pub fn from_item(item: T) -> Self {
+        let mut tree = Self::new();
+        tree.push(item);
+        tree
+    }
+
+    pub fn items(&self) -> Vec<T> {
+        let mut cursor = self.cursor::<(), ()>();
+        cursor.descend_to_first_item(self, |_| true);
+        cursor.cloned().collect()
+    }
+
+    pub fn cursor<'a, S, U>(&'a self) -> Cursor<T, S, U>
+    where
+        S: Dimension<'a, T::Summary>,
+        U: Dimension<'a, T::Summary>,
+    {
+        Cursor::new(self)
+    }
+
+    pub fn filter<'a, F, U>(&'a self, filter_node: F) -> FilterCursor<F, T, U>
+    where
+        F: Fn(&T::Summary) -> bool,
+        U: Dimension<'a, T::Summary>,
+    {
+        FilterCursor::new(self, filter_node)
+    }
+
+    #[allow(dead_code)]
+    pub fn first(&self) -> Option<&T> {
+        self.leftmost_leaf().0.items().first()
+    }
+
+    pub fn last(&self) -> Option<&T> {
+        self.rightmost_leaf().0.items().last()
+    }
+
+    pub fn extent<'a, D: Dimension<'a, T::Summary>>(&'a self) -> D {
+        let mut extent = D::default();
+        match self.0.as_ref() {
+            Node::Internal { summary, .. } | Node::Leaf { summary, .. } => {
+                extent.add_summary(summary)
+            }
+        }
+        extent
+    }
+
+    pub fn summary(&self) -> T::Summary {
+        match self.0.as_ref() {
+            Node::Internal { summary, .. } => summary.clone(),
+            Node::Leaf { summary, .. } => summary.clone(),
+        }
+    }
+
+    #[cfg(test)]
+    pub fn is_empty(&self) -> bool {
+        match self.0.as_ref() {
+            Node::Internal { .. } => false,
+            Node::Leaf { items, .. } => items.is_empty(),
+        }
+    }
+
+    pub fn extend<I>(&mut self, iter: I)
+    where
+        I: IntoIterator<Item = T>,
+    {
+        let mut leaf: Option<Node<T>> = None;
+
+        for item in iter {
+            if leaf.is_some() && leaf.as_ref().unwrap().items().len() == 2 * TREE_BASE {
+                self.push_tree(SumTree(Arc::new(leaf.take().unwrap())));
+            }
+
+            if leaf.is_none() {
+                leaf = Some(Node::Leaf::<T> {
+                    summary: T::Summary::default(),
+                    items: ArrayVec::new(),
+                    item_summaries: ArrayVec::new(),
+                });
+            }
+
+            if let Some(Node::Leaf {
+                summary,
+                items,
+                item_summaries,
+            }) = leaf.as_mut()
+            {
+                let item_summary = item.summary();
+                *summary += &item_summary;
+                items.push(item);
+                item_summaries.push(item_summary);
+            } else {
+                unreachable!()
+            }
+        }
+
+        if leaf.is_some() {
+            self.push_tree(SumTree(Arc::new(leaf.take().unwrap())));
+        }
+    }
+
+    pub fn push(&mut self, item: T) {
+        let summary = item.summary();
+        self.push_tree(SumTree::from_child_trees(vec![SumTree(Arc::new(
+            Node::Leaf {
+                summary: summary.clone(),
+                items: ArrayVec::from_iter(Some(item)),
+                item_summaries: ArrayVec::from_iter(Some(summary)),
+            },
+        ))]))
+    }
+
+    pub fn push_tree(&mut self, other: Self) {
+        let other_node = other.0.clone();
+        if !other_node.is_leaf() || other_node.items().len() > 0 {
+            if self.0.height() < other_node.height() {
+                for tree in other_node.child_trees() {
+                    self.push_tree(tree.clone());
+                }
+            } else if let Some(split_tree) = self.push_tree_recursive(other) {
+                *self = Self::from_child_trees(vec![self.clone(), split_tree]);
+            }
+        }
+    }
+
+    fn push_tree_recursive(&mut self, other: SumTree<T>) -> Option<SumTree<T>> {
+        match Arc::make_mut(&mut self.0) {
+            Node::Internal {
+                height,
+                summary,
+                child_summaries,
+                child_trees,
+                ..
+            } => {
+                let other_node = other.0.clone();
+                *summary += other_node.summary();
+
+                let height_delta = *height - other_node.height();
+                let mut summaries_to_append = ArrayVec::<[T::Summary; 2 * TREE_BASE]>::new();
+                let mut trees_to_append = ArrayVec::<[SumTree<T>; 2 * TREE_BASE]>::new();
+                if height_delta == 0 {
+                    summaries_to_append.extend(other_node.child_summaries().iter().cloned());
+                    trees_to_append.extend(other_node.child_trees().iter().cloned());
+                } else if height_delta == 1 && !other_node.is_underflowing() {
+                    summaries_to_append.push(other_node.summary().clone());
+                    trees_to_append.push(other)
+                } else {
+                    let tree_to_append = child_trees.last_mut().unwrap().push_tree_recursive(other);
+                    *child_summaries.last_mut().unwrap() =
+                        child_trees.last().unwrap().0.summary().clone();
+
+                    if let Some(split_tree) = tree_to_append {
+                        summaries_to_append.push(split_tree.0.summary().clone());
+                        trees_to_append.push(split_tree);
+                    }
+                }
+
+                let child_count = child_trees.len() + trees_to_append.len();
+                if child_count > 2 * TREE_BASE {
+                    let left_summaries: ArrayVec<_>;
+                    let right_summaries: ArrayVec<_>;
+                    let left_trees;
+                    let right_trees;
+
+                    let midpoint = (child_count + child_count % 2) / 2;
+                    {
+                        let mut all_summaries = child_summaries
+                            .iter()
+                            .chain(summaries_to_append.iter())
+                            .cloned();
+                        left_summaries = all_summaries.by_ref().take(midpoint).collect();
+                        right_summaries = all_summaries.collect();
+                        let mut all_trees =
+                            child_trees.iter().chain(trees_to_append.iter()).cloned();
+                        left_trees = all_trees.by_ref().take(midpoint).collect();
+                        right_trees = all_trees.collect();
+                    }
+                    *summary = sum(left_summaries.iter());
+                    *child_summaries = left_summaries;
+                    *child_trees = left_trees;
+
+                    Some(SumTree(Arc::new(Node::Internal {
+                        height: *height,
+                        summary: sum(right_summaries.iter()),
+                        child_summaries: right_summaries,
+                        child_trees: right_trees,
+                    })))
+                } else {
+                    child_summaries.extend(summaries_to_append);
+                    child_trees.extend(trees_to_append);
+                    None
+                }
+            }
+            Node::Leaf {
+                summary,
+                items,
+                item_summaries,
+            } => {
+                let other_node = other.0;
+
+                let child_count = items.len() + other_node.items().len();
+                if child_count > 2 * TREE_BASE {
+                    let left_items;
+                    let right_items;
+                    let left_summaries;
+                    let right_summaries: ArrayVec<[T::Summary; 2 * TREE_BASE]>;
+
+                    let midpoint = (child_count + child_count % 2) / 2;
+                    {
+                        let mut all_items = items.iter().chain(other_node.items().iter()).cloned();
+                        left_items = all_items.by_ref().take(midpoint).collect();
+                        right_items = all_items.collect();
+
+                        let mut all_summaries = item_summaries
+                            .iter()
+                            .chain(other_node.child_summaries())
+                            .cloned();
+                        left_summaries = all_summaries.by_ref().take(midpoint).collect();
+                        right_summaries = all_summaries.collect();
+                    }
+                    *items = left_items;
+                    *item_summaries = left_summaries;
+                    *summary = sum(item_summaries.iter());
+                    Some(SumTree(Arc::new(Node::Leaf {
+                        items: right_items,
+                        summary: sum(right_summaries.iter()),
+                        item_summaries: right_summaries,
+                    })))
+                } else {
+                    *summary += other_node.summary();
+                    items.extend(other_node.items().iter().cloned());
+                    item_summaries.extend(other_node.child_summaries().iter().cloned());
+                    None
+                }
+            }
+        }
+    }
+
+    fn from_child_trees(child_trees: Vec<SumTree<T>>) -> Self {
+        let height = child_trees[0].0.height() + 1;
+        let mut child_summaries = ArrayVec::new();
+        for child in &child_trees {
+            child_summaries.push(child.0.summary().clone());
+        }
+        let summary = sum(child_summaries.iter());
+        SumTree(Arc::new(Node::Internal {
+            height,
+            summary,
+            child_summaries,
+            child_trees: ArrayVec::from_iter(child_trees),
+        }))
+    }
+
+    fn leftmost_leaf(&self) -> &Self {
+        match *self.0 {
+            Node::Leaf { .. } => self,
+            Node::Internal {
+                ref child_trees, ..
+            } => child_trees.first().unwrap().leftmost_leaf(),
+        }
+    }
+
+    fn rightmost_leaf(&self) -> &Self {
+        match *self.0 {
+            Node::Leaf { .. } => self,
+            Node::Internal {
+                ref child_trees, ..
+            } => child_trees.last().unwrap().rightmost_leaf(),
+        }
+    }
+}
+
+impl<T: KeyedItem> SumTree<T> {
+    pub fn insert(&mut self, item: T) {
+        *self = {
+            let mut cursor = self.cursor::<T::Key, ()>();
+            let mut new_tree = cursor.slice(&item.key(), SeekBias::Left);
+            new_tree.push(item);
+            new_tree.push_tree(cursor.suffix());
+            new_tree
+        };
+    }
+
+    pub fn edit(&mut self, edits: &mut [Edit<T>]) {
+        if edits.is_empty() {
+            return;
+        }
+
+        edits.sort_unstable_by_key(|item| item.key());
+
+        *self = {
+            let mut cursor = self.cursor::<T::Key, ()>();
+            let mut new_tree = SumTree::new();
+            let mut buffered_items = Vec::new();
+
+            cursor.seek(&T::Key::default(), SeekBias::Left);
+            for edit in edits {
+                let new_key = edit.key();
+                let mut old_item = cursor.item();
+
+                if old_item
+                    .as_ref()
+                    .map_or(false, |old_item| old_item.key() < new_key)
+                {
+                    new_tree.extend(buffered_items.drain(..));
+                    let slice = cursor.slice(&new_key, SeekBias::Left);
+                    new_tree.push_tree(slice);
+                    old_item = cursor.item();
+                }
+                if old_item.map_or(false, |old_item| old_item.key() == new_key) {
+                    cursor.next();
+                }
+                match edit {
+                    Edit::Insert(item) => {
+                        buffered_items.push(item.clone());
+                    }
+                    Edit::Remove(_) => {}
+                }
+            }
+
+            new_tree.extend(buffered_items);
+            new_tree.push_tree(cursor.suffix());
+            new_tree
+        };
+    }
+}
+
+#[derive(Clone, Debug)]
+pub enum Node<T: Item> {
+    Internal {
+        height: u8,
+        summary: T::Summary,
+        child_summaries: ArrayVec<[T::Summary; 2 * TREE_BASE]>,
+        child_trees: ArrayVec<[SumTree<T>; 2 * TREE_BASE]>,
+    },
+    Leaf {
+        summary: T::Summary,
+        items: ArrayVec<[T; 2 * TREE_BASE]>,
+        item_summaries: ArrayVec<[T::Summary; 2 * TREE_BASE]>,
+    },
+}
+
+impl<T: Item> Node<T> {
+    fn is_leaf(&self) -> bool {
+        match self {
+            Node::Leaf { .. } => true,
+            _ => false,
+        }
+    }
+
+    fn height(&self) -> u8 {
+        match self {
+            Node::Internal { height, .. } => *height,
+            Node::Leaf { .. } => 0,
+        }
+    }
+
+    fn summary(&self) -> &T::Summary {
+        match self {
+            Node::Internal { summary, .. } => summary,
+            Node::Leaf { summary, .. } => summary,
+        }
+    }
+
+    fn child_summaries(&self) -> &[T::Summary] {
+        match self {
+            Node::Internal {
+                child_summaries, ..
+            } => child_summaries.as_slice(),
+            Node::Leaf { item_summaries, .. } => item_summaries.as_slice(),
+        }
+    }
+
+    fn child_trees(&self) -> &ArrayVec<[SumTree<T>; 2 * TREE_BASE]> {
+        match self {
+            Node::Internal { child_trees, .. } => child_trees,
+            Node::Leaf { .. } => panic!("Leaf nodes have no child trees"),
+        }
+    }
+
+    fn items(&self) -> &ArrayVec<[T; 2 * TREE_BASE]> {
+        match self {
+            Node::Leaf { items, .. } => items,
+            Node::Internal { .. } => panic!("Internal nodes have no items"),
+        }
+    }
+
+    fn is_underflowing(&self) -> bool {
+        match self {
+            Node::Internal { child_trees, .. } => child_trees.len() < TREE_BASE,
+            Node::Leaf { items, .. } => items.len() < TREE_BASE,
+        }
+    }
+}
+
+#[derive(Debug)]
+pub enum Edit<T: KeyedItem> {
+    Insert(T),
+    Remove(T),
+}
+
+impl<T: KeyedItem> Edit<T> {
+    fn key(&self) -> T::Key {
+        match self {
+            Edit::Insert(item) | Edit::Remove(item) => item.key(),
+        }
+    }
+}
+
+fn sum<'a, T, I>(iter: I) -> T
+where
+    T: 'a + Default + AddAssign<&'a T>,
+    I: Iterator<Item = &'a T>,
+{
+    let mut sum = T::default();
+    for value in iter {
+        sum += value;
+    }
+    sum
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::ops::Add;
+
+    #[test]
+    fn test_extend_and_push_tree() {
+        let mut tree1 = SumTree::new();
+        tree1.extend(0..20);
+
+        let mut tree2 = SumTree::new();
+        tree2.extend(50..100);
+
+        tree1.push_tree(tree2);
+        assert_eq!(tree1.items(), (0..20).chain(50..100).collect::<Vec<u8>>());
+    }
+
+    #[test]
+    fn test_random() {
+        for seed in 0..100 {
+            use rand::{distributions, prelude::*};
+
+            let rng = &mut StdRng::seed_from_u64(seed);
+
+            let mut tree = SumTree::<u8>::new();
+            let count = rng.gen_range(0..10);
+            tree.extend(rng.sample_iter(distributions::Standard).take(count));
+
+            for _ in 0..5 {
+                let splice_end = rng.gen_range(0..tree.extent::<Count>().0 + 1);
+                let splice_start = rng.gen_range(0..splice_end + 1);
+                let count = rng.gen_range(0..3);
+                let tree_end = tree.extent::<Count>();
+                let new_items = rng
+                    .sample_iter(distributions::Standard)
+                    .take(count)
+                    .collect::<Vec<u8>>();
+
+                let mut reference_items = tree.items();
+                reference_items.splice(splice_start..splice_end, new_items.clone());
+
+                tree = {
+                    let mut cursor = tree.cursor::<Count, ()>();
+                    let mut new_tree = cursor.slice(&Count(splice_start), SeekBias::Right);
+                    new_tree.extend(new_items);
+                    cursor.seek(&Count(splice_end), SeekBias::Right);
+                    new_tree.push_tree(cursor.slice(&tree_end, SeekBias::Right));
+                    new_tree
+                };
+
+                assert_eq!(tree.items(), reference_items);
+
+                let mut filter_cursor = tree.filter::<_, Count>(|summary| summary.contains_even);
+                let mut reference_filter = tree
+                    .items()
+                    .into_iter()
+                    .enumerate()
+                    .filter(|(_, item)| (item & 1) == 0);
+                while let Some(actual_item) = filter_cursor.item() {
+                    let (reference_index, reference_item) = reference_filter.next().unwrap();
+                    assert_eq!(actual_item, &reference_item);
+                    assert_eq!(filter_cursor.start().0, reference_index);
+                    filter_cursor.next();
+                }
+                assert!(reference_filter.next().is_none());
+
+                let mut pos = rng.gen_range(0..tree.extent::<Count>().0 + 1);
+                let mut before_start = false;
+                let mut cursor = tree.cursor::<Count, Count>();
+                cursor.seek(&Count(pos), SeekBias::Right);
+
+                for i in 0..10 {
+                    assert_eq!(cursor.start().0, pos);
+
+                    if pos > 0 {
+                        assert_eq!(cursor.prev_item().unwrap(), &reference_items[pos - 1]);
+                    } else {
+                        assert_eq!(cursor.prev_item(), None);
+                    }
+
+                    if pos < reference_items.len() && !before_start {
+                        assert_eq!(cursor.item().unwrap(), &reference_items[pos]);
+                    } else {
+                        assert_eq!(cursor.item(), None);
+                    }
+
+                    if i < 5 {
+                        cursor.next();
+                        if pos < reference_items.len() {
+                            pos += 1;
+                            before_start = false;
+                        }
+                    } else {
+                        cursor.prev();
+                        if pos == 0 {
+                            before_start = true;
+                        }
+                        pos = pos.saturating_sub(1);
+                    }
+                }
+            }
+
+            for _ in 0..10 {
+                let end = rng.gen_range(0..tree.extent::<Count>().0 + 1);
+                let start = rng.gen_range(0..end + 1);
+                let start_bias = if rng.gen() {
+                    SeekBias::Left
+                } else {
+                    SeekBias::Right
+                };
+                let end_bias = if rng.gen() {
+                    SeekBias::Left
+                } else {
+                    SeekBias::Right
+                };
+
+                let mut cursor = tree.cursor::<Count, ()>();
+                cursor.seek(&Count(start), start_bias);
+                let slice = cursor.slice(&Count(end), end_bias);
+
+                cursor.seek(&Count(start), start_bias);
+                let summary = cursor.summary::<Sum>(&Count(end), end_bias);
+
+                assert_eq!(summary, slice.summary().sum);
+            }
+        }
+    }
+
+    #[test]
+    fn test_cursor() {
+        // Empty tree
+        let tree = SumTree::<u8>::new();
+        let mut cursor = tree.cursor::<Count, Sum>();
+        assert_eq!(
+            cursor.slice(&Count(0), SeekBias::Right).items(),
+            Vec::<u8>::new()
+        );
+        assert_eq!(cursor.item(), None);
+        assert_eq!(cursor.prev_item(), None);
+        assert_eq!(cursor.start(), &Sum(0));
+
+        // Single-element tree
+        let mut tree = SumTree::<u8>::new();
+        tree.extend(vec![1]);
+        let mut cursor = tree.cursor::<Count, Sum>();
+        assert_eq!(
+            cursor.slice(&Count(0), SeekBias::Right).items(),
+            Vec::<u8>::new()
+        );
+        assert_eq!(cursor.item(), Some(&1));
+        assert_eq!(cursor.prev_item(), None);
+        assert_eq!(cursor.start(), &Sum(0));
+
+        cursor.next();
+        assert_eq!(cursor.item(), None);
+        assert_eq!(cursor.prev_item(), Some(&1));
+        assert_eq!(cursor.start(), &Sum(1));
+
+        cursor.prev();
+        assert_eq!(cursor.item(), Some(&1));
+        assert_eq!(cursor.prev_item(), None);
+        assert_eq!(cursor.start(), &Sum(0));
+
+        let mut cursor = tree.cursor::<Count, Sum>();
+        assert_eq!(cursor.slice(&Count(1), SeekBias::Right).items(), [1]);
+        assert_eq!(cursor.item(), None);
+        assert_eq!(cursor.prev_item(), Some(&1));
+        assert_eq!(cursor.start(), &Sum(1));
+
+        cursor.seek(&Count(0), SeekBias::Right);
+        assert_eq!(
+            cursor
+                .slice(&tree.extent::<Count>(), SeekBias::Right)
+                .items(),
+            [1]
+        );
+        assert_eq!(cursor.item(), None);
+        assert_eq!(cursor.prev_item(), Some(&1));
+        assert_eq!(cursor.start(), &Sum(1));
+
+        // Multiple-element tree
+        let mut tree = SumTree::new();
+        tree.extend(vec![1, 2, 3, 4, 5, 6]);
+        let mut cursor = tree.cursor::<Count, Sum>();
+
+        assert_eq!(cursor.slice(&Count(2), SeekBias::Right).items(), [1, 2]);
+        assert_eq!(cursor.item(), Some(&3));
+        assert_eq!(cursor.prev_item(), Some(&2));
+        assert_eq!(cursor.start(), &Sum(3));
+
+        cursor.next();
+        assert_eq!(cursor.item(), Some(&4));
+        assert_eq!(cursor.prev_item(), Some(&3));
+        assert_eq!(cursor.start(), &Sum(6));
+
+        cursor.next();
+        assert_eq!(cursor.item(), Some(&5));
+        assert_eq!(cursor.prev_item(), Some(&4));
+        assert_eq!(cursor.start(), &Sum(10));
+
+        cursor.next();
+        assert_eq!(cursor.item(), Some(&6));
+        assert_eq!(cursor.prev_item(), Some(&5));
+        assert_eq!(cursor.start(), &Sum(15));
+
+        cursor.next();
+        cursor.next();
+        assert_eq!(cursor.item(), None);
+        assert_eq!(cursor.prev_item(), Some(&6));
+        assert_eq!(cursor.start(), &Sum(21));
+
+        cursor.prev();
+        assert_eq!(cursor.item(), Some(&6));
+        assert_eq!(cursor.prev_item(), Some(&5));
+        assert_eq!(cursor.start(), &Sum(15));
+
+        cursor.prev();
+        assert_eq!(cursor.item(), Some(&5));
+        assert_eq!(cursor.prev_item(), Some(&4));
+        assert_eq!(cursor.start(), &Sum(10));
+
+        cursor.prev();
+        assert_eq!(cursor.item(), Some(&4));
+        assert_eq!(cursor.prev_item(), Some(&3));
+        assert_eq!(cursor.start(), &Sum(6));
+
+        cursor.prev();
+        assert_eq!(cursor.item(), Some(&3));
+        assert_eq!(cursor.prev_item(), Some(&2));
+        assert_eq!(cursor.start(), &Sum(3));
+
+        cursor.prev();
+        assert_eq!(cursor.item(), Some(&2));
+        assert_eq!(cursor.prev_item(), Some(&1));
+        assert_eq!(cursor.start(), &Sum(1));
+
+        cursor.prev();
+        assert_eq!(cursor.item(), Some(&1));
+        assert_eq!(cursor.prev_item(), None);
+        assert_eq!(cursor.start(), &Sum(0));
+
+        cursor.prev();
+        assert_eq!(cursor.item(), None);
+        assert_eq!(cursor.prev_item(), None);
+        assert_eq!(cursor.start(), &Sum(0));
+
+        cursor.next();
+        assert_eq!(cursor.item(), Some(&1));
+        assert_eq!(cursor.prev_item(), None);
+        assert_eq!(cursor.start(), &Sum(0));
+
+        let mut cursor = tree.cursor::<Count, Sum>();
+        assert_eq!(
+            cursor
+                .slice(&tree.extent::<Count>(), SeekBias::Right)
+                .items(),
+            tree.items()
+        );
+        assert_eq!(cursor.item(), None);
+        assert_eq!(cursor.prev_item(), Some(&6));
+        assert_eq!(cursor.start(), &Sum(21));
+
+        cursor.seek(&Count(3), SeekBias::Right);
+        assert_eq!(
+            cursor
+                .slice(&tree.extent::<Count>(), SeekBias::Right)
+                .items(),
+            [4, 5, 6]
+        );
+        assert_eq!(cursor.item(), None);
+        assert_eq!(cursor.prev_item(), Some(&6));
+        assert_eq!(cursor.start(), &Sum(21));
+
+        // Seeking can bias left or right
+        cursor.seek(&Count(1), SeekBias::Left);
+        assert_eq!(cursor.item(), Some(&1));
+        cursor.seek(&Count(1), SeekBias::Right);
+        assert_eq!(cursor.item(), Some(&2));
+
+        // Slicing without resetting starts from where the cursor is parked at.
+        cursor.seek(&Count(1), SeekBias::Right);
+        assert_eq!(cursor.slice(&Count(3), SeekBias::Right).items(), vec![2, 3]);
+        assert_eq!(cursor.slice(&Count(6), SeekBias::Left).items(), vec![4, 5]);
+        assert_eq!(cursor.slice(&Count(6), SeekBias::Right).items(), vec![6]);
+    }
+
+    #[derive(Clone, Default, Debug)]
+    pub struct IntegersSummary {
+        count: Count,
+        sum: Sum,
+        contains_even: bool,
+    }
+
+    #[derive(Ord, PartialOrd, Default, Eq, PartialEq, Clone, Debug)]
+    struct Count(usize);
+
+    #[derive(Ord, PartialOrd, Default, Eq, PartialEq, Clone, Debug)]
+    struct Sum(usize);
+
+    impl Item for u8 {
+        type Summary = IntegersSummary;
+
+        fn summary(&self) -> Self::Summary {
+            IntegersSummary {
+                count: Count(1),
+                sum: Sum(*self as usize),
+                contains_even: (*self & 1) == 0,
+            }
+        }
+    }
+
+    impl<'a> AddAssign<&'a Self> for IntegersSummary {
+        fn add_assign(&mut self, other: &Self) {
+            self.count.0 += &other.count.0;
+            self.sum.0 += &other.sum.0;
+            self.contains_even |= other.contains_even;
+        }
+    }
+
+    impl<'a> Dimension<'a, IntegersSummary> for Count {
+        fn add_summary(&mut self, summary: &IntegersSummary) {
+            self.0 += summary.count.0;
+        }
+    }
+
+    // impl<'a> Add<&'a Self> for Count {
+    //     type Output = Self;
+    //
+    //     fn add(mut self, other: &Self) -> Self {
+    //         self.0 += other.0;
+    //         self
+    //     }
+    // }
+
+    impl<'a> Dimension<'a, IntegersSummary> for Sum {
+        fn add_summary(&mut self, summary: &IntegersSummary) {
+            self.0 += summary.sum.0;
+        }
+    }
+
+    impl<'a> Add<&'a Self> for Sum {
+        type Output = Self;
+
+        fn add(mut self, other: &Self) -> Self {
+            self.0 += other.0;
+            self
+        }
+    }
+}

zed/src/time.rs 🔗

@@ -0,0 +1,140 @@
+use std::cmp::{self, Ordering};
+use std::collections::HashMap;
+use std::mem;
+use std::ops::{Add, AddAssign};
+use std::sync::Arc;
+
+pub type ReplicaId = u16;
+
+#[derive(Clone, Copy, Debug, Default, Eq, Hash, PartialEq, Ord, PartialOrd)]
+pub struct Local {
+    pub replica_id: ReplicaId,
+    pub value: u64,
+}
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct Global(Arc<HashMap<ReplicaId, u64>>);
+
+#[derive(Clone, Copy, Debug, Default, Eq, Hash, Ord, PartialEq, PartialOrd)]
+pub struct Lamport {
+    pub value: u64,
+    pub replica_id: ReplicaId,
+}
+
+impl Local {
+    pub fn new(replica_id: ReplicaId) -> Self {
+        Self {
+            replica_id,
+            value: 1,
+        }
+    }
+
+    pub fn tick(&mut self) -> Self {
+        let timestamp = *self;
+        self.value += 1;
+        timestamp
+    }
+
+    pub fn observe(&mut self, timestamp: Self) {
+        if timestamp.replica_id == self.replica_id {
+            self.value = cmp::max(self.value, timestamp.value + 1);
+        }
+    }
+}
+
+impl<'a> Add<&'a Self> for Local {
+    type Output = Local;
+
+    fn add(self, other: &'a Self) -> Self::Output {
+        cmp::max(&self, other).clone()
+    }
+}
+
+impl<'a> AddAssign<&'a Local> for Local {
+    fn add_assign(&mut self, other: &Self) {
+        if *self < *other {
+            *self = other.clone();
+        }
+    }
+}
+
+impl Global {
+    pub fn new() -> Self {
+        Global(Arc::new(HashMap::new()))
+    }
+
+    pub fn get(&self, replica_id: ReplicaId) -> u64 {
+        *self.0.get(&replica_id).unwrap_or(&0)
+    }
+
+    pub fn observe(&mut self, timestamp: Local) {
+        let map = Arc::make_mut(&mut self.0);
+        let value = map.entry(timestamp.replica_id).or_insert(0);
+        *value = cmp::max(*value, timestamp.value);
+    }
+
+    pub fn observe_all(&mut self, other: &Self) {
+        for (replica_id, value) in other.0.as_ref() {
+            self.observe(Local {
+                replica_id: *replica_id,
+                value: *value,
+            });
+        }
+    }
+
+    pub fn observed(&self, timestamp: Local) -> bool {
+        self.get(timestamp.replica_id) >= timestamp.value
+    }
+
+    pub fn changed_since(&self, other: &Self) -> bool {
+        self.0
+            .iter()
+            .any(|(replica_id, value)| *value > other.get(*replica_id))
+    }
+}
+
+impl PartialOrd for Global {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        let mut global_ordering = Ordering::Equal;
+
+        for replica_id in self.0.keys().chain(other.0.keys()) {
+            let ordering = self.get(*replica_id).cmp(&other.get(*replica_id));
+            if ordering != Ordering::Equal {
+                if global_ordering == Ordering::Equal {
+                    global_ordering = ordering;
+                } else if ordering != global_ordering {
+                    return None;
+                }
+            }
+        }
+
+        Some(global_ordering)
+    }
+}
+
+impl Lamport {
+    pub fn new(replica_id: ReplicaId) -> Self {
+        Self {
+            value: 1,
+            replica_id,
+        }
+    }
+
+    pub fn tick(&mut self) -> Self {
+        let timestamp = *self;
+        self.value += 1;
+        timestamp
+    }
+
+    pub fn observe(&mut self, timestamp: Self) {
+        self.value = cmp::max(self.value, timestamp.value) + 1;
+    }
+
+    pub fn to_bytes(&self) -> [u8; 24] {
+        let mut bytes = [0; 24];
+        bytes[0..8].copy_from_slice(unsafe { &mem::transmute::<u64, [u8; 8]>(self.value.to_be()) });
+        bytes[8..10]
+            .copy_from_slice(unsafe { &mem::transmute::<u16, [u8; 2]>(self.replica_id.to_be()) });
+        bytes
+    }
+}