1use std::{any::Any, cell::Cell, fmt::Debug, ops::Range, rc::Rc, sync::Arc};
2
3use crate::{IntoElement, prelude::*, px, relative};
4use gpui::{
5 Along, App, Axis as ScrollbarAxis, BorderStyle, Bounds, ContentMask, Corners, Edges, Element,
6 ElementId, Entity, EntityId, GlobalElementId, Hitbox, Hsla, IsZero, LayoutId, ListState,
7 MouseDownEvent, MouseMoveEvent, MouseUpEvent, Pixels, Point, ScrollHandle, ScrollWheelEvent,
8 Size, Style, UniformListScrollHandle, Window, quad,
9};
10
11pub struct Scrollbar {
12 thumb: Range<f32>,
13 state: ScrollbarState,
14 kind: ScrollbarAxis,
15}
16
17#[derive(Default, Debug, Clone, Copy)]
18enum ThumbState {
19 #[default]
20 Inactive,
21 Hover,
22 Dragging(Pixels),
23}
24
25impl ScrollableHandle for UniformListScrollHandle {
26 fn content_size(&self) -> Size<Pixels> {
27 self.0.borrow().base_handle.content_size()
28 }
29
30 fn set_offset(&self, point: Point<Pixels>) {
31 self.0.borrow().base_handle.set_offset(point);
32 }
33
34 fn offset(&self) -> Point<Pixels> {
35 self.0.borrow().base_handle.offset()
36 }
37
38 fn viewport(&self) -> Bounds<Pixels> {
39 self.0.borrow().base_handle.bounds()
40 }
41}
42
43impl ScrollableHandle for ListState {
44 fn content_size(&self) -> Size<Pixels> {
45 self.content_size_for_scrollbar()
46 }
47
48 fn set_offset(&self, point: Point<Pixels>) {
49 self.set_offset_from_scrollbar(point);
50 }
51
52 fn offset(&self) -> Point<Pixels> {
53 self.scroll_px_offset_for_scrollbar()
54 }
55
56 fn drag_started(&self) {
57 self.scrollbar_drag_started();
58 }
59
60 fn drag_ended(&self) {
61 self.scrollbar_drag_ended();
62 }
63
64 fn viewport(&self) -> Bounds<Pixels> {
65 self.viewport_bounds()
66 }
67}
68
69impl ScrollableHandle for ScrollHandle {
70 fn content_size(&self) -> Size<Pixels> {
71 self.padded_content_size()
72 }
73
74 fn set_offset(&self, point: Point<Pixels>) {
75 self.set_offset(point);
76 }
77
78 fn offset(&self) -> Point<Pixels> {
79 self.offset()
80 }
81
82 fn viewport(&self) -> Bounds<Pixels> {
83 self.bounds()
84 }
85}
86
87pub trait ScrollableHandle: Any + Debug {
88 fn content_size(&self) -> Size<Pixels>;
89 fn set_offset(&self, point: Point<Pixels>);
90 fn offset(&self) -> Point<Pixels>;
91 fn viewport(&self) -> Bounds<Pixels>;
92 fn drag_started(&self) {}
93 fn drag_ended(&self) {}
94}
95
96/// A scrollbar state that should be persisted across frames.
97#[derive(Clone, Debug)]
98pub struct ScrollbarState {
99 thumb_state: Rc<Cell<ThumbState>>,
100 parent_id: Option<EntityId>,
101 scroll_handle: Arc<dyn ScrollableHandle>,
102}
103
104impl ScrollbarState {
105 pub fn new(scroll: impl ScrollableHandle) -> Self {
106 Self {
107 thumb_state: Default::default(),
108 parent_id: None,
109 scroll_handle: Arc::new(scroll),
110 }
111 }
112
113 /// Set a parent model which should be notified whenever this Scrollbar gets a scroll event.
114 pub fn parent_entity<V: 'static>(mut self, v: &Entity<V>) -> Self {
115 self.parent_id = Some(v.entity_id());
116 self
117 }
118
119 pub fn scroll_handle(&self) -> &Arc<dyn ScrollableHandle> {
120 &self.scroll_handle
121 }
122
123 pub fn is_dragging(&self) -> bool {
124 matches!(self.thumb_state.get(), ThumbState::Dragging(_))
125 }
126
127 fn set_dragging(&self, drag_offset: Pixels) {
128 self.set_thumb_state(ThumbState::Dragging(drag_offset));
129 self.scroll_handle.drag_started();
130 }
131
132 fn set_thumb_hovered(&self, hovered: bool) {
133 self.set_thumb_state(if hovered {
134 ThumbState::Hover
135 } else {
136 ThumbState::Inactive
137 });
138 }
139
140 fn set_thumb_state(&self, state: ThumbState) {
141 self.thumb_state.set(state);
142 }
143
144 fn thumb_range(&self, axis: ScrollbarAxis) -> Option<Range<f32>> {
145 const MINIMUM_THUMB_SIZE: Pixels = px(25.);
146 let content_size = self.scroll_handle.content_size().along(axis);
147 let viewport_size = self.scroll_handle.viewport().size.along(axis);
148 if content_size.is_zero() || viewport_size.is_zero() || content_size < viewport_size {
149 return None;
150 }
151
152 let max_offset = content_size - viewport_size;
153 let current_offset = self
154 .scroll_handle
155 .offset()
156 .along(axis)
157 .clamp(-max_offset, Pixels::ZERO)
158 .abs();
159
160 let visible_percentage = viewport_size / content_size;
161 let thumb_size = MINIMUM_THUMB_SIZE.max(viewport_size * visible_percentage);
162 if thumb_size > viewport_size {
163 return None;
164 }
165 let start_offset = (current_offset / max_offset) * (viewport_size - thumb_size);
166 let thumb_percentage_start = start_offset / viewport_size;
167 let thumb_percentage_end = (start_offset + thumb_size) / viewport_size;
168 Some(thumb_percentage_start..thumb_percentage_end)
169 }
170}
171
172impl Scrollbar {
173 pub fn vertical(state: ScrollbarState) -> Option<Self> {
174 Self::new(state, ScrollbarAxis::Vertical)
175 }
176
177 pub fn horizontal(state: ScrollbarState) -> Option<Self> {
178 Self::new(state, ScrollbarAxis::Horizontal)
179 }
180
181 fn new(state: ScrollbarState, kind: ScrollbarAxis) -> Option<Self> {
182 let thumb = state.thumb_range(kind)?;
183 Some(Self { thumb, state, kind })
184 }
185}
186
187impl Element for Scrollbar {
188 type RequestLayoutState = ();
189 type PrepaintState = Hitbox;
190
191 fn id(&self) -> Option<ElementId> {
192 None
193 }
194
195 fn source_location(&self) -> Option<&'static core::panic::Location<'static>> {
196 None
197 }
198
199 fn request_layout(
200 &mut self,
201 _id: Option<&GlobalElementId>,
202 _inspector_id: Option<&gpui::InspectorElementId>,
203 window: &mut Window,
204 cx: &mut App,
205 ) -> (LayoutId, Self::RequestLayoutState) {
206 let mut style = Style::default();
207 style.flex_grow = 1.;
208 style.flex_shrink = 1.;
209
210 if self.kind == ScrollbarAxis::Vertical {
211 style.size.width = px(12.).into();
212 style.size.height = relative(1.).into();
213 } else {
214 style.size.width = relative(1.).into();
215 style.size.height = px(12.).into();
216 }
217
218 (window.request_layout(style, None, cx), ())
219 }
220
221 fn prepaint(
222 &mut self,
223 _id: Option<&GlobalElementId>,
224 _inspector_id: Option<&gpui::InspectorElementId>,
225 bounds: Bounds<Pixels>,
226 _request_layout: &mut Self::RequestLayoutState,
227 window: &mut Window,
228 _: &mut App,
229 ) -> Self::PrepaintState {
230 window.with_content_mask(Some(ContentMask { bounds }), |window| {
231 window.insert_hitbox(bounds, false)
232 })
233 }
234
235 fn paint(
236 &mut self,
237 _id: Option<&GlobalElementId>,
238 _inspector_id: Option<&gpui::InspectorElementId>,
239 bounds: Bounds<Pixels>,
240 _request_layout: &mut Self::RequestLayoutState,
241 _prepaint: &mut Self::PrepaintState,
242 window: &mut Window,
243 cx: &mut App,
244 ) {
245 const EXTRA_PADDING: Pixels = px(5.0);
246 window.with_content_mask(Some(ContentMask { bounds }), |window| {
247 let axis = self.kind;
248 let colors = cx.theme().colors();
249 let thumb_base_color = match self.state.thumb_state.get() {
250 ThumbState::Dragging(_) => colors.scrollbar_thumb_active_background,
251 ThumbState::Hover => colors.scrollbar_thumb_hover_background,
252 ThumbState::Inactive => colors.scrollbar_thumb_background,
253 };
254
255 let thumb_background = colors.surface_background.blend(thumb_base_color);
256
257 let padded_bounds = Bounds::from_corners(
258 bounds
259 .origin
260 .apply_along(axis, |origin| origin + EXTRA_PADDING),
261 bounds
262 .bottom_right()
263 .apply_along(axis, |track_end| track_end - 3.0 * EXTRA_PADDING),
264 );
265
266 let thumb_offset = self.thumb.start * padded_bounds.size.along(axis);
267 let thumb_end = self.thumb.end * padded_bounds.size.along(axis);
268
269 let thumb_bounds = Bounds::new(
270 padded_bounds
271 .origin
272 .apply_along(axis, |origin| origin + thumb_offset),
273 padded_bounds
274 .size
275 .apply_along(axis, |_| thumb_end - thumb_offset)
276 .apply_along(axis.invert(), |width| width / 1.5),
277 );
278
279 let corners = Corners::all(thumb_bounds.size.along(axis.invert()) / 2.0);
280
281 window.paint_quad(quad(
282 thumb_bounds,
283 corners,
284 thumb_background,
285 Edges::default(),
286 Hsla::transparent_black(),
287 BorderStyle::default(),
288 ));
289
290 let scroll = self.state.scroll_handle.clone();
291
292 enum ScrollbarMouseEvent {
293 GutterClick,
294 ThumbDrag(Pixels),
295 }
296
297 let compute_click_offset =
298 move |event_position: Point<Pixels>,
299 item_size: Size<Pixels>,
300 event_type: ScrollbarMouseEvent| {
301 let viewport_size = padded_bounds.size.along(axis);
302
303 let thumb_size = thumb_bounds.size.along(axis);
304
305 let thumb_offset = match event_type {
306 ScrollbarMouseEvent::GutterClick => thumb_size / 2.,
307 ScrollbarMouseEvent::ThumbDrag(thumb_offset) => thumb_offset,
308 };
309
310 let thumb_start = (event_position.along(axis)
311 - padded_bounds.origin.along(axis)
312 - thumb_offset)
313 .clamp(px(0.), viewport_size - thumb_size);
314
315 let max_offset = (item_size.along(axis) - viewport_size).max(px(0.));
316 let percentage = if viewport_size > thumb_size {
317 thumb_start / (viewport_size - thumb_size)
318 } else {
319 0.
320 };
321
322 -max_offset * percentage
323 };
324
325 window.on_mouse_event({
326 let scroll = scroll.clone();
327 let state = self.state.clone();
328 move |event: &MouseDownEvent, phase, _, _| {
329 if !(phase.bubble() && bounds.contains(&event.position)) {
330 return;
331 }
332
333 if thumb_bounds.contains(&event.position) {
334 let offset = event.position.along(axis) - thumb_bounds.origin.along(axis);
335 state.set_dragging(offset);
336 } else {
337 let click_offset = compute_click_offset(
338 event.position,
339 scroll.content_size(),
340 ScrollbarMouseEvent::GutterClick,
341 );
342 scroll.set_offset(scroll.offset().apply_along(axis, |_| click_offset));
343 }
344 }
345 });
346
347 window.on_mouse_event({
348 let scroll = scroll.clone();
349 move |event: &ScrollWheelEvent, phase, window, _| {
350 if phase.bubble() && bounds.contains(&event.position) {
351 let current_offset = scroll.offset();
352 scroll.set_offset(
353 current_offset + event.delta.pixel_delta(window.line_height()),
354 );
355 }
356 }
357 });
358
359 let state = self.state.clone();
360 window.on_mouse_event(move |event: &MouseMoveEvent, _, window, cx| {
361 match state.thumb_state.get() {
362 ThumbState::Dragging(drag_state) if event.dragging() => {
363 let drag_offset = compute_click_offset(
364 event.position,
365 scroll.content_size(),
366 ScrollbarMouseEvent::ThumbDrag(drag_state),
367 );
368 scroll.set_offset(scroll.offset().apply_along(axis, |_| drag_offset));
369 window.refresh();
370 if let Some(id) = state.parent_id {
371 cx.notify(id);
372 }
373 }
374 _ => state.set_thumb_hovered(thumb_bounds.contains(&event.position)),
375 }
376 });
377 let state = self.state.clone();
378 let scroll = self.state.scroll_handle.clone();
379 window.on_mouse_event(move |event: &MouseUpEvent, phase, _, cx| {
380 if phase.bubble() {
381 if state.is_dragging() {
382 state.set_thumb_hovered(thumb_bounds.contains(&event.position));
383 }
384 scroll.drag_ended();
385 if let Some(id) = state.parent_id {
386 cx.notify(id);
387 }
388 }
389 });
390 })
391 }
392}
393
394impl IntoElement for Scrollbar {
395 type Element = Self;
396
397 fn into_element(self) -> Self::Element {
398 self
399 }
400}