1//! A list element that can be used to render a large number of differently sized elements
2//! efficiently. Clients of this API need to ensure that elements outside of the scrolled
3//! area do not change their height for this element to function correctly. If your elements
4//! do change height, notify the list element via [`ListState::splice`] or [`ListState::reset`].
5//! In order to minimize re-renders, this element's state is stored intrusively
6//! on your own views, so that your code can coordinate directly with the list element's cached state.
7//!
8//! If all of your elements are the same height, see [`crate::UniformList`] for a simpler API
9
10use crate::{
11 AnyElement, App, AvailableSpace, Bounds, ContentMask, DispatchPhase, Edges, Element, EntityId,
12 FocusHandle, GlobalElementId, Hitbox, HitboxBehavior, InspectorElementId, IntoElement,
13 Overflow, Pixels, Point, ScrollDelta, ScrollWheelEvent, Size, Style, StyleRefinement, Styled,
14 Window, point, px, size,
15};
16use collections::VecDeque;
17use refineable::Refineable as _;
18use std::{cell::RefCell, ops::Range, rc::Rc};
19use sum_tree::{Bias, Dimensions, SumTree};
20
21type RenderItemFn = dyn FnMut(usize, &mut Window, &mut App) -> AnyElement + 'static;
22
23/// Construct a new list element
24pub fn list(
25 state: ListState,
26 render_item: impl FnMut(usize, &mut Window, &mut App) -> AnyElement + 'static,
27) -> List {
28 List {
29 state,
30 render_item: Box::new(render_item),
31 style: StyleRefinement::default(),
32 sizing_behavior: ListSizingBehavior::default(),
33 }
34}
35
36/// A list element
37pub struct List {
38 state: ListState,
39 render_item: Box<RenderItemFn>,
40 style: StyleRefinement,
41 sizing_behavior: ListSizingBehavior,
42}
43
44impl List {
45 /// Set the sizing behavior for the list.
46 pub fn with_sizing_behavior(mut self, behavior: ListSizingBehavior) -> Self {
47 self.sizing_behavior = behavior;
48 self
49 }
50}
51
52/// The list state that views must hold on behalf of the list element.
53#[derive(Clone)]
54pub struct ListState(Rc<RefCell<StateInner>>);
55
56impl std::fmt::Debug for ListState {
57 fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
58 f.write_str("ListState")
59 }
60}
61
62struct StateInner {
63 last_layout_bounds: Option<Bounds<Pixels>>,
64 last_padding: Option<Edges<Pixels>>,
65 items: SumTree<ListItem>,
66 logical_scroll_top: Option<ListOffset>,
67 alignment: ListAlignment,
68 overdraw: Pixels,
69 reset: bool,
70 #[allow(clippy::type_complexity)]
71 scroll_handler: Option<Box<dyn FnMut(&ListScrollEvent, &mut Window, &mut App)>>,
72 scrollbar_drag_start_height: Option<Pixels>,
73}
74
75/// Whether the list is scrolling from top to bottom or bottom to top.
76#[derive(Clone, Copy, Debug, Eq, PartialEq)]
77pub enum ListAlignment {
78 /// The list is scrolling from top to bottom, like most lists.
79 Top,
80 /// The list is scrolling from bottom to top, like a chat log.
81 Bottom,
82}
83
84/// A scroll event that has been converted to be in terms of the list's items.
85pub struct ListScrollEvent {
86 /// The range of items currently visible in the list, after applying the scroll event.
87 pub visible_range: Range<usize>,
88
89 /// The number of items that are currently visible in the list, after applying the scroll event.
90 pub count: usize,
91
92 /// Whether the list has been scrolled.
93 pub is_scrolled: bool,
94}
95
96/// The sizing behavior to apply during layout.
97#[derive(Clone, Copy, Debug, Default, PartialEq, Eq, PartialOrd, Ord, Hash)]
98pub enum ListSizingBehavior {
99 /// The list should calculate its size based on the size of its items.
100 Infer,
101 /// The list should not calculate a fixed size.
102 #[default]
103 Auto,
104}
105
106/// The horizontal sizing behavior to apply during layout.
107#[derive(Clone, Copy, Debug, Default, PartialEq, Eq, PartialOrd, Ord, Hash)]
108pub enum ListHorizontalSizingBehavior {
109 /// List items' width can never exceed the width of the list.
110 #[default]
111 FitList,
112 /// List items' width may go over the width of the list, if any item is wider.
113 Unconstrained,
114}
115
116struct LayoutItemsResponse {
117 max_item_width: Pixels,
118 scroll_top: ListOffset,
119 item_layouts: VecDeque<ItemLayout>,
120}
121
122struct ItemLayout {
123 index: usize,
124 element: AnyElement,
125 size: Size<Pixels>,
126}
127
128/// Frame state used by the [List] element after layout.
129pub struct ListPrepaintState {
130 hitbox: Hitbox,
131 layout: LayoutItemsResponse,
132}
133
134#[derive(Clone)]
135enum ListItem {
136 Unmeasured {
137 focus_handle: Option<FocusHandle>,
138 },
139 Measured {
140 size: Size<Pixels>,
141 focus_handle: Option<FocusHandle>,
142 },
143}
144
145impl ListItem {
146 fn size(&self) -> Option<Size<Pixels>> {
147 if let ListItem::Measured { size, .. } = self {
148 Some(*size)
149 } else {
150 None
151 }
152 }
153
154 fn focus_handle(&self) -> Option<FocusHandle> {
155 match self {
156 ListItem::Unmeasured { focus_handle } | ListItem::Measured { focus_handle, .. } => {
157 focus_handle.clone()
158 }
159 }
160 }
161
162 fn contains_focused(&self, window: &Window, cx: &App) -> bool {
163 match self {
164 ListItem::Unmeasured { focus_handle } | ListItem::Measured { focus_handle, .. } => {
165 focus_handle
166 .as_ref()
167 .is_some_and(|handle| handle.contains_focused(window, cx))
168 }
169 }
170 }
171}
172
173#[derive(Clone, Debug, Default, PartialEq)]
174struct ListItemSummary {
175 count: usize,
176 rendered_count: usize,
177 unrendered_count: usize,
178 height: Pixels,
179 has_focus_handles: bool,
180}
181
182#[derive(Clone, Debug, Default, PartialEq, Eq, PartialOrd, Ord)]
183struct Count(usize);
184
185#[derive(Clone, Debug, Default)]
186struct Height(Pixels);
187
188impl ListState {
189 /// Construct a new list state, for storage on a view.
190 ///
191 /// The overdraw parameter controls how much extra space is rendered
192 /// above and below the visible area. Elements within this area will
193 /// be measured even though they are not visible. This can help ensure
194 /// that the list doesn't flicker or pop in when scrolling.
195 pub fn new(item_count: usize, alignment: ListAlignment, overdraw: Pixels) -> Self {
196 let this = Self(Rc::new(RefCell::new(StateInner {
197 last_layout_bounds: None,
198 last_padding: None,
199 items: SumTree::default(),
200 logical_scroll_top: None,
201 alignment,
202 overdraw,
203 scroll_handler: None,
204 reset: false,
205 scrollbar_drag_start_height: None,
206 })));
207 this.splice(0..0, item_count);
208 this
209 }
210
211 /// Reset this instantiation of the list state.
212 ///
213 /// Note that this will cause scroll events to be dropped until the next paint.
214 pub fn reset(&self, element_count: usize) {
215 let old_count = {
216 let state = &mut *self.0.borrow_mut();
217 state.reset = true;
218 state.logical_scroll_top = None;
219 state.scrollbar_drag_start_height = None;
220 state.items.summary().count
221 };
222
223 self.splice(0..old_count, element_count);
224 }
225
226 /// The number of items in this list.
227 pub fn item_count(&self) -> usize {
228 self.0.borrow().items.summary().count
229 }
230
231 /// Inform the list state that the items in `old_range` have been replaced
232 /// by `count` new items that must be recalculated.
233 pub fn splice(&self, old_range: Range<usize>, count: usize) {
234 self.splice_focusable(old_range, (0..count).map(|_| None))
235 }
236
237 /// Register with the list state that the items in `old_range` have been replaced
238 /// by new items. As opposed to [`Self::splice`], this method allows an iterator of optional focus handles
239 /// to be supplied to properly integrate with items in the list that can be focused. If a focused item
240 /// is scrolled out of view, the list will continue to render it to allow keyboard interaction.
241 pub fn splice_focusable(
242 &self,
243 old_range: Range<usize>,
244 focus_handles: impl IntoIterator<Item = Option<FocusHandle>>,
245 ) {
246 let state = &mut *self.0.borrow_mut();
247
248 let mut old_items = state.items.cursor::<Count>(());
249 let mut new_items = old_items.slice(&Count(old_range.start), Bias::Right);
250 old_items.seek_forward(&Count(old_range.end), Bias::Right);
251
252 let mut spliced_count = 0;
253 new_items.extend(
254 focus_handles.into_iter().map(|focus_handle| {
255 spliced_count += 1;
256 ListItem::Unmeasured { focus_handle }
257 }),
258 (),
259 );
260 new_items.append(old_items.suffix(), ());
261 drop(old_items);
262 state.items = new_items;
263
264 if let Some(ListOffset {
265 item_ix,
266 offset_in_item,
267 }) = state.logical_scroll_top.as_mut()
268 {
269 if old_range.contains(item_ix) {
270 *item_ix = old_range.start;
271 *offset_in_item = px(0.);
272 } else if old_range.end <= *item_ix {
273 *item_ix = *item_ix - (old_range.end - old_range.start) + spliced_count;
274 }
275 }
276 }
277
278 /// Set a handler that will be called when the list is scrolled.
279 pub fn set_scroll_handler(
280 &self,
281 handler: impl FnMut(&ListScrollEvent, &mut Window, &mut App) + 'static,
282 ) {
283 self.0.borrow_mut().scroll_handler = Some(Box::new(handler))
284 }
285
286 /// Get the current scroll offset, in terms of the list's items.
287 pub fn logical_scroll_top(&self) -> ListOffset {
288 self.0.borrow().logical_scroll_top()
289 }
290
291 /// Scroll the list by the given offset
292 pub fn scroll_by(&self, distance: Pixels) {
293 if distance == px(0.) {
294 return;
295 }
296
297 let current_offset = self.logical_scroll_top();
298 let state = &mut *self.0.borrow_mut();
299 let mut cursor = state.items.cursor::<ListItemSummary>(());
300 cursor.seek(&Count(current_offset.item_ix), Bias::Right);
301
302 let start_pixel_offset = cursor.start().height + current_offset.offset_in_item;
303 let new_pixel_offset = (start_pixel_offset + distance).max(px(0.));
304 if new_pixel_offset > start_pixel_offset {
305 cursor.seek_forward(&Height(new_pixel_offset), Bias::Right);
306 } else {
307 cursor.seek(&Height(new_pixel_offset), Bias::Right);
308 }
309
310 state.logical_scroll_top = Some(ListOffset {
311 item_ix: cursor.start().count,
312 offset_in_item: new_pixel_offset - cursor.start().height,
313 });
314 }
315
316 /// Scroll the list to the given offset
317 pub fn scroll_to(&self, mut scroll_top: ListOffset) {
318 let state = &mut *self.0.borrow_mut();
319 let item_count = state.items.summary().count;
320 if scroll_top.item_ix >= item_count {
321 scroll_top.item_ix = item_count;
322 scroll_top.offset_in_item = px(0.);
323 }
324
325 state.logical_scroll_top = Some(scroll_top);
326 }
327
328 /// Scroll the list to the given item, such that the item is fully visible.
329 pub fn scroll_to_reveal_item(&self, ix: usize) {
330 let state = &mut *self.0.borrow_mut();
331
332 let mut scroll_top = state.logical_scroll_top();
333 let height = state
334 .last_layout_bounds
335 .map_or(px(0.), |bounds| bounds.size.height);
336 let padding = state.last_padding.unwrap_or_default();
337
338 if ix <= scroll_top.item_ix {
339 scroll_top.item_ix = ix;
340 scroll_top.offset_in_item = px(0.);
341 } else {
342 let mut cursor = state.items.cursor::<ListItemSummary>(());
343 cursor.seek(&Count(ix + 1), Bias::Right);
344 let bottom = cursor.start().height + padding.top;
345 let goal_top = px(0.).max(bottom - height + padding.bottom);
346
347 cursor.seek(&Height(goal_top), Bias::Left);
348 let start_ix = cursor.start().count;
349 let start_item_top = cursor.start().height;
350
351 if start_ix >= scroll_top.item_ix {
352 scroll_top.item_ix = start_ix;
353 scroll_top.offset_in_item = goal_top - start_item_top;
354 }
355 }
356
357 state.logical_scroll_top = Some(scroll_top);
358 }
359
360 /// Get the bounds for the given item in window coordinates, if it's
361 /// been rendered.
362 pub fn bounds_for_item(&self, ix: usize) -> Option<Bounds<Pixels>> {
363 let state = &*self.0.borrow();
364
365 let bounds = state.last_layout_bounds.unwrap_or_default();
366 let scroll_top = state.logical_scroll_top();
367 if ix < scroll_top.item_ix {
368 return None;
369 }
370
371 let mut cursor = state.items.cursor::<Dimensions<Count, Height>>(());
372 cursor.seek(&Count(scroll_top.item_ix), Bias::Right);
373
374 let scroll_top = cursor.start().1.0 + scroll_top.offset_in_item;
375
376 cursor.seek_forward(&Count(ix), Bias::Right);
377 if let Some(&ListItem::Measured { size, .. }) = cursor.item() {
378 let &Dimensions(Count(count), Height(top), _) = cursor.start();
379 if count == ix {
380 let top = bounds.top() + top - scroll_top;
381 return Some(Bounds::from_corners(
382 point(bounds.left(), top),
383 point(bounds.right(), top + size.height),
384 ));
385 }
386 }
387 None
388 }
389
390 /// Call this method when the user starts dragging the scrollbar.
391 ///
392 /// This will prevent the height reported to the scrollbar from changing during the drag
393 /// as items in the overdraw get measured, and help offset scroll position changes accordingly.
394 pub fn scrollbar_drag_started(&self) {
395 let mut state = self.0.borrow_mut();
396 state.scrollbar_drag_start_height = Some(state.items.summary().height);
397 }
398
399 /// Called when the user stops dragging the scrollbar.
400 ///
401 /// See `scrollbar_drag_started`.
402 pub fn scrollbar_drag_ended(&self) {
403 self.0.borrow_mut().scrollbar_drag_start_height.take();
404 }
405
406 /// Set the offset from the scrollbar
407 pub fn set_offset_from_scrollbar(&self, point: Point<Pixels>) {
408 self.0.borrow_mut().set_offset_from_scrollbar(point);
409 }
410
411 /// Returns the maximum scroll offset according to the items we have measured.
412 /// This value remains constant while dragging to prevent the scrollbar from moving away unexpectedly.
413 pub fn max_offset_for_scrollbar(&self) -> Size<Pixels> {
414 let state = self.0.borrow();
415 let bounds = state.last_layout_bounds.unwrap_or_default();
416
417 let height = state
418 .scrollbar_drag_start_height
419 .unwrap_or_else(|| state.items.summary().height);
420
421 Size::new(Pixels::ZERO, Pixels::ZERO.max(height - bounds.size.height))
422 }
423
424 /// Returns the current scroll offset adjusted for the scrollbar
425 pub fn scroll_px_offset_for_scrollbar(&self) -> Point<Pixels> {
426 let state = &self.0.borrow();
427 let logical_scroll_top = state.logical_scroll_top();
428
429 let mut cursor = state.items.cursor::<ListItemSummary>(());
430 let summary: ListItemSummary =
431 cursor.summary(&Count(logical_scroll_top.item_ix), Bias::Right);
432 let content_height = state.items.summary().height;
433 let drag_offset =
434 // if dragging the scrollbar, we want to offset the point if the height changed
435 content_height - state.scrollbar_drag_start_height.unwrap_or(content_height);
436 let offset = summary.height + logical_scroll_top.offset_in_item - drag_offset;
437
438 Point::new(px(0.), -offset)
439 }
440
441 /// Return the bounds of the viewport in pixels.
442 pub fn viewport_bounds(&self) -> Bounds<Pixels> {
443 self.0.borrow().last_layout_bounds.unwrap_or_default()
444 }
445}
446
447impl StateInner {
448 fn visible_range(&self, height: Pixels, scroll_top: &ListOffset) -> Range<usize> {
449 let mut cursor = self.items.cursor::<ListItemSummary>(());
450 cursor.seek(&Count(scroll_top.item_ix), Bias::Right);
451 let start_y = cursor.start().height + scroll_top.offset_in_item;
452 cursor.seek_forward(&Height(start_y + height), Bias::Left);
453 scroll_top.item_ix..cursor.start().count + 1
454 }
455
456 fn scroll(
457 &mut self,
458 scroll_top: &ListOffset,
459 height: Pixels,
460 delta: Point<Pixels>,
461 current_view: EntityId,
462 window: &mut Window,
463 cx: &mut App,
464 ) {
465 // Drop scroll events after a reset, since we can't calculate
466 // the new logical scroll top without the item heights
467 if self.reset {
468 return;
469 }
470
471 let padding = self.last_padding.unwrap_or_default();
472 let scroll_max =
473 (self.items.summary().height + padding.top + padding.bottom - height).max(px(0.));
474 let new_scroll_top = (self.scroll_top(scroll_top) - delta.y)
475 .max(px(0.))
476 .min(scroll_max);
477
478 if self.alignment == ListAlignment::Bottom && new_scroll_top == scroll_max {
479 self.logical_scroll_top = None;
480 } else {
481 let mut cursor = self.items.cursor::<ListItemSummary>(());
482 cursor.seek(&Height(new_scroll_top), Bias::Right);
483 let item_ix = cursor.start().count;
484 let offset_in_item = new_scroll_top - cursor.start().height;
485 self.logical_scroll_top = Some(ListOffset {
486 item_ix,
487 offset_in_item,
488 });
489 }
490
491 if self.scroll_handler.is_some() {
492 let visible_range = self.visible_range(height, scroll_top);
493 self.scroll_handler.as_mut().unwrap()(
494 &ListScrollEvent {
495 visible_range,
496 count: self.items.summary().count,
497 is_scrolled: self.logical_scroll_top.is_some(),
498 },
499 window,
500 cx,
501 );
502 }
503
504 cx.notify(current_view);
505 }
506
507 fn logical_scroll_top(&self) -> ListOffset {
508 self.logical_scroll_top
509 .unwrap_or_else(|| match self.alignment {
510 ListAlignment::Top => ListOffset {
511 item_ix: 0,
512 offset_in_item: px(0.),
513 },
514 ListAlignment::Bottom => ListOffset {
515 item_ix: self.items.summary().count,
516 offset_in_item: px(0.),
517 },
518 })
519 }
520
521 fn scroll_top(&self, logical_scroll_top: &ListOffset) -> Pixels {
522 let mut cursor = self.items.cursor::<ListItemSummary>(());
523 cursor.seek(&Count(logical_scroll_top.item_ix), Bias::Right);
524 cursor.start().height + logical_scroll_top.offset_in_item
525 }
526
527 fn layout_items(
528 &mut self,
529 available_width: Option<Pixels>,
530 available_height: Pixels,
531 padding: &Edges<Pixels>,
532 render_item: &mut RenderItemFn,
533 window: &mut Window,
534 cx: &mut App,
535 ) -> LayoutItemsResponse {
536 let old_items = self.items.clone();
537 let mut measured_items = VecDeque::new();
538 let mut item_layouts = VecDeque::new();
539 let mut rendered_height = padding.top;
540 let mut max_item_width = px(0.);
541 let mut scroll_top = self.logical_scroll_top();
542 let mut rendered_focused_item = false;
543
544 let available_item_space = size(
545 available_width.map_or(AvailableSpace::MinContent, |width| {
546 AvailableSpace::Definite(width)
547 }),
548 AvailableSpace::MinContent,
549 );
550
551 let mut cursor = old_items.cursor::<Count>(());
552
553 // Render items after the scroll top, including those in the trailing overdraw
554 cursor.seek(&Count(scroll_top.item_ix), Bias::Right);
555 for (ix, item) in cursor.by_ref().enumerate() {
556 let visible_height = rendered_height - scroll_top.offset_in_item;
557 if visible_height >= available_height + self.overdraw {
558 break;
559 }
560
561 // Use the previously cached height and focus handle if available
562 let mut size = item.size();
563
564 // If we're within the visible area or the height wasn't cached, render and measure the item's element
565 if visible_height < available_height || size.is_none() {
566 let item_index = scroll_top.item_ix + ix;
567 let mut element = render_item(item_index, window, cx);
568 let element_size = element.layout_as_root(available_item_space, window, cx);
569 size = Some(element_size);
570 if visible_height < available_height {
571 item_layouts.push_back(ItemLayout {
572 index: item_index,
573 element,
574 size: element_size,
575 });
576 if item.contains_focused(window, cx) {
577 rendered_focused_item = true;
578 }
579 }
580 }
581
582 let size = size.unwrap();
583 rendered_height += size.height;
584 max_item_width = max_item_width.max(size.width);
585 measured_items.push_back(ListItem::Measured {
586 size,
587 focus_handle: item.focus_handle(),
588 });
589 }
590 rendered_height += padding.bottom;
591
592 // Prepare to start walking upward from the item at the scroll top.
593 cursor.seek(&Count(scroll_top.item_ix), Bias::Right);
594
595 // If the rendered items do not fill the visible region, then adjust
596 // the scroll top upward.
597 if rendered_height - scroll_top.offset_in_item < available_height {
598 while rendered_height < available_height {
599 cursor.prev();
600 if let Some(item) = cursor.item() {
601 let item_index = cursor.start().0;
602 let mut element = render_item(item_index, window, cx);
603 let element_size = element.layout_as_root(available_item_space, window, cx);
604 let focus_handle = item.focus_handle();
605 rendered_height += element_size.height;
606 measured_items.push_front(ListItem::Measured {
607 size: element_size,
608 focus_handle,
609 });
610 item_layouts.push_front(ItemLayout {
611 index: item_index,
612 element,
613 size: element_size,
614 });
615 if item.contains_focused(window, cx) {
616 rendered_focused_item = true;
617 }
618 } else {
619 break;
620 }
621 }
622
623 scroll_top = ListOffset {
624 item_ix: cursor.start().0,
625 offset_in_item: rendered_height - available_height,
626 };
627
628 match self.alignment {
629 ListAlignment::Top => {
630 scroll_top.offset_in_item = scroll_top.offset_in_item.max(px(0.));
631 self.logical_scroll_top = Some(scroll_top);
632 }
633 ListAlignment::Bottom => {
634 scroll_top = ListOffset {
635 item_ix: cursor.start().0,
636 offset_in_item: rendered_height - available_height,
637 };
638 self.logical_scroll_top = None;
639 }
640 };
641 }
642
643 // Measure items in the leading overdraw
644 let mut leading_overdraw = scroll_top.offset_in_item;
645 while leading_overdraw < self.overdraw {
646 cursor.prev();
647 if let Some(item) = cursor.item() {
648 let size = if let ListItem::Measured { size, .. } = item {
649 *size
650 } else {
651 let mut element = render_item(cursor.start().0, window, cx);
652 element.layout_as_root(available_item_space, window, cx)
653 };
654
655 leading_overdraw += size.height;
656 measured_items.push_front(ListItem::Measured {
657 size,
658 focus_handle: item.focus_handle(),
659 });
660 } else {
661 break;
662 }
663 }
664
665 let measured_range = cursor.start().0..(cursor.start().0 + measured_items.len());
666 let mut cursor = old_items.cursor::<Count>(());
667 let mut new_items = cursor.slice(&Count(measured_range.start), Bias::Right);
668 new_items.extend(measured_items, ());
669 cursor.seek(&Count(measured_range.end), Bias::Right);
670 new_items.append(cursor.suffix(), ());
671 self.items = new_items;
672
673 // If none of the visible items are focused, check if an off-screen item is focused
674 // and include it to be rendered after the visible items so keyboard interaction continues
675 // to work for it.
676 if !rendered_focused_item {
677 let mut cursor = self
678 .items
679 .filter::<_, Count>((), |summary| summary.has_focus_handles);
680 cursor.next();
681 while let Some(item) = cursor.item() {
682 if item.contains_focused(window, cx) {
683 let item_index = cursor.start().0;
684 let mut element = render_item(cursor.start().0, window, cx);
685 let size = element.layout_as_root(available_item_space, window, cx);
686 item_layouts.push_back(ItemLayout {
687 index: item_index,
688 element,
689 size,
690 });
691 break;
692 }
693 cursor.next();
694 }
695 }
696
697 LayoutItemsResponse {
698 max_item_width,
699 scroll_top,
700 item_layouts,
701 }
702 }
703
704 fn prepaint_items(
705 &mut self,
706 bounds: Bounds<Pixels>,
707 padding: Edges<Pixels>,
708 autoscroll: bool,
709 render_item: &mut RenderItemFn,
710 window: &mut Window,
711 cx: &mut App,
712 ) -> Result<LayoutItemsResponse, ListOffset> {
713 window.transact(|window| {
714 let mut layout_response = self.layout_items(
715 Some(bounds.size.width),
716 bounds.size.height,
717 &padding,
718 render_item,
719 window,
720 cx,
721 );
722
723 // Avoid honoring autoscroll requests from elements other than our children.
724 window.take_autoscroll();
725
726 // Only paint the visible items, if there is actually any space for them (taking padding into account)
727 if bounds.size.height > padding.top + padding.bottom {
728 let mut item_origin = bounds.origin + Point::new(px(0.), padding.top);
729 item_origin.y -= layout_response.scroll_top.offset_in_item;
730 for item in &mut layout_response.item_layouts {
731 window.with_content_mask(Some(ContentMask { bounds }), |window| {
732 item.element.prepaint_at(item_origin, window, cx);
733 });
734
735 if let Some(autoscroll_bounds) = window.take_autoscroll()
736 && autoscroll
737 {
738 if autoscroll_bounds.top() < bounds.top() {
739 return Err(ListOffset {
740 item_ix: item.index,
741 offset_in_item: autoscroll_bounds.top() - item_origin.y,
742 });
743 } else if autoscroll_bounds.bottom() > bounds.bottom() {
744 let mut cursor = self.items.cursor::<Count>(());
745 cursor.seek(&Count(item.index), Bias::Right);
746 let mut height = bounds.size.height - padding.top - padding.bottom;
747
748 // Account for the height of the element down until the autoscroll bottom.
749 height -= autoscroll_bounds.bottom() - item_origin.y;
750
751 // Keep decreasing the scroll top until we fill all the available space.
752 while height > Pixels::ZERO {
753 cursor.prev();
754 let Some(item) = cursor.item() else { break };
755
756 let size = item.size().unwrap_or_else(|| {
757 let mut item = render_item(cursor.start().0, window, cx);
758 let item_available_size =
759 size(bounds.size.width.into(), AvailableSpace::MinContent);
760 item.layout_as_root(item_available_size, window, cx)
761 });
762 height -= size.height;
763 }
764
765 return Err(ListOffset {
766 item_ix: cursor.start().0,
767 offset_in_item: if height < Pixels::ZERO {
768 -height
769 } else {
770 Pixels::ZERO
771 },
772 });
773 }
774 }
775
776 item_origin.y += item.size.height;
777 }
778 } else {
779 layout_response.item_layouts.clear();
780 }
781
782 Ok(layout_response)
783 })
784 }
785
786 // Scrollbar support
787
788 fn set_offset_from_scrollbar(&mut self, point: Point<Pixels>) {
789 let Some(bounds) = self.last_layout_bounds else {
790 return;
791 };
792 let height = bounds.size.height;
793
794 let padding = self.last_padding.unwrap_or_default();
795 let content_height = self.items.summary().height;
796 let scroll_max = (content_height + padding.top + padding.bottom - height).max(px(0.));
797 let drag_offset =
798 // if dragging the scrollbar, we want to offset the point if the height changed
799 content_height - self.scrollbar_drag_start_height.unwrap_or(content_height);
800 let new_scroll_top = (point.y - drag_offset).abs().max(px(0.)).min(scroll_max);
801
802 if self.alignment == ListAlignment::Bottom && new_scroll_top == scroll_max {
803 self.logical_scroll_top = None;
804 } else {
805 let mut cursor = self.items.cursor::<ListItemSummary>(());
806 cursor.seek(&Height(new_scroll_top), Bias::Right);
807
808 let item_ix = cursor.start().count;
809 let offset_in_item = new_scroll_top - cursor.start().height;
810 self.logical_scroll_top = Some(ListOffset {
811 item_ix,
812 offset_in_item,
813 });
814 }
815 }
816}
817
818impl std::fmt::Debug for ListItem {
819 fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
820 match self {
821 Self::Unmeasured { .. } => write!(f, "Unrendered"),
822 Self::Measured { size, .. } => f.debug_struct("Rendered").field("size", size).finish(),
823 }
824 }
825}
826
827/// An offset into the list's items, in terms of the item index and the number
828/// of pixels off the top left of the item.
829#[derive(Debug, Clone, Copy, Default)]
830pub struct ListOffset {
831 /// The index of an item in the list
832 pub item_ix: usize,
833 /// The number of pixels to offset from the item index.
834 pub offset_in_item: Pixels,
835}
836
837impl Element for List {
838 type RequestLayoutState = ();
839 type PrepaintState = ListPrepaintState;
840
841 fn id(&self) -> Option<crate::ElementId> {
842 None
843 }
844
845 fn source_location(&self) -> Option<&'static core::panic::Location<'static>> {
846 None
847 }
848
849 fn request_layout(
850 &mut self,
851 _id: Option<&GlobalElementId>,
852 _inspector_id: Option<&InspectorElementId>,
853 window: &mut Window,
854 cx: &mut App,
855 ) -> (crate::LayoutId, Self::RequestLayoutState) {
856 let layout_id = match self.sizing_behavior {
857 ListSizingBehavior::Infer => {
858 let mut style = Style::default();
859 style.overflow.y = Overflow::Scroll;
860 style.refine(&self.style);
861 window.with_text_style(style.text_style().cloned(), |window| {
862 let state = &mut *self.state.0.borrow_mut();
863
864 let available_height = if let Some(last_bounds) = state.last_layout_bounds {
865 last_bounds.size.height
866 } else {
867 // If we don't have the last layout bounds (first render),
868 // we might just use the overdraw value as the available height to layout enough items.
869 state.overdraw
870 };
871 let padding = style.padding.to_pixels(
872 state.last_layout_bounds.unwrap_or_default().size.into(),
873 window.rem_size(),
874 );
875
876 let layout_response = state.layout_items(
877 None,
878 available_height,
879 &padding,
880 &mut self.render_item,
881 window,
882 cx,
883 );
884 let max_element_width = layout_response.max_item_width;
885
886 let summary = state.items.summary();
887 let total_height = summary.height;
888
889 window.request_measured_layout(
890 style,
891 move |known_dimensions, available_space, _window, _cx| {
892 let width =
893 known_dimensions
894 .width
895 .unwrap_or(match available_space.width {
896 AvailableSpace::Definite(x) => x,
897 AvailableSpace::MinContent | AvailableSpace::MaxContent => {
898 max_element_width
899 }
900 });
901 let height = match available_space.height {
902 AvailableSpace::Definite(height) => total_height.min(height),
903 AvailableSpace::MinContent | AvailableSpace::MaxContent => {
904 total_height
905 }
906 };
907 size(width, height)
908 },
909 )
910 })
911 }
912 ListSizingBehavior::Auto => {
913 let mut style = Style::default();
914 style.refine(&self.style);
915 window.with_text_style(style.text_style().cloned(), |window| {
916 window.request_layout(style, None, cx)
917 })
918 }
919 };
920 (layout_id, ())
921 }
922
923 fn prepaint(
924 &mut self,
925 _id: Option<&GlobalElementId>,
926 _inspector_id: Option<&InspectorElementId>,
927 bounds: Bounds<Pixels>,
928 _: &mut Self::RequestLayoutState,
929 window: &mut Window,
930 cx: &mut App,
931 ) -> ListPrepaintState {
932 let state = &mut *self.state.0.borrow_mut();
933 state.reset = false;
934
935 let mut style = Style::default();
936 style.refine(&self.style);
937
938 let hitbox = window.insert_hitbox(bounds, HitboxBehavior::Normal);
939
940 // If the width of the list has changed, invalidate all cached item heights
941 if state
942 .last_layout_bounds
943 .is_none_or(|last_bounds| last_bounds.size.width != bounds.size.width)
944 {
945 let new_items = SumTree::from_iter(
946 state.items.iter().map(|item| ListItem::Unmeasured {
947 focus_handle: item.focus_handle(),
948 }),
949 (),
950 );
951
952 state.items = new_items;
953 }
954
955 let padding = style
956 .padding
957 .to_pixels(bounds.size.into(), window.rem_size());
958 let layout =
959 match state.prepaint_items(bounds, padding, true, &mut self.render_item, window, cx) {
960 Ok(layout) => layout,
961 Err(autoscroll_request) => {
962 state.logical_scroll_top = Some(autoscroll_request);
963 state
964 .prepaint_items(bounds, padding, false, &mut self.render_item, window, cx)
965 .unwrap()
966 }
967 };
968
969 state.last_layout_bounds = Some(bounds);
970 state.last_padding = Some(padding);
971 ListPrepaintState { hitbox, layout }
972 }
973
974 fn paint(
975 &mut self,
976 _id: Option<&GlobalElementId>,
977 _inspector_id: Option<&InspectorElementId>,
978 bounds: Bounds<crate::Pixels>,
979 _: &mut Self::RequestLayoutState,
980 prepaint: &mut Self::PrepaintState,
981 window: &mut Window,
982 cx: &mut App,
983 ) {
984 let current_view = window.current_view();
985 window.with_content_mask(Some(ContentMask { bounds }), |window| {
986 for item in &mut prepaint.layout.item_layouts {
987 item.element.paint(window, cx);
988 }
989 });
990
991 let list_state = self.state.clone();
992 let height = bounds.size.height;
993 let scroll_top = prepaint.layout.scroll_top;
994 let hitbox_id = prepaint.hitbox.id;
995 let mut accumulated_scroll_delta = ScrollDelta::default();
996 window.on_mouse_event(move |event: &ScrollWheelEvent, phase, window, cx| {
997 if phase == DispatchPhase::Bubble && hitbox_id.should_handle_scroll(window) {
998 accumulated_scroll_delta = accumulated_scroll_delta.coalesce(event.delta);
999 let pixel_delta = accumulated_scroll_delta.pixel_delta(px(20.));
1000 list_state.0.borrow_mut().scroll(
1001 &scroll_top,
1002 height,
1003 pixel_delta,
1004 current_view,
1005 window,
1006 cx,
1007 )
1008 }
1009 });
1010 }
1011}
1012
1013impl IntoElement for List {
1014 type Element = Self;
1015
1016 fn into_element(self) -> Self::Element {
1017 self
1018 }
1019}
1020
1021impl Styled for List {
1022 fn style(&mut self) -> &mut StyleRefinement {
1023 &mut self.style
1024 }
1025}
1026
1027impl sum_tree::Item for ListItem {
1028 type Summary = ListItemSummary;
1029
1030 fn summary(&self, _: ()) -> Self::Summary {
1031 match self {
1032 ListItem::Unmeasured { focus_handle } => ListItemSummary {
1033 count: 1,
1034 rendered_count: 0,
1035 unrendered_count: 1,
1036 height: px(0.),
1037 has_focus_handles: focus_handle.is_some(),
1038 },
1039 ListItem::Measured {
1040 size, focus_handle, ..
1041 } => ListItemSummary {
1042 count: 1,
1043 rendered_count: 1,
1044 unrendered_count: 0,
1045 height: size.height,
1046 has_focus_handles: focus_handle.is_some(),
1047 },
1048 }
1049 }
1050}
1051
1052impl sum_tree::ContextLessSummary for ListItemSummary {
1053 fn zero() -> Self {
1054 Default::default()
1055 }
1056
1057 fn add_summary(&mut self, summary: &Self) {
1058 self.count += summary.count;
1059 self.rendered_count += summary.rendered_count;
1060 self.unrendered_count += summary.unrendered_count;
1061 self.height += summary.height;
1062 self.has_focus_handles |= summary.has_focus_handles;
1063 }
1064}
1065
1066impl<'a> sum_tree::Dimension<'a, ListItemSummary> for Count {
1067 fn zero(_cx: ()) -> Self {
1068 Default::default()
1069 }
1070
1071 fn add_summary(&mut self, summary: &'a ListItemSummary, _: ()) {
1072 self.0 += summary.count;
1073 }
1074}
1075
1076impl<'a> sum_tree::Dimension<'a, ListItemSummary> for Height {
1077 fn zero(_cx: ()) -> Self {
1078 Default::default()
1079 }
1080
1081 fn add_summary(&mut self, summary: &'a ListItemSummary, _: ()) {
1082 self.0 += summary.height;
1083 }
1084}
1085
1086impl sum_tree::SeekTarget<'_, ListItemSummary, ListItemSummary> for Count {
1087 fn cmp(&self, other: &ListItemSummary, _: ()) -> std::cmp::Ordering {
1088 self.0.partial_cmp(&other.count).unwrap()
1089 }
1090}
1091
1092impl sum_tree::SeekTarget<'_, ListItemSummary, ListItemSummary> for Height {
1093 fn cmp(&self, other: &ListItemSummary, _: ()) -> std::cmp::Ordering {
1094 self.0.partial_cmp(&other.height).unwrap()
1095 }
1096}
1097
1098#[cfg(test)]
1099mod test {
1100
1101 use gpui::{ScrollDelta, ScrollWheelEvent};
1102
1103 use crate::{self as gpui, TestAppContext};
1104
1105 #[gpui::test]
1106 fn test_reset_after_paint_before_scroll(cx: &mut TestAppContext) {
1107 use crate::{
1108 AppContext, Context, Element, IntoElement, ListState, Render, Styled, Window, div,
1109 list, point, px, size,
1110 };
1111
1112 let cx = cx.add_empty_window();
1113
1114 let state = ListState::new(5, crate::ListAlignment::Top, px(10.));
1115
1116 // Ensure that the list is scrolled to the top
1117 state.scroll_to(gpui::ListOffset {
1118 item_ix: 0,
1119 offset_in_item: px(0.0),
1120 });
1121
1122 struct TestView(ListState);
1123 impl Render for TestView {
1124 fn render(&mut self, _: &mut Window, _: &mut Context<Self>) -> impl IntoElement {
1125 list(self.0.clone(), |_, _, _| {
1126 div().h(px(10.)).w_full().into_any()
1127 })
1128 .w_full()
1129 .h_full()
1130 }
1131 }
1132
1133 // Paint
1134 cx.draw(point(px(0.), px(0.)), size(px(100.), px(20.)), |_, cx| {
1135 cx.new(|_| TestView(state.clone()))
1136 });
1137
1138 // Reset
1139 state.reset(5);
1140
1141 // And then receive a scroll event _before_ the next paint
1142 cx.simulate_event(ScrollWheelEvent {
1143 position: point(px(1.), px(1.)),
1144 delta: ScrollDelta::Pixels(point(px(0.), px(-500.))),
1145 ..Default::default()
1146 });
1147
1148 // Scroll position should stay at the top of the list
1149 assert_eq!(state.logical_scroll_top().item_ix, 0);
1150 assert_eq!(state.logical_scroll_top().offset_in_item, px(0.));
1151 }
1152
1153 #[gpui::test]
1154 fn test_scroll_by_positive_and_negative_distance(cx: &mut TestAppContext) {
1155 use crate::{
1156 AppContext, Context, Element, IntoElement, ListState, Render, Styled, Window, div,
1157 list, point, px, size,
1158 };
1159
1160 let cx = cx.add_empty_window();
1161
1162 let state = ListState::new(5, crate::ListAlignment::Top, px(10.));
1163
1164 struct TestView(ListState);
1165 impl Render for TestView {
1166 fn render(&mut self, _: &mut Window, _: &mut Context<Self>) -> impl IntoElement {
1167 list(self.0.clone(), |_, _, _| {
1168 div().h(px(20.)).w_full().into_any()
1169 })
1170 .w_full()
1171 .h_full()
1172 }
1173 }
1174
1175 // Paint
1176 cx.draw(point(px(0.), px(0.)), size(px(100.), px(100.)), |_, cx| {
1177 cx.new(|_| TestView(state.clone()))
1178 });
1179
1180 // Test positive distance: start at item 1, move down 30px
1181 state.scroll_by(px(30.));
1182
1183 // Should move to item 2
1184 let offset = state.logical_scroll_top();
1185 assert_eq!(offset.item_ix, 1);
1186 assert_eq!(offset.offset_in_item, px(10.));
1187
1188 // Test negative distance: start at item 2, move up 30px
1189 state.scroll_by(px(-30.));
1190
1191 // Should move back to item 1
1192 let offset = state.logical_scroll_top();
1193 assert_eq!(offset.item_ix, 0);
1194 assert_eq!(offset.offset_in_item, px(0.));
1195
1196 // Test zero distance
1197 state.scroll_by(px(0.));
1198 let offset = state.logical_scroll_top();
1199 assert_eq!(offset.item_ix, 0);
1200 assert_eq!(offset.offset_in_item, px(0.));
1201 }
1202}