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