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 const 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 measuring_behavior: ListMeasuringBehavior,
74}
75
76/// Whether the list is scrolling from top to bottom or bottom to top.
77#[derive(Clone, Copy, Debug, Eq, PartialEq)]
78pub enum ListAlignment {
79 /// The list is scrolling from top to bottom, like most lists.
80 Top,
81 /// The list is scrolling from bottom to top, like a chat log.
82 Bottom,
83}
84
85/// A scroll event that has been converted to be in terms of the list's items.
86pub struct ListScrollEvent {
87 /// The range of items currently visible in the list, after applying the scroll event.
88 pub visible_range: Range<usize>,
89
90 /// The number of items that are currently visible in the list, after applying the scroll event.
91 pub count: usize,
92
93 /// Whether the list has been scrolled.
94 pub is_scrolled: bool,
95}
96
97/// The sizing behavior to apply during layout.
98#[derive(Clone, Copy, Debug, Default, PartialEq, Eq, PartialOrd, Ord, Hash)]
99pub enum ListSizingBehavior {
100 /// The list should calculate its size based on the size of its items.
101 Infer,
102 /// The list should not calculate a fixed size.
103 #[default]
104 Auto,
105}
106
107/// The measuring behavior to apply during layout.
108#[derive(Clone, Copy, Debug, Default, PartialEq, Eq, PartialOrd, Ord, Hash)]
109pub enum ListMeasuringBehavior {
110 /// Measure all items in the list.
111 /// Note: This can be expensive for the first frame in a large list.
112 Measure(bool),
113 /// Only measure visible items
114 #[default]
115 Visible,
116}
117
118impl ListMeasuringBehavior {
119 const fn reset(&mut self) {
120 match self {
121 ListMeasuringBehavior::Measure(has_measured) => *has_measured = false,
122 ListMeasuringBehavior::Visible => {}
123 }
124 }
125}
126
127/// The horizontal sizing behavior to apply during layout.
128#[derive(Clone, Copy, Debug, Default, PartialEq, Eq, PartialOrd, Ord, Hash)]
129pub enum ListHorizontalSizingBehavior {
130 /// List items' width can never exceed the width of the list.
131 #[default]
132 FitList,
133 /// List items' width may go over the width of the list, if any item is wider.
134 Unconstrained,
135}
136
137struct LayoutItemsResponse {
138 max_item_width: Pixels,
139 scroll_top: ListOffset,
140 item_layouts: VecDeque<ItemLayout>,
141}
142
143struct ItemLayout {
144 index: usize,
145 element: AnyElement,
146 size: Size<Pixels>,
147}
148
149/// Frame state used by the [List] element after layout.
150pub struct ListPrepaintState {
151 hitbox: Hitbox,
152 layout: LayoutItemsResponse,
153}
154
155#[derive(Clone)]
156enum ListItem {
157 Unmeasured {
158 focus_handle: Option<FocusHandle>,
159 },
160 Measured {
161 size: Size<Pixels>,
162 focus_handle: Option<FocusHandle>,
163 },
164}
165
166impl ListItem {
167 const fn size(&self) -> Option<Size<Pixels>> {
168 if let ListItem::Measured { size, .. } = self {
169 Some(*size)
170 } else {
171 None
172 }
173 }
174
175 fn focus_handle(&self) -> Option<FocusHandle> {
176 match self {
177 ListItem::Unmeasured { focus_handle } | ListItem::Measured { focus_handle, .. } => {
178 focus_handle.clone()
179 }
180 }
181 }
182
183 fn contains_focused(&self, window: &Window, cx: &App) -> bool {
184 match self {
185 ListItem::Unmeasured { focus_handle } | ListItem::Measured { focus_handle, .. } => {
186 focus_handle
187 .as_ref()
188 .is_some_and(|handle| handle.contains_focused(window, cx))
189 }
190 }
191 }
192}
193
194#[derive(Clone, Debug, Default, PartialEq)]
195struct ListItemSummary {
196 count: usize,
197 rendered_count: usize,
198 unrendered_count: usize,
199 height: Pixels,
200 has_focus_handles: bool,
201}
202
203#[derive(Clone, Debug, Default, PartialEq, Eq, PartialOrd, Ord)]
204struct Count(usize);
205
206#[derive(Clone, Debug, Default)]
207struct Height(Pixels);
208
209impl ListState {
210 /// Construct a new list state, for storage on a view.
211 ///
212 /// The overdraw parameter controls how much extra space is rendered
213 /// above and below the visible area. Elements within this area will
214 /// be measured even though they are not visible. This can help ensure
215 /// that the list doesn't flicker or pop in when scrolling.
216 pub fn new(item_count: usize, alignment: ListAlignment, overdraw: Pixels) -> Self {
217 let this = Self(Rc::new(RefCell::new(StateInner {
218 last_layout_bounds: None,
219 last_padding: None,
220 items: SumTree::default(),
221 logical_scroll_top: None,
222 alignment,
223 overdraw,
224 scroll_handler: None,
225 reset: false,
226 scrollbar_drag_start_height: None,
227 measuring_behavior: ListMeasuringBehavior::default(),
228 })));
229 this.splice(0..0, item_count);
230 this
231 }
232
233 /// Set the list to measure all items in the list in the first layout phase.
234 ///
235 /// This is useful for ensuring that the scrollbar size is correct instead of based on only rendered elements.
236 pub fn measure_all(self) -> Self {
237 self.0.borrow_mut().measuring_behavior = ListMeasuringBehavior::Measure(false);
238 self
239 }
240
241 /// Reset this instantiation of the list state.
242 ///
243 /// Note that this will cause scroll events to be dropped until the next paint.
244 pub fn reset(&self, element_count: usize) {
245 let old_count = {
246 let state = &mut *self.0.borrow_mut();
247 state.reset = true;
248 state.measuring_behavior.reset();
249 state.logical_scroll_top = None;
250 state.scrollbar_drag_start_height = None;
251 state.items.summary().count
252 };
253
254 self.splice(0..old_count, element_count);
255 }
256
257 /// The number of items in this list.
258 pub fn item_count(&self) -> usize {
259 self.0.borrow().items.summary().count
260 }
261
262 /// Inform the list state that the items in `old_range` have been replaced
263 /// by `count` new items that must be recalculated.
264 pub fn splice(&self, old_range: Range<usize>, count: usize) {
265 self.splice_focusable(old_range, (0..count).map(|_| None))
266 }
267
268 /// Register with the list state that the items in `old_range` have been replaced
269 /// by new items. As opposed to [`Self::splice`], this method allows an iterator of optional focus handles
270 /// to be supplied to properly integrate with items in the list that can be focused. If a focused item
271 /// is scrolled out of view, the list will continue to render it to allow keyboard interaction.
272 pub fn splice_focusable(
273 &self,
274 old_range: Range<usize>,
275 focus_handles: impl IntoIterator<Item = Option<FocusHandle>>,
276 ) {
277 let state = &mut *self.0.borrow_mut();
278
279 let mut old_items = state.items.cursor::<Count>(());
280 let mut new_items = old_items.slice(&Count(old_range.start), Bias::Right);
281 old_items.seek_forward(&Count(old_range.end), Bias::Right);
282
283 let mut spliced_count = 0;
284 new_items.extend(
285 focus_handles.into_iter().map(|focus_handle| {
286 spliced_count += 1;
287 ListItem::Unmeasured { focus_handle }
288 }),
289 (),
290 );
291 new_items.append(old_items.suffix(), ());
292 drop(old_items);
293 state.items = new_items;
294
295 if let Some(ListOffset {
296 item_ix,
297 offset_in_item,
298 }) = state.logical_scroll_top.as_mut()
299 {
300 if old_range.contains(item_ix) {
301 *item_ix = old_range.start;
302 *offset_in_item = px(0.);
303 } else if old_range.end <= *item_ix {
304 *item_ix = *item_ix - (old_range.end - old_range.start) + spliced_count;
305 }
306 }
307 }
308
309 /// Set a handler that will be called when the list is scrolled.
310 pub fn set_scroll_handler(
311 &self,
312 handler: impl FnMut(&ListScrollEvent, &mut Window, &mut App) + 'static,
313 ) {
314 self.0.borrow_mut().scroll_handler = Some(Box::new(handler))
315 }
316
317 /// Get the current scroll offset, in terms of the list's items.
318 pub fn logical_scroll_top(&self) -> ListOffset {
319 self.0.borrow().logical_scroll_top()
320 }
321
322 /// Scroll the list by the given offset
323 pub fn scroll_by(&self, distance: Pixels) {
324 if distance == px(0.) {
325 return;
326 }
327
328 let current_offset = self.logical_scroll_top();
329 let state = &mut *self.0.borrow_mut();
330 let mut cursor = state.items.cursor::<ListItemSummary>(());
331 cursor.seek(&Count(current_offset.item_ix), Bias::Right);
332
333 let start_pixel_offset = cursor.start().height + current_offset.offset_in_item;
334 let new_pixel_offset = (start_pixel_offset + distance).max(px(0.));
335 if new_pixel_offset > start_pixel_offset {
336 cursor.seek_forward(&Height(new_pixel_offset), Bias::Right);
337 } else {
338 cursor.seek(&Height(new_pixel_offset), Bias::Right);
339 }
340
341 state.logical_scroll_top = Some(ListOffset {
342 item_ix: cursor.start().count,
343 offset_in_item: new_pixel_offset - cursor.start().height,
344 });
345 }
346
347 /// Scroll the list to the given offset
348 pub fn scroll_to(&self, mut scroll_top: ListOffset) {
349 let state = &mut *self.0.borrow_mut();
350 let item_count = state.items.summary().count;
351 if scroll_top.item_ix >= item_count {
352 scroll_top.item_ix = item_count;
353 scroll_top.offset_in_item = px(0.);
354 }
355
356 state.logical_scroll_top = Some(scroll_top);
357 }
358
359 /// Scroll the list to the given item, such that the item is fully visible.
360 pub fn scroll_to_reveal_item(&self, ix: usize) {
361 let state = &mut *self.0.borrow_mut();
362
363 let mut scroll_top = state.logical_scroll_top();
364 let height = state
365 .last_layout_bounds
366 .map_or(px(0.), |bounds| bounds.size.height);
367 let padding = state.last_padding.unwrap_or_default();
368
369 if ix <= scroll_top.item_ix {
370 scroll_top.item_ix = ix;
371 scroll_top.offset_in_item = px(0.);
372 } else {
373 let mut cursor = state.items.cursor::<ListItemSummary>(());
374 cursor.seek(&Count(ix + 1), Bias::Right);
375 let bottom = cursor.start().height + padding.top;
376 let goal_top = px(0.).max(bottom - height + padding.bottom);
377
378 cursor.seek(&Height(goal_top), Bias::Left);
379 let start_ix = cursor.start().count;
380 let start_item_top = cursor.start().height;
381
382 if start_ix >= scroll_top.item_ix {
383 scroll_top.item_ix = start_ix;
384 scroll_top.offset_in_item = goal_top - start_item_top;
385 }
386 }
387
388 state.logical_scroll_top = Some(scroll_top);
389 }
390
391 /// Get the bounds for the given item in window coordinates, if it's
392 /// been rendered.
393 pub fn bounds_for_item(&self, ix: usize) -> Option<Bounds<Pixels>> {
394 let state = &*self.0.borrow();
395
396 let bounds = state.last_layout_bounds.unwrap_or_default();
397 let scroll_top = state.logical_scroll_top();
398 if ix < scroll_top.item_ix {
399 return None;
400 }
401
402 let mut cursor = state.items.cursor::<Dimensions<Count, Height>>(());
403 cursor.seek(&Count(scroll_top.item_ix), Bias::Right);
404
405 let scroll_top = cursor.start().1.0 + scroll_top.offset_in_item;
406
407 cursor.seek_forward(&Count(ix), Bias::Right);
408 if let Some(&ListItem::Measured { size, .. }) = cursor.item() {
409 let &Dimensions(Count(count), Height(top), _) = cursor.start();
410 if count == ix {
411 let top = bounds.top() + top - scroll_top;
412 return Some(Bounds::from_corners(
413 point(bounds.left(), top),
414 point(bounds.right(), top + size.height),
415 ));
416 }
417 }
418 None
419 }
420
421 /// Call this method when the user starts dragging the scrollbar.
422 ///
423 /// This will prevent the height reported to the scrollbar from changing during the drag
424 /// as items in the overdraw get measured, and help offset scroll position changes accordingly.
425 pub fn scrollbar_drag_started(&self) {
426 let mut state = self.0.borrow_mut();
427 state.scrollbar_drag_start_height = Some(state.items.summary().height);
428 }
429
430 /// Called when the user stops dragging the scrollbar.
431 ///
432 /// See `scrollbar_drag_started`.
433 pub fn scrollbar_drag_ended(&self) {
434 self.0.borrow_mut().scrollbar_drag_start_height.take();
435 }
436
437 /// Set the offset from the scrollbar
438 pub fn set_offset_from_scrollbar(&self, point: Point<Pixels>) {
439 self.0.borrow_mut().set_offset_from_scrollbar(point);
440 }
441
442 /// Returns the maximum scroll offset according to the items we have measured.
443 /// This value remains constant while dragging to prevent the scrollbar from moving away unexpectedly.
444 pub fn max_offset_for_scrollbar(&self) -> Size<Pixels> {
445 let state = self.0.borrow();
446 let bounds = state.last_layout_bounds.unwrap_or_default();
447
448 let height = state
449 .scrollbar_drag_start_height
450 .unwrap_or_else(|| state.items.summary().height);
451
452 Size::new(Pixels::ZERO, Pixels::ZERO.max(height - bounds.size.height))
453 }
454
455 /// Returns the current scroll offset adjusted for the scrollbar
456 pub fn scroll_px_offset_for_scrollbar(&self) -> Point<Pixels> {
457 let state = &self.0.borrow();
458 let logical_scroll_top = state.logical_scroll_top();
459
460 let mut cursor = state.items.cursor::<ListItemSummary>(());
461 let summary: ListItemSummary =
462 cursor.summary(&Count(logical_scroll_top.item_ix), Bias::Right);
463 let content_height = state.items.summary().height;
464 let drag_offset =
465 // if dragging the scrollbar, we want to offset the point if the height changed
466 content_height - state.scrollbar_drag_start_height.unwrap_or(content_height);
467 let offset = summary.height + logical_scroll_top.offset_in_item - drag_offset;
468
469 Point::new(px(0.), -offset)
470 }
471
472 /// Return the bounds of the viewport in pixels.
473 pub fn viewport_bounds(&self) -> Bounds<Pixels> {
474 self.0.borrow().last_layout_bounds.unwrap_or_default()
475 }
476}
477
478impl StateInner {
479 fn visible_range(&self, height: Pixels, scroll_top: &ListOffset) -> Range<usize> {
480 let mut cursor = self.items.cursor::<ListItemSummary>(());
481 cursor.seek(&Count(scroll_top.item_ix), Bias::Right);
482 let start_y = cursor.start().height + scroll_top.offset_in_item;
483 cursor.seek_forward(&Height(start_y + height), Bias::Left);
484 scroll_top.item_ix..cursor.start().count + 1
485 }
486
487 fn scroll(
488 &mut self,
489 scroll_top: &ListOffset,
490 height: Pixels,
491 delta: Point<Pixels>,
492 current_view: EntityId,
493 window: &mut Window,
494 cx: &mut App,
495 ) {
496 // Drop scroll events after a reset, since we can't calculate
497 // the new logical scroll top without the item heights
498 if self.reset {
499 return;
500 }
501
502 let padding = self.last_padding.unwrap_or_default();
503 let scroll_max =
504 (self.items.summary().height + padding.top + padding.bottom - height).max(px(0.));
505 let new_scroll_top = (self.scroll_top(scroll_top) - delta.y)
506 .max(px(0.))
507 .min(scroll_max);
508
509 if self.alignment == ListAlignment::Bottom && new_scroll_top == scroll_max {
510 self.logical_scroll_top = None;
511 } else {
512 let mut cursor = self.items.cursor::<ListItemSummary>(());
513 cursor.seek(&Height(new_scroll_top), Bias::Right);
514 let item_ix = cursor.start().count;
515 let offset_in_item = new_scroll_top - cursor.start().height;
516 self.logical_scroll_top = Some(ListOffset {
517 item_ix,
518 offset_in_item,
519 });
520 }
521
522 if self.scroll_handler.is_some() {
523 let visible_range = self.visible_range(height, scroll_top);
524 self.scroll_handler.as_mut().unwrap()(
525 &ListScrollEvent {
526 visible_range,
527 count: self.items.summary().count,
528 is_scrolled: self.logical_scroll_top.is_some(),
529 },
530 window,
531 cx,
532 );
533 }
534
535 cx.notify(current_view);
536 }
537
538 fn logical_scroll_top(&self) -> ListOffset {
539 self.logical_scroll_top
540 .unwrap_or_else(|| match self.alignment {
541 ListAlignment::Top => ListOffset {
542 item_ix: 0,
543 offset_in_item: px(0.),
544 },
545 ListAlignment::Bottom => ListOffset {
546 item_ix: self.items.summary().count,
547 offset_in_item: px(0.),
548 },
549 })
550 }
551
552 fn scroll_top(&self, logical_scroll_top: &ListOffset) -> Pixels {
553 let mut cursor = self.items.cursor::<ListItemSummary>(());
554 cursor.seek(&Count(logical_scroll_top.item_ix), Bias::Right);
555 cursor.start().height + logical_scroll_top.offset_in_item
556 }
557
558 fn layout_all_items(
559 &mut self,
560 available_width: Pixels,
561 render_item: &mut RenderItemFn,
562 window: &mut Window,
563 cx: &mut App,
564 ) {
565 match &mut self.measuring_behavior {
566 ListMeasuringBehavior::Visible => {
567 return;
568 }
569 ListMeasuringBehavior::Measure(has_measured) => {
570 if *has_measured {
571 return;
572 }
573 *has_measured = true;
574 }
575 }
576
577 let mut cursor = self.items.cursor::<Count>(());
578 let available_item_space = size(
579 AvailableSpace::Definite(available_width),
580 AvailableSpace::MinContent,
581 );
582
583 let mut measured_items = Vec::default();
584
585 for (ix, item) in cursor.enumerate() {
586 let size = item.size().unwrap_or_else(|| {
587 let mut element = render_item(ix, window, cx);
588 element.layout_as_root(available_item_space, window, cx)
589 });
590
591 measured_items.push(ListItem::Measured {
592 size,
593 focus_handle: item.focus_handle(),
594 });
595 }
596
597 self.items = SumTree::from_iter(measured_items, ());
598 }
599
600 fn layout_items(
601 &mut self,
602 available_width: Option<Pixels>,
603 available_height: Pixels,
604 padding: &Edges<Pixels>,
605 render_item: &mut RenderItemFn,
606 window: &mut Window,
607 cx: &mut App,
608 ) -> LayoutItemsResponse {
609 let old_items = self.items.clone();
610 let mut measured_items = VecDeque::new();
611 let mut item_layouts = VecDeque::new();
612 let mut rendered_height = padding.top;
613 let mut max_item_width = px(0.);
614 let mut scroll_top = self.logical_scroll_top();
615 let mut rendered_focused_item = false;
616
617 let available_item_space = size(
618 available_width.map_or(AvailableSpace::MinContent, |width| {
619 AvailableSpace::Definite(width)
620 }),
621 AvailableSpace::MinContent,
622 );
623
624 let mut cursor = old_items.cursor::<Count>(());
625
626 // Render items after the scroll top, including those in the trailing overdraw
627 cursor.seek(&Count(scroll_top.item_ix), Bias::Right);
628 for (ix, item) in cursor.by_ref().enumerate() {
629 let visible_height = rendered_height - scroll_top.offset_in_item;
630 if visible_height >= available_height + self.overdraw {
631 break;
632 }
633
634 // Use the previously cached height and focus handle if available
635 let mut size = item.size();
636
637 // If we're within the visible area or the height wasn't cached, render and measure the item's element
638 if visible_height < available_height || size.is_none() {
639 let item_index = scroll_top.item_ix + ix;
640 let mut element = render_item(item_index, window, cx);
641 let element_size = element.layout_as_root(available_item_space, window, cx);
642 size = Some(element_size);
643 if visible_height < available_height {
644 item_layouts.push_back(ItemLayout {
645 index: item_index,
646 element,
647 size: element_size,
648 });
649 if item.contains_focused(window, cx) {
650 rendered_focused_item = true;
651 }
652 }
653 }
654
655 let size = size.unwrap();
656 rendered_height += size.height;
657 max_item_width = max_item_width.max(size.width);
658 measured_items.push_back(ListItem::Measured {
659 size,
660 focus_handle: item.focus_handle(),
661 });
662 }
663 rendered_height += padding.bottom;
664
665 // Prepare to start walking upward from the item at the scroll top.
666 cursor.seek(&Count(scroll_top.item_ix), Bias::Right);
667
668 // If the rendered items do not fill the visible region, then adjust
669 // the scroll top upward.
670 if rendered_height - scroll_top.offset_in_item < available_height {
671 while rendered_height < available_height {
672 cursor.prev();
673 if let Some(item) = cursor.item() {
674 let item_index = cursor.start().0;
675 let mut element = render_item(item_index, window, cx);
676 let element_size = element.layout_as_root(available_item_space, window, cx);
677 let focus_handle = item.focus_handle();
678 rendered_height += element_size.height;
679 measured_items.push_front(ListItem::Measured {
680 size: element_size,
681 focus_handle,
682 });
683 item_layouts.push_front(ItemLayout {
684 index: item_index,
685 element,
686 size: element_size,
687 });
688 if item.contains_focused(window, cx) {
689 rendered_focused_item = true;
690 }
691 } else {
692 break;
693 }
694 }
695
696 scroll_top = ListOffset {
697 item_ix: cursor.start().0,
698 offset_in_item: rendered_height - available_height,
699 };
700
701 match self.alignment {
702 ListAlignment::Top => {
703 scroll_top.offset_in_item = scroll_top.offset_in_item.max(px(0.));
704 self.logical_scroll_top = Some(scroll_top);
705 }
706 ListAlignment::Bottom => {
707 scroll_top = ListOffset {
708 item_ix: cursor.start().0,
709 offset_in_item: rendered_height - available_height,
710 };
711 self.logical_scroll_top = None;
712 }
713 };
714 }
715
716 // Measure items in the leading overdraw
717 let mut leading_overdraw = scroll_top.offset_in_item;
718 while leading_overdraw < self.overdraw {
719 cursor.prev();
720 if let Some(item) = cursor.item() {
721 let size = if let ListItem::Measured { size, .. } = item {
722 *size
723 } else {
724 let mut element = render_item(cursor.start().0, window, cx);
725 element.layout_as_root(available_item_space, window, cx)
726 };
727
728 leading_overdraw += size.height;
729 measured_items.push_front(ListItem::Measured {
730 size,
731 focus_handle: item.focus_handle(),
732 });
733 } else {
734 break;
735 }
736 }
737
738 let measured_range = cursor.start().0..(cursor.start().0 + measured_items.len());
739 let mut cursor = old_items.cursor::<Count>(());
740 let mut new_items = cursor.slice(&Count(measured_range.start), Bias::Right);
741 new_items.extend(measured_items, ());
742 cursor.seek(&Count(measured_range.end), Bias::Right);
743 new_items.append(cursor.suffix(), ());
744 self.items = new_items;
745
746 // If none of the visible items are focused, check if an off-screen item is focused
747 // and include it to be rendered after the visible items so keyboard interaction continues
748 // to work for it.
749 if !rendered_focused_item {
750 let mut cursor = self
751 .items
752 .filter::<_, Count>((), |summary| summary.has_focus_handles);
753 cursor.next();
754 while let Some(item) = cursor.item() {
755 if item.contains_focused(window, cx) {
756 let item_index = cursor.start().0;
757 let mut element = render_item(cursor.start().0, window, cx);
758 let size = element.layout_as_root(available_item_space, window, cx);
759 item_layouts.push_back(ItemLayout {
760 index: item_index,
761 element,
762 size,
763 });
764 break;
765 }
766 cursor.next();
767 }
768 }
769
770 LayoutItemsResponse {
771 max_item_width,
772 scroll_top,
773 item_layouts,
774 }
775 }
776
777 fn prepaint_items(
778 &mut self,
779 bounds: Bounds<Pixels>,
780 padding: Edges<Pixels>,
781 autoscroll: bool,
782 render_item: &mut RenderItemFn,
783 window: &mut Window,
784 cx: &mut App,
785 ) -> Result<LayoutItemsResponse, ListOffset> {
786 window.transact(|window| {
787 match self.measuring_behavior {
788 ListMeasuringBehavior::Measure(has_measured) if !has_measured => {
789 self.layout_all_items(bounds.size.width, render_item, window, cx);
790 }
791 _ => {}
792 }
793
794 let mut layout_response = self.layout_items(
795 Some(bounds.size.width),
796 bounds.size.height,
797 &padding,
798 render_item,
799 window,
800 cx,
801 );
802
803 // Avoid honoring autoscroll requests from elements other than our children.
804 window.take_autoscroll();
805
806 // Only paint the visible items, if there is actually any space for them (taking padding into account)
807 if bounds.size.height > padding.top + padding.bottom {
808 let mut item_origin = bounds.origin + Point::new(px(0.), padding.top);
809 item_origin.y -= layout_response.scroll_top.offset_in_item;
810 for item in &mut layout_response.item_layouts {
811 window.with_content_mask(Some(ContentMask { bounds }), |window| {
812 item.element.prepaint_at(item_origin, window, cx);
813 });
814
815 if let Some(autoscroll_bounds) = window.take_autoscroll()
816 && autoscroll
817 {
818 if autoscroll_bounds.top() < bounds.top() {
819 return Err(ListOffset {
820 item_ix: item.index,
821 offset_in_item: autoscroll_bounds.top() - item_origin.y,
822 });
823 } else if autoscroll_bounds.bottom() > bounds.bottom() {
824 let mut cursor = self.items.cursor::<Count>(());
825 cursor.seek(&Count(item.index), Bias::Right);
826 let mut height = bounds.size.height - padding.top - padding.bottom;
827
828 // Account for the height of the element down until the autoscroll bottom.
829 height -= autoscroll_bounds.bottom() - item_origin.y;
830
831 // Keep decreasing the scroll top until we fill all the available space.
832 while height > Pixels::ZERO {
833 cursor.prev();
834 let Some(item) = cursor.item() else { break };
835
836 let size = item.size().unwrap_or_else(|| {
837 let mut item = render_item(cursor.start().0, window, cx);
838 let item_available_size =
839 size(bounds.size.width.into(), AvailableSpace::MinContent);
840 item.layout_as_root(item_available_size, window, cx)
841 });
842 height -= size.height;
843 }
844
845 return Err(ListOffset {
846 item_ix: cursor.start().0,
847 offset_in_item: if height < Pixels::ZERO {
848 -height
849 } else {
850 Pixels::ZERO
851 },
852 });
853 }
854 }
855
856 item_origin.y += item.size.height;
857 }
858 } else {
859 layout_response.item_layouts.clear();
860 }
861
862 Ok(layout_response)
863 })
864 }
865
866 // Scrollbar support
867
868 fn set_offset_from_scrollbar(&mut self, point: Point<Pixels>) {
869 let Some(bounds) = self.last_layout_bounds else {
870 return;
871 };
872 let height = bounds.size.height;
873
874 let padding = self.last_padding.unwrap_or_default();
875 let content_height = self.items.summary().height;
876 let scroll_max = (content_height + padding.top + padding.bottom - height).max(px(0.));
877 let drag_offset =
878 // if dragging the scrollbar, we want to offset the point if the height changed
879 content_height - self.scrollbar_drag_start_height.unwrap_or(content_height);
880 let new_scroll_top = (point.y - drag_offset).abs().max(px(0.)).min(scroll_max);
881
882 if self.alignment == ListAlignment::Bottom && new_scroll_top == scroll_max {
883 self.logical_scroll_top = None;
884 } else {
885 let mut cursor = self.items.cursor::<ListItemSummary>(());
886 cursor.seek(&Height(new_scroll_top), Bias::Right);
887
888 let item_ix = cursor.start().count;
889 let offset_in_item = new_scroll_top - cursor.start().height;
890 self.logical_scroll_top = Some(ListOffset {
891 item_ix,
892 offset_in_item,
893 });
894 }
895 }
896}
897
898impl std::fmt::Debug for ListItem {
899 fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
900 match self {
901 Self::Unmeasured { .. } => write!(f, "Unrendered"),
902 Self::Measured { size, .. } => f.debug_struct("Rendered").field("size", size).finish(),
903 }
904 }
905}
906
907/// An offset into the list's items, in terms of the item index and the number
908/// of pixels off the top left of the item.
909#[derive(Debug, Clone, Copy, Default)]
910pub struct ListOffset {
911 /// The index of an item in the list
912 pub item_ix: usize,
913 /// The number of pixels to offset from the item index.
914 pub offset_in_item: Pixels,
915}
916
917impl Element for List {
918 type RequestLayoutState = ();
919 type PrepaintState = ListPrepaintState;
920
921 fn id(&self) -> Option<crate::ElementId> {
922 None
923 }
924
925 fn source_location(&self) -> Option<&'static core::panic::Location<'static>> {
926 None
927 }
928
929 fn request_layout(
930 &mut self,
931 _id: Option<&GlobalElementId>,
932 _inspector_id: Option<&InspectorElementId>,
933 window: &mut Window,
934 cx: &mut App,
935 ) -> (crate::LayoutId, Self::RequestLayoutState) {
936 let layout_id = match self.sizing_behavior {
937 ListSizingBehavior::Infer => {
938 let mut style = Style::default();
939 style.overflow.y = Overflow::Scroll;
940 style.refine(&self.style);
941 window.with_text_style(style.text_style().cloned(), |window| {
942 let state = &mut *self.state.0.borrow_mut();
943
944 let available_height = if let Some(last_bounds) = state.last_layout_bounds {
945 last_bounds.size.height
946 } else {
947 // If we don't have the last layout bounds (first render),
948 // we might just use the overdraw value as the available height to layout enough items.
949 state.overdraw
950 };
951 let padding = style.padding.to_pixels(
952 state.last_layout_bounds.unwrap_or_default().size.into(),
953 window.rem_size(),
954 );
955
956 let layout_response = state.layout_items(
957 None,
958 available_height,
959 &padding,
960 &mut self.render_item,
961 window,
962 cx,
963 );
964 let max_element_width = layout_response.max_item_width;
965
966 let summary = state.items.summary();
967 let total_height = summary.height;
968
969 window.request_measured_layout(
970 style,
971 move |known_dimensions, available_space, _window, _cx| {
972 let width =
973 known_dimensions
974 .width
975 .unwrap_or(match available_space.width {
976 AvailableSpace::Definite(x) => x,
977 AvailableSpace::MinContent | AvailableSpace::MaxContent => {
978 max_element_width
979 }
980 });
981 let height = match available_space.height {
982 AvailableSpace::Definite(height) => total_height.min(height),
983 AvailableSpace::MinContent | AvailableSpace::MaxContent => {
984 total_height
985 }
986 };
987 size(width, height)
988 },
989 )
990 })
991 }
992 ListSizingBehavior::Auto => {
993 let mut style = Style::default();
994 style.refine(&self.style);
995 window.with_text_style(style.text_style().cloned(), |window| {
996 window.request_layout(style, None, cx)
997 })
998 }
999 };
1000 (layout_id, ())
1001 }
1002
1003 fn prepaint(
1004 &mut self,
1005 _id: Option<&GlobalElementId>,
1006 _inspector_id: Option<&InspectorElementId>,
1007 bounds: Bounds<Pixels>,
1008 _: &mut Self::RequestLayoutState,
1009 window: &mut Window,
1010 cx: &mut App,
1011 ) -> ListPrepaintState {
1012 let state = &mut *self.state.0.borrow_mut();
1013 state.reset = false;
1014
1015 let mut style = Style::default();
1016 style.refine(&self.style);
1017
1018 let hitbox = window.insert_hitbox(bounds, HitboxBehavior::Normal);
1019
1020 // If the width of the list has changed, invalidate all cached item heights
1021 if state
1022 .last_layout_bounds
1023 .is_none_or(|last_bounds| last_bounds.size.width != bounds.size.width)
1024 {
1025 let new_items = SumTree::from_iter(
1026 state.items.iter().map(|item| ListItem::Unmeasured {
1027 focus_handle: item.focus_handle(),
1028 }),
1029 (),
1030 );
1031
1032 state.items = new_items;
1033 }
1034
1035 let padding = style
1036 .padding
1037 .to_pixels(bounds.size.into(), window.rem_size());
1038 let layout =
1039 match state.prepaint_items(bounds, padding, true, &mut self.render_item, window, cx) {
1040 Ok(layout) => layout,
1041 Err(autoscroll_request) => {
1042 state.logical_scroll_top = Some(autoscroll_request);
1043 state
1044 .prepaint_items(bounds, padding, false, &mut self.render_item, window, cx)
1045 .unwrap()
1046 }
1047 };
1048
1049 state.last_layout_bounds = Some(bounds);
1050 state.last_padding = Some(padding);
1051 ListPrepaintState { hitbox, layout }
1052 }
1053
1054 fn paint(
1055 &mut self,
1056 _id: Option<&GlobalElementId>,
1057 _inspector_id: Option<&InspectorElementId>,
1058 bounds: Bounds<crate::Pixels>,
1059 _: &mut Self::RequestLayoutState,
1060 prepaint: &mut Self::PrepaintState,
1061 window: &mut Window,
1062 cx: &mut App,
1063 ) {
1064 let current_view = window.current_view();
1065 window.with_content_mask(Some(ContentMask { bounds }), |window| {
1066 for item in &mut prepaint.layout.item_layouts {
1067 item.element.paint(window, cx);
1068 }
1069 });
1070
1071 let list_state = self.state.clone();
1072 let height = bounds.size.height;
1073 let scroll_top = prepaint.layout.scroll_top;
1074 let hitbox_id = prepaint.hitbox.id;
1075 let mut accumulated_scroll_delta = ScrollDelta::default();
1076 window.on_mouse_event(move |event: &ScrollWheelEvent, phase, window, cx| {
1077 if phase == DispatchPhase::Bubble && hitbox_id.should_handle_scroll(window) {
1078 accumulated_scroll_delta = accumulated_scroll_delta.coalesce(event.delta);
1079 let pixel_delta = accumulated_scroll_delta.pixel_delta(px(20.));
1080 list_state.0.borrow_mut().scroll(
1081 &scroll_top,
1082 height,
1083 pixel_delta,
1084 current_view,
1085 window,
1086 cx,
1087 )
1088 }
1089 });
1090 }
1091}
1092
1093impl IntoElement for List {
1094 type Element = Self;
1095
1096 fn into_element(self) -> Self::Element {
1097 self
1098 }
1099}
1100
1101impl Styled for List {
1102 fn style(&mut self) -> &mut StyleRefinement {
1103 &mut self.style
1104 }
1105}
1106
1107impl sum_tree::Item for ListItem {
1108 type Summary = ListItemSummary;
1109
1110 fn summary(&self, _: ()) -> Self::Summary {
1111 match self {
1112 ListItem::Unmeasured { focus_handle } => ListItemSummary {
1113 count: 1,
1114 rendered_count: 0,
1115 unrendered_count: 1,
1116 height: px(0.),
1117 has_focus_handles: focus_handle.is_some(),
1118 },
1119 ListItem::Measured {
1120 size, focus_handle, ..
1121 } => ListItemSummary {
1122 count: 1,
1123 rendered_count: 1,
1124 unrendered_count: 0,
1125 height: size.height,
1126 has_focus_handles: focus_handle.is_some(),
1127 },
1128 }
1129 }
1130}
1131
1132impl sum_tree::ContextLessSummary for ListItemSummary {
1133 fn zero() -> Self {
1134 Default::default()
1135 }
1136
1137 fn add_summary(&mut self, summary: &Self) {
1138 self.count += summary.count;
1139 self.rendered_count += summary.rendered_count;
1140 self.unrendered_count += summary.unrendered_count;
1141 self.height += summary.height;
1142 self.has_focus_handles |= summary.has_focus_handles;
1143 }
1144}
1145
1146impl<'a> sum_tree::Dimension<'a, ListItemSummary> for Count {
1147 fn zero(_cx: ()) -> Self {
1148 Default::default()
1149 }
1150
1151 fn add_summary(&mut self, summary: &'a ListItemSummary, _: ()) {
1152 self.0 += summary.count;
1153 }
1154}
1155
1156impl<'a> sum_tree::Dimension<'a, ListItemSummary> for Height {
1157 fn zero(_cx: ()) -> Self {
1158 Default::default()
1159 }
1160
1161 fn add_summary(&mut self, summary: &'a ListItemSummary, _: ()) {
1162 self.0 += summary.height;
1163 }
1164}
1165
1166impl sum_tree::SeekTarget<'_, ListItemSummary, ListItemSummary> for Count {
1167 fn cmp(&self, other: &ListItemSummary, _: ()) -> std::cmp::Ordering {
1168 self.0.partial_cmp(&other.count).unwrap()
1169 }
1170}
1171
1172impl sum_tree::SeekTarget<'_, ListItemSummary, ListItemSummary> for Height {
1173 fn cmp(&self, other: &ListItemSummary, _: ()) -> std::cmp::Ordering {
1174 self.0.partial_cmp(&other.height).unwrap()
1175 }
1176}
1177
1178#[cfg(test)]
1179mod test {
1180
1181 use gpui::{ScrollDelta, ScrollWheelEvent};
1182
1183 use crate::{self as gpui, TestAppContext};
1184
1185 #[gpui::test]
1186 fn test_reset_after_paint_before_scroll(cx: &mut TestAppContext) {
1187 use crate::{
1188 AppContext, Context, Element, IntoElement, ListState, Render, Styled, Window, div,
1189 list, point, px, size,
1190 };
1191
1192 let cx = cx.add_empty_window();
1193
1194 let state = ListState::new(5, crate::ListAlignment::Top, px(10.));
1195
1196 // Ensure that the list is scrolled to the top
1197 state.scroll_to(gpui::ListOffset {
1198 item_ix: 0,
1199 offset_in_item: px(0.0),
1200 });
1201
1202 struct TestView(ListState);
1203 impl Render for TestView {
1204 fn render(&mut self, _: &mut Window, _: &mut Context<Self>) -> impl IntoElement {
1205 list(self.0.clone(), |_, _, _| {
1206 div().h(px(10.)).w_full().into_any()
1207 })
1208 .w_full()
1209 .h_full()
1210 }
1211 }
1212
1213 // Paint
1214 cx.draw(point(px(0.), px(0.)), size(px(100.), px(20.)), |_, cx| {
1215 cx.new(|_| TestView(state.clone()))
1216 });
1217
1218 // Reset
1219 state.reset(5);
1220
1221 // And then receive a scroll event _before_ the next paint
1222 cx.simulate_event(ScrollWheelEvent {
1223 position: point(px(1.), px(1.)),
1224 delta: ScrollDelta::Pixels(point(px(0.), px(-500.))),
1225 ..Default::default()
1226 });
1227
1228 // Scroll position should stay at the top of the list
1229 assert_eq!(state.logical_scroll_top().item_ix, 0);
1230 assert_eq!(state.logical_scroll_top().offset_in_item, px(0.));
1231 }
1232
1233 #[gpui::test]
1234 fn test_scroll_by_positive_and_negative_distance(cx: &mut TestAppContext) {
1235 use crate::{
1236 AppContext, Context, Element, IntoElement, ListState, Render, Styled, Window, div,
1237 list, point, px, size,
1238 };
1239
1240 let cx = cx.add_empty_window();
1241
1242 let state = ListState::new(5, crate::ListAlignment::Top, px(10.));
1243
1244 struct TestView(ListState);
1245 impl Render for TestView {
1246 fn render(&mut self, _: &mut Window, _: &mut Context<Self>) -> impl IntoElement {
1247 list(self.0.clone(), |_, _, _| {
1248 div().h(px(20.)).w_full().into_any()
1249 })
1250 .w_full()
1251 .h_full()
1252 }
1253 }
1254
1255 // Paint
1256 cx.draw(point(px(0.), px(0.)), size(px(100.), px(100.)), |_, cx| {
1257 cx.new(|_| TestView(state.clone()))
1258 });
1259
1260 // Test positive distance: start at item 1, move down 30px
1261 state.scroll_by(px(30.));
1262
1263 // Should move to item 2
1264 let offset = state.logical_scroll_top();
1265 assert_eq!(offset.item_ix, 1);
1266 assert_eq!(offset.offset_in_item, px(10.));
1267
1268 // Test negative distance: start at item 2, move up 30px
1269 state.scroll_by(px(-30.));
1270
1271 // Should move back to item 1
1272 let offset = state.logical_scroll_top();
1273 assert_eq!(offset.item_ix, 0);
1274 assert_eq!(offset.offset_in_item, px(0.));
1275
1276 // Test zero distance
1277 state.scroll_by(px(0.));
1278 let offset = state.logical_scroll_top();
1279 assert_eq!(offset.item_ix, 0);
1280 assert_eq!(offset.offset_in_item, px(0.));
1281 }
1282}