From 914b0117fb5a23469af85e567d5723eca6b53635 Mon Sep 17 00:00:00 2001 From: Antonio Scandurra Date: Tue, 16 Dec 2025 16:59:26 +0100 Subject: [PATCH] Optimize editor rendering when clipped by parent containers (#44995) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Fixes #44997 ## Summary Optimizes editor rendering when an editor is partially clipped by a parent container (e.g., a `List`). The editor now only lays out and renders lines that are actually visible within the viewport, rather than all lines in the document. ## Problem When an `AutoHeight` editor with thousands of lines is placed inside a scrollable `List` (such as in the Agent Panel thread view), the editor would lay out **all** lines during prepaint, even though only a small portion was visible. Profiling showed that ~50% of frame time was spent in `EditorElement::prepaint` → `LineWithInvisibles::from_chunks`, processing thousands of invisible lines. ## Solution Calculate the intersection of the editor's bounds with the current content mask (which represents the visible viewport after all parent clipping). Use this to determine: 1. `clipped_top_in_lines` - how many lines are clipped above the viewport 2. `visible_height_in_lines` - how many lines are actually visible Then adjust `start_row` and `end_row` to only include visible lines. The parent container handles positioning, so `scroll_position` remains unchanged for paint calculations. ## Example For a 3000-line editor where only 50 lines are visible: - **Before**: Lay out and render 3000 lines - **After**: Lay out and render ~50 lines ## Testing Verified the following scenarios work correctly: - Editor fully visible (no clipping) - Editor clipped from top - Editor clipped from bottom - Editor completely outside viewport (renders nothing) - Fractional line clipping at boundaries - Scrollable editors with internal scroll state inside a clipped container Release Notes: - Improved agent panel performance when rendering large diffs. --- crates/editor/src/element.rs | 17 +++++++++++++++-- crates/editor/src/test.rs | 8 +++----- 2 files changed, 18 insertions(+), 7 deletions(-) diff --git a/crates/editor/src/element.rs b/crates/editor/src/element.rs index 8de660275ba9b455aec610568c41347888654495..95047569c31c2e306b0f984832b568f052e4179a 100644 --- a/crates/editor/src/element.rs +++ b/crates/editor/src/element.rs @@ -9164,6 +9164,15 @@ impl Element for EditorElement { let height_in_lines = f64::from(bounds.size.height / line_height); let max_row = snapshot.max_point().row().as_f64(); + // Calculate how much of the editor is clipped by parent containers (e.g., List). + // This allows us to only render lines that are actually visible, which is + // critical for performance when large AutoHeight editors are inside Lists. + let visible_bounds = window.content_mask().bounds; + let clipped_top = (visible_bounds.origin.y - bounds.origin.y).max(px(0.)); + let clipped_top_in_lines = f64::from(clipped_top / line_height); + let visible_height_in_lines = + f64::from(visible_bounds.size.height / line_height); + // The max scroll position for the top of the window let max_scroll_top = if matches!( snapshot.mode, @@ -9220,10 +9229,14 @@ impl Element for EditorElement { let mut scroll_position = snapshot.scroll_position(); // The scroll position is a fractional point, the whole number of which represents // the top of the window in terms of display rows. - let start_row = DisplayRow(scroll_position.y as u32); + // We add clipped_top_in_lines to skip rows that are clipped by parent containers, + // but we don't modify scroll_position itself since the parent handles positioning. + let start_row = + DisplayRow((scroll_position.y + clipped_top_in_lines).floor() as u32); let max_row = snapshot.max_point().row(); let end_row = cmp::min( - (scroll_position.y + height_in_lines).ceil() as u32, + (scroll_position.y + clipped_top_in_lines + visible_height_in_lines).ceil() + as u32, max_row.next_row().0, ); let end_row = DisplayRow(end_row); diff --git a/crates/editor/src/test.rs b/crates/editor/src/test.rs index 5a0652bdd199a638f92234b1d50232071db18e07..1cc619385446502db6a3a0dceb6e70fa4b4e8416 100644 --- a/crates/editor/src/test.rs +++ b/crates/editor/src/test.rs @@ -176,11 +176,9 @@ pub fn block_content_for_tests( } pub fn editor_content_with_blocks(editor: &Entity, cx: &mut VisualTestContext) -> String { - cx.draw( - gpui::Point::default(), - size(px(3000.0), px(3000.0)), - |_, _| editor.clone(), - ); + let draw_size = size(px(3000.0), px(3000.0)); + cx.simulate_resize(draw_size); + cx.draw(gpui::Point::default(), draw_size, |_, _| editor.clone()); let (snapshot, mut lines, blocks) = editor.update_in(cx, |editor, window, cx| { let snapshot = editor.snapshot(window, cx); let text = editor.display_text(cx);