Reduce render allocations and redundant work in core components

crates/core/src/alert.rs

@@ -304,7 +304,7 @@ impl RenderOnce for AlertsView {
         let theme = cx.theme();
         let enter_duration = theme.motion.overlay;
 
-        let entries: Vec<AlertEntry> = self.alerts.read(cx).entries().to_vec();
+        let entries = self.alerts.read(cx).entries();
 
         deferred(
             div()

crates/core/src/combobox.rs

@@ -604,8 +604,8 @@ where
                     div()
                         .id(("option", row))
                         .debug_selector({
-                            let name = format!("{id}-option-{row}");
+                            let id = id.clone();
-                            move || name
+                            move || format!("{id}-option-{row}")
                         })
                         .flex()
                         .items_center()
@@ -681,8 +681,8 @@ where
             let panel = v_flex()
                 .id((id.clone(), "panel"))
                 .debug_selector({
-                    let name = format!("{id}-panel");
+                    let id = id.clone();
-                    move || name
+                    move || format!("{id}-panel")
                 })
                 .w(popup_width)
                 .p_1()

crates/core/src/command_palette.rs

@@ -335,8 +335,8 @@ impl Render for CommandPaletteState {
                 h_flex()
                     .id(("command", row))
                     .debug_selector({
-                        let name = format!("{id}-command-{row}");
+                        let id = id.clone();
-                        move || name
+                        move || format!("{id}-command-{row}")
                     })
                     .gap_2()
                     .px_2()
@@ -409,8 +409,8 @@ impl Render for CommandPaletteState {
         let panel = v_flex()
             .id((id.clone(), "panel"))
             .debug_selector({
-                let name = format!("{id}-panel");
+                let id = id.clone();
-                move || name
+                move || format!("{id}-panel")
             })
             .key_context(COMMAND_PALETTE_CONTEXT)
             .role(Role::Dialog)

crates/core/src/dropdown_menu.rs

@@ -422,10 +422,10 @@ impl RenderOnce for DropdownMenu {
 
         let items = if self.open {
             self.items
-                .map(|build| build(window, cx))
+                .map(|build| Rc::from(build(window, cx)))
-                .unwrap_or_default()
+                .unwrap_or_else(|| Rc::from([]))
         } else {
-            Vec::new()
+            Rc::from([])
         };
 
         if let Some(panel) = anchored_menu_panel(

crates/core/src/field.rs

@@ -95,8 +95,8 @@ impl RenderOnce for Field {
 
         let title = div()
             .debug_selector({
-                let name = format!("{id}-label");
+                let id = id.clone();
-                move || name
+                move || format!("{id}-label")
             })
             .text_size(metrics.text_size)
             .child(self.label.clone());
@@ -105,16 +105,16 @@ impl RenderOnce for Field {
             .items_center()
             .gap_2()
             .debug_selector({
-                let name = format!("{id}-control");
+                let id = id.clone();
-                move || name
+                move || format!("{id}-control")
             })
             .children(self.control);
 
         let error = self.error.map(|error| {
             div()
                 .debug_selector({
-                    let name = format!("{id}-error");
+                    let id = id.clone();
-                    move || name
+                    move || format!("{id}-error")
                 })
                 .text_size(metrics.caption_size)
                 .text_color(error_color)

crates/core/src/input.rs

@@ -2051,7 +2051,11 @@ impl RenderOnce for Input {
                 canvas
                     .with_animation(
                         animation_id,
-                        Animation::new(CARET_BLINK_INTERVAL * 2).repeat(),
+                        // The blink needs four repaints per period,
+                        // not the display's refresh rate.
+                        Animation::new(CARET_BLINK_INTERVAL * 2)
+                            .repeat()
+                            .with_max_fps(4.0),
                         |canvas, _| canvas,
                     )
                     .into_any_element()

crates/core/src/menu.rs

@@ -336,11 +336,11 @@ impl RenderOnce for Menu {
 
         let items = if self.open {
             match self.items {
-                Some(build) => build(window, cx),
+                Some(build) => Rc::from(build(window, cx)),
-                None => Vec::new(),
+                None => Rc::from([]),
             }
         } else {
-            Vec::new()
+            Rc::from([])
         };
 
         if let Some(panel) = anchored_menu_panel(
@@ -372,7 +372,7 @@ pub(crate) fn anchored_menu_panel(
     cx: &mut App,
     id: &ElementId,
     open: bool,
-    items: Vec<MenuItem>,
+    items: Rc<[MenuItem]>,
     initial_selection: Option<usize>,
     preselect: bool,
     on_change: Option<ChangeHandler>,

crates/core/src/segmented.rs

@@ -9,7 +9,7 @@ use gpui::{
 };
 use gpui_native_icons::{IconRole, icon};
 use gpui_native_theme::{ActiveTheme as _, Size};
-use gpui_native_utils::{adjacent_selectable, focus_handle, focus_ring};
+use gpui_native_utils::{focus_handle, focus_ring};
 
 use crate::common::{Sizable, StyledExt, h_flex};
 
@@ -64,7 +64,8 @@ where
     T: Clone + PartialEq + 'static,
 {
     id: ElementId,
-    options: Vec<SegmentedOption<T>>,
+    /// Shared with the per-segment and key handlers, so captures are bumps.
+    options: Rc<[SegmentedOption<T>]>,
     selected: T,
     a11y_label: Option<SharedString>,
     size: Size,
@@ -82,7 +83,7 @@ where
     {
         Self {
             id: id.into(),
-            options: Vec::new(),
+            options: Rc::from([]),
             selected,
             a11y_label: None,
             size: Size::Small,
@@ -163,12 +164,12 @@ where
             .options
             .iter()
             .position(|segment| segment.value == self.selected);
+        let option_count = self.options.len();
 
-        let selectable: Vec<usize> = (0..self.options.len()).collect();
         let on_change = self.on_change.clone();
         let key_on_change = on_change.clone();
         let key_options = self.options.clone();
-        let key_selectable = selectable.clone();
+        let options = self.options.clone();
 
         let label = self
             .a11y_label
@@ -176,14 +177,13 @@ where
             .unwrap_or_else(|| SharedString::from(self.id.to_string()));
 
         window.with_element_namespace(self.id.clone(), |window| {
-            let focus = focus_handle(&self.id, window, cx);
-
             let geometry: Entity<Vec<Option<Bounds<gpui::Pixels>>>> =
                 window.use_keyed_state("segmented-geometry", cx, |_, _| Vec::new());
 
             let track_origin: Entity<Option<Point<gpui::Pixels>>> =
                 window.use_keyed_state("segmented-track-origin", cx, |_, _| None);
 
+            let focus = focus_handle(&self.id, window, cx);
             let anim_config = SpringConfig::new(500., 35., 1.);
             let track_point = *track_origin.read(cx);
 
@@ -197,12 +197,13 @@ where
 
             let segments = self
                 .options
-                .into_iter()
+                .iter()
                 .enumerate()
                 .map(move |(index, segment)| {
                     let is_selected = Some(index) == selected_index;
                     let on_change = on_change.clone();
-                    let value = segment.value;
+                    let options = options.clone();
+
                     let content_color = if is_selected {
                         foreground
                     } else {
@@ -228,7 +229,7 @@ where
                         .when_some(segment.icon, |segment, role| {
                             segment.child(icon(role).size(icon_size).color(content_color))
                         })
-                        .child(segment.label)
+                        .child(segment.label.clone())
                         .child(
                             canvas(
                                 {
@@ -251,8 +252,9 @@ where
                             move |_, window, cx| {
                                 if Some(index) != selected_index
                                     && let Some(on_change) = &on_change
+                                    && let Some(option) = options.get(index)
                                 {
-                                    on_change(value.clone(), window, cx);
+                                    on_change(option.value.clone(), window, cx);
                                 }
                             }
                         })
@@ -319,22 +321,26 @@ where
                     .on_key_down({
                         move |event: &KeyDownEvent, window, cx| {
                             let target = match event.keystroke.key.as_str() {
-                                "right" => {
+                                "right" => match selected_index {
-                                    adjacent_selectable(&key_selectable, selected_index, true)
+                                    Some(index) => {
+                                        index.checked_add(1).filter(|next| *next < option_count)
                                     }
-                                "left" => {
+                                    None => (option_count > 0).then_some(0),
-                                    adjacent_selectable(&key_selectable, selected_index, false)
+                                },
-                                }
+                                "left" => selected_index.and_then(|index| index.checked_sub(1)),
-                                "home" => key_selectable.first().copied(),
+                                "home" => (option_count > 0).then_some(0),
-                                "end" => key_selectable.last().copied(),
+                                "end" => option_count.checked_sub(1),
                                 _ => return,
                             };
+
                             if let Some(next) = target
                                 && Some(next) != selected_index
                                 && let Some(on_change) = &key_on_change
+                                && let Some(option) = key_options.get(next)
                             {
-                                on_change(key_options[next].value.clone(), window, cx);
+                                on_change(option.value.clone(), window, cx);
                             }
+
                             cx.stop_propagation();
                         }
                     })

crates/core/src/select.rs

@@ -206,24 +206,18 @@ where
                 .position(|option| &option.value == value)
         });
 
-        let trigger_options = self.options.clone();
+        // The trigger's text is fixed at render time; only it moves into the closure.
-        let trigger_selected = self.selected.clone();
+        let trigger_text = selected_index
-        let trigger_placeholder = self.placeholder.clone();
+            .and_then(|index| self.options.get(index))
+            .map(|option| option.label.clone())
+            .unwrap_or_else(|| self.placeholder.clone());
+
+        let trigger_has_value = self.selected.is_some();
         let trigger_id = self.id.clone();
         let trigger_label = label.clone();
         let trigger_style = self.style;
 
         let trigger = move |_window: &mut Window, _cx: &mut App| {
-            let text = trigger_selected
-                .as_ref()
-                .and_then(|value| {
-                    trigger_options
-                        .iter()
-                        .find(|option| &option.value == value)
-                        .map(|option| option.label.clone())
-                })
-                .unwrap_or_else(|| trigger_placeholder.clone());
-
             h_flex()
                 .id((trigger_id.clone(), "select-trigger"))
                 .debug_selector(|| "select-trigger".to_string())
@@ -240,7 +234,7 @@ where
                 .border_color(rest_border)
                 .bg(input)
                 .text_size(metrics.text_size)
-                .text_color(if trigger_selected.is_some() {
+                .text_color(if trigger_has_value {
                     foreground
                 } else {
                     muted_foreground
@@ -249,7 +243,7 @@ where
                     trigger.shadow(focus_ring(ring))
                 })
                 .hover(|style| style.bg(muted).border_color(hover_border))
-                .child(text)
+                .child(trigger_text.clone())
                 .child(
                     icon(IconRole::ChevronDown)
                         .size(icon_size)

crates/core/src/switch.rs

@@ -133,10 +133,7 @@ impl RenderOnce for Switch {
                 div()
                     .flex_none()
                     .relative()
-                    .debug_selector({
+                    .debug_selector(move || format!("{id}-track"))
-                        let name = format!("{id}-track");
-                        move || name
-                    })
                     .w(track_width)
                     .h(track_height)
                     .rounded(theme.radius.full)

crates/core/src/tooltip.rs

@@ -34,8 +34,8 @@ impl Tooltip {
     {
         let text = text.into();
         let anchor_id = anchor_id.into();
-        move |_window, cx| {
+        move |window, cx| {
-            let anchor = anchor_bounds(&anchor_id, cx);
+            let anchor = anchor_bounds(window.window_handle().window_id(), &anchor_id, cx);
             cx.new(|_| Self {
                 text: text.clone(),
                 anchor,
@@ -92,11 +92,13 @@ impl Render for Tooltip {
                 let origin = window.mouse_position() + point(px(1.), px(1.));
                 let viewport_height = window.viewport_size().height;
 
-                let height = anchor_bounds(&ElementId::from(PANEL_BOUNDS_ID), cx)
+                let height = anchor_bounds(
+                    window.window_handle().window_id(),
+                    &ElementId::from(PANEL_BOUNDS_ID),
+                    cx,
+                )
                 .map(|bounds| bounds.size.height)
-                    .unwrap_or_else(|| {
+                .unwrap_or_else(|| text_size * 1.5 + window.rem_size() * 0.5 + BORDER_WIDTH * 2.0);
-                        text_size * 1.5 + window.rem_size() * 0.5 + BORDER_WIDTH * 2.0
-                    });
 
                 let below = viewport_height - spacing_unit - parent.bottom();
                 let above = parent.top() - spacing_unit;

crates/core/tests/field_bench.rs

@@ -1,3 +1,5 @@
+use std::{cell::Cell, rc::Rc, time::Duration};
+
 use gpui::{
     AppContext as _, Context, Entity, IntoElement, ParentElement as _, Render, SharedString,
     Styled as _, TestAppContext, VisualTestContext, Window, div,
@@ -9,10 +11,12 @@ use gpui_native_core::input::{Input, InputState};
 
 struct FieldHost {
     url: Entity<InputState>,
+    renders: Rc<Cell<usize>>,
 }
 
 impl Render for FieldHost {
     fn render(&mut self, _window: &mut Window, cx: &mut Context<Self>) -> impl IntoElement {
+        self.renders.set(self.renders.get() + 1);
         let url_error = self
             .url
             .read(cx)
@@ -34,15 +38,27 @@ impl Render for FieldHost {
 
 /// A field page in a real window; the url input is focused unless
 /// `focus` is false, which leaves the page truly idle.
-fn field_host(focus: bool) -> (TestAppContext, Entity<InputState>, VisualTestContext) {
+fn field_host(
+    focus: bool,
+) -> (
+    TestAppContext,
+    Entity<InputState>,
+    VisualTestContext,
+    Rc<Cell<usize>>,
+) {
     let cx = TestAppContext::single();
     cx.update(init);
+    let renders = Rc::new(Cell::new(0));
+    let renders_for_host = renders.clone();
     let (url, window) = cx.update(|cx| {
         let url = InputState::new(cx);
         let url_for_host = url.clone();
         let window = cx
             .open_window(gpui::WindowOptions::default(), |_, cx| {
-                cx.new(|_| FieldHost { url: url_for_host })
+                cx.new(|_| FieldHost {
+                    url: url_for_host,
+                    renders: renders_for_host.clone(),
+                })
             })
             .unwrap();
         (url, window)
@@ -55,12 +71,12 @@ fn field_host(focus: bool) -> (TestAppContext, Entity<InputState>, VisualTestCon
         }
         window.draw(cx).clear(cx);
     });
-    (cx, url, visual)
+    (cx, url, visual, renders)
 }
 
 #[test]
 fn an_idle_field_page_schedules_no_frames() {
-    let (_cx, _url, mut visual) = field_host(false);
+    let (_cx, _url, mut visual, _renders) = field_host(false);
     let frames = visual.update(|window, cx| window.simulate_next_frame(cx));
     assert_eq!(
         frames, 0,
@@ -68,12 +84,25 @@ fn an_idle_field_page_schedules_no_frames() {
     );
 }
 
+/// The caret blink is fps-capped: it must never demand a next frame, and its
+/// redraws arrive on the executor timer at the blink cadence.
 #[test]
-fn a_focused_field_page_schedules_frames_for_its_blink() {
+fn a_focused_field_blink_is_fps_capped_and_still_redraws() {
-    let (_cx, _url, mut visual) = field_host(true);
+    let (cx, _url, mut visual, renders) = field_host(true);
+    let renders_after_focus = renders.get();
+
     let frames = visual.update(|window, cx| window.simulate_next_frame(cx));
+    assert_eq!(
+        frames, 0,
+        "the blink must be fps-capped, not per-frame scheduled"
+    );
+
+    // The blink redraws through the executor timer (4 fps cap).
+    cx.executor().advance_clock(Duration::from_millis(251));
+    cx.run_until_parked();
+    visual.update(|window, cx| window.draw(cx).clear(cx));
     assert!(
-        frames > 0,
+        renders.get() > renders_after_focus,
-        "the focused caret's blink needs frames to redraw at the blink cadence"
+        "the capped blink must still redraw its page"
     );
 }

crates/data/src/sidebar.rs

@@ -195,7 +195,6 @@ impl RenderOnce for Sidebar {
             .clone()
             .unwrap_or_else(|| SharedString::from(self.id.to_string()));
 
-        let id_text = self.id.to_string();
         let scroll_area_id = (self.id.clone(), "entries");
 
         // Entry paint reads the theme through this borrow.
@@ -216,9 +215,10 @@ impl RenderOnce for Sidebar {
             })
             .collect();
 
+        let id = self.id;
         div()
-            .id(self.id)
+            .id(id.clone())
-            .debug_selector(move || format!("sidebar-{id_text}"))
+            .debug_selector(move || format!("sidebar-{id}"))
             .size_full()
             .flex()
             .flex_col()

crates/data/src/tabs.rs

@@ -307,8 +307,9 @@ fn render_tab(
     let mut strip_tab = div()
         .id((tab.key.clone(), "tab"))
         .debug_selector({
-            let id = format!("{tabs_id}-tab-{}", tab.label);
+            let tabs_id = tabs_id.clone();
-            move || id
+            let label = tab.label.clone();
+            move || format!("{tabs_id}-tab-{}", label)
         })
         .flex()
         .items_center()
@@ -411,8 +412,9 @@ fn render_tab_close(
         .small()
         .tab_stop(false)
         .debug_selector({
-            let id = format!("{tabs_id}-close-{}", tab.label);
+            let tabs_id = tabs_id.clone();
-            move || id.clone()
+            let label = tab.label.clone();
+            move || format!("{tabs_id}-close-{}", label)
         })
         .tooltip(Tooltip::text("Close"))
         .accessibility_label(SharedString::from(format!("Close {}", tab.label)))

crates/editor/src/code_view.rs

@@ -462,10 +462,10 @@ fn render_row(
     line_height: Pixels,
     cx: &App,
 ) -> gpui::AnyElement {
-    let line = code.code().lines.get(line_ix).cloned().unwrap_or_default();
+    let line = code.code().lines.get(line_ix);
 
     let mut text = String::new();
-    for span in &line.spans {
+    for span in line.map_or(&[][..], |line| line.spans.as_slice()) {
         text.push_str(&span.text);
     }
 
@@ -473,7 +473,7 @@ fn render_row(
     let mut roles = vec![Role::Text; char_count];
     let mut offset = 0usize;
 
-    for span in &line.spans {
+    for span in line.map_or(&[][..], |line| line.spans.as_slice()) {
         let chars = span.text.chars().count();
         for slot in &mut roles[offset..offset + chars] {
             *slot = span.role;
@@ -543,10 +543,7 @@ fn render_row(
     };
 
     div()
-        .debug_selector({
+        .debug_selector(move || format!("{id}-row-{line_ix}"))
-            let name = format!("{id}-row-{line_ix}");
-            move || name
-        })
         .id(("code-row", line_ix))
         .w_full()
         .h(line_height)

crates/editor/src/diff_view.rs

@@ -237,6 +237,8 @@ pub fn diff_rows(old: &str, new: &str, language: Language) -> Vec<DiffRow> {
 pub struct DiffViewState {
     id: ElementId,
     rows: Vec<DiffRow>,
+    /// The row whose width drives horizontal scroll extent, `rows`-derived.
+    widest_row: Option<usize>,
     options: DiffViewOptions,
     /// Drives both scroll axes of the virtualized row list.
     handle: UniformListScrollHandle,
@@ -251,13 +253,32 @@ impl DiffViewState {
         O: AsRef<str>,
         N: AsRef<str>,
     {
-        Self {
+        let mut state = Self {
             id: id.into(),
-            rows: diff_rows(old.as_ref(), new.as_ref(), language),
+            rows: Vec::new(),
+            widest_row: None,
             options: DiffViewOptions::default(),
             handle: UniformListScrollHandle::new(),
             a11y_label: None,
+        };
+        state.set_rows(old, new, language);
+        state
     }
+
+    /// Replaces the rows, recomputing `widest_row` with them.
+    fn set_rows<O, N>(&mut self, old: O, new: N, language: Language)
+    where
+        O: AsRef<str>,
+        N: AsRef<str>,
+    {
+        self.rows = diff_rows(old.as_ref(), new.as_ref(), language);
+        self.widest_row = self
+            .rows
+            .iter()
+            .enumerate()
+            .filter(|(_, row)| row.kind != DiffRowKind::Hunk)
+            .max_by_key(|(_, row)| row.char_count())
+            .map(|(ix, _)| ix);
     }
 
     /// Sets how changed rows are marked.
@@ -284,7 +305,7 @@ impl DiffViewState {
         O: AsRef<str>,
         N: AsRef<str>,
     {
-        self.rows = diff_rows(old.as_ref(), new.as_ref(), language);
+        self.set_rows(old, new, language);
         self.handle.scroll_to_item(0, ScrollStrategy::Top);
         // The replaced versions rarely share the old width; start at the left.
         let offset = ScrollbarHandle::offset(&self.handle);
@@ -328,14 +349,7 @@ impl Render for DiffViewState {
         let state = cx.entity();
         let row_count = self.rows.len();
         let options = self.options;
-
+        let widest_row = self.widest_row;
-        let widest_row = self
-            .rows
-            .iter()
-            .enumerate()
-            .filter(|(_, row)| row.kind != DiffRowKind::Hunk)
-            .max_by_key(|(_, row)| row.char_count())
-            .map(|(ix, _)| ix);
 
         let mut rows = uniform_list((id.clone(), "rows"), row_count, {
             move |range, _window, cx| {

crates/editor/src/markdown.rs

@@ -784,8 +784,8 @@ fn block_frame(
     let theme = cx.theme();
     let content = div()
         .debug_selector({
-            let name = SharedString::from(format!("{id}"));
+            let id = id.clone();
-            move || name.to_string()
+            move || id.to_string()
         })
         .w_full()
         .flex()

crates/layout/src/dock.rs

@@ -969,15 +969,10 @@ fn render_pane(
         .map(|tab| tab.view.clone());
 
     // The cache keeps an un-notified panel from re-rendering on dock frames.
+    let content_id = SharedString::from(format!("{dock_id}-content-{}", pane.key));
     let content = div()
-        .id(SharedString::from(format!(
+        .id(content_id.clone())
-            "{dock_id}-content-{}",
+        .debug_selector(move || content_id.to_string())
-            pane.key
-        )))
-        .debug_selector({
-            let id = SharedString::from(format!("{dock_id}-content-{}", pane.key));
-            move || id.to_string()
-        })
         .flex_1()
         .min_h_0()
         .overflow_hidden()
@@ -999,6 +994,7 @@ fn render_pane(
         let pane = pane.clone();
         let titlebar = *titlebar;
         let padding_x = metrics.dense_padding_x;
+
         move |window, cx| {
             let selected = pane
                 .active
@@ -1065,15 +1061,11 @@ fn render_pane(
                 }
             });
 
+            let bar_id = SharedString::from(format!("{dock_id}-pane-{}-bar", pane.key));
+
             h_flex()
-                .id(SharedString::from(format!(
+                .id(bar_id.clone())
-                    "{dock_id}-pane-{}-bar",
+                .debug_selector(move || bar_id.to_string())
-                    pane.key
-                )))
-                .debug_selector({
-                    let id = SharedString::from(format!("{dock_id}-pane-{}-bar", pane.key));
-                    move || id.to_string()
-                })
                 .flex_none()
                 .w_full()
                 .h(titlebar.height)

crates/utils/src/lib.rs

@@ -1,7 +1,8 @@
 use gpui::prelude::FluentBuilder as _;
 use gpui::{
     App, Bounds, BoxShadow, Div, ElementId, FocusHandle, Global, Hsla, IntoElement, Pixels,
-    Refineable as _, StatefulInteractiveElement, StyleRefinement, Styled, Window, div, px,
+    Refineable as _, StatefulInteractiveElement, StyleRefinement, Styled, Window, WindowId, div,
+    px,
 };
 use gpui_native_theme::ActiveTheme as _;
 use std::collections::HashMap;
@@ -36,39 +37,36 @@ pub fn focus_handle(id: &ElementId, window: &mut Window, cx: &mut App) -> FocusH
         .clone()
 }
 
-/// The painted bounds of elements that tooltips anchor to, keyed by element id.
+/// The painted bounds of elements that tooltips anchor to, per window and element id.
-#[derive(Clone, Default)]
+#[derive(Default)]
-struct AnchorBoundsRegistry(HashMap<ElementId, Bounds<Pixels>>);
+struct AnchorBoundsRegistry(HashMap<(WindowId, ElementId), Bounds<Pixels>>);
 
 impl Global for AnchorBoundsRegistry {}
 
 impl AnchorBoundsRegistry {
-    fn record(&mut self, id: ElementId, bounds: Bounds<Pixels>) {
+    fn record(&mut self, window: WindowId, id: ElementId, bounds: Bounds<Pixels>) {
-        self.0.insert(id, bounds);
+        self.0.insert((window, id), bounds);
     }
 
-    fn get(&self, id: &ElementId) -> Option<Bounds<Pixels>> {
+    fn get(&self, window: WindowId, id: &ElementId) -> Option<Bounds<Pixels>> {
-        self.0.get(id).copied()
+        self.0.get(&(window, id.clone())).copied()
     }
 }
 
-/// The last bounds an element painted at.
+/// The last bounds an element painted at, in the given window.
-pub fn anchor_bounds(id: &ElementId, cx: &mut App) -> Option<Bounds<Pixels>> {
+pub fn anchor_bounds(window: WindowId, id: &ElementId, cx: &App) -> Option<Bounds<Pixels>> {
     cx.try_global::<AnchorBoundsRegistry>()
-        .and_then(|registry| registry.get(id))
+        .and_then(|registry| registry.get(window, id))
 }
 
 /// A canvas prepaint closure recording the element's painted bounds.
 pub fn record_anchor_bounds(
     id: ElementId,
 ) -> impl Fn(Bounds<Pixels>, &mut Window, &mut App) + 'static {
-    move |bounds, _window, cx| {
+    move |bounds, window, cx| {
-        let mut registry = cx
+        let window_id = window.window_handle().window_id();
-            .try_global::<AnchorBoundsRegistry>()
+        cx.default_global::<AnchorBoundsRegistry>()
-            .cloned()
+            .record(window_id, id.clone(), bounds);
-            .unwrap_or_default();
-        registry.record(id.clone(), bounds);
-        cx.set_global(registry);
     }
 }