feat: add scrollbar for virtualized lists

examples/gallery/src/main.rs

@@ -3,8 +3,9 @@ use std::time::Duration;
 use gpui::prelude::FluentBuilder as _;
 use gpui::{
     App, AppContext as _, Bounds, Context, Entity, FontWeight, InteractiveElement as _,
-    IntoElement, KeyBinding, ParentElement as _, Pixels, Render, SharedString, Styled as _,
-    WeakEntity, Window, WindowBounds, WindowOptions, actions, div, px, size,
+    IntoElement, KeyBinding, ListAlignment, ListState, ParentElement as _, Pixels, Render,
+    SharedString, Styled as _, UniformListScrollHandle, WeakEntity, Window, WindowBounds,
+    WindowOptions, actions, div, list, px, size, uniform_list,
 };
 use gpui_native_core::alert::{Alert, AlertSeverity, Alerts, AlertsView};
 use gpui_native_core::avatar::Avatar;
@@ -25,6 +26,7 @@ use gpui_native_core::popover::Popover;
 use gpui_native_core::progress::Progress;
 use gpui_native_core::radio::{Radio, RadioGroup};
 use gpui_native_core::scroll_area::{ScrollArea, ScrollAxes};
+use gpui_native_core::scrollbar::{Scrollbar, ScrollbarVisibility};
 use gpui_native_core::segmented::{Segmented, SegmentedOption};
 use gpui_native_core::select::{Select, SelectOption};
 use gpui_native_core::slider::Slider;
@@ -93,6 +95,7 @@ const CATALOG: &[(&str, &[(&str, &str)])] = &[
             ("tooltip", "Tooltip"),
             ("empty-state", "Empty state"),
             ("scroll-area", "Scroll area"),
+            ("scrollbar", "Scrollbar"),
         ],
     ),
     (
@@ -614,6 +617,12 @@ impl Gallery {
             }),
             cx,
         );
+        dock.register_panel(
+            PanelDescriptor::new("scrollbar", "Scrollbar", |_, cx| {
+                cx.new(|_| ScrollbarDemo::new()).into()
+            }),
+            cx,
+        );
         dock.register_panel(
             PanelDescriptor::new("sidebar", "Sidebar", |_, cx| {
                 cx.new(|_| SidebarDemo { selected: None }).into()
@@ -2614,6 +2623,119 @@ impl Render for ScrollAreaDemo {
     }
 }
 
+/// The virtualized lists a [Scrollbar] drives: gpui's `uniform_list` and
+/// `list`, whose handles the overlay reads and writes.
+struct ScrollbarDemo {
+    uniform: UniformListScrollHandle,
+    list: ListState,
+    visibility: ScrollbarVisibility,
+}
+
+impl ScrollbarDemo {
+    fn new() -> Self {
+        Self {
+            uniform: UniformListScrollHandle::new(),
+            list: ListState::new(64, ListAlignment::Top, px(400.)),
+            visibility: ScrollbarVisibility::Platform,
+        }
+    }
+}
+
+impl Render for ScrollbarDemo {
+    fn render(&mut self, _window: &mut Window, cx: &mut Context<Self>) -> impl IntoElement {
+        let theme = cx.theme();
+        let colors = theme.colors;
+        let radius = theme.radius;
+        let list_state = self.list.clone();
+        let visibility = self.visibility;
+        let view = cx.entity();
+
+        ScrollArea::new("scrollbar-demo").size_full().p_4().child(
+            v_flex()
+                .gap_3()
+                .child(demo_section(
+                    "visibility",
+                    colors,
+                    Segmented::new("scrollbar-demo-visibility", visibility)
+                        .options(vec![
+                            (ScrollbarVisibility::Platform, "Platform"),
+                            (ScrollbarVisibility::Always, "Always"),
+                            (ScrollbarVisibility::Autohide, "Autohide"),
+                        ])
+                        .on_change(move |next, _, cx| {
+                            view.update(cx, |demo, cx| {
+                                demo.visibility = next;
+                                cx.notify();
+                            });
+                        }),
+                ))
+                .child(demo_section(
+                    "uniform_list",
+                    colors,
+                    div()
+                        .relative()
+                        .h(px(240.))
+                        .rounded(radius.control)
+                        .border_1()
+                        .border_color(colors.border)
+                        .overflow_hidden()
+                        .child(
+                            uniform_list("scrollbar-demo-uniform", 120, move |range, _, _| {
+                                range
+                                    .map(|row| {
+                                        div()
+                                            .h(px(24.))
+                                            .px_3()
+                                            .flex()
+                                            .items_center()
+                                            .border_b_1()
+                                            .border_color(colors.border)
+                                            .child(format!("Row {row} of 120"))
+                                    })
+                                    .collect()
+                            })
+                            .track_scroll(&self.uniform)
+                            .h_full()
+                            .w_full(),
+                        )
+                        .child(Scrollbar::vertical(self.uniform.clone()).visibility(visibility)),
+                ))
+                .child(demo_section(
+                    "list",
+                    colors,
+                    div()
+                        .relative()
+                        .h(px(240.))
+                        .rounded(radius.control)
+                        .border_1()
+                        .border_color(colors.border)
+                        .overflow_hidden()
+                        .child(
+                            list(list_state, move |row, _, _| {
+                                div()
+                                    .px_3()
+                                    .py_1()
+                                    .border_b_1()
+                                    .border_color(colors.border)
+                                    .child(format!("Item {row} — {} lines tall", 1 + row % 3))
+                                    .h(px(28. + (row % 3) as f32 * 12.))
+                                    .into_any_element()
+                            })
+                            .h_full()
+                            .w_full(),
+                        )
+                        .child(Scrollbar::vertical(self.list.clone()).visibility(visibility)),
+                ))
+                .child(
+                    div()
+                        .text_xs()
+                        .text_color(colors.muted_foreground)
+                        .child("Platform follows the running OS; scroll or grab the rail to reveal an autohidden thumb."),
+                ),
+        )
+    }
+}
+
 struct SidebarDemo {
     selected: Option<usize>,
 }