docking: a press in a group header focuses the shown panel

Host widgets in the header, such as a menu button or the host's own tabs,
focus the panel the way a press on its tab or body does.

crates/ui/src/docking/group_tests.rs

@@ -284,7 +284,10 @@ fn top_border_drags_the_group_and_the_menu_button_only_clicks() {
     assert!(held.group_drag.is_none());
     let out = d.step(vec![button(menu + vec2(0.0, 200.0), false)]);
     assert!(out.actions.iter().all(|a| !matches!(a, Action::MoveGroup { .. } | Action::Move { .. } | Action::Float { .. })), "{:?}", out.actions);
-    d.click(menu);
+    // A press in the header focuses the group's shown panel, like a press on its tab.
+    let pressed = d.step(vec![Event::PointerMoved(menu), button(menu, true)]);
+    assert_eq!(pressed.focused, Some(3));
+    d.step(vec![button(menu, false)]);
     assert_eq!(d.content.header_clicks, 1);
 
     let out = d.drag(over_tab, d.tab(1).center());

crates/ui/src/docking/render/group.rs

@@ -75,6 +75,10 @@ impl<P: Clone + Eq + Hash + Debug + Send + Sync + 'static> Renderer<'_, P> {
             let mut child = ui.new_child(UiBuilder::new().id(self.id.with(("header", selected))).max_rect(header));
             child.set_clip_rect(header.intersect(ui.clip_rect()));
             self.content.group_header(&mut child, panels, selected, floating);
+            // A press in the header focuses the shown panel, as a press on its tab does.
+            if child.rect_contains_pointer(header) && child.input(|i| i.pointer.any_pressed()) {
+                self.output.focused = Some(selected.clone());
+            }
         }
         // The drag bar keeps its reserved width: tabs overflow before it narrows.
         let bar_width = self.style.drag_bar_width.clamp(0.0, (strip.width() - header_width).max(0.0));
@@ -176,7 +180,7 @@ impl<P: Clone + Eq + Hash + Debug + Send + Sync + 'static> Renderer<'_, P> {
         }
         let active = response.has_focus() || response.hovered();
         if movable {
-            // A grip mark at rest, centerd in the bar's reserved width beside the header.
+            // A grip mark at rest, centered in the bar's reserved width beside the header.
             let grip = if self.style.right_to_left {
                 Rect::from_min_max(hit.min, pos2((hit.left() + self.style.drag_bar_width).min(hit.right()), hit.bottom()))
             } else {

crates/ui/src/docking/surface.rs

@@ -218,7 +218,8 @@ pub struct DockOutput<P> {
     pub actions: Vec<Action<P>>,
     pub error: Option<DockError>,
     /// The panel the user focused this frame: a clicked tab or menu entry, a drop, or a press
-    /// of any pointer button in a panel body, stripless panels included. Only user input sets
+    /// of any pointer button in a panel body (stripless panels included) or in a group header,
+    /// which focuses the group's shown panel. Only user input sets
     /// it; [`DockArea::raise_panel`] and host commands do not.
     pub focused: Option<P>,
     /// Whole-floating-group gesture identity; host may display its own group drop preview.

docs/ui-docking.md

@@ -112,7 +112,8 @@ survives.
 `DockOutput` also has:
 
 - `focused`: the panel the user focused this frame: a clicked tab, a drop, or a press of any
-  pointer button in a panel body, bare and protected panels included. Commands, `raise_panel` and
+  pointer button in a panel body (bare and protected panels included) or in the group header,
+  which focuses the group's shown panel. Commands, `raise_panel` and
   workspace resets never set it; a host that tracks the last focused panel clears it when a reset
   or command hides, closes or moves that panel.
 - `events`: requests outside the layout, such as `DockEvent::ToggleMaximize` (Frame) and