Merge #244: a native window moved by its only tab joins a body's center

crates/ui/src/docking/native_tests.rs

@@ -859,6 +859,43 @@ fn the_only_tab_of_a_native_window_docks_it_with_title_bar_docks_off() {
     assert!(!in_root(&d, 7));
 }
 
+#[test]
+fn the_only_tab_of_a_native_window_fills_and_joins_a_frame_bodys_center() {
+    let mut layout = layout(false);
+    layout.floating.push(Floating::single(vec![7], 0, [300.0, 80.0, 240.0, 200.0]));
+    let style = |s: &mut super::DockStyle| {
+        s.side_edge_zones = true;
+        s.title_bar_docks = false;
+        s.float_hint = false;
+    };
+    let mut d = DockDriver::new(layout, Content::default()).with_style(style).with_native_host(ORIGIN);
+    let id = window(&d, 7).id;
+    // The middle of frame [3, 4], in the main window.
+    let middle = pos2(600.0, 300.0);
+    let from = pos2(15.0, TAB_ROW);
+    d.window_step(id, vec![Event::PointerMoved(from), button(from, true)]);
+    d.window_step(id, vec![Event::PointerMoved(from + vec2(8.0, 6.0))]);
+    for _ in 0..2 {
+        let local = d.window_local(id, ORIGIN + middle.to_vec2()).unwrap();
+        d.window_step(id, vec![Event::PointerMoved(local)]);
+    }
+    // The center rectangle is the only zone around the pointer: outlined and filled.
+    let zone = |filled: bool| {
+        d.shapes().iter().any(|clipped| match &clipped.shape {
+            egui::Shape::Path(path) => {
+                path.closed && (path.fill != Color32::TRANSPARENT) == filled && Rect::from_points(&path.points).contains(middle)
+            }
+            _ => false,
+        })
+    };
+    assert!(zone(false), "outlined");
+    assert!(zone(true), "filled");
+    let local = d.window_local(id, ORIGIN + middle.to_vec2()).unwrap();
+    let out = d.window_step(id, vec![button(local, false)]);
+    assert!(matches!(window_move(&out), Some(Target::At { anchor: 3 | 4, placement: Placement::Split(super::Zone::Center) })), "{:?}", out.actions);
+    assert!(in_root(&d, 7));
+}
+
 #[test]
 fn a_native_window_forwards_no_keys_while_one_of_its_widgets_has_focus() {
     let mut d = driver(layout(true));

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

@@ -116,7 +116,8 @@ impl<P: Clone + Eq + Hash + Debug + Send + Sync + 'static> Renderer<'_, P> {
 
     /// The valid target under the pointer for a whole group. A target holding the group
     /// itself is a no-op proposal; a target the model would reject is no target. A window
-    /// moving live looks through itself and does not split frames or join a body's center.
+    /// moving live looks through itself and does not split frames or, moved by its bar, join
+    /// a body's center.
     pub(super) fn group_proposal(&self, drag: &GroupDrag<P>, pointer: Pos2) -> Option<DropProposal<P>> {
         let window = drag.gesture == GroupGesture::Window;
         if let Some(proposal) = self.extra_proposal(&drag.members, pointer, window) {
@@ -148,14 +149,16 @@ impl<P: Clone + Eq + Hash + Debug + Send + Sync + 'static> Renderer<'_, P> {
         }
         let proposal = self.resolve_roomy(&drag.panel, pointer, std::slice::from_ref(target), |to| group_action(drag, to))?;
         // A window moving live splits only groups of other floating windows. A native
-        // window's bar also takes the main window's frame edges, but not a body's center.
+        // window's bar also takes the main window's frame edges, but not a body's center. A
+        // native window moved by its only tab or group joins a body's center too, as that tab
+        // or group drag would.
         let into_window = matches!(self.place(&proposal.anchor), Some(Place::Floating { .. }));
         #[cfg(feature = "native-windows")]
-        let edges = self.cross.bar;
+        let (edges, joins) = (self.cross.bar, self.cross.docks);
         #[cfg(not(feature = "native-windows"))]
-        let edges = false;
+        let (edges, joins) = (false, false);
         let split = match proposal.placement {
-            Placement::Split(Zone::Center) => true,
+            Placement::Split(Zone::Center) => !joins,
             Placement::Split(_) => !edges,
             _ => false,
         };

docs/ui-docking.md

@@ -439,7 +439,8 @@ that is not floatable, stays in-window. Floating windows get no taskbar or Alt-T
     `DockStyle::title_bar_docks`; the only tab or group docks either way, since it is the way
     back in with that flag off. Targets: in the
     main window a dock line, a frame's tab row or edge zone, or the layout's outer edge; in a
-    floating window a frame zone or tab row. A frame body's center takes no whole window. Over
+    floating window a frame zone or tab row. A frame body's center takes a window moved by its
+    only tab or group, as that tab or group drag would, but not one moved by its bar. Over
     the desktop, or with Ctrl/Cmd held, it stays where it was moved, and the layout takes its
     place once, at the release. Escape puts it back. An
     in-window floating window's title bar still splits only groups of other floating windows.