fix(ui): a MIDI editor behind another tab leaves the arrows to the Edit window (review)

The piano roll's rect stayed recorded after its tab went behind another
one, so with the pointer over the panel now in front, Left and Right
still went to the hidden piano roll and the Edit window did not scroll.
The rect is now recorded only by a frame that draws the MIDI panel.

crates/ui-egui/src/docking.rs

@@ -472,6 +472,11 @@ pub fn show(app: &mut crate::SoundApp, ui: &mut egui::Ui, window: crate::MainWin
     // and bottom edges take frames (`drop_edges` keeps its default).
     style.new_dock_zones = true;
     style.side_edge_zones = false;
+    // The MIDI body's rect stands for a piano roll on screen (the arrow keys go to it), so only a
+    // frame that draws the panel records one: open behind another tab, the old rect is gone.
+    if edit {
+        ui.ctx().data_mut(|data| data.remove::<egui::Rect>(egui::Id::unique("soundcraft-midi-body")));
+    }
     let output = DockArea::new(area(edit)).show_with_limits(
         ui,
         &workspace.layout,

crates/ui-egui/tests/it/shortcuts.rs

@@ -190,3 +190,32 @@ fn the_piano_roll_keeps_the_plain_arrows() {
     assert!(note_start(&app) > before, "the note moved right");
     assert_eq!(app.engine.session().edit.zoom.scroll, scroll, "the Edit window kept its view");
 }
+
+/// The MIDI editor open behind another tab has no piano roll on screen: the panel in front of it takes no
+/// arrows, so they centre the Edit window there as anywhere else.
+#[test]
+fn a_midi_editor_behind_another_tab_leaves_the_arrows_to_the_edit_window() {
+    let mut app = SoundApp::new(soundcraft_engine::demo::demo_engine(), None, Services::default());
+    app.ui.show_midi_editor = true;
+    let (clip_id, clip) = app.engine.session().tracks.iter().flat_map(|t| t.clips()).find(|c| c.start > 100_000).map(|c| (c.id, c.range())).unwrap();
+    app.run("view.zoom_set", json!({"samples_per_px": 10.0})).unwrap();
+    app.run("view.scroll", json!({"to": 0})).unwrap();
+    let ctx = egui::Context::default();
+    for _ in 0..6 {
+        app_frame(&ctx, &mut app, vec![]);
+    }
+    let body = ctx.data(|d| d.get_temp::<egui::Rect>(egui::Id::unique("soundcraft-midi-body"))).unwrap();
+    app.run("ui.dock", json!({"operation": "open", "panel": "history"})).unwrap();
+    app.run("ui.dock", json!({"operation": "move", "panel": "history", "target": "midi", "zone": "tab"})).unwrap();
+    for _ in 0..3 {
+        app_frame(&ctx, &mut app, vec![]);
+    }
+    assert!(app.ui.show_midi_editor, "the MIDI editor is still open");
+    assert_ne!(app.ui.docking.layout.panel_state(&soundcraft_ui_egui::docking::Panel::Midi), craft_ui::docking::PanelState::Front);
+    app_frame(&ctx, &mut app, vec![egui::Event::PointerMoved(body.center())]);
+    app.run("edit.select", json!({"clips": [clip_id.0]})).unwrap();
+
+    app_frame(&ctx, &mut app, arrow(Key::ArrowLeft));
+    let (x, middle) = x_and_middle(&app, clip.start);
+    assert!((x - middle).abs() < 1.0, "Left: the clip start at {x}, the middle at {middle}");
+}