Merge PR #1993: Grid: the selection outline follows a mouse drag at once

Conflicts:
- docs/ui-parity.md: header keeps main's change list plus the outline entry; both log rows kept

crates/ui-egui/src/grid.rs

@@ -722,6 +722,9 @@ pub fn show(app: &mut SheetApp, ui: &mut egui::Ui) {
     app.grid.cells_rect = Some(geo.mirror_rect(geo.cells));
     // The selection outline glides to a new selection. It stays on its cells when Animations is
     // off, when egui's animations are (the headless harness), and while a screenshot is on its way.
+    // A mouse button held down (a click or a drag selecting cells) moves it at once, as in Excel:
+    // a gliding outline trails the pointer and reads as lag.
+    let pointer_selecting = ui.input(|i| i.pointer.any_down());
     let outline = app.grid.glide.frame(crate::selection_glide::Frame {
         place,
         range: sel.current(),
@@ -729,7 +732,7 @@ pub fn show(app: &mut SheetApp, ui: &mut egui::Ui) {
         view: geo.cells,
         now,
         frame_nr: ui.ctx().cumulative_frame_nr(),
-        animate: app.ui.animations && ui.ctx().global_style().animation_time > 0.0 && !app.shots.in_flight(),
+        animate: app.ui.animations && ui.ctx().global_style().animation_time > 0.0 && !app.shots.in_flight() && !pointer_selecting,
     });
     if app.grid.glide.is_gliding() {
         ui.ctx().request_repaint();

crates/ui-egui/tests/selection_glide.rs

@@ -201,3 +201,29 @@ fn agents_find_run_and_read_the_setting_over_the_control_channel() {
     assert_eq!(set["result"]["animations"], json!(true));
     assert!(a.ui.animations);
 }
+
+#[test]
+fn a_mouse_drag_keeps_the_outline_on_its_cells() {
+    // A gliding outline trails the pointer while selecting with the mouse and reads as lag; Excel
+    // draws it on the selection at once. Keyboard moves still glide (above).
+    let mut h = animated();
+    let (b2, e8) = (cell_rect(&h, "B2"), cell_rect(&h, "E8"));
+    let m = egui::Modifiers::NONE;
+    h.input_mut().events.extend([
+        egui::Event::PointerMoved(b2.center()),
+        egui::Event::PointerButton { pos: b2.center(), button: egui::PointerButton::Primary, pressed: true, modifiers: m },
+    ]);
+    h.step();
+    for k in 1..=6 {
+        let p = b2.center() + (e8.center() - b2.center()) * (k as f32 / 6.0);
+        h.input_mut().events.push(egui::Event::PointerMoved(p));
+        steps(&mut h, 2);
+        let sel = h.state().session.active().map(|d| d.selection.current()).unwrap();
+        let shown = cell_rect(&h, &sel.start.a1()).union(cell_rect(&h, &sel.end.a1()));
+        assert!(!gliding(&h), "no glide while the button is held");
+        assert_eq!(outline(&h), shown, "the outline is on the dragged range {}", sel.a1());
+    }
+    h.input_mut().events.push(egui::Event::PointerButton { pos: e8.center(), button: egui::PointerButton::Primary, pressed: false, modifiers: m });
+    h.step();
+    assert_eq!(h.state().session.active().map(|d| d.selection.current().a1()).as_deref(), Some("B2:E8"));
+}