Canvas: Shift, Alt and Cmd/Ctrl pressed or released mid-drag apply with the pointer held still (#4711)

crates/ui-egui/src/canvas/drag.rs

@@ -78,6 +78,16 @@ pub(super) fn tool_drag_moved(ui: &Ui, xf: &Xf, p: Pos2, pointer: &egui::Pointer
     true
 }
 
+/// Whether the tool should get another drag event at a pointer held still because Shift, Alt,
+/// Cmd/Ctrl or Space went down or up (#4711): a scale switches to proportional or from the centre
+/// at once. Records `m` as the modifiers last seen; only once the press has dragged.
+pub(super) fn tool_drag_mods_changed(ui: &Ui, m: Mods) -> bool {
+    let id = egui::Id::unique("canvas-tool-drag-mods");
+    let (dragged, last) = ui.data(|d| (d.get_temp::<Point>(tool_drag_doc_id()).is_some(), d.get_temp::<Mods>(id)));
+    ui.data_mut(|d| d.insert_temp(id, m));
+    dragged && last.is_some_and(|l| l != m)
+}
+
 /// The pen pressure (0..1) of the press in progress: the force of this frame's pen or touch
 /// input, else the pressure in the host's feed while a pen is the pointer that moved last
 /// ([`crate::Services::stylus`]: [`StylusFeed::press`] for a new press, [`StylusFeed::held`]

crates/ui-egui/src/canvas/input.rs

@@ -1,7 +1,7 @@
 use super::artboards::{artboard_name_at, begin_artboard_name_edit, name_press_id, select_named_artboard};
 use super::drag::{
     HoverContext, apply_requests, dispatch, drag_art_out, drag_id, drag_layer_id, drag_pos_id, drop_press, mods, on_canvas, pen_pressure,
-    tool_drag_doc_id, tool_drag_moved, tool_frame_moves, tool_holds, tool_press_doc_id,
+    tool_drag_doc_id, tool_drag_mods_changed, tool_drag_moved, tool_frame_moves, tool_holds, tool_press_doc_id,
 };
 use super::view::{
     HOLD_DELAY, HOLD_ZOOM, SCRUB_SLOP, SCRUB_ZOOM, WheelTurn, animated_zoom, pan_pixels, rotate_about, scroll_view, touch_gestures, trackpad_turn,
@@ -361,7 +361,8 @@ fn drag_held(app: &mut VectorcraftApp, ui: &Ui, f: &Pointing, d: Drag, p: Pos2)
             // the last position only, so a costly drag preview runs once a frame.
             let moves = tool_frame_moves(ui, app);
             // A frame whose pointer ends where the last one did still moved in between.
-            if tool_drag_moved(ui, &xf, p, pointer) || !moves.is_empty() {
+            let mods_changed = tool_drag_mods_changed(ui, mods(m, space));
+            if tool_drag_moved(ui, &xf, p, pointer) || mods_changed || !moves.is_empty() {
                 for (at, force) in moves {
                     let pressure = force.unwrap_or_else(|| pen_pressure(ui, app, false));
                     dispatch(app, &PointerEvent { kind: PointerKind::Drag, pos: xf.to_doc(at), mods: mods(m, space), pressure }, view);

crates/ui-egui/src/canvas/tests.rs

@@ -6054,6 +6054,43 @@ fn tool_drag_moved_without_pointer_delta() {
     assert!(moved, "a new document position runs even when egui reports no delta");
 }
 
+/// #4711: Shift pressed and released while a corner handle is held still scales proportionally and
+/// then freely again at once, without waiting for the pointer to move.
+#[test]
+fn a_modifier_changed_mid_scale_applies_with_the_pointer_held_still() {
+    use egui::{Event, Modifiers};
+    let mut app = VectorcraftApp::new(Session::new(), Default::default());
+    app.session.execute("file.new", &json!({"width": 400, "height": 300})).unwrap();
+    app.ui.view.smart_guides = false;
+    app.ui.view.snap_to_point = false;
+    let id = app.session.execute("shape.rectangle", &json!({"x": 100, "y": 100, "width": 100, "height": 50})).unwrap()["id"].as_u64().unwrap();
+    app.select_tool("selection");
+    let ctx = egui::Context::default();
+    frame(&mut app, &ctx, vec![]);
+    let xf = Xf::new(app.canvas_rect.unwrap(), app.view().unwrap());
+    let with = |app: &mut VectorcraftApp, mut events: Vec<Event>, modifiers: Modifiers| {
+        events.insert(0, Event::ModifiersChanged(modifiers));
+        let raw = egui::RawInput { screen_rect: Some(egui::Rect::from_min_size(Pos2::ZERO, vec2(800.0, 600.0))), events, ..Default::default() };
+        let mut out = ctx.run_ui(raw, |ui| show(app, ui));
+        out.textures_delta.clear();
+    };
+    let button = |pos, pressed| Event::PointerButton { pos, button: egui::PointerButton::Primary, pressed, modifiers: Modifiers::NONE };
+    let height =
+        |app: &VectorcraftApp| app.session.active().unwrap().doc.node(vectorcraft_doc::NodeId(id)).unwrap().geometric_bounds().unwrap().height();
+    let corner = xf.to_screen(Point::new(200.0, 150.0));
+    let to = xf.to_screen(Point::new(300.0, 150.0));
+    with(&mut app, vec![Event::PointerMoved(corner)], Modifiers::NONE);
+    with(&mut app, vec![button(corner, true)], Modifiers::NONE);
+    with(&mut app, vec![Event::PointerMoved(to)], Modifiers::NONE);
+    assert!((height(&app) - 50.0).abs() < 1e-6, "a free scale keeps the height: {}", height(&app));
+    with(&mut app, vec![], Modifiers::SHIFT);
+    assert!((height(&app) - 100.0).abs() < 1e-6, "Shift scales proportionally at once: {}", height(&app));
+    with(&mut app, vec![], Modifiers::NONE);
+    assert!((height(&app) - 50.0).abs() < 1e-6, "releasing Shift frees it at once: {}", height(&app));
+    with(&mut app, vec![button(to, false)], Modifiers::NONE);
+    assert!(app.session.active().unwrap().interaction.is_none(), "committed");
+}
+
 /// #834 review: a press held still is not a drag. Before the press has dragged, the first held
 /// frame without a delta at the press's own position sends nothing, so a click stays a click;
 /// the first move after it does.