Fix #570: connect brush strokes on Shift-click (#654)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot-Session: e77cd34a-ce3e-4981-996f-4d37d49df90d

crates/ui-egui/src/canvas.rs

@@ -304,6 +304,16 @@ fn pointer_moves(events: &[egui::Event], button: egui::PointerButton, down_at_st
     out
 }
 
+/// Modifiers attached to the pointer event itself. Some input sources provide these without a
+/// separate `ModifiersChanged` event, so use them for click gestures before falling back to the
+/// frame-wide modifier state.
+fn pointer_button_modifiers(events: &[egui::Event], button: egui::PointerButton) -> Option<egui::Modifiers> {
+    events.iter().rev().find_map(|e| match e {
+        egui::Event::PointerButton { button: b, modifiers, .. } if *b == button => Some(*modifiers),
+        _ => None,
+    })
+}
+
 /// Abstract tool event, produced by the mouse or by automation (`ui.pointer`).
 #[derive(Clone, Copy, Debug, PartialEq)]
 pub enum ToolEvent {
@@ -1761,10 +1771,12 @@ pub fn canvas_view(app: &mut PhotocraftApp, ui: &mut egui::Ui, idx: usize, rect:
         if buttons.clicked
             && let Some(p) = response.interact_pointer_pos()
         {
+            let click_button = if app.secondary_erase { PointerButton::Secondary } else { PointerButton::Primary };
+            let click_mods = ui.input(|i| pointer_button_modifiers(&i.events, click_button)).unwrap_or(mods);
             let d = xf.to_doc(p);
             match tool {
                 Tool::Zoom => {
-                    let nz = zoom_step(view.zoom, if zoom_out(mods.alt) { -1 } else { 1 });
+                    let nz = zoom_step(view.zoom, if zoom_out(click_mods.alt) { -1 } else { 1 });
                     zoom_about(&mut view, &xf, p, nz);
                 }
                 // A click with the (temporary) Hand does nothing, never the tool underneath.
@@ -1777,8 +1789,8 @@ pub fn canvas_view(app: &mut PhotocraftApp, ui: &mut egui::Ui, idx: usize, rect:
                     if tool == Tool::Move && app.ui.transform.is_none() {
                         begin_transform_controls_at(app, &ctx, &xf, p);
                     }
-                    tool_event(app, ToolEvent::Down { x: d[0], y: d[1], pressure: 1.0 }, mods);
-                    tool_event(app, ToolEvent::Up { x: d[0], y: d[1] }, mods);
+                    tool_event(app, ToolEvent::Down { x: d[0], y: d[1], pressure: 1.0 }, click_mods);
+                    tool_event(app, ToolEvent::Up { x: d[0], y: d[1] }, click_mods);
                 }
             }
         }

crates/ui-egui/src/paint_mouse.rs

@@ -223,6 +223,38 @@ mod tests {
         assert!(alpha_at(&h, a + (b - a) * 0.5) > 0.9);
     }
 
+    #[test]
+    fn shift_click_connects_to_the_previous_brush_stroke() {
+        use egui::{Event, Modifiers};
+
+        let mut h = harness(None);
+        let (_, end) = drag(&mut h, PointerButton::Primary);
+        let previous = h
+            .state()
+            .session
+            .journal
+            .iter()
+            .rev()
+            .find(|(id, _)| id == "paint.stroke")
+            .map(|(_, p)| p["points"].as_array().unwrap().last().unwrap().clone())
+            .unwrap();
+        let target = end + vec2(120.0, 80.0);
+        h.event(Event::PointerMoved(target));
+        h.run_steps(1);
+        for pressed in [true, false] {
+            h.event(Event::PointerButton { pos: target, button: PointerButton::Primary, pressed, modifiers: Modifiers::SHIFT });
+            h.run_steps(2);
+        }
+
+        let strokes = strokes(&h);
+        assert_eq!(strokes.len(), 2, "a Shift-click commits one connected stroke");
+        let points = strokes[1]["points"].as_array().unwrap();
+        assert_eq!(points.len(), 2, "a click has the previous endpoint and clicked endpoint");
+        assert_eq!(points[0][0], previous[0]);
+        assert_eq!(points[0][1], previous[1]);
+        assert!(alpha_at(&h, end + vec2(60.0, 40.0)) > 0.9, "the segment between the strokes is painted");
+    }
+
     #[test]
     fn right_click_opens_the_brush_picker_and_never_paints() {
         let mut h = harness(None);