fix(ui): a camera click is located where it came up

Found in review (CodeRabbit): the last fix located a camera click by the pointer, which can have
moved on by the end of the release's frame. A click pressed on page 2 and released on page 1,
with the pointer back on page 2 by then, moved the quadrilateral to page 2. `PagePointer` keeps
each release's position, so `PagePointer::released` gives where the click came up, and the click
is located there.

Test: `a_camera_click_released_off_its_page_moves_nothing`, seen failing without the fix.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

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

@@ -78,6 +78,15 @@ impl PagePointer {
     pub(crate) fn pressed(&self) -> Option<Pos2> {
         first_press(&self.edges)
     }
+
+    /// Where this frame's last primary release was: where a click came up, which the pointer may
+    /// have left by the frame's end.
+    pub(crate) fn released(&self) -> Option<Pos2> {
+        self.edges.iter().rev().find_map(|e| match e {
+            Edge::Release(p) => Some(*p),
+            Edge::Press(_) => None,
+        })
+    }
 }
 
 /// Whether egui gives the drag to a widget that is not the pages' (a panel's tab, a floating panel's

crates/ui-egui/src/tools/camera_ui.rs

@@ -99,8 +99,9 @@ pub(crate) fn page_input(resp: &egui::Response, xf: &PageXform, ptr: &PagePointe
         view.camera = Some(CameraQuad::inset(page, xf.pw, xf.ph));
     }
     // A press nobody holds on a page without the quadrilateral moves it there: a drag from where it
-    // began, a click where it came up (egui has cleared the press's origin by its release).
-    let at = if resp.clicked() { pointer } else { origin };
+    // began, a click where it came up (egui has cleared the press's origin by its release, and the
+    // pointer may have moved on in the same frame).
+    let at = if resp.clicked() { ptr.released() } else { origin };
     if (resp.drag_started() || resp.clicked())
         && press == PagePress::Free
         && at.is_some_and(|p| xf.rect.contains(p))

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

@@ -1739,3 +1739,22 @@ fn a_camera_click_on_another_page_moves_the_quadrilateral_there() {
     mouse_click(&mut h, two.min + egui::vec2(100.0, 60.0));
     assert_eq!(h.state().views[0].camera.map(|q| q.page), Some(1));
 }
+
+/// A camera click is located where it came up, not where the pointer went after it in the same
+/// frame: pressed on page 2 and released on page 1 (the gaps hidden), it moves nothing, though the
+/// pointer is back on page 2 by the frame's end. The pointer's last position used to move the
+/// quadrilateral to page 2.
+#[test]
+fn a_camera_click_released_off_its_page_moves_nothing() {
+    let (mut h, seam) = touching_pages(|app| app.quick_tool = QuickTool::EnhanceCamera);
+    assert_eq!(h.state().views[0].camera.map(|q| q.page), Some(0), "it starts on the current page");
+    let (press, release, back) = (seam + egui::vec2(0.0, 2.0), seam - egui::vec2(0.0, 2.0), seam + egui::vec2(0.0, 40.0));
+    h.hover_at(press);
+    h.run_steps(1);
+    h.drag_at(press);
+    h.run_steps(1);
+    let up = egui::Event::PointerButton { pos: release, button: egui::PointerButton::Primary, pressed: false, modifiers: egui::Modifiers::NONE };
+    one_frame(&mut h, [up, egui::Event::PointerMoved(back)]);
+    h.run_steps(2);
+    assert_eq!(h.state().views[0].camera.map(|q| q.page), Some(0));
+}