Implement mouse capture on WASM

This fixes dock widget undocking - previously, without the capture, any
widget that the mouse accidentally entered would get the event,
resulting in re-docking problems, cursor issues etc.

Fixes: QTBUG-105621
Pick-to: 6.4
Change-Id: Ia1f2c91578018f2ae9df903bc0730200ede17d32
Reviewed-by: Lorn Potter <lorn.potter@gmail.com>

src/plugins/platforms/wasm/qwasmcompositor.cpp

@@ -581,9 +581,10 @@ bool QWasmCompositor::processPointer(const PointerEvent& event)
     const QPoint targetPointInScreenCoords = screen()->geometry().topLeft() + event.point;
 
     QWindow *const targetWindow = ([this, &targetPointInScreenCoords]() -> QWindow * {
-        auto *targetWindow =
-            m_windowManipulation.operation() == WindowManipulation::Operation::None ?
-                screen()->compositor()->windowAt(targetPointInScreenCoords, 5) : nullptr;
+        auto *targetWindow = m_mouseCaptureWindow != nullptr ? m_mouseCaptureWindow.get()
+                : m_windowManipulation.operation() == WindowManipulation::Operation::None
+                ? screen()->compositor()->windowAt(targetPointInScreenCoords, 5)
+                : nullptr;
 
         return targetWindow ? targetWindow : m_lastMouseTargetWindow.get();
     })();
@@ -679,6 +680,8 @@ bool QWasmCompositor::processPointer(const PointerEvent& event)
 
 bool QWasmCompositor::deliverEventToTarget(const PointerEvent &event, QWindow *eventTarget)
 {
+    Q_ASSERT(!m_mouseCaptureWindow || m_mouseCaptureWindow.get() == eventTarget);
+
     const QPoint pointInScreenCoords = screen()->geometry().topLeft() + event.point;
     const QPoint targetPointClippedToScreen(
             std::max(screen()->geometry().left(),
@@ -698,8 +701,8 @@ bool QWasmCompositor::deliverEventToTarget(const PointerEvent &event, QWindow *e
     }
 
     WindowArea windowArea = WindowArea::Client;
-    if (!eventTarget->geometry().contains(targetPointClippedToScreen)
-        && !deliveringToPreviouslyClickedWindow) {
+    if (!deliveringToPreviouslyClickedWindow && !m_mouseCaptureWindow
+        && !eventTarget->geometry().contains(targetPointClippedToScreen)) {
         if (!eventTarget->frameGeometry().contains(targetPointClippedToScreen))
             return false;
         windowArea = WindowArea::NonClient;
@@ -972,6 +975,17 @@ int QWasmCompositor::handleTouch(int eventType, const EmscriptenTouchEvent *touc
     return static_cast<int>(accepted);
 }
 
+void QWasmCompositor::setCapture(QWasmWindow *window)
+{
+    Q_ASSERT(std::find(m_windowStack.begin(), m_windowStack.end(), window) != m_windowStack.end());
+    m_mouseCaptureWindow = window->window();
+}
+
+void QWasmCompositor::releaseCapture()
+{
+    m_mouseCaptureWindow = nullptr;
+}
+
 void QWasmCompositor::leaveWindow(QWindow *window)
 {
     m_windowUnderMouse = nullptr;

src/plugins/platforms/wasm/qwasmcompositor.h

@@ -82,6 +82,8 @@ public:
     bool processKeyboard(int eventType, const EmscriptenKeyboardEvent *keyEvent);
     bool processWheel(int eventType, const EmscriptenWheelEvent *wheelEvent);
     int handleTouch(int eventType, const EmscriptenTouchEvent *touchEvent);
+    void setCapture(QWasmWindow *window);
+    void releaseCapture();
 
     bool processMouseEnter(const EmscriptenMouseEvent *mouseEvent);
     bool processMouseLeave();
@@ -173,6 +175,7 @@ private:
 
     QPointer<QWindow> m_pressedWindow;
     QPointer<QWindow> m_lastMouseTargetWindow;
+    QPointer<QWindow> m_mouseCaptureWindow;
 
     std::unique_ptr<qstdweb::EventCallback> m_pointerDownCallback;
     std::unique_ptr<qstdweb::EventCallback> m_pointerMoveCallback;

src/plugins/platforms/wasm/qwasmwindow.cpp

@@ -605,4 +605,13 @@ void QWasmWindow::requestActivateWindow()
     QPlatformWindow::requestActivateWindow();
 }
 
+bool QWasmWindow::setMouseGrabEnabled(bool grab)
+{
+    if (grab)
+        m_compositor->setCapture(this);
+    else
+        m_compositor->releaseCapture();
+    return true;
+}
+
 QT_END_NAMESPACE

src/plugins/platforms/wasm/qwasmwindow.h

@@ -65,7 +65,7 @@ public:
     void setWindowState(Qt::WindowStates state) override;
     void applyWindowState();
     bool setKeyboardGrabEnabled(bool) override { return false; }
-    bool setMouseGrabEnabled(bool) override { return false; }
+    bool setMouseGrabEnabled(bool grab) final;
 
     void drawTitleBar(QPainter *painter) const;