Track mouse leave

Author: franciscojma86

shell/platform/windows/win32_flutter_window.cc

@@ -125,6 +125,12 @@ void Win32FlutterWindow::OnPointerUp(double x, double y) {
   }
 }
 
+void Win32FlutterWindow::OnPointerLeave() {
+  if (process_events_) {
+    SendPointerLeave();
+  }
+}
+
 void Win32FlutterWindow::OnChar(char32_t code_point) {
   if (process_events_) {
     SendChar(code_point);
@@ -207,6 +213,12 @@ void Win32FlutterWindow::SendPointerUp(double x, double y) {
   SendPointerEventWithData(event);
 }
 
+void Win32FlutterWindow::SendPointerLeave() {
+  FlutterPointerEvent event = {};
+  event.phase = FlutterPointerPhase::kRemove;
+  SendPointerEventWithData(event);
+}
+
 void Win32FlutterWindow::SendChar(char32_t code_point) {
   for (const auto& handler : keyboard_hook_handlers_) {
     handler->CharHook(this, code_point);

shell/platform/windows/win32_flutter_window.h

@@ -53,6 +53,9 @@ class Win32FlutterWindow : public Win32Window {
   // |Win32Window|
   void OnPointerUp(double x, double y) override;
 
+  // |Win32Window|
+  void OnPointerLeave() override;
+
   // |Win32Window|
   void OnChar(char32_t code_point) override;
 
@@ -102,6 +105,9 @@ class Win32FlutterWindow : public Win32Window {
   // Reports mouse release to Flutter engine.
   void SendPointerUp(double x, double y);
 
+  // Reports mouse left the window client area.
+  void SendPointerLeave();
+
   // Reports a keyboard character to Flutter engine.
   void SendChar(char32_t code_point);
 

shell/platform/windows/win32_window.cc

@@ -107,6 +107,7 @@ Win32Window::MessageHandler(HWND hwnd,
   UINT width = 0, height = 0;
   auto window =
       reinterpret_cast<Win32Window*>(GetWindowLongPtr(hwnd, GWLP_USERDATA));
+  static bool tracking_mouse_events = false;
 
   if (window != nullptr) {
     switch (message) {
@@ -131,12 +132,28 @@ Win32Window::MessageHandler(HWND hwnd,
         break;
 
       case WM_MOUSEMOVE:
+        if (!tracking_mouse_events) {
+          TRACKMOUSEEVENT tme;
+          tme.cbSize = sizeof(tme);
+          tme.hwndTrack = hwnd;
+          // Not tracking Hover since the engine handles that logic.
+          tme.dwFlags = TME_LEAVE;
+          TrackMouseEvent(&tme);
+          tracking_mouse_events = true;
+        }
         xPos = GET_X_LPARAM(lparam);
         yPos = GET_Y_LPARAM(lparam);
 
         window->OnPointerMove(static_cast<double>(xPos),
                               static_cast<double>(yPos));
         break;
+      case WM_MOUSELEAVE:;
+        window->OnPointerLeave();
+        // Once the tracked event is received, the TrackMouseEvent function
+        // resets. Set to false to make sure it's called once mouse movement is
+        // detected again.
+        tracking_mouse_events = false;
+        break;
       case WM_LBUTTONDOWN:
         xPos = GET_X_LPARAM(lparam);
         yPos = GET_Y_LPARAM(lparam);

shell/platform/windows/win32_window.h

@@ -88,6 +88,9 @@ class Win32Window {
   // down to up
   virtual void OnPointerUp(double x, double y) = 0;
 
+  // Called when the mouse leaves the window.
+  virtual void OnPointerLeave() = 0;
+
   // Called when character input occurs.
   virtual void OnChar(char32_t code_point) = 0;