Windows QPA: Fix QWheelEvent::buttons() after click on title bar

When the left or right mouse buttons are pressed over the window title
bar a WM_NCLBUTTONDOWN/WM_NCRBUTTONDOWN message is received. But when the
button is released, no corresponding UP message is received, but only
a WM_NCMOUSEMOVE or WM_MOUSEMOVE. This makes the internal mouse button
state stored in QGuiApplication get out of sync with the actual state,
resulting in an incorrect button state being used in QWheelEvent.
This patch detects the button release condition and generates the missing
release event.

Change-Id: I6dd9f8580bd6ba772522574f9a08298e49c43e61
Fixes: QTBUG-75678
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>

1 files changed, 4 insertions, 1 deletions

diff --git a/src/plugins/platforms/windows/qwindowspointerhandler.h b/src/plugins/platforms/windows/qwindowspointerhandler.h
index aebef062bc..ccbb1d3939 100644
--- a/src/plugins/platforms/windows/qwindowspointerhandler.h
+++ b/src/plugins/platforms/windows/qwindowspointerhandler.h
@@ -46,7 +46,7 @@
 #include <QtCore/qpointer.h>
 #include <QtCore/qscopedpointer.h>
 #include <QtCore/qhash.h>
-#include <qpa/qwindowsysteminterface.h>
+#include <QtGui/qevent.h>
 
 QT_BEGIN_NAMESPACE
 
@@ -64,6 +64,7 @@ public:
     QTouchDevice *ensureTouchDevice();
     QWindow *windowUnderMouse() const { return m_windowUnderPointer.data(); }
     void clearWindowUnderMouse() { m_windowUnderPointer = nullptr; }
+    void clearEvents();
 
 private:
     bool translateTouchEvent(QWindow *window, HWND hwnd, QtWindows::WindowsEventType et, MSG msg, PVOID vTouchInfo, unsigned int count);
@@ -79,6 +80,8 @@ private:
     QPointer<QWindow> m_currentWindow;
     QWindow *m_previousCaptureWindow = nullptr;
     bool m_needsEnterOnPointerUpdate = false;
+    QEvent::Type m_lastEventType = QEvent::None;
+    Qt::MouseButton m_lastEventButton = Qt::NoButton;
 };
 
 QT_END_NAMESPACE