Fix QVTKWidget problem on Windows with Aero off.

Need to invalidate the whole region at the start of WM_PAINT so the
desktop compositor will composite the whole area.

Change-Id: Id659f35ecbac16466d7ff68603607dff2d40c50e

GUISupport/Qt/QVTKWidget.cxx

@@ -47,6 +47,10 @@
 #include "qx11info_x11.h"
 #endif
 
+#if defined(Q_WS_WIN)
+# include <windows.h>
+#endif
+
 #include "vtkInteractorStyleTrackballCamera.h"
 #include "vtkRenderWindow.h"
 #if defined(QVTK_USE_CARBON)
@@ -821,6 +825,17 @@ void QVTKWidget::x11_setup_window()
 #endif
 }
 
+#if defined(Q_WS_WIN)
+bool QVTKWidget::winEvent(MSG* msg, long*)
+{
+  if(msg->message == WM_PAINT)
+    {
+    InvalidateRect(this->winId(), NULL, FALSE);
+    }
+  return false;
+}
+#endif
+
 #if defined (QVTK_USE_CARBON)
 OSStatus QVTKWidget::DirtyRegionProcessor(EventHandlerCallRef, EventRef event, void* wid)
 {

GUISupport/Qt/QVTKWidget.h

@@ -247,6 +247,10 @@ protected:
   // that VTK chooses
   void x11_setup_window();
 
+#if defined(Q_WS_WIN)
+  bool winEvent(MSG* msg, long* result);
+#endif
+
 #if defined(QVTK_USE_CARBON)
   EventHandlerUPP DirtyRegionHandlerUPP;
   EventHandlerRef DirtyRegionHandler;