1 files changed, 36 insertions, 4 deletions

diff --git a/src/gui/kernel/qwidget.cpp b/src/gui/kernel/qwidget.cpp
index 9b44f15..e22ec55 100644
--- a/src/gui/kernel/qwidget.cpp
+++ b/src/gui/kernel/qwidget.cpp
@@ -236,6 +236,17 @@ void QWidgetBackingStoreTracker::unregisterWidget(QWidget *w)
     }
 }
 
+/*!
+    \internal
+    Recursively remove widget and all of its descendents.
+ */
+void QWidgetBackingStoreTracker::unregisterWidgetSubtree(QWidget *widget)
+{
+    unregisterWidget(widget);
+    foreach (QObject *child, widget->children())
+        if (QWidget *childWidget = qobject_cast<QWidget *>(child))
+            unregisterWidgetSubtree(childWidget);
+}
 
 QWidgetPrivate::QWidgetPrivate(int version)
     : QObjectPrivate(version)
@@ -326,15 +337,27 @@ QWidgetPrivate::~QWidgetPrivate()
 #endif //QT_NO_GRAPHICSEFFECT
 }
 
+class QDummyWindowSurface : public QWindowSurface
+{
+public:
+    QDummyWindowSurface(QWidget *window) : QWindowSurface(window) {}
+    QPaintDevice *paintDevice() { return window(); }
+    void flush(QWidget *, const QRegion &, const QPoint &) {}
+};
+
 QWindowSurface *QWidgetPrivate::createDefaultWindowSurface()
 {
     Q_Q(QWidget);
 
     QWindowSurface *surface;
-    if (QApplicationPrivate::graphicsSystem())
-        surface = QApplicationPrivate::graphicsSystem()->createWindowSurface(q);
-    else
-        surface = createDefaultWindowSurface_sys();
+    if (q->property("_q_DummyWindowSurface").toBool()) {
+        surface = new QDummyWindowSurface(q);
+    } else {
+        if (QApplicationPrivate::graphicsSystem())
+            surface = QApplicationPrivate::graphicsSystem()->createWindowSurface(q);
+        else
+            surface = createDefaultWindowSurface_sys();
+    }
 
     return surface;
 }
@@ -10031,7 +10054,16 @@ void QWidget::setParent(QWidget *parent, Qt::WindowFlags f)
     if (newParent && isAncestorOf(focusWidget()))
         focusWidget()->clearFocus();
 
+    QTLWExtra *oldTopExtra = window()->d_func()->maybeTopData();
+    QWidgetBackingStoreTracker *oldBsTracker = oldTopExtra ? &oldTopExtra->backingStore : 0;
+
     d->setParent_sys(parent, f);
+
+    QTLWExtra *topExtra = window()->d_func()->maybeTopData();
+    QWidgetBackingStoreTracker *bsTracker = topExtra ? &topExtra->backingStore : 0;
+    if (oldBsTracker && oldBsTracker != bsTracker)
+        oldBsTracker->unregisterWidgetSubtree(this);
+
     if (desktopWidget)
         parent = 0;