Fixed a consistency problem in the backing store.

Widgets maintain an internal state (inDirtyList) which says whether
that widget is in the backing store's list of dirty widgets.
Naturally this list has to be kept in sync with the actual list
contents. This did not happen if the backing store was destroyed and
recreated; if the list had any contents it would be destroyed without
resetting the widget flags. Destroying and recreating the backing
store is common on S60 where we try to save memory.

Fixed by making sure those flags are reset during backing store
destruction.

Done together with Jason.
RevBy:    Jason Barron
RevBy:    bnilsen
AutoTest: Included

2 files changed, 33 insertions, 0 deletions

diff --git a/src/gui/painting/qbackingstore.cpp b/src/gui/painting/qbackingstore.cpp
index 34bc57820..405acb731 100644
--- a/src/gui/painting/qbackingstore.cpp
+++ b/src/gui/painting/qbackingstore.cpp
@@ -829,6 +829,10 @@ QWidgetBackingStore::QWidgetBackingStore(QWidget *topLevel)
 
 QWidgetBackingStore::~QWidgetBackingStore()
 {
+    for (int c = 0; c < dirtyWidgets.size(); ++c) {
+        resetWidget(dirtyWidgets.at(c));
+    }
+
     delete windowSurface;
     windowSurface = 0;
     delete dirtyOnScreenWidgets;
diff --git a/tests/auto/qwidget/tst_qwidget.cpp b/tests/auto/qwidget/tst_qwidget.cpp
index 4ddc6c4d1..e148fdbe8 100644
--- a/tests/auto/qwidget/tst_qwidget.cpp
+++ b/tests/auto/qwidget/tst_qwidget.cpp
@@ -67,6 +67,7 @@
 #include <qcalendarwidget.h>
 #include <qmainwindow.h>
 #include <QtGui/qpaintengine.h>
+#include <private/qbackingstore_p.h>
 
 #ifdef Q_WS_S60
 #include <avkon.hrh>                // EEikStatusPaneUidTitle
@@ -361,6 +362,8 @@ private slots:
 
     void focusWidget_task254563();
 
+    void destroyBackingStore();
+
 private:
     bool ensureScreenSize(int width, int height);
     QWidget *testWidget;
@@ -9199,5 +9202,31 @@ void tst_QWidget::focusWidget_task254563()
     QVERIFY(top.focusWidget() != widget); //dangling pointer
 }
 
+void tst_QWidget::destroyBackingStore()
+{
+    UpdateWidget w;
+    w.show();
+
+#ifdef Q_WS_X11
+    qt_x11_wait_for_window_manager(&w);
+#endif
+    QApplication::processEvents();
+
+    w.reset();
+    w.update();
+    delete qt_widget_private(&w)->topData()->backingStore;
+    qt_widget_private(&w)->topData()->backingStore = 0;
+    qt_widget_private(&w)->topData()->backingStore = new QWidgetBackingStore(&w);
+
+    w.update();
+    QApplication::processEvents();
+    QCOMPARE(w.numPaintEvents, 1);
+
+    // Check one more time, because the second time around does more caching.
+    w.update();
+    QApplication::processEvents();
+    QCOMPARE(w.numPaintEvents, 2);
+}
+
 QTEST_MAIN(tst_QWidget)
 #include "tst_qwidget.moc"