Merge branch '4.6' of scm.dev.nokia.troll.no:qt/qt-s60-public into 4.6-integration

* '4.6' of scm.dev.nokia.troll.no:qt/qt-s60-public:
  Fix QWS build failure
  Removed compiler warnings
  Window visibility changes update TLW backing store reference count
  Enable visibility change events on all Symbian native windows
  Added reference counting to QWidgetBackingStore
  Added tst_QWidget::destroyBackingStoreWhenHidden

14 files changed, 378 insertions, 36 deletions

diff --git a/src/3rdparty/phonon/mmf/abstractaudioeffect.cpp b/src/3rdparty/phonon/mmf/abstractaudioeffect.cpp
index 6cfeb768ae..9b64ab3ff2 100644
--- a/src/3rdparty/phonon/mmf/abstractaudioeffect.cpp
+++ b/src/3rdparty/phonon/mmf/abstractaudioeffect.cpp
@@ -184,6 +184,8 @@ int AbstractAudioEffect::effectParameterChanged(
     const EffectParameter &param, const QVariant &value)
 {
     // Default implementation
+    Q_UNUSED(param)
+    Q_UNUSED(value)
     Q_ASSERT_X(false, Q_FUNC_INFO, "Effect has no parameters");
     return 0;
 }
diff --git a/src/3rdparty/phonon/mmf/abstractaudioeffect.h b/src/3rdparty/phonon/mmf/abstractaudioeffect.h
index d71993b146..70adcf644f 100644
--- a/src/3rdparty/phonon/mmf/abstractaudioeffect.h
+++ b/src/3rdparty/phonon/mmf/abstractaudioeffect.h
@@ -118,6 +118,10 @@ private:
 // for each of the effects.  Using this reduces repetition of boilerplate
 // in the implementations of the backend effect nodes.
 
+#ifdef Q_CC_NOKIAX86
+#   pragma warn_illtokenpasting off
+#endif
+
 #define PHONON_MMF_DEFINE_EFFECT_FUNCTIONS(Effect)                      \
                                                                         \
 void Effect##::createEffect(AudioPlayer::NativePlayer *player)          \
diff --git a/src/3rdparty/phonon/mmf/audiooutput.cpp b/src/3rdparty/phonon/mmf/audiooutput.cpp
index c6be20b3de..358868379b 100644
--- a/src/3rdparty/phonon/mmf/audiooutput.cpp
+++ b/src/3rdparty/phonon/mmf/audiooutput.cpp
@@ -78,6 +78,9 @@ bool MMF::AudioOutput::setOutputDevice(int index)
 {
     Q_ASSERT_X(index == AudioOutputDeviceID, Q_FUNC_INFO,
                "We only support one output device, with id 0");
+#ifdef QT_NO_DEBUG
+    Q_UNUSED(index)
+#endif
     return true;
 }
 
diff --git a/src/3rdparty/phonon/mmf/bassboost.cpp b/src/3rdparty/phonon/mmf/bassboost.cpp
index c7af93924b..67076f62d0 100644
--- a/src/3rdparty/phonon/mmf/bassboost.cpp
+++ b/src/3rdparty/phonon/mmf/bassboost.cpp
@@ -49,6 +49,7 @@ const char* BassBoost::description()
 bool BassBoost::getParameters(CMdaAudioOutputStream *stream,
     QList<EffectParameter> &parameters)
 {
+    Q_UNUSED(parameters)
     QScopedPointer<CBassBoost> effect;
     TRAPD(err, effect.reset(CBassBoost::NewL(*stream)));
     return (KErrNone == err);
diff --git a/src/3rdparty/phonon/mmf/effectfactory.cpp b/src/3rdparty/phonon/mmf/effectfactory.cpp
index c5e33d5c7a..4643978d2f 100644
--- a/src/3rdparty/phonon/mmf/effectfactory.cpp
+++ b/src/3rdparty/phonon/mmf/effectfactory.cpp
@@ -183,8 +183,9 @@ EffectFactory::EffectData EffectFactory::getData()
          /* defaultValue */       QVariant(bool(true)));
     data.m_parameters.append(param);
 
-    if (data.m_supported = BackendNode::getParameters
-            (stream.data(), data.m_parameters)) {
+    data.m_supported = BackendNode::getParameters(stream.data(),
+                                                  data.m_parameters);
+    if (data.m_supported) {
         const QString description = QCoreApplication::translate
             ("Phonon::MMF::EffectFactory", BackendNode::description());
         data.m_descriptions.insert("name", description);
diff --git a/src/3rdparty/phonon/mmf/loudness.cpp b/src/3rdparty/phonon/mmf/loudness.cpp
index 1079a35653..ca05ab0989 100644
--- a/src/3rdparty/phonon/mmf/loudness.cpp
+++ b/src/3rdparty/phonon/mmf/loudness.cpp
@@ -49,6 +49,7 @@ const char* Loudness::description()
 bool Loudness::getParameters(CMdaAudioOutputStream *stream,
     QList<EffectParameter> &parameters)
 {
+    Q_UNUSED(parameters)
     QScopedPointer<CLoudness> effect;
     TRAPD(err, effect.reset(CLoudness::NewL(*stream)));
     return (KErrNone == err);
diff --git a/src/gui/embedded/qwsmanager_qws.cpp b/src/gui/embedded/qwsmanager_qws.cpp
index d6ef14858b..ac6d36eb25 100644
--- a/src/gui/embedded/qwsmanager_qws.cpp
+++ b/src/gui/embedded/qwsmanager_qws.cpp
@@ -392,7 +392,7 @@ void QWSManagerPrivate::dirtyRegion(int decorationRegion,
                                     const QRegion &clip)
 {
     QTLWExtra *topextra = managed->d_func()->extra->topextra;
-    QWidgetBackingStore *bs = topextra->backingStore;
+    QWidgetBackingStore *bs = topextra->backingStore.data();
     const bool pendingUpdateRequest = bs->isDirty();
 
     if (decorationRegion == QDecoration::All) {
diff --git a/src/gui/kernel/qapplication_s60.cpp b/src/gui/kernel/qapplication_s60.cpp
index b1e0f63d0f..78027b2752 100644
--- a/src/gui/kernel/qapplication_s60.cpp
+++ b/src/gui/kernel/qapplication_s60.cpp
@@ -1703,19 +1703,27 @@ int QApplicationPrivate::symbianProcessWsEvent(const QSymbianEvent *symbianEvent
                 return 1;
             const TWsVisibilityChangedEvent *visChangedEvent = event->VisibilityChanged();
             QWidget *w = QWidgetPrivate::mapper->value(control);
-            if (!w->d_func()->maybeTopData())
+            QWidget *const window = w->window();
+            if (!window->d_func()->maybeTopData())
                 break;
+            QRefCountedWidgetBackingStore &backingStore = window->d_func()->maybeTopData()->backingStore;
             if (visChangedEvent->iFlags & TWsVisibilityChangedEvent::ENotVisible) {
-                delete w->d_func()->topData()->backingStore;
-                w->d_func()->topData()->backingStore = 0;
+                // Decrement backing store reference count
+                backingStore.deref();
                 // In order to ensure that any resources used by the window surface
                 // are immediately freed, we flush the WSERV command buffer.
                 S60->wsSession().Flush();
-            } else if ((visChangedEvent->iFlags & TWsVisibilityChangedEvent::EPartiallyVisible)
-                       && !w->d_func()->maybeBackingStore()) {
-                w->d_func()->topData()->backingStore = new QWidgetBackingStore(w);
-                w->d_func()->invalidateBuffer(w->rect());
-                w->repaint();
+            } else if (visChangedEvent->iFlags & TWsVisibilityChangedEvent::EPartiallyVisible) {
+                if (backingStore.data()) {
+                    // Increment backing store reference count
+                    backingStore.ref();
+                } else {
+                    // Create backing store with an initial reference count of 1
+                    backingStore.create(window);
+                    backingStore.ref();
+                    w->d_func()->invalidateBuffer(w->rect());
+                    w->repaint();
+                }
             }
             return 1;
         }
diff --git a/src/gui/kernel/qapplication_x11.cpp b/src/gui/kernel/qapplication_x11.cpp
index 25a7750d96..304cd173e9 100644
--- a/src/gui/kernel/qapplication_x11.cpp
+++ b/src/gui/kernel/qapplication_x11.cpp
@@ -5245,7 +5245,7 @@ bool QETWidget::translateConfigEvent(const XEvent *event)
 
         if (isVisible() && data->crect.size() != oldSize) {
             Q_ASSERT(d->extra->topextra);
-            QWidgetBackingStore *bs = d->extra->topextra->backingStore;
+            QWidgetBackingStore *bs = d->extra->topextra->backingStore.data();
             const bool hasStaticContents = bs && bs->hasStaticContents();
             // If we have a backing store with static contents, we have to disable the top-level
             // resize optimization in order to get invalidated regions for resized widgets.
diff --git a/src/gui/kernel/qwidget.cpp b/src/gui/kernel/qwidget.cpp
index e180001291..a9ea9ac563 100644
--- a/src/gui/kernel/qwidget.cpp
+++ b/src/gui/kernel/qwidget.cpp
@@ -161,6 +161,51 @@ static inline bool hasBackingStoreSupport()
 extern bool qt_sendSpontaneousEvent(QObject*, QEvent*); // qapplication.cpp
 extern QDesktopWidget *qt_desktopWidget; // qapplication.cpp
 
+
+QRefCountedWidgetBackingStore::QRefCountedWidgetBackingStore()
+    :   m_ptr(0)
+    ,   m_count(0)
+{
+
+}
+
+QRefCountedWidgetBackingStore::~QRefCountedWidgetBackingStore()
+{
+    delete m_ptr;
+}
+
+void QRefCountedWidgetBackingStore::create(QWidget *widget)
+{
+    destroy();
+    m_ptr = new QWidgetBackingStore(widget);
+    m_count = 0;
+}
+
+void QRefCountedWidgetBackingStore::destroy()
+{
+    delete m_ptr;
+    m_ptr = 0;
+    m_count = 0;
+}
+
+void QRefCountedWidgetBackingStore::ref()
+{
+    Q_ASSERT(m_ptr);
+    ++m_count;
+}
+
+void QRefCountedWidgetBackingStore::deref()
+{
+    if (m_count) {
+        Q_ASSERT(m_ptr);
+        if (0 == --m_count) {
+            delete m_ptr;
+            m_ptr = 0;
+        }
+    }
+}
+
+
 QWidgetPrivate::QWidgetPrivate(int version)
     : QObjectPrivate(version)
       , extra(0)
@@ -1324,11 +1369,9 @@ void QWidget::create(WId window, bool initializeWindow, bool destroyOldWindow)
 
     // a real toplevel window needs a backing store
     if (isWindow() && windowType() != Qt::Desktop) {
-        delete d->topData()->backingStore;
-        // QWidgetBackingStore will check this variable, hence it must be 0
-        d->topData()->backingStore = 0;
+        d->topData()->backingStore.destroy();
         if (hasBackingStoreSupport())
-            d->topData()->backingStore = new QWidgetBackingStore(this);
+            d->topData()->backingStore.create(this);
     }
 
     d->setModal_sys();
@@ -1451,8 +1494,7 @@ QWidget::~QWidget()
         // the backing store will delete its window surface, which may or may
         // not have a reference to this widget that will be used later to
         // notify the window it no longer has a surface.
-        delete d->extra->topextra->backingStore;
-        d->extra->topextra->backingStore = 0;
+        d->extra->topextra->backingStore.destroy();
     }
 #endif
     if (QWidgetBackingStore *bs = d->maybeBackingStore()) {
@@ -1540,7 +1582,6 @@ void QWidgetPrivate::createTLExtra()
         QTLWExtra* x = extra->topextra = new QTLWExtra;
         x->icon = 0;
         x->iconPixmap = 0;
-        x->backingStore = 0;
         x->windowSurface = 0;
         x->sharedPainter = 0;
         x->incw = x->inch = 0;
@@ -1619,7 +1660,7 @@ void QWidgetPrivate::deleteExtra()
 #endif
         if (extra->topextra) {
             deleteTLSysExtra();
-            delete extra->topextra->backingStore;
+            extra->topextra->backingStore.destroy();
             delete extra->topextra->icon;
             delete extra->topextra->iconPixmap;
 #if defined(Q_WS_QWS) && !defined(QT_NO_QWS_MANAGER)
diff --git a/src/gui/kernel/qwidget_p.h b/src/gui/kernel/qwidget_p.h
index 555647c1df..9f7ad95aac 100644
--- a/src/gui/kernel/qwidget_p.h
+++ b/src/gui/kernel/qwidget_p.h
@@ -110,13 +110,53 @@ class QWidgetItemV2;
 
 class QStyle;
 
+class Q_AUTOTEST_EXPORT QRefCountedWidgetBackingStore
+{
+public:
+    QRefCountedWidgetBackingStore();
+    ~QRefCountedWidgetBackingStore();
+
+    void create(QWidget *tlw);
+    void destroy();
+
+    void ref();
+    void deref();
+
+    inline QWidgetBackingStore* data()
+    {
+        return m_ptr;
+    }
+
+    inline QWidgetBackingStore* operator->()
+    {
+        return m_ptr;
+    }
+
+    inline QWidgetBackingStore& operator*()
+    {
+        return *m_ptr;
+    }
+
+    inline operator bool() const
+    {
+        return (0 != m_ptr);
+    }
+
+private:
+    Q_DISABLE_COPY(QRefCountedWidgetBackingStore)
+
+private:
+    QWidgetBackingStore* m_ptr;
+    int m_count;
+};
+
 struct QTLWExtra {
     // *************************** Cross-platform variables *****************************
 
     // Regular pointers (keep them together to avoid gaps on 64 bits architectures).
     QIcon *icon; // widget icon
     QPixmap *iconPixmap;
-    QWidgetBackingStore *backingStore;
+    QRefCountedWidgetBackingStore backingStore;
     QWindowSurface *windowSurface;
     QPainter *sharedPainter;
 
@@ -907,7 +947,7 @@ inline QWidgetBackingStore *QWidgetPrivate::maybeBackingStore() const
 {
     Q_Q(const QWidget);
     QTLWExtra *x = q->window()->d_func()->maybeTopData();
-    return x ? x->backingStore : 0;
+    return x ? x->backingStore.data() : 0;
 }
 
 QT_END_NAMESPACE
diff --git a/src/gui/kernel/qwidget_s60.cpp b/src/gui/kernel/qwidget_s60.cpp
index 438c2a303a..86b858dabd 100644
--- a/src/gui/kernel/qwidget_s60.cpp
+++ b/src/gui/kernel/qwidget_s60.cpp
@@ -433,6 +433,7 @@ void QWidgetPrivate::create_sys(WId window, bool /* initializeWindow */, bool de
         // Request mouse move events.
         drawableWindow->PointerFilter(EPointerFilterEnterExit
             | EPointerFilterMove | EPointerFilterDrag, 0);
+        drawableWindow->EnableVisibilityChangeEvents();
 
         if (q->isVisible() && q->testAttribute(Qt::WA_Mapped)) {
             activateSymbianWindow(control.data());
@@ -908,14 +909,12 @@ void QWidgetPrivate::registerDropSite(bool /* on */)
 
 void QWidgetPrivate::createTLSysExtra()
 {
-    extra->topextra->backingStore = 0;
     extra->topextra->inExpose = 0;
 }
 
 void QWidgetPrivate::deleteTLSysExtra()
 {
-    delete extra->topextra->backingStore;
-    extra->topextra->backingStore = 0;
+    extra->topextra->backingStore.destroy();
 }
 
 void QWidgetPrivate::createSysExtra()
diff --git a/src/gui/painting/qbackingstore.cpp b/src/gui/painting/qbackingstore.cpp
index 8de9eaa5c8..14f715f9ad 100644
--- a/src/gui/painting/qbackingstore.cpp
+++ b/src/gui/painting/qbackingstore.cpp
@@ -884,7 +884,7 @@ void QWidgetPrivate::moveRect(const QRect &rect, int dx, int dy)
     QWidgetPrivate *pd = pw->d_func();
     QRect clipR(pd->clipRect());
 #ifdef Q_WS_QWS
-    QWidgetBackingStore *wbs = x->backingStore;
+    QWidgetBackingStore *wbs = x->backingStore.data();
     QWSWindowSurface *surface = static_cast<QWSWindowSurface*>(wbs->windowSurface);
     clipR = clipR.intersected(surface->clipRegion().translated(-toplevelOffset).boundingRect());
 #endif
@@ -914,7 +914,7 @@ void QWidgetPrivate::moveRect(const QRect &rect, int dx, int dy)
         invalidateBuffer((newRect & clipR).translated(-data.crect.topLeft()));
     } else {
 
-        QWidgetBackingStore *wbs = x->backingStore;
+        QWidgetBackingStore *wbs = x->backingStore.data();
         QRegion childExpose(newRect & clipR);
 
         if (sourceRect.isValid() && wbs->bltRect(sourceRect, dx, dy, pw))
@@ -957,7 +957,7 @@ void QWidgetPrivate::scrollRect(const QRect &rect, int dx, int dy)
     if (x->inTopLevelResize)
         return;
 
-    QWidgetBackingStore *wbs = x->backingStore;
+    QWidgetBackingStore *wbs = x->backingStore.data();
     if (!wbs)
         return;
 
diff --git a/tests/auto/qwidget/tst_qwidget.cpp b/tests/auto/qwidget/tst_qwidget.cpp
index 76e20b997e..7d4f8ffa1a 100644
--- a/tests/auto/qwidget/tst_qwidget.cpp
+++ b/tests/auto/qwidget/tst_qwidget.cpp
@@ -385,6 +385,7 @@ private slots:
     void setGraphicsEffect();
 
     void destroyBackingStore();
+    void destroyBackingStoreWhenHidden();
 
     void activateWindow();
 
@@ -9499,9 +9500,7 @@ void tst_QWidget::destroyBackingStore()
     QTRY_VERIFY(w.numPaintEvents > 0);
     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);
+    qt_widget_private(&w)->topData()->backingStore.create(&w);
 
     w.update();
     QApplication::processEvents();
@@ -9517,6 +9516,252 @@ void tst_QWidget::destroyBackingStore()
 #endif
 }
 
+// Helper function
+QWidgetBackingStore* backingStore(QWidget &widget)
+{
+    QWidgetBackingStore *backingStore = 0;
+#ifdef QT_BUILD_INTERNAL
+    if (QTLWExtra *topExtra = qt_widget_private(&widget)->maybeTopData())
+        backingStore = topExtra->backingStore.data();
+#endif
+    return backingStore;
+}
+
+// Wait for a condition to be true, timing out after 1 second
+// This is used following calls to QWidget::show() and QWidget::hide(), which are
+// expected to asynchronously trigger native window visibility events.
+#define WAIT_AND_VERIFY(condition)                                              \
+    do {                                                                        \
+        QTime start = QTime::currentTime();                                     \
+        while (!(condition) && (start.elapsed() < 1000)) {                      \
+            qApp->processEvents();                                              \
+            QTest::qWait(50);                                                   \
+        }                                                                       \
+        if (!QTest::qVerify((condition), #condition, "", __FILE__, __LINE__))   \
+            return;                                                             \
+    } while (0)
+
+void tst_QWidget::destroyBackingStoreWhenHidden()
+{
+#ifndef QT_BUILD_INTERNAL
+    QSKIP("Test step requires access to Q_AUTOTEST_EXPORT", SkipAll);
+#endif
+
+#ifndef Q_OS_SYMBIAN
+    QSKIP("Only Symbian destroys backing store when native window becomes invisible", SkipAll);
+#endif
+
+    testWidget->hide();
+    QTest::qWait(1000);
+
+    // 1. Single top-level QWidget
+    {
+    QWidget w;
+    w.setAutoFillBackground(true);
+    w.setPalette(Qt::yellow);
+    w.setGeometry(0, 0, 100, 100);
+    w.show();
+    QTest::qWaitForWindowShown(&w);
+    QVERIFY(0 != backingStore(w));
+
+    w.hide();
+    WAIT_AND_VERIFY(0 == backingStore(w));
+
+    w.show();
+    QTest::qWaitForWindowShown(&w);
+    QVERIFY(0 != backingStore(w));
+    }
+
+    // 2. Two top-level widgets
+    {
+    QWidget w1;
+    w1.setGeometry(0, 0, 100, 100);
+    w1.setAutoFillBackground(true);
+    w1.setPalette(Qt::red);
+    w1.show();
+    QTest::qWaitForWindowShown(&w1);
+    QVERIFY(0 != backingStore(w1));
+
+    QWidget w2;
+    w2.setGeometry(w1.geometry());
+    w1.setAutoFillBackground(true);
+    w1.setPalette(Qt::blue);
+    w2.show();
+    QTest::qWaitForWindowShown(&w2);
+    QVERIFY(0 != backingStore(w2));
+
+    // Check that w1 deleted its backing store when obscured by w2
+    QVERIFY(0 == backingStore(w1));
+
+    w2.move(w2.pos() + QPoint(10, 10));
+
+    // Check that w1 recreates its backing store when partially revealed
+    WAIT_AND_VERIFY(0 != backingStore(w1));
+    }
+
+    // 3. Native child widget
+    {
+    QWidget parent;
+    parent.setGeometry(0, 0, 100, 100);
+    parent.setAutoFillBackground(true);
+    parent.setPalette(Qt::yellow);
+
+    QWidget child(&parent);
+    child.setAutoFillBackground(true);
+    child.setPalette(Qt::green);
+
+    QVBoxLayout layout(&parent);
+    layout.setContentsMargins(10, 10, 10, 10);
+    layout.addWidget(&child);
+    parent.setLayout(&layout);
+
+    child.winId();
+
+    parent.show();
+    QTest::qWaitForWindowShown(&parent);
+
+    // Check that child window does not obscure parent window
+    QVERIFY(!parent.visibleRegion().subtracted(child.visibleRegion()).isEmpty());
+
+    // Native child widget should share parent's backing store
+    QWidgetBackingStore *const parentBs = backingStore(parent);
+    QVERIFY(0 != parentBs);
+    QVERIFY(0 == backingStore(child));
+
+    // Set margins to zero so that child widget totally obscures parent
+    layout.setContentsMargins(0, 0, 0, 0);
+
+    WAIT_AND_VERIFY(parent.visibleRegion().subtracted(child.visibleRegion()).isEmpty());
+
+    // Backing store should remain unchanged despite child window obscuring
+    // parent window
+    QVERIFY(parentBs == backingStore(parent));
+    QVERIFY(0 == backingStore(child));
+    }
+
+    // 4. Alien child widget which is made full-screen
+    {
+    QWidget parent;
+    parent.setGeometry(0, 0, 100, 100);
+    parent.setAutoFillBackground(true);
+    parent.setPalette(Qt::red);
+
+    QWidget child(&parent);
+    child.setAutoFillBackground(true);
+    child.setPalette(Qt::blue);
+
+    QVBoxLayout layout(&parent);
+    layout.setContentsMargins(10, 10, 10, 10);
+    layout.addWidget(&child);
+    parent.setLayout(&layout);
+
+    parent.show();
+    QTest::qWaitForWindowShown(&parent);
+
+    // Check that child window does not obscure parent window
+    QVERIFY(!parent.visibleRegion().subtracted(child.visibleRegion()).isEmpty());
+
+    // Native child widget should share parent's backing store
+    QVERIFY(0 != backingStore(parent));
+    QVERIFY(0 == backingStore(child));
+
+    // Make child widget full screen
+    child.setWindowFlags((child.windowFlags() | Qt::Window) ^ Qt::SubWindow);
+    child.setWindowState(child.windowState() | Qt::WindowFullScreen);
+    child.show();
+    QTest::qWaitForWindowShown(&child);
+
+    // Check that child window obscures parent window
+    QVERIFY(parent.visibleRegion().subtracted(child.visibleRegion()).isEmpty());
+
+    // Now that extent of child widget goes beyond parent's extent,
+    // a new backing store should be created for the child widget.
+    QVERIFY(0 != backingStore(child));
+
+    // Parent is obscured, therefore its backing store should be destroyed
+    QVERIFY(0 == backingStore(parent));
+
+    // Disable full screen
+    child.setWindowFlags(child.windowFlags() ^ (Qt::Window | Qt::SubWindow));
+    child.setWindowState(child.windowState() ^ Qt::WindowFullScreen);
+    child.show();
+    QTest::qWaitForWindowShown(&child);
+
+    // Check that parent is now visible again
+    QVERIFY(!parent.visibleRegion().subtracted(child.visibleRegion()).isEmpty());
+
+    // Native child widget should once again share parent's backing store
+    QVERIFY(0 != backingStore(parent));
+    QEXPECT_FAIL("", "QTBUG-10643", Continue);
+    QVERIFY(0 == backingStore(child));
+    }
+
+    // 5. Native child widget which is made full-screen
+    {
+    QWidget parent;
+    parent.setGeometry(0, 0, 100, 100);
+    parent.setAutoFillBackground(true);
+    parent.setPalette(Qt::red);
+
+    QWidget child(&parent);
+    child.setAutoFillBackground(true);
+    child.setPalette(Qt::blue);
+
+    QVBoxLayout layout(&parent);
+    layout.setContentsMargins(10, 10, 10, 10);
+    layout.addWidget(&child);
+    parent.setLayout(&layout);
+
+    child.winId();
+
+    parent.show();
+    QTest::qWaitForWindowShown(&parent);
+
+    // Check that child window does not obscure parent window
+    QVERIFY(!parent.visibleRegion().subtracted(child.visibleRegion()).isEmpty());
+
+    // Native child widget should share parent's backing store
+    QVERIFY(0 != backingStore(parent));
+    QVERIFY(0 == backingStore(child));
+
+    // Make child widget full screen
+    child.setWindowFlags((child.windowFlags() | Qt::Window) ^ Qt::SubWindow);
+    child.setWindowState(child.windowState() | Qt::WindowFullScreen);
+    child.show();
+    QTest::qWaitForWindowShown(&child);
+
+    // Ensure that 'window hidden' event is received by parent
+    qApp->processEvents();
+
+    // Check that child window obscures parent window
+    QVERIFY(parent.visibleRegion().subtracted(child.visibleRegion()).isEmpty());
+
+    // Now that extent of child widget goes beyond parent's extent,
+    // a new backing store should be created for the child widget.
+    QVERIFY(0 != backingStore(child));
+
+    // Parent is obscured, therefore its backing store should be destroyed
+    QEXPECT_FAIL("", "QTBUG-10643", Continue);
+    QVERIFY(0 == backingStore(parent));
+
+    // Disable full screen
+    child.setWindowFlags(child.windowFlags() ^ (Qt::Window | Qt::SubWindow));
+    child.setWindowState(child.windowState() ^ Qt::WindowFullScreen);
+    child.show();
+    QTest::qWaitForWindowShown(&child);
+
+    // Check that parent is now visible again
+    QVERIFY(!parent.visibleRegion().subtracted(child.visibleRegion()).isEmpty());
+
+    // Native child widget should once again share parent's backing store
+    QVERIFY(0 != backingStore(parent));
+    QEXPECT_FAIL("", "QTBUG-10643", Continue);
+    QVERIFY(0 == backingStore(child));
+    }
+}
+
+#undef WAIT_AND_VERIFY
+
 void tst_QWidget::rectOutsideCoordinatesLimit_task144779()
 {
 #ifdef Q_OS_WINCE_WM
@@ -9997,15 +10242,12 @@ class scrollWidgetWBS : public QWidget
 public:
     void deleteBackingStore()
     {
-        if (static_cast<QWidgetPrivate*>(d_ptr.data())->maybeBackingStore()) {
-            delete static_cast<QWidgetPrivate*>(d_ptr.data())->topData()->backingStore;
-            static_cast<QWidgetPrivate*>(d_ptr.data())->topData()->backingStore = 0;
-        }
+        static_cast<QWidgetPrivate*>(d_ptr.data())->topData()->backingStore.destroy();
     }
     void enableBackingStore()
     {
         if (!static_cast<QWidgetPrivate*>(d_ptr.data())->maybeBackingStore()) {
-            static_cast<QWidgetPrivate*>(d_ptr.data())->topData()->backingStore = new QWidgetBackingStore(this);
+            static_cast<QWidgetPrivate*>(d_ptr.data())->topData()->backingStore.create(this);
             static_cast<QWidgetPrivate*>(d_ptr.data())->invalidateBuffer(this->rect());
             repaint();
         }