Repaint widgets on screen change.

Add a screenChanged handler slot to QWidgetWindow,
which calls markDirty() on the backing store with
the BufferInvalid and UpdateNow flags set.

Update CocoaBackingStore to create a new buffer on
window devicePixelRatio change. Use the
QCocoaWindow::devicePixelRatio() implementation instead
of a duplicate implementation in the backing store.

The plan is to replace this implementation with one
based on QUpdateWindowRequestEvent for Qt 5.4

Change-Id: I8e521c53df4ac90815613e730fe821996334721f
Reviewed-by: Jørgen Lind <jorgen.lind@digia.com>

2 files changed, 15 insertions, 0 deletions

diff --git a/src/widgets/kernel/qwidgetwindow.cpp b/src/widgets/kernel/qwidgetwindow.cpp
index e50736d6b8..ef138267bb 100644
--- a/src/widgets/kernel/qwidgetwindow.cpp
+++ b/src/widgets/kernel/qwidgetwindow.cpp
@@ -100,6 +100,7 @@ QWidgetWindow::QWidgetWindow(QWidget *widget)
         setSurfaceType(QSurface::RasterGLSurface);
     }
     connect(m_widget, &QObject::objectNameChanged, this, &QWidgetWindow::updateObjectName);
+    connect(this, SIGNAL(screenChanged(QScreen*)), this, SLOT(repaintWindow()));
 }
 
 QWidgetWindow::~QWidgetWindow()
@@ -560,6 +561,19 @@ void QWidgetWindow::updateGeometry()
     m_widget->data->fstrut_dirty = false;
 }
 
+// Invalidates the backing store buffer and repaints immediately.
+// ### Qt 5.4: replace with QUpdateWindowRequestEvent.
+void QWidgetWindow::repaintWindow()
+{
+    if (!m_widget->isVisible() || !m_widget->updatesEnabled())
+        return;
+
+    QTLWExtra *tlwExtra = m_widget->window()->d_func()->maybeTopData();
+    if (tlwExtra && !tlwExtra->inTopLevelResize && tlwExtra->backingStore)
+        tlwExtra->backingStoreTracker->markDirty(m_widget->rect(), m_widget,
+                                                 QWidgetBackingStore::UpdateNow, QWidgetBackingStore::BufferInvalid);
+}
+
 Qt::WindowState effectiveState(Qt::WindowStates state);
 
 // Store normal geometry used for saving application settings.
diff --git a/src/widgets/kernel/qwidgetwindow_qpa_p.h b/src/widgets/kernel/qwidgetwindow_qpa_p.h
index 8d6f14a669..06ba8ea646 100644
--- a/src/widgets/kernel/qwidgetwindow_qpa_p.h
+++ b/src/widgets/kernel/qwidgetwindow_qpa_p.h
@@ -101,6 +101,7 @@ protected:
 
 private slots:
     void updateObjectName();
+    void repaintWindow();
 
 private:
     void updateGeometry();