Fix the ignored Qt::WA_StaticContents on Windows

This restores the ability from the Qt 4.x series to honor the static
contents region in the backbuffer when resizing a widget. The fix
only applies when running under Windows.

Task-number: QTBUG-34799

[ChangeLog][QtWidgets][Windows] Update QWidgetBackingStore and QWindowsBackingStore to support Qt::WA_StaticContents
QWidgetBackingStore::staticContents() was updated for windows to *not* unconditionally return false. It now
returns true if it has a non-empty static widgets list. QWindowsBackingStore::resize(...) was updated to honor
the provided static contents region. It now copies the static region into the new backbuffer in a manner similar
to what was done in Qt4. The difference is that this version accounts for the possibility of the new buffer having
a smaller region than the old buffer. In Qt4 the ::prepareBuffer method was only called when the buffer was resized
larger.

Change-Id: I135ff8fb16f52759089f1e7353426303c4504db3
Reviewed-by: Gunnar Sletta <gunnar.sletta@digia.com>

1 files changed, 7 insertions, 1 deletions

diff --git a/src/widgets/kernel/qwidgetbackingstore_p.h b/src/widgets/kernel/qwidgetbackingstore_p.h
index 39583c8caa..b6c3e13cb0 100644
--- a/src/widgets/kernel/qwidgetbackingstore_p.h
+++ b/src/widgets/kernel/qwidgetbackingstore_p.h
@@ -240,7 +240,13 @@ private:
     }
 
     inline bool hasStaticContents() const
-    { return !staticWidgets.isEmpty() && false; }
+    {
+#if defined(Q_OS_WIN)
+        return !staticWidgets.isEmpty();
+#else
+        return !staticWidgets.isEmpty() && false;
+#endif
+    }
 
     friend QRegion qt_dirtyRegion(QWidget *);
     friend class QWidgetPrivate;