Windows: Use Format_ARGB32_Premultiplied for backing store with alpha.

Following the logic in Qt 4's QRasterWindowSurface::setGeometry().

Task-number: QTBUG-30302
Change-Id: Ica571cfd5098e3d9faedefaff0880acfb2209958
Reviewed-by: Shawn Rutledge <shawn.rutledge@digia.com>
Reviewed-by: Laszlo Agocs <laszlo.agocs@digia.com>

1 files changed, 2 insertions, 3 deletions

diff --git a/src/plugins/platforms/windows/qwindowsbackingstore.cpp b/src/plugins/platforms/windows/qwindowsbackingstore.cpp
index 1abf447709..34a9c1df5f 100644
--- a/src/plugins/platforms/windows/qwindowsbackingstore.cpp
+++ b/src/plugins/platforms/windows/qwindowsbackingstore.cpp
@@ -145,9 +145,8 @@ void QWindowsBackingStore::resize(const QSize &size, const QRegion &region)
                 << " from: " << (m_image.isNull() ? QSize() : m_image->image().size());
         }
 #endif
-        QImage::Format format = QWindowsNativeImage::systemFormat();
-        if (format == QImage::Format_RGB32 && window()->format().hasAlpha())
-            format = QImage::Format_ARGB32_Premultiplied;
+        const QImage::Format format = window()->format().hasAlpha() ?
+            QImage::Format_ARGB32_Premultiplied : QWindowsNativeImage::systemFormat();
 
         QWindowsNativeImage *oldwni = m_image.data();
         QWindowsNativeImage *newwni = new QWindowsNativeImage(size.width(), size.height(), format);