1 files changed, 19 insertions, 3 deletions
diff --git a/src/platformsupport/eglconvenience/qeglplatformbackingstore.cpp b/src/platformsupport/eglconvenience/qeglplatformbackingstore.cpp
index ab92bac37d..8abfbf2763 100644
--- a/src/platformsupport/eglconvenience/qeglplatformbackingstore.cpp
+++ b/src/platformsupport/eglconvenience/qeglplatformbackingstore.cpp
@@ -41,6 +41,7 @@
 
 #include <QtGui/QOpenGLShaderProgram>
 #include <QtGui/QOpenGLContext>
+#include <QtGui/QPainter>
 
 #include "qeglplatformbackingstore_p.h"
 #include "qeglcompositor_p.h"
@@ -209,9 +210,16 @@ void QEGLPlatformBackingStore::composited()
     }
 }
 
-void QEGLPlatformBackingStore::beginPaint(const QRegion &rgn)
+void QEGLPlatformBackingStore::beginPaint(const QRegion &region)
 {
-    m_dirty |= rgn;
+    m_dirty |= region;
+
+    if (m_image.hasAlphaChannel()) {
+        QPainter p(&m_image);
+        p.setCompositionMode(QPainter::CompositionMode_Source);
+        foreach (const QRect &r, region.rects())
+            p.fillRect(r, Qt::transparent);
+    }
 }
 
 void QEGLPlatformBackingStore::resize(const QSize &size, const QRegion &staticContents)
@@ -223,7 +231,15 @@ void QEGLPlatformBackingStore::resize(const QSize &size, const QRegion &staticCo
     if (!dstWin || (!dstWin->isRaster() && dstWin->window()->surfaceType() != QSurface::RasterGLSurface))
         return;
 
-    m_image = QImage(size, QImage::Format_RGB32);
+    // Child windows do not get real native surfaces and so share the same
+    // format as the parent, regardless of what has been requested. The
+    // exception is WA_TranslucentBackground that sets alphaBufferSize in the
+    // requested format, this has to be taken into account when compositing.
+    const bool translucent = m_window->window()->requestedFormat().alphaBufferSize() > 0;
+    const QImage::Format format = translucent ? QImage::Format_RGBA8888 : QImage::Format_RGBX8888;
+
+    m_image = QImage(size, format);
+
     m_window->create();
 
     screen->compositingContext()->makeCurrent(dstWin->window());