1 files changed, 26 insertions, 4 deletions
diff --git a/src/gui/painting/qrhibackingstore.cpp b/src/gui/painting/qrhibackingstore.cpp
index 71b5ccf6cf..586dfb44a4 100644
--- a/src/gui/painting/qrhibackingstore.cpp
+++ b/src/gui/painting/qrhibackingstore.cpp
@@ -2,6 +2,7 @@
 // SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
 
 #include "qrhibackingstore_p.h"
+#include <private/qimage_p.h>
 
 QT_BEGIN_NAMESPACE
 
@@ -14,17 +15,24 @@ QRhiBackingStore::~QRhiBackingStore()
 {
 }
 
-void QRhiBackingStore::flush(QWindow *window, const QRegion &region, const QPoint &offset)
+void QRhiBackingStore::flush(QWindow *flushedWindow, const QRegion &region, const QPoint &offset)
 {
     Q_UNUSED(region);
     Q_UNUSED(offset);
 
-    if (window != this->window())
+    if (flushedWindow->surfaceType() != window()->surfaceType()) {
+        qWarning() << "Cannot flush child window" << flushedWindow
+            << "with surface type" << flushedWindow->surfaceType() << ";"
+            << "Must match" << window()->surfaceType() << "of" << window();
+
+        // FIXME: Support different surface types by not tying the
+        // RHI config to the backing store itself (per window config).
         return;
+    }
 
     if (!rhi()) {
         QPlatformBackingStoreRhiConfig rhiConfig;
-        switch (window->surfaceType()) {
+        switch (window()->surfaceType()) {
         case QSurface::OpenGLSurface:
             rhiConfig.setApi(QPlatformBackingStoreRhiConfig::OpenGL);
             break;
@@ -40,7 +48,21 @@ void QRhiBackingStore::flush(QWindow *window, const QRegion &region, const QPoin
 
     static QPlatformTextureList emptyTextureList;
     bool translucentBackground = m_image.hasAlphaChannel();
-    rhiFlush(window, region, offset, &emptyTextureList, translucentBackground);
+    rhiFlush(flushedWindow, flushedWindow->devicePixelRatio(),
+        region, offset, &emptyTextureList, translucentBackground);
+}
+
+QImage::Format QRhiBackingStore::format() const
+{
+    QImage::Format fmt = QRasterBackingStore::format();
+
+    // With render-to-texture widgets and QRhi-based flushing the backingstore
+    // image must have an alpha channel. Hence upgrading the format. Matches
+    // what other platforms (Windows, xcb) do.
+    if (QImage::toPixelFormat(fmt).alphaUsage() != QPixelFormat::UsesAlpha)
+        fmt = qt_maybeDataCompatibleAlphaVersion(fmt);
+
+    return fmt;
 }
 
 QT_END_NAMESPACE