QWindowsBackingStore::flush(): Add warning for UpdateLayeredWindowIndirect() failures.

Task-number: QTBUG-49785
Change-Id: I881e6d294ae6b23e280e727ee1fc48ee6562f2fe
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@theqtcompany.com>

1 files changed, 6 insertions, 1 deletions

diff --git a/src/plugins/platforms/windows/qwindowsbackingstore.cpp b/src/plugins/platforms/windows/qwindowsbackingstore.cpp
index bd5c35037d..135c9eb601 100644
--- a/src/plugins/platforms/windows/qwindowsbackingstore.cpp
+++ b/src/plugins/platforms/windows/qwindowsbackingstore.cpp
@@ -96,7 +96,12 @@ void QWindowsBackingStore::flush(QWindow *window, const QRegion &region,
             RECT dirty = {dirtyRect.x(), dirtyRect.y(),
                 dirtyRect.x() + dirtyRect.width(), dirtyRect.y() + dirtyRect.height()};
             UPDATELAYEREDWINDOWINFO info = {sizeof(info), NULL, &ptDst, &size, m_image->hdc(), &ptSrc, 0, &blend, ULW_ALPHA, &dirty};
-            QWindowsContext::user32dll.updateLayeredWindowIndirect(rw->handle(), &info);
+            const BOOL result = QWindowsContext::user32dll.updateLayeredWindowIndirect(rw->handle(), &info);
+            if (!result)
+                qErrnoWarning("UpdateLayeredWindowIndirect failed for ptDst=(%d, %d),"
+                              " size=(%dx%d), dirty=(%dx%d %d, %d)", r.x(), r.y(),
+                              r.width(), r.height(), dirtyRect.width(), dirtyRect.height(),
+                              dirtyRect.x(), dirtyRect.y());
         } else {
             QWindowsContext::user32dll.updateLayeredWindow(rw->handle(), NULL, &ptDst, &size, m_image->hdc(), &ptSrc, 0, &blend, ULW_ALPHA);
         }