Fix clipRect interpretation in composited backingstores

Empty clipRect means "clip away completely", not "no clipping".

Task-number: QTBUG-50719
Change-Id: I6a9dd66130716a921fe9fc245582274e3c9718fe
Reviewed-by: Paul Olav Tvete <paul.tvete@theqtcompany.com>

2 files changed, 8 insertions, 6 deletions

diff --git a/src/gui/painting/qplatformbackingstore.cpp b/src/gui/painting/qplatformbackingstore.cpp
index 8e40eb6dff..5ac903c71d 100644
--- a/src/gui/painting/qplatformbackingstore.cpp
+++ b/src/gui/painting/qplatformbackingstore.cpp
@@ -263,12 +263,14 @@ static inline QRect toBottomLeftRect(const QRect &topLeftRect, int windowHeight)
 static void blitTextureForWidget(const QPlatformTextureList *textures, int idx, QWindow *window, const QRect &deviceWindowRect,
                                  QOpenGLTextureBlitter *blitter, const QPoint &offset)
 {
+    const QRect clipRect = textures->clipRect(idx);
+    if (clipRect.isEmpty())
+        return;
+
     QRect rectInWindow = textures->geometry(idx);
     // relative to the TLW, not necessarily our window (if the flush is for a native child widget), have to adjust
     rectInWindow.translate(-offset);
-    QRect clipRect = textures->clipRect(idx);
-    if (clipRect.isEmpty())
-        clipRect = QRect(QPoint(0, 0), rectInWindow.size());
+
     const QRect clippedRectInWindow = rectInWindow & clipRect.translated(rectInWindow.topLeft());
     const QRect srcRect = toBottomLeftRect(clipRect, rectInWindow.height());
 
diff --git a/src/platformsupport/platformcompositor/qopenglcompositor.cpp b/src/platformsupport/platformcompositor/qopenglcompositor.cpp
index 7e0973040a..c65d69e842 100644
--- a/src/platformsupport/platformcompositor/qopenglcompositor.cpp
+++ b/src/platformsupport/platformcompositor/qopenglcompositor.cpp
@@ -177,11 +177,11 @@ static inline QRect toBottomLeftRect(const QRect &topLeftRect, int windowHeight)
 
 static void clippedBlit(const QPlatformTextureList *textures, int idx, const QRect &targetWindowRect, QOpenGLTextureBlitter *blitter)
 {
-    const QRect rectInWindow = textures->geometry(idx);
-    QRect clipRect = textures->clipRect(idx);
+    const QRect clipRect = textures->clipRect(idx);
     if (clipRect.isEmpty())
-        clipRect = QRect(QPoint(0, 0), rectInWindow.size());
+        return;
 
+    const QRect rectInWindow = textures->geometry(idx);
     const QRect clippedRectInWindow = rectInWindow & clipRect.translated(rectInWindow.topLeft());
     const QRect srcRect = toBottomLeftRect(clipRect, rectInWindow.height());