Sometimes wrong clipping in QWidget::render() when passing a device or

an untransformed painter

When passing a painter to QWidget::render, we use the
painter->paintEngine()->systemClip() as the "system viewport",
i.e. all painting triggered by render() should be limited to
this area. The only way to achieve this is by always ensuring the
system clip is clipped to the same area (systemClip &= systemViewport).
The problem however, was that we only did this for transformed
painters. We must of course always do it when there's a systemViewport
set, regardless of whether the painter is transformed or not.

Auto test included.

Task-number: 248852
Reviewed-by: Trond

2 files changed, 9 insertions, 7 deletions

diff --git a/src/gui/painting/qpaintengine.cpp b/src/gui/painting/qpaintengine.cpp
index ad09060..7de1ec4 100644
--- a/src/gui/painting/qpaintengine.cpp
+++ b/src/gui/painting/qpaintengine.cpp
@@ -949,8 +949,8 @@ void QPaintEngine::setSystemClip(const QRegion &region)
     Q_D(QPaintEngine);
     d->systemClip = region;
     // Be backward compatible and only call d->systemStateChanged()
-    // if we currently have a system transform set.
-    if (d->hasSystemTransform) {
+    // if we currently have a system transform/viewport set.
+    if (d->hasSystemTransform || d->hasSystemViewport) {
         d->transformSystemClip();
         d->systemStateChanged();
     }
diff --git a/src/gui/painting/qpaintengine_p.h b/src/gui/painting/qpaintengine_p.h
index eeba7ec..0b5e175 100644
--- a/src/gui/painting/qpaintengine_p.h
+++ b/src/gui/painting/qpaintengine_p.h
@@ -83,10 +83,12 @@ public:
         if (systemClip.isEmpty())
             return;
 
-        if (systemTransform.type() <= QTransform::TxTranslate)
-            systemClip.translate(qRound(systemTransform.dx()), qRound(systemTransform.dy()));
-        else
-            systemClip = systemTransform.map(systemClip);
+        if (hasSystemTransform) {
+            if (systemTransform.type() <= QTransform::TxTranslate)
+                systemClip.translate(qRound(systemTransform.dx()), qRound(systemTransform.dy()));
+            else
+                systemClip = systemTransform.map(systemClip);
+        }
 
         // Make sure we're inside the viewport.
         if (hasSystemViewport) {
@@ -101,7 +103,7 @@ public:
     inline void setSystemTransform(const QTransform &xform)
     {
         systemTransform = xform;
-        if ((hasSystemTransform = !xform.isIdentity()))
+        if ((hasSystemTransform = !xform.isIdentity()) || hasSystemViewport)
             transformSystemClip();
         systemStateChanged();
     }