add toImage() function to QSGPainterNode

src/declarative/scenegraph/util/qsgpainternode.cpp

@@ -407,5 +407,12 @@ void QSGPainterNode::setContentsScale(qreal s)
     markDirty(DirtyMaterial);
 }
 
+QImage QSGPainterNode::toImage() const
+{
+    if (m_actualRenderTarget == QSGPaintedItem::Image)
+        return m_image;
+    else
+        return m_fbo->toImage();
+}
 
 QT_END_NAMESPACE

src/declarative/scenegraph/util/qsgpainternode_p.h

@@ -99,6 +99,7 @@ public:
     void setContentsScale(qreal s);
     qreal contentsScale() const { return m_contentsScale; }
 
+    QImage toImage() const;
     void update();
 
     void paint();