software backend: Fix clipping of QSGRenderNodes

Change-Id: I27aa5f94165fb07807d2bb711d81eade552b9f76
Reviewed-by: Andy Nichols <andy.nichols@qt.io>

2 files changed, 14 insertions, 8 deletions

diff --git a/src/quick/scenegraph/adaptations/software/qsgsoftwarerenderablenode.cpp b/src/quick/scenegraph/adaptations/software/qsgsoftwarerenderablenode.cpp
index 59c47db0c4..7adb39d9a8 100644
--- a/src/quick/scenegraph/adaptations/software/qsgsoftwarerenderablenode.cpp
+++ b/src/quick/scenegraph/adaptations/software/qsgsoftwarerenderablenode.cpp
@@ -254,18 +254,21 @@ QRegion QSGSoftwareRenderableNode::renderNode(QPainter *painter, bool forceOpaqu
             QMatrix4x4 m = m_transform;
             rd->m_matrix = &m;
             rd->m_opacity = m_opacity;
-            RenderNodeState rs;
-            rs.cr = m_clipRegion;
 
-            const QRect br = m_handle.renderNode->flags().testFlag(QSGRenderNode::BoundedRectRendering)
-                ? m_boundingRect :
-                QRect(0, 0, painter->device()->width(), painter->device()->height());
+            // all the clip region below is in world coordinates, taking m_transform into account already
+            QRegion cr = m_dirtyRegion;
+            if (m_clipRegion.rectCount() > 1)
+                cr &= m_clipRegion;
 
             painter->save();
-            painter->setClipRegion(br, Qt::ReplaceClip);
+            RenderNodeState rs;
+            rs.cr = cr;
             m_handle.renderNode->render(&rs);
             painter->restore();
 
+            const QRect br = m_handle.renderNode->flags().testFlag(QSGRenderNode::BoundedRectRendering)
+                ? m_boundingRect // already mapped to world
+                : QRect(0, 0, painter->device()->width(), painter->device()->height());
             m_previousDirtyRegion = QRegion(br);
             m_isDirty = false;
             m_dirtyRegion = QRegion();
@@ -276,7 +279,7 @@ QRegion QSGSoftwareRenderableNode::renderNode(QPainter *painter, bool forceOpaqu
     painter->save();
     painter->setOpacity(m_opacity);
 
-    // Set clipRegion to m_dirtyRegion (in world coordinates)
+    // Set clipRegion to m_dirtyRegion (in world coordinates, so must be done before the setTransform below)
     // as m_dirtyRegion already accounts for clipRegion
     painter->setClipRegion(m_dirtyRegion, Qt::ReplaceClip);
     if (m_clipRegion.rectCount() > 1)
diff --git a/src/quick/scenegraph/coreapi/qsgrendernode.cpp b/src/quick/scenegraph/coreapi/qsgrendernode.cpp
index 1bc0210b72..3007e0000c 100644
--- a/src/quick/scenegraph/coreapi/qsgrendernode.cpp
+++ b/src/quick/scenegraph/coreapi/qsgrendernode.cpp
@@ -359,7 +359,10 @@ QSGRenderNode::RenderState::~RenderState()
     of the render state is not in use. However, the clip region that can be set
     on the QPainter still has to be communicated since reconstructing this
     manually in render() is not reasonable. It can therefore be queried via
-    this function.
+    this function. The region is in world coordinates and can be passed
+    to QPainter::setClipRegion() with Qt::ReplaceClip. This must be done before
+    calling QPainter::setTransform() since the clip region is already mapped to
+    the transform provided in QSGRenderNode::matrix().
  */
 
 /*!