Software Renderer: Call QBackingStore::beginPaint with correct QRegion

When rendering into QBackingStores, it is important to let the
backingstore know what region you intended to paint into before you
start rendering. Previously we were calling QBackingStore::beginPaint on
the whole window area, but then only rendering and flushing for a subset
of that area.  This causes issues on platforms that depend on
QBackingStore::beginPaint to be all area that will be repainted before
the next flush, so that they can for example clear those areas.

This change required a bit of extra plumbing in the Software Renderer,
but now it is possible to calculate the area that will be repainted
before painting it, and pass that region to QBackingStore::beginPaint().

Change-Id: I90be1916ebbe8fc182cd13246bb6690cc7e16d27
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>

1 files changed, 5 insertions, 1 deletions

diff --git a/src/quick/scenegraph/adaptations/software/qsgabstractsoftwarerenderer.cpp b/src/quick/scenegraph/adaptations/software/qsgabstractsoftwarerenderer.cpp
index eb0e26462a..26efba5b13 100644
--- a/src/quick/scenegraph/adaptations/software/qsgabstractsoftwarerenderer.cpp
+++ b/src/quick/scenegraph/adaptations/software/qsgabstractsoftwarerenderer.cpp
@@ -149,7 +149,7 @@ void QSGAbstractSoftwareRenderer::buildRenderList()
     QSGSoftwareRenderListBuilder(this).visitChildren(rootNode());
 }
 
-void QSGAbstractSoftwareRenderer::optimizeRenderList()
+QRegion QSGAbstractSoftwareRenderer::optimizeRenderList()
 {
     // Iterate through the renderlist from front to back
     // Objective is to update the dirty status and rects.
@@ -212,9 +212,13 @@ void QSGAbstractSoftwareRenderer::optimizeRenderList()
         m_dirtyRegion += node->dirtyRegion();
     }
 
+    QRegion updateRegion = m_dirtyRegion;
+
     // Empty dirtyRegion
     m_dirtyRegion = QRegion();
     m_obscuredRegion = QRegion();
+
+    return updateRegion;
 }
 
 void QSGAbstractSoftwareRenderer::setBackgroundColor(const QColor &color)