Mark foregroundLayer under scrollingContentsLayer GraphicsLayerPaintOverflowContents

third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp

Index: third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
diff --git a/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp b/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
index f15c88fcc8d5d07d447502a497437bd4c6dc7f68..440b4dbae721090d718b15d81db53d1e832bb281 100644
--- a/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
+++ b/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
@@ -1137,10 +1137,14 @@ void CompositedLayerMapping::updatePaintingPhases()
 {
     m_graphicsLayer->setPaintingPhase(paintingPhaseForPrimaryLayer());
     if (m_scrollingContentsLayer) {
-        GraphicsLayerPaintingPhase paintPhase = GraphicsLayerPaintOverflowContents | GraphicsLayerPaintCompositedScroll;
-        if (!m_foregroundLayer)
-            paintPhase |= GraphicsLayerPaintForeground;
-        m_scrollingContentsLayer->setPaintingPhase(paintPhase);
+        GraphicsLayerPaintingPhase scrollingContentsLayerPaintingPhase = GraphicsLayerPaintOverflowContents | GraphicsLayerPaintCompositedScroll;
+        if (m_foregroundLayer)
+            m_foregroundLayer->setPaintingPhase(m_foregroundLayer->paintingPhase() | GraphicsLayerPaintOverflowContents);
+        else
+            scrollingContentsLayerPaintingPhase |= GraphicsLayerPaintForeground;
+        m_scrollingContentsLayer->setPaintingPhase(scrollingContentsLayerPaintingPhase);
+    } else if (m_foregroundLayer) {
+        m_foregroundLayer->setPaintingPhase(m_foregroundLayer->paintingPhase() & ~GraphicsLayerPaintOverflowContents);

[aelias_OOO_until_Jul13, 2016/04/16 00:33:19]

The bit-setting/clearing logic is a bit hard to read, and mutating the existing
phase state isn't a pattern that's followed elsewhere in this file, and it
doesn't look needed for this either.  I'd rather we only set the state from
scratch.

How about removing the
m_foregroundLayer->setPaintingPhase(GraphicsLayerPaintForeground) call in
updateForegroundLayer() and in this method, write:

GraphicsLayerPaintingPhase foregroundLayerPaintingPhase =
GraphicsLayerPaintForeground;
if (m_scrollingContentsLayer) {
  foregroundLayerPaintingPhase |= GraphicsLayerPaintOverflowContents;
  ...
}
if (m_foregroundLayer)
  m_foregroundLayer->setPaintingPhase(foregroundLayerPaintingPhase);

[Xianzhu, 2016/04/16 22:07:36]

Done with slight difference. Ptal.

[aelias_OOO_until_Jul13, 2016/04/18 17:09:41]

Slight difference looks fine, but can you also delete the the line
m_foregroundLayer>setPaintingPhase(GraphicsLayerPaintForeground) in
updateForegroundLayer() too?  I believe that line is now no-op because
updatePaintingPhases() will always be called when updateForegroundLayer() adds a
new foreground layer.

[Xianzhu, 2016/04/18 18:06:47]

Done.

     }
 }