[CSS Blending] Fix blending when mix-blend-mode is set from javascript

Source/core/rendering/RenderLayer.cpp

Index: Source/core/rendering/RenderLayer.cpp
diff --git a/Source/core/rendering/RenderLayer.cpp b/Source/core/rendering/RenderLayer.cpp
index 43edddd8dcb9a71c920c39cd357ffb8ef81f560a..7768e755d24d29899169b0fa0d611c0dee803862 100644
--- a/Source/core/rendering/RenderLayer.cpp
+++ b/Source/core/rendering/RenderLayer.cpp
@@ -533,8 +533,8 @@ void RenderLayer::updateBlendMode()
         m_blendMode = newBlendMode;
 
         // Only update the flag if a blend mode is set or unset.
-        if (!hadBlendMode || !hasBlendMode())
-            dirtyAncestorChainBlendedDescendantStatus();
+        if (parent() && (!hadBlendMode || !hasBlendMode()))

[Stephen Chennney, 2013/11/27 13:06:26]

My only concern is that, without a parent, should you still be executing the
former code (that is, calling dirtyAncestor... on this)?

[rosca, 2013/11/27 13:34:08]

If we change the blendMode for an element we should mark as dirty
m_childLayerHasBlendMode for all its ancestors up to the first stacking context.
If it has no ancestor, we'll call setAncestorChainBlendedDescendant [1] at the
time  this element gets added as a child, so that the new ancestors know that
they have a child with blendMode.
The former code was dirtying m_childLayerHasBlendMode for the blending element
itself (B), so it would have recalculated the blending state of B's descendants,
which didn't change actually.

[1]
https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit...

+            parent()->dirtyAncestorChainBlendedDescendantStatus();
 
         if (hasCompositedLayerMapping())
             compositedLayerMapping()->setBlendMode(newBlendMode);
@@ -861,6 +861,7 @@ void RenderLayer::updateDescendantDependentFlags()
     }
 
     if (m_childLayerHasBlendModeStatusDirty) {
+        m_childLayerHasBlendMode = false;
         for (RenderLayer* child = firstChild(); child; child = child->nextSibling()) {
             if (!child->stackingNode()->isStackingContext())
                 child->updateDescendantDependentFlags();