mix-blend-mode implementation for accelerated layers - blink part

Source/core/rendering/CompositedLayerMapping.cpp

Index: Source/core/rendering/CompositedLayerMapping.cpp
diff --git a/Source/core/rendering/CompositedLayerMapping.cpp b/Source/core/rendering/CompositedLayerMapping.cpp
index 1beb7cc164262f6339bd2d03b1cfc88dbb9bae0d..547ef946ccc0d3ee8cef87ddfb444a5de904b2b8 100644
--- a/Source/core/rendering/CompositedLayerMapping.cpp
+++ b/Source/core/rendering/CompositedLayerMapping.cpp
@@ -211,8 +211,10 @@ void CompositedLayerMapping::createPrimaryGraphicsLayer()
     updateTransform(renderer()->style());
     updateFilters(renderer()->style());
 
-    if (RuntimeEnabledFeatures::cssCompositingEnabled())
+    if (RuntimeEnabledFeatures::cssCompositingEnabled()) {
         updateLayerBlendMode(renderer()->style());
+        updateIsRootForIsolatedGroup();
+    }
 }
 
 void CompositedLayerMapping::destroyGraphicsLayers()
@@ -269,8 +271,19 @@ void CompositedLayerMapping::updateFilters(const RenderStyle* style)
     }
 }
 
-void CompositedLayerMapping::updateLayerBlendMode(const RenderStyle*)
+void CompositedLayerMapping::updateLayerBlendMode(const RenderStyle* style)
 {
+    setBlendMode(style->blendMode());
+}
+
+void CompositedLayerMapping::updateIsRootForIsolatedGroup()
+{
+    bool isolate = m_owningLayer->shouldIsolateCompositedDescendants();
+
+    // non stacking context layers should never isolate
+    ASSERT(m_owningLayer->stackingNode()->isStackingContext() || !isolate);
+
+    m_graphicsLayer->setIsRootForIsolatedGroup(isolate);
 }
 
 void CompositedLayerMapping::updateContentsOpaque()
@@ -522,8 +535,10 @@ void CompositedLayerMapping::updateGraphicsLayerGeometry()
     if (!renderer()->animation().isRunningAcceleratedAnimationOnRenderer(renderer(), CSSPropertyOpacity))
         updateOpacity(renderer()->style());
 
-    if (RuntimeEnabledFeatures::cssCompositingEnabled())
+    if (RuntimeEnabledFeatures::cssCompositingEnabled()) {

[shawnsingh, 2013/11/23 00:38:13]

I think it would be equivalent to move these down to the end of this function
along with all the other updateXXX functions, right?  If that's true, let's do
it that way.

[rosca, 2013/11/25 21:11:41]

It should be the same. Done.

         updateLayerBlendMode(renderer()->style());
+        updateIsRootForIsolatedGroup();
+    }
 
     bool isSimpleContainer = isSimpleContainerCompositingLayer();
 
@@ -1586,8 +1601,15 @@ void CompositedLayerMapping::paintsIntoCompositedAncestorChanged()
     compositor()->repaintInCompositedAncestor(m_owningLayer, compositedBounds());
 }
 
-void CompositedLayerMapping::setBlendMode(BlendMode)
+void CompositedLayerMapping::setBlendMode(BlendMode blendMode)
 {
+    if (m_ancestorClippingLayer) {

[shawnsingh, 2013/11/23 00:38:13]

lately we are adding more layers in the CompositedLayerMapping, each of which
may be the childForSuperlayers() under different scenarios.  So it's probably
best not to rely on childForSuperLayers() unless you intend to reset the blend
mode to BlendModeNormal for all these other layers, too.

Would it work to simply use m_graphicsLayer to house the blend mode always?  Why
does it need to be the root-most layer of this cluster?

[rosca, 2013/11/25 21:11:41]

The same approach is used by scrolling coordinator (updateScrollParent). We
should keep this in sync when other childForSuperlayers are added.
Blending doesn't work if the blend mode is set on m_graphicsLayer being clipped
by an ancestorClippingLayer. It seems like such a structure doesn't allow cc
renderer to copy the correct backdrop. I should look more into this. I'd prefer
to address this with a follow-up patch if you are ok with this.
Added a layout test with this scenario.

+        ASSERT(childForSuperlayers() == m_ancestorClippingLayer.get());
+        m_graphicsLayer->setBlendMode(BlendModeNormal);
+    } else {
+        ASSERT(childForSuperlayers() == m_graphicsLayer.get());
+    }
+    childForSuperlayers()->setBlendMode(blendMode);
 }
 
 void CompositedLayerMapping::setContentsNeedDisplay()