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

Source/core/rendering/RenderLayerCompositor.cpp

Index: Source/core/rendering/RenderLayerCompositor.cpp
diff --git a/Source/core/rendering/RenderLayerCompositor.cpp b/Source/core/rendering/RenderLayerCompositor.cpp
index 7115eaf47758f6c6eb8cdb29755a4fd19f703ffa..134694740631c109509ef0841b8adaf768147170 100644
--- a/Source/core/rendering/RenderLayerCompositor.cpp
+++ b/Source/core/rendering/RenderLayerCompositor.cpp
@@ -180,6 +180,7 @@ struct CompositingState {
     CompositingState(RenderLayer* compAncestor, bool testOverlap)
         : m_compositingAncestor(compAncestor)
         , m_subtreeIsCompositing(false)
+        , m_hasCompositedBlendingDescendents(false)
         , m_testingOverlap(testOverlap)
 #ifndef NDEBUG
         , m_depth(0)
@@ -190,6 +191,7 @@ struct CompositingState {
     CompositingState(const CompositingState& other)
         : m_compositingAncestor(other.m_compositingAncestor)
         , m_subtreeIsCompositing(other.m_subtreeIsCompositing)
+        , m_hasCompositedBlendingDescendents(other.m_hasCompositedBlendingDescendents)
         , m_testingOverlap(other.m_testingOverlap)
 #ifndef NDEBUG
         , m_depth(other.m_depth + 1)
@@ -199,6 +201,7 @@ struct CompositingState {
 
     RenderLayer* m_compositingAncestor;
     bool m_subtreeIsCompositing;
+    bool m_hasCompositedBlendingDescendents;
     bool m_testingOverlap;
 #ifndef NDEBUG
     int m_depth;
@@ -778,6 +781,7 @@ void RenderLayerCompositor::computeCompositingRequirements(RenderLayer* ancestor
 
     // Clear the flag
     layer->setHasCompositingDescendant(false);
+    layer->setShouldIsolateCompositedBlendingDescendants(false);
 
     // Start by assuming this layer will not need to composite.
     CompositingReasons reasonsToComposite = CompositingReasonNone;
@@ -912,6 +916,16 @@ void RenderLayerCompositor::computeCompositingRequirements(RenderLayer* ancestor
     if (overlapMap && childState.m_compositingAncestor && !childState.m_compositingAncestor->isRootLayer())
         addToOverlapMap(*overlapMap, layer, absBounds, haveComputedBounds);
 
+    // According to http://dev.w3.org/fxtf/compositing-1/#csscompositingrules_CSS,
+    // an element that has blending applied, must blend with all the underlying
+    // content of the stacking context [CSS21] that element belongs to.
+    // We should isolate and accelerate the stacking contexts containing
+    // accelerated blending descendants
+    if (layer->isStackingContext())
+        layer->setShouldIsolateCompositedBlendingDescendants(childState.m_hasCompositedBlendingDescendents);
+    else
+        compositingState.m_hasCompositedBlendingDescendents = childState.m_hasCompositedBlendingDescendents;
+
     // Now check for reasons to become composited that depend on the state of descendant layers.
     CompositingReasons subtreeCompositingReasons = subtreeReasonsForCompositing(layer->renderer(), childState.m_subtreeIsCompositing, anyDescendantHas3DTransform);
     reasonsToComposite |= subtreeCompositingReasons;
@@ -937,6 +951,8 @@ void RenderLayerCompositor::computeCompositingRequirements(RenderLayer* ancestor
     // Subsequent layers in the parent's stacking context may also need to composite.
     if (childState.m_subtreeIsCompositing)
         compositingState.m_subtreeIsCompositing = true;
+    if (willBeComposited && layer->hasBlendMode())
+        compositingState.m_hasCompositedBlendingDescendents = true;
 
     // Set the flag to say that this SC has compositing children.
     layer->setHasCompositingDescendant(childState.m_subtreeIsCompositing);
@@ -1574,6 +1590,7 @@ bool RenderLayerCompositor::requiresOwnBackingStore(const RenderLayer* layer, co
         | CompositingReasonMaskWithCompositedDescendants
         | CompositingReasonFilterWithCompositedDescendants
         | CompositingReasonBlendingWithCompositedDescendants
+        | CompositingReasonIsolateCompositedDescendants
         | CompositingReasonPreserve3D; // preserve-3d has to create backing store to ensure that 3d-transformed elements intersect.
     return layer->compositingReasons() & indirectReasonsThatNeedBacking;
 }
@@ -1898,6 +1915,8 @@ CompositingReasons RenderLayerCompositor::subtreeReasonsForCompositing(RenderObj
     if (hasCompositedDescendants) {
         if (layer->transform())
             subtreeReasons |= CompositingReasonTransformWithCompositedDescendants;
+        if (layer->shouldIsolateCompositedBlendingDescendants())
+            subtreeReasons |= CompositingReasonIsolateCompositedDescendants;
 
         // If the implementation of createsGroup changes, we need to be aware of that in this part of code.
         ASSERT((renderer->isTransparent() || renderer->hasMask() || renderer->hasFilter() || renderer->hasBlendMode()) == renderer->createsGroup());