[SPv2] Add CSS mix-blend-mode support

third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.cpp

Index: third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.cpp b/third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.cpp
index a0a17d3962ef13e7d138575fc7b25be600a0f5ca..165538ff94d47c1aaa21db5523ae1217814c8971 100644
--- a/third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.cpp
@@ -364,6 +364,9 @@ void PaintPropertyTreeBuilder::updateEffect(
     PaintPropertyTreeBuilderContext& context) {
   const ComputedStyle& style = object.styleRef();
 
+  // TODO(crbug.com/673500): style.isStackingContext() is only meaningful for
+  // HTML elements. What we really want to ask is whether the element starts
+  // an isolated group, and SVGs use a different rule.
   if (!style.isStackingContext()) {
     if (object.needsPaintPropertyUpdate() || context.forceSubtreeUpdate) {
       if (auto* properties = object.getMutableForPainting().paintProperties())
@@ -373,10 +376,26 @@ void PaintPropertyTreeBuilder::updateEffect(
   }
 
   // TODO(trchen): Can't omit effect node if we have 3D children.
-  // TODO(trchen): Can't omit effect node if we have blending children.
   if (object.needsPaintPropertyUpdate() || context.forceSubtreeUpdate) {
     bool effectNodeNeeded = false;
 
+    // Can't omit effect node if we have paint children with exotic blending.
+    if (object.isSVG()) {
+      // Yes, including LayoutSVGRoot, because SVG layout objects don't create

[pdr., 2016/12/14 01:05:18]

Do we need to special-case isSVG here?

IOW, could we write this instead?
if (PaintLayer* layer = toLayoutBoxModelObject(object).layer()) {
  if (layer->hasNonIsolatedDescendantWithBlendMode())
    effectNodeNeeded = true;
} else if (object.hasNonIsolatedDescendantWithBlendMode()) {
  effectNodeIsNeeded = true;
}

[trchen, 2016/12/14 01:12:35]

Type checking needs to come first. object may not be LayoutBoxModelObject. Also
object.hasNonIsolatedDescendantWithBlendMode() is only implemented for SVG.
Invoking it with anything other than SVG should die in panic.

I'm working on a SVG & effect node CL that should add some sense into this code.
:)

+      // PaintLayer so PaintLayer::hasNonIsolatedDescendantWithBlendMode()
+      // doesn't catch SVG descendants.
+      if (object.hasNonIsolatedBlendingDescendants())
+        effectNodeNeeded = true;
+    } else if (PaintLayer* layer = toLayoutBoxModelObject(object).layer()) {
+      if (layer->hasNonIsolatedDescendantWithBlendMode())
+        effectNodeNeeded = true;
+    }
+
+    SkBlendMode blendMode =
+        WebCoreCompositeToSkiaComposite(CompositeSourceOver, style.blendMode());
+    if (blendMode != SkBlendMode::kSrcOver)
+      effectNodeNeeded = true;
+
     float opacity = style.opacity();
     if (opacity != 1.0f)
       effectNodeNeeded = true;
@@ -421,7 +440,7 @@ void PaintPropertyTreeBuilder::updateEffect(
       auto& properties = object.getMutableForPainting().ensurePaintProperties();
       context.forceSubtreeUpdate |= properties.updateEffect(
           context.currentEffect, context.current.transform, outputClip,
-          std::move(filter), opacity);
+          std::move(filter), opacity, blendMode);
     } else {
       if (auto* properties = object.getMutableForPainting().paintProperties())
         context.forceSubtreeUpdate |= properties->clearEffect();