[SPv2] Add CSS mix-blend-mode support

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

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/paint/PaintPropertyTreeBuilder.h"
 
 #include "core/frame/FrameView.h"
 #include "core/frame/LocalFrame.h"
 #include "core/frame/Settings.h"
 #include "core/layout/LayoutInline.h"
@@ skipping 346 matching lines @@
       context.current.shouldFlattenInheritedTransform = true;
     }
   }
 }
 
 void PaintPropertyTreeBuilder::updateEffect(
     const LayoutObject& object,
     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())
         context.forceSubtreeUpdate |= properties->clearEffect();
     }
     return;
   }
 
   // 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;
 
     CompositorFilterOperations filter;
     if (object.isSVG() && !object.isSVGRoot()) {
       // TODO(trchen): SVG caches filters in SVGResources. Implement it.
     } else if (PaintLayer* layer = toLayoutBoxModelObject(object).layer()) {
       // TODO(trchen): Eliminate PaintLayer dependency.
       filter = layer->createCompositorFilterOperationsForFilter(style);
@@ skipping 24 matching lines @@
 
       // TODO(trchen): A filter may contain spatial operations such that an
       // output pixel may depend on an input pixel outside of the output clip.
       // We should generate a special clip node to represent this expansion.
     }
 
     if (effectNodeNeeded) {
       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();
     }
   }
 
   const auto* properties = object.paintProperties();
   if (properties && properties->effect()) {
     context.currentEffect = properties->effect();
     if (!properties->effect()->filter().isEmpty()) {
@@ skipping 472 matching lines @@
 #endif
 
   updateOverflowClip(object, context);
   updatePerspective(object, context);
   updateSvgLocalToBorderBoxTransform(object, context);
   updateScrollAndScrollTranslation(object, context);
   updateOutOfFlowContext(object, context);
 }
 
 }  // namespace blink