Adds filter support for offscreen canvas

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

 /*
  * Copyright (C) 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 139 matching lines @@
 bool FilterEffectBuilder::build(Element* element, const FilterOperations& operations, float zoom, const FloatSize* zoomedReferenceBoxSize, const SkPaint* fillPaint, const SkPaint* strokePaint)
 {
     // Create a parent filter for shorthand filters. These have already been scaled by the CSS code for page zoom, so scale is 1.0 here.
     Filter* parentFilter = Filter::create(1.0f);
     FilterEffect* previousEffect = parentFilter->getSourceGraphic();
     for (size_t i = 0; i < operations.operations().size(); ++i) {
         FilterEffect* effect = nullptr;
         FilterOperation* filterOperation = operations.operations().at(i).get();
         switch (filterOperation->type()) {
         case FilterOperation::REFERENCE: {
+            if (!element)

[esprehn, 2016/09/12 20:53:12]

In general core/paint is not thread safe, this code would need to be refactored
out, someone will just break it.

+                break;
             Filter* referenceFilter = buildReferenceFilter(toReferenceFilterOperation(*filterOperation), zoomedReferenceBoxSize, fillPaint, strokePaint, *element, previousEffect, zoom);
             if (referenceFilter)
                 effect = referenceFilter->lastEffect();
             break;
         }
         case FilterOperation::GRAYSCALE: {
             Vector<float> inputParameters = grayscaleMatrix(toBasicColorMatrixFilterOperation(filterOperation)->amount());
             effect = FEColorMatrix::create(parentFilter, FECOLORMATRIX_TYPE_MATRIX, inputParameters);
             break;
         }
@@ skipping 144 matching lines @@
     Filter* result = Filter::create(referenceBox, filterRegion, zoom, unitScaling);
     if (!previousEffect)
         previousEffect = result->getSourceGraphic();
     SVGFilterBuilder builder(previousEffect, nodeMap, fillPaint, strokePaint);
     builder.buildGraph(result, filterElement, referenceBox);
     result->setLastEffect(builder.lastEffect());
     return result;
 }
 
 } // namespace blink
-