Add "alpha" option to PaintWorklet

third_party/WebKit/Source/modules/csspaint/PaintRenderingContext2D.h

 // Copyright 2016 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.
 
 #ifndef PaintRenderingContext2D_h
 #define PaintRenderingContext2D_h
 
 #include "bindings/core/v8/ScriptWrappable.h"
 #include "modules/ModulesExport.h"
 #include "modules/canvas2d/BaseRenderingContext2D.h"
 #include "platform/graphics/ImageBuffer.h"
 #include <memory>
 
 class SkCanvas;
 
 namespace blink {
 
 class CanvasImageSource;
 class Color;
 
 class MODULES_EXPORT PaintRenderingContext2D : public BaseRenderingContext2D, public GarbageCollectedFinalized<PaintRenderingContext2D>, public ScriptWrappable {
     DEFINE_WRAPPERTYPEINFO();
     USING_GARBAGE_COLLECTED_MIXIN(PaintRenderingContext2D);
     WTF_MAKE_NONCOPYABLE(PaintRenderingContext2D);
 public:
-    static PaintRenderingContext2D* create(std::unique_ptr<ImageBuffer> imageBuffer)
+    static PaintRenderingContext2D* create(std::unique_ptr<ImageBuffer> imageBuffer, bool hasAlpha)
     {
-        return new PaintRenderingContext2D(std::move(imageBuffer));
+        return new PaintRenderingContext2D(std::move(imageBuffer), hasAlpha);
     }
 
     // BaseRenderingContext2D
 
     // PaintRenderingContext2D doesn't have any pixel readback so the origin
     // is always clean, and unable to taint it.
     bool originClean() const final { return true; }
     void setOriginTainted() final { }
     bool wouldTaintOrigin(CanvasImageSource*, ExecutionContext*) final { return false; }
 
@@ skipping 16 matching lines @@
     // TODO(ikilpatrick): We'll need to either only accept resolved filters
     // from a typed-om <filter> object, or use the appropriate style resolution
     // host to determine 'em' units etc in filters. At the moment just pretend
     // that we don't have a filter set.
     bool stateHasFilter() final { return false; }
     SkImageFilter* stateGetFilter() final { return nullptr; }
     void snapshotStateForFilter() final { }
 
     void validateStateStack() final;
 
-    bool hasAlpha() const final { return true; }
+    bool hasAlpha() const final { return m_hasAlpha; }

[ikilpatrick, 2016/06/23 16:53:42]

This method can probably be now implemented as a non-virtual on
BaseRenderingContext2D instead?

[Gleb Lanbin, 2016/06/23 22:26:03]

I tried to pass hasAlpha directly to BaseRenderingContext2D but it didn't work.
For example CanvasRenderingContext2D doesn't call the super class constructor by
intention and it's not allowed to initialize   base class members from
initialization list directly.

 
     // PaintRenderingContext2D cannot lose it's context.
     bool isContextLost() const final { return false; }
 
 private:
-    explicit PaintRenderingContext2D(std::unique_ptr<ImageBuffer>);
+    PaintRenderingContext2D(std::unique_ptr<ImageBuffer>, bool hasAlpha);
 
     std::unique_ptr<ImageBuffer> m_imageBuffer;
+    bool m_hasAlpha;
 };
 
 } // namespace blink
 
 #endif // PaintRenderingContext2D_h