Prevent implicit framebuffer clear from clobbering alpha in emulated RGB

third_party/WebKit/Source/modules/webgl/WebGLRenderingContextBase.h

 /*
  * Copyright (C) 2009 Apple 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
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 93 matching lines @@
 class WebGLSharedObject;
 class WebGLUniformLocation;
 class WebGLVertexArrayObjectBase;
 
 class WebGLRenderingContextErrorMessageCallback;
 
 // This class uses the color mask to prevent drawing to the alpha channel, if
 // the DrawingBuffer requires RGB emulation.
 class ScopedRGBEmulationColorMask {
  public:
-  ScopedRGBEmulationColorMask(gpu::gles2::GLES2Interface*,
+  ScopedRGBEmulationColorMask(WebGLRenderingContextBase*,
                               GLboolean* colorMask,
                               DrawingBuffer*);
   ~ScopedRGBEmulationColorMask();
 
  private:
-  gpu::gles2::GLES2Interface* m_contextGL;
+  WeakPersistent<WebGLRenderingContextBase> m_context;

[Ken Russell (switch to Gerrit), 2016/12/01 07:20:43]

I'm concerned about the performance impact of allocating a WeakPersistent during
every draw call. haraken@, sigbjornf@, could you comment on that? These data
structures are only stack-allocated. Is there some cheaper way to be safe with
regard to Oilpan but still maintain temporary pointers to the
WebGLRenderingContextBase? With Oilpan's clang plugin, we found this necessary
to compile.

[Ken Russell (switch to Gerrit), 2016/12/01 08:36:47]

I just learned from looking at another CL (
https://codereview.chromium.org/2476693002/ ) that the way to handle this is to
declare this STACK_ALLOCATED(), and use a Member. Kai, could you make that
change?

Kentaro, Sigbjorn, no longer necessary to look at this.

[Kai Ninomiya, 2016/12/01 23:30:20]

Done.

   GLboolean m_colorMask[4];
   const bool m_requiresEmulation;
 };
 
 class MODULES_EXPORT WebGLRenderingContextBase : public CanvasRenderingContext,
                                                  public DrawingBuffer::Client {
   WTF_MAKE_NONCOPYABLE(WebGLRenderingContextBase);
 
  public:
   ~WebGLRenderingContextBase() override;
@@ skipping 454 matching lines @@
 
   PassRefPtr<Image> getImage(AccelerationHint, SnapshotReason) const override;
   ImageData* toImageData(SnapshotReason) const override;
   void setFilterQuality(SkFilterQuality) override;
   bool isWebGL2OrHigher() { return version() >= 2; }
 
   void getHTMLOrOffscreenCanvas(HTMLCanvasElementOrOffscreenCanvas&) const;
 
   void commit(ScriptState*, ExceptionState&);
 
+  std::list<ScopedRGBEmulationColorMask*> activeScopedRGBEmulationColorMasks;

[Ken Russell (switch to Gerrit), 2016/12/01 07:20:43]

Please put all of this in the private section and make
ScopedRGBEmulationColorMask a friend.

[Kai Ninomiya, 2016/12/01 23:30:20]

Done.

+  void pushActiveScopedRGBEmulationColorMask(ScopedRGBEmulationColorMask* val) {
+    activeScopedRGBEmulationColorMasks.push_back(val);
+  }
+  ScopedRGBEmulationColorMask* popActiveScopedRGBEmulationColorMask() {
+    auto removed = activeScopedRGBEmulationColorMasks.back();
+    activeScopedRGBEmulationColorMasks.pop_back();
+    return removed;
+  }
+
  protected:
   friend class EXTDisjointTimerQuery;
   friend class EXTDisjointTimerQueryWebGL2;
   friend class WebGLDrawBuffers;
   friend class WebGLFramebuffer;
   friend class WebGLObject;
   friend class WebGLContextObject;
   friend class OESVertexArrayObject;
   friend class WebGLDebugShaders;
   friend class WebGLCompressedTextureASTC;
@@ skipping 1063 matching lines @@
                   context,
                   context->is3d(),
                   context.is3d());
 
 }  // namespace blink
 
 WTF_ALLOW_MOVE_INIT_AND_COMPARE_WITH_MEM_FUNCTIONS(
     blink::WebGLRenderingContextBase::TextureUnitState);
 
 #endif  // WebGLRenderingContextBase_h