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 92 matching lines @@
 class WebGLShaderPrecisionFormat;
 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 {
+  STACK_ALLOCATED();
+
  public:
-  ScopedRGBEmulationColorMask(gpu::gles2::GLES2Interface*,
+  ScopedRGBEmulationColorMask(WebGLRenderingContextBase*,
                               GLboolean* colorMask,
                               DrawingBuffer*);
   ~ScopedRGBEmulationColorMask();
 
  private:
-  gpu::gles2::GLES2Interface* m_contextGL;
+  Member<WebGLRenderingContextBase> m_context;
   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 1395 matching lines @@
   static void addToEvictedList(WebGLRenderingContextBase*);
   static void removeFromEvictedList(WebGLRenderingContextBase*);
   static void willDestroyContext(WebGLRenderingContextBase*);
   static void forciblyLoseOldestContext(const String& reason);
   // Return the least recently used context's position in the active context
   // vector.  If the vector is empty, return the maximum allowed active context
   // number.
   static WebGLRenderingContextBase* oldestContext();
   static WebGLRenderingContextBase* oldestEvictedContext();
 
+  friend class ScopedRGBEmulationColorMask;
+  std::list<ScopedRGBEmulationColorMask*> activeScopedRGBEmulationColorMasks;
+  void pushActiveScopedRGBEmulationColorMask(ScopedRGBEmulationColorMask* val) {
+    activeScopedRGBEmulationColorMasks.push_back(val);
+  }
+  ScopedRGBEmulationColorMask* popActiveScopedRGBEmulationColorMask() {

[Ken Russell (switch to Gerrit), 2016/12/01 23:45:30]

It occurs to me that since the WebGLRenderingContextBase code only checks
activeScopedRGBEmulationColorMasks.empty(), we could just use a simple int to
track the active count instead of a std::list. I'd ask that this change be made
for simplicity.

[Kai Ninomiya, 2016/12/02 00:05:27]

Great point, thanks. I was thinking of trying to simplify it from a std::list
but I forgot to figure out if I could.

Done.

+    auto removed = activeScopedRGBEmulationColorMasks.back();
+    activeScopedRGBEmulationColorMasks.pop_back();
+    return removed;
+  }
+
   ImageBitmap* transferToImageBitmapBase(ScriptState*);
 
   // Helper functions for tex(Sub)Image2D && texSubImage3D
   void texImageHelperDOMArrayBufferView(TexImageFunctionID,
                                         GLenum,
                                         GLint,
                                         GLint,
                                         GLsizei,
                                         GLsizei,
                                         GLsizei,
@@ skipping 122 matching lines @@
                   context,
                   context->is3d(),
                   context.is3d());
 
 }  // namespace blink
 
 WTF_ALLOW_MOVE_INIT_AND_COMPARE_WITH_MEM_FUNCTIONS(
     blink::WebGLRenderingContextBase::TextureUnitState);
 
 #endif  // WebGLRenderingContextBase_h