Avoid GPU readback in tex(Sub)Image2D(ImageBitmap)

third_party/WebKit/Source/platform/graphics/Image.h

 /*
  * Copyright (C) 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2004, 2005, 2006 Apple Computer, 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 16 matching lines @@
 #ifndef Image_h
 #define Image_h
 
 #include "platform/PlatformExport.h"
 #include "platform/geometry/IntRect.h"
 #include "platform/graphics/Color.h"
 #include "platform/graphics/GraphicsTypes.h"
 #include "platform/graphics/ImageAnimationPolicy.h"
 #include "platform/graphics/ImageObserver.h"
 #include "platform/graphics/ImageOrientation.h"
+#include "public/platform/WebGraphicsContext3DProvider.h"
 #include "wtf/Assertions.h"
 #include "wtf/Noncopyable.h"
 #include "wtf/PassRefPtr.h"
 #include "wtf/RefCounted.h"
 #include "wtf/RefPtr.h"
 #include "wtf/text/WTFString.h"
 
 class SkBitmap;
 class SkCanvas;
 class SkImage;
@@ skipping 83 matching lines @@
     virtual void advanceAnimationForTesting() { }
 
     // Typically the ImageResource that owns us.
     ImageObserver* getImageObserver() const { return m_imageObserverDisabled ? nullptr : m_imageObserver; }
     void clearImageObserver() { m_imageObserver = nullptr; }
     // Do not call setImageObserverDisabled() other than from ImageObserverDisabler to avoid interleaved accesses to |m_imageObserverDisabled|.
     void setImageObserverDisabled(bool disabled) { m_imageObserverDisabled = disabled; }
 
     enum TileRule { StretchTile, RoundTile, SpaceTile, RepeatTile };
 
-    virtual PassRefPtr<SkImage> imageForCurrentFrame() = 0;
+    // The returned SkImage may or may not be texture-backed. If the caller needs a texture-backed
+    // image in a 3D context such as WebGL context, it must specify the desired context provider.
+    virtual PassRefPtr<SkImage> imageForCurrentFrame(WebGraphicsContext3DProvider* = nullptr) = 0;

[f(malita), 2016/06/15 12:39:32]

Looks like we only ever pass a WebGraphicsContext3DProvider argument when
calling on a StaticBitmapImage object (in
WebGLRenderingContextBase::texImageBitmapByGPU).  Rather than exposing this on
the Image interface (encumbers all subclasses), why not make it a
StaticBitmapImage method?  Then you would also have more freedom in naming -
maybe StaticBitmapImage::imageForContext3DProvider(...)?

     virtual PassRefPtr<Image> imageForDefaultFrame();
 
     virtual void drawPattern(GraphicsContext&, const FloatRect&,
         const FloatSize&, const FloatPoint& phase, SkXfermode::Mode,
         const FloatRect&, const FloatSize& repeatSpacing = FloatSize());
 
     enum ImageClampingMode {
         ClampImageToSourceRect,
         DoNotClampImageToSourceRect
     };
@@ skipping 30 matching lines @@
     UntracedMember<ImageObserver> m_imageObserver;
     bool m_imageObserverDisabled;
 };
 
 #define DEFINE_IMAGE_TYPE_CASTS(typeName) \
     DEFINE_TYPE_CASTS(typeName, Image, image, image->is##typeName(), image.is##typeName())
 
 } // namespace blink
 
 #endif