Add ability to extract YUV planes from SkImage

include/core/SkImage.h

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkImage_DEFINED
 #define SkImage_DEFINED
 
@@ skipping 136 matching lines @@
 
     ///////////////////////////////////////////////////////////////////////////////////////////////
 
     int width() const { return fWidth; }
     int height() const { return fHeight; }
     SkISize dimensions() const { return SkISize::Make(fWidth, fHeight); }
     SkIRect bounds() const { return SkIRect::MakeWH(fWidth, fHeight); }
     uint32_t uniqueID() const { return fUniqueID; }
     virtual bool isOpaque() const { return false; }
 
+    bool asYUV8Planes(const SkISize[3], void* const planes[3], const size_t rowBytes[3],

[bsalomon, 2016/01/26 16:23:48]

One thing I wondered is whether this should take a SkFilterQuality for scaling
the planes. Currently I use bilerp which should be OK for the common case of a
scale factor of 2. Our reverse conversions don't take a quality so maybe
assuming bilerp is alright.

+                      SkYUVColorSpace);
+
     virtual SkShader* newShader(SkShader::TileMode,
                                 SkShader::TileMode,
                                 const SkMatrix* localMatrix = NULL) const;
 
     /**
      *  If the image has direct access to its pixels (i.e. they are in local
      *  RAM) return the (const) address of those pixels, and if not null, return
      *  the ImageInfo and rowBytes. The returned address is only valid while
      *  the image object is in scope.
      *
@@ skipping 162 matching lines @@
 
 private:
     const int       fWidth;
     const int       fHeight;
     const uint32_t  fUniqueID;
 
     typedef SkRefCnt INHERITED;
 };
 
 #endif