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],

[reed1, 2016/01/26 16:06:45]

Is this intended to always succeed, even if the underlying form is not
intrinsically YUV? (e.g. rgb or picture)

Matt and Leon have gone to great lengths to allow the codec to specify the
sizes/rowbytes for each plane (including padding sometimes). How does the caller
arrive at the specified sizes here?

[bsalomon, 2016/01/26 16:32:50]

Yes, it is for turning a SkImage into a video frame. The motivating use case is
for taking rendered canvas2D frames and turning them into a video stream. So
typically the content behind the image is a newImageSnapshot ()from a GPU
(though probably could be CPU) SkSurface. I hadn't thought about cases where the
original data is YUV. That would accelerate that use but isn't really the target
use case.
That would based on what the video encoder can ingest, probably 4:2:0 (y full
sized, u and v half sized in both dimensions).

+                      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