Add subsets to SkImageGenerator and SkImageCacherator .

include/core/SkImageGenerator.h

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkImageGenerator_DEFINED
 #define SkImageGenerator_DEFINED
 
@@ skipping 130 matching lines @@
      *  - its internal context is the same
      *  - it can somehow convert its texture into one that is valid for the provided context.
      *
      *  Regarding the SkImageUsageType parameter:
      *
      *  If the context (the provided one or the generator's intrinsic one) determines that to
      *  support the specified usage, it must return a different sized texture it may,
      *  so the caller must inspect the texture's width/height and compare them to the generator's
      *  getInfo() width/height.
      */
-    GrTexture* generateTexture(GrContext*, SkImageUsageType);
+    GrTexture* generateTexture(GrContext*, SkImageUsageType, const SkIRect* subset = nullptr);
 
     /**
      *  If the default image decoder system can interpret the specified (encoded) data, then
      *  this returns a new ImageGenerator for it. Otherwise this returns NULL. Either way
      *  the caller is still responsible for managing their ownership of the data.
      */
     static SkImageGenerator* NewFromEncoded(SkData*);
 
     /** Return a new image generator backed by the specified picture.  If the size is empty or
      *  the picture is NULL, this returns NULL.
      *  The optional matrix and paint arguments are passed to drawPicture() at rasterization
      *  time.
      */
     static SkImageGenerator* NewFromPicture(const SkISize&, const SkPicture*, const SkMatrix*,
                                             const SkPaint*);
 
 protected:
     SkImageGenerator(const SkImageInfo& info);
 
     virtual SkData* onRefEncodedData();
 
     virtual bool onGetPixels(const SkImageInfo& info, void* pixels, size_t rowBytes,
                              SkPMColor ctable[], int* ctableCount);
     virtual bool onGetYUV8Planes(SkISize sizes[3], void* planes[3], size_t rowBytes[3]);
     virtual bool onGetYUV8Planes(SkISize sizes[3], void* planes[3], size_t rowBytes[3],
                                  SkYUVColorSpace* colorSpace);
 
-    virtual GrTexture* onGenerateTexture(GrContext*, SkImageUsageType) { return nullptr; }
+    virtual GrTexture* onGenerateTexture(GrContext*, SkImageUsageType, const SkIRect*) {
+        return nullptr;
+    }
 
 private:
     const SkImageInfo fInfo;
     const uint32_t fUniqueID;
 
     // This is our default impl, which may be different on different platforms.
     // It is called from NewFromEncoded() after it has checked for any runtime factory.
     // The SkData will never be NULL, as that will have been checked by NewFromEncoded.
     static SkImageGenerator* NewFromEncodedImpl(SkData*);
 };
 
 #endif  // SkImageGenerator_DEFINED