add readPixels to SkImage

src/image/SkImage_Base.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_Base_DEFINED
 #define SkImage_Base_DEFINED
 
@@ skipping 23 matching lines @@
         new (mutableProps) SkSurfaceProps(props);
     }
 
     const SkSurfaceProps& props() const { return fProps; }
 
     virtual void onDraw(SkCanvas*, SkScalar x, SkScalar y, const SkPaint*) const = 0;
     virtual void onDrawRect(SkCanvas*, const SkRect* src,
                                   const SkRect& dst, const SkPaint*) const = 0;
     virtual SkSurface* onNewSurface(const SkImageInfo&, const SkSurfaceProps&) const = 0;
 
-    // Default impl calls onDraw
-    virtual bool onReadPixels(SkBitmap*, const SkIRect& subset) const;
-
     virtual const void* onPeekPixels(SkImageInfo*, size_t* /*rowBytes*/) const {
         return NULL;
     }
 
+    // Default impl calls onDraw
+    virtual bool onReadPixels(const SkImageInfo& dstInfo, void* dstPixels, size_t dstRowBytes,
+                              int srcX, int srcY) const;
+    
     virtual GrTexture* onGetTexture() const { return NULL; }
 
     // return a read-only copy of the pixels. We promise to not modify them,
     // but only inspect them (or encode them).
     virtual bool getROPixels(SkBitmap*) const { return false; }
 
     virtual SkShader* onNewShader(SkShader::TileMode,
                                   SkShader::TileMode,
                                   const SkMatrix* localMatrix) const { return NULL; };
 
 private:
     const SkSurfaceProps fProps;
 
     typedef SkImage INHERITED;
 };
 
 static inline SkImage_Base* as_IB(SkImage* image) {
     return static_cast<SkImage_Base*>(image);
 }
 
 static inline const SkImage_Base* as_IB(const SkImage* image) {
     return static_cast<const SkImage_Base*>(image);
 }
 
 #endif