Image filters: implement offsets in GPU path.

include/core/SkImageFilter.h

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkImageFilter_DEFINED
 #define SkImageFilter_DEFINED
 
@@ skipping 91 matching lines @@
      *  The default implementation returns asNewEffect(NULL, NULL).
      */
     virtual bool canFilterImageGPU() const;
 
     /**
      *  Process this image filter on the GPU.  This is most often used for
      *  multi-pass effects, where intermediate results must be rendered to
      *  textures.  For single-pass effects, use asNewEffect().  src is the
      *  source image for processing, as a texture-backed bitmap.  result is
      *  the destination bitmap, which should contain a texture-backed pixelref
-     *  on success.  The default implementation does single-pass processing
-     *  using asNewEffect().
+     *  on success.  offset is the amount to translate the resulting image 
+     *  relative to the src when it is drawn. The default implementation does
+     *  single-pass processing using asNewEffect().
      */
-    virtual bool filterImageGPU(Proxy*, const SkBitmap& src, SkBitmap* result);
+    virtual bool filterImageGPU(Proxy*, const SkBitmap& src, SkBitmap* result, SkIPoint* offset);
 
     /**
      *  Returns whether this image filter is a color filter and puts the color filter into the
      *  "filterPtr" parameter if it can. Does nothing otherwise.
      *  If this returns false, then the filterPtr is unchanged.
      *  If this returns true, then if filterPtr is not null, it must be set to a ref'd colorfitler
      *  (i.e. it may not be set to NULL).
      */
     virtual bool asColorFilter(SkColorFilter** filterPtr) const;
 
@@ skipping 33 matching lines @@
     // Default impl copies src into dst and returns true
     virtual bool onFilterBounds(const SkIRect&, const SkMatrix&, SkIRect*);
 
 private:
     typedef SkFlattenable INHERITED;
     int fInputCount;
     SkImageFilter** fInputs;
 };
 
 #endif