Add blend optimization helpers and use to convert rect draws to clears.

include/gpu/GrSurface.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 GrSurface_DEFINED
 #define GrSurface_DEFINED
 
 #include "GrTypes.h"
 #include "GrResource.h"
+#include "SkRect.h"
 
 class GrTexture;
 class GrRenderTarget;
 
 class GrSurface : public GrResource {
 public:
     SK_DECLARE_INST_COUNT(GrSurface);
 
     /**
      * Retrieves the width of the surface.
      *
      * @return the width in texels
      */
     int width() const { return fDesc.fWidth; }
 
     /**
      * Retrieves the height of the surface.
      *
      * @return the height in texels
      */
     int height() const { return fDesc.fHeight; }
 
+    /**
+     * Helper that gets the width and height of the surface as a bounding rectangle.
+     */
+    void getBoundsRect(SkRect* rect) const { rect->setWH(SkIntToScalar(this->width()),
+                                                         SkIntToScalar(this->height())); }
+
     GrSurfaceOrigin origin() const {
         GrAssert(kTopLeft_GrSurfaceOrigin == fDesc.fOrigin || kBottomLeft_GrSurfaceOrigin == fDesc.fOrigin);
         return fDesc.fOrigin;
     }
 
     /**
      * Retrieves the pixel config specified when the surface was created.
      * For render targets this can be kUnknown_GrPixelConfig
      * if client asked us to render to a target that has a pixel
      * config that isn't equivalent with one of our configs.
@@ skipping 79 matching lines @@
     , fDesc(desc) {
     }
 
     GrTextureDesc fDesc;
 
 private:
     typedef GrResource INHERITED;
 };
 
 #endif // GrSurface_DEFINED