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

include/core/SkMatrix.h

 
 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #ifndef SkMatrix_DEFINED
@@ skipping 452 matching lines @@
     /** Apply this matrix to the rectangle, and write the transformed rectangle
         back into it. This is accomplished by transforming the 4 corners of
         rect, and then setting it to the bounds of those points
         @param rect The rectangle to transform.
         @return the result of calling rectStaysRect()
     */
     bool mapRect(SkRect* rect) const {
         return this->mapRect(rect, *rect);
     }
 
+    /** Apply this matrix to the src rectangle, and write the four transformed
+        points into dst. The points written to dst will be the original top-left, top-right,
+        bottom-right, and bottom-left points transformed by the matrix.
+        @param dst  Where the transformed quad is written.
+        @param rect The original rectangle to be transformed.
+    */
+    void mapRectToQuad(SkPoint dst[4], const SkRect& rect) const {
+        // This could potentially be faster if we only transformed each x and y of the rect once.
+        rect.toQuad(dst);
+        this->mapPoints(dst, 4);
+    }
+
     /** Return the mean radius of a circle after it has been mapped by
         this matrix. NOTE: in perspective this value assumes the circle
         has its center at the origin.
     */
     SkScalar mapRadius(SkScalar radius) const;
 
     typedef void (*MapXYProc)(const SkMatrix& mat, SkScalar x, SkScalar y,
                                  SkPoint* result);
 
     static MapXYProc GetMapXYProc(TypeMask mask) {
@@ skipping 182 matching lines @@
     static void RotTrans_pts(const SkMatrix&, SkPoint dst[], const SkPoint[],
                              int count);
     static void Persp_pts(const SkMatrix&, SkPoint dst[], const SkPoint[], int);
 
     static const MapPtsProc gMapPtsProcs[];
 
     friend class SkPerspIter;
 };
 
 #endif