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

include/core/SkRect.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 SkRect_DEFINED
@@ skipping 448 matching lines @@
     SkScalar    centerY() const { return SkScalarHalf(fTop + fBottom); }
 
     friend bool operator==(const SkRect& a, const SkRect& b) {
         return SkScalarsEqual((SkScalar*)&a, (SkScalar*)&b, 4);
     }
 
     friend bool operator!=(const SkRect& a, const SkRect& b) {
         return !SkScalarsEqual((SkScalar*)&a, (SkScalar*)&b, 4);
     }
 
-    /** return the 4 points that enclose the rectangle
-    */
+    /** return the 4 points that enclose the rectangle (top-left, top-right, bottom-right,
+        bottom-left). TODO: Consider adding param to control whether quad is CW or CCW.
+     */
     void toQuad(SkPoint quad[4]) const;
 
     /** Set this rectangle to the empty rectangle (0,0,0,0)
     */
     void setEmpty() { memset(this, 0, sizeof(*this)); }
 
     void set(const SkIRect& src) {
         fLeft   = SkIntToScalar(src.fLeft);
         fTop    = SkIntToScalar(src.fTop);
         fRight  = SkIntToScalar(src.fRight);
@@ skipping 300 matching lines @@
      */
     void sort();
 
     /**
      *  cast-safe way to treat the rect as an array of (4) SkScalars.
      */
     const SkScalar* asScalars() const { return &fLeft; }
 };
 
 #endif