Implement canvas's globalCompositeOperation lighter properly....

skia/include/SkMask.h

 /*
  * Copyright (C) 2006 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
@@ skipping 22 matching lines @@
     
     enum {
         kCountMaskFormats = kLCD_Format + 1
     };
 
     uint8_t*    fImage;
     SkIRect     fBounds;
     uint16_t    fRowBytes;
     uint8_t     fFormat;    // Format
 
+    /** Returns true if the mask is empty: i.e. it has an empty bounds.
+     */
+    bool isEmpty() const { return fBounds.isEmpty(); }
+
     /** Return the byte size of the mask, assuming only 1 plane.
-        Does not account for k3D_Format. For that, use computeFormatImageSize()
+        Does not account for k3D_Format. For that, use computeTotalImageSize()
+        If there is an overflow of 32bits, then returns 0.
     */
     size_t computeImageSize() const;
     /** Return the byte size of the mask, taking into account
         any extra planes (e.g. k3D_Format).
+        If there is an overflow of 32bits, then returns 0.
     */
     size_t computeTotalImageSize() const;
 
     /** Returns the address of the byte that holds the specified bit.
         Asserts that the mask is kBW_Format, and that x,y are in range.
         x,y are in the same coordiate space as fBounds.
     */
     uint8_t* getAddr1(int x, int y) const
     {
         SkASSERT(fFormat == kBW_Format);
@@ skipping 18 matching lines @@
     
     enum CreateMode {
         kJustComputeBounds_CreateMode,      //!< compute bounds and return
         kJustRenderImage_CreateMode,        //!< render into preallocate mask
         kComputeBoundsAndRenderImage_CreateMode  //!< compute bounds, alloc image and render into it
     };
 };
 
 #endif