Android编程实现擦除Bitmap中某一块的方法

public static Bitmap setTransparentAreaForBitmap(Bitmap b,
    int width, int height, int paddingleft, int paddingtop) {
  if (b == null) {
    return null;
  }
  int []pix = new int[width * height];
  for (int j = 0; j < height; j++) {
    for (int i = 0; i < width; i++) {
      int index = j * width + i;
      pix[index] = 0x00000000;
    }
  }
  b.setPixels(pix, 0, width, paddingleft, paddingtop, width, height);
  return b;
}