AlphaPatternDrawable.java 文件源码

/**
 * This will generate a bitmap with the pattern as big as the rectangle we were allow to draw on.
 * We do this to chache the bitmap so we don't need to recreate it each time draw() is called since it takes a few milliseconds
 */
private void generatePatternBitmap() {
  if (getBounds().width() <= 0 || getBounds().height() <= 0) {
    return;
  }

  bitmap = Bitmap.createBitmap(getBounds().width(), getBounds().height(), Config.ARGB_8888);
  Canvas canvas = new Canvas(bitmap);

  Rect r = new Rect();
  boolean verticalStartWhite = true;
  for (int i = 0; i <= numRectanglesVertical; i++) {
    boolean isWhite = verticalStartWhite;
    for (int j = 0; j <= numRectanglesHorizontal; j++) {
      r.top = i * rectangleSize;
      r.left = j * rectangleSize;
      r.bottom = r.top + rectangleSize;
      r.right = r.left + rectangleSize;
      canvas.drawRect(r, isWhite ? paintWhite : paintGray);
      isWhite = !isWhite;
    }
    verticalStartWhite = !verticalStartWhite;
  }
}