code: private static BufferedImage draw(BufferedImage backgroundImg, Image img, Rectangle rectangle, float alpha) {
  		final Graphics2D g = backgroundImg.createGraphics();
  		g.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_ATOP, alpha));
  		g.drawImage(img, rectangle.x, rectangle.y, rectangle.width, rectangle.height, null); // 绘制切割后的图
  		g.dispose();
  		return backgroundImg;
  	}
docs: 将图片绘制在背景上
  
  @param backgroundImg 背景图片
  @param img 要绘制的图片
  @param rectangle 矩形对象，表示矩形区域的x，y，width，height，x,y从背景图片中心计算
  @return 绘制后的背景