code: public Img round(double arc) {
  		final BufferedImage srcImage = getValidSrcImg();
  		final int width = srcImage.getWidth();
  		final int height = srcImage.getHeight();
  		
  		// 通过弧度占比计算弧度
  		arc = NumberUtil.mul(arc, Math.min(width, height));
  		
  		final BufferedImage targetImage = new BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB);
  		final Graphics2D g2 = targetImage.createGraphics();
  		g2.setComposite(AlphaComposite.Src);
  		// 抗锯齿
  		g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
  		g2.fill(new RoundRectangle2D.Double(0, 0, width, height, arc, arc));
  		g2.setComposite(AlphaComposite.SrcAtop);
  		g2.drawImage(srcImage, 0, 0, null);
  		g2.dispose();
  		this.targetImage = targetImage;
  		return this;
  	}
docs: 图片圆角处理
  
  @param arc 圆角弧度，0~1，为长宽占比
  @return this
  @since 4.5.3