我们要做的第一件事是制作一个基于“alpha”的蒙版，以遮盖我们想要透明的区域。为此，我使用了RadialGradientPaint，因为它允许我在边缘周围产生“淡入淡出”效果。

现在，我已经完成了所有的计算（使用一个简单的图像编辑器来计算），所以我知道我想要“洞”出现在哪里

BufferedImage city = ImageIO.read(new File("/Users/swhitehead/Downloads/City.jpg"));

BufferedImage mask = new BufferedImage(city.getWidth(), city.getHeight(), BufferedImage.TYPE_INT_ARGB);

Graphics2D g2d = mask.createGraphics();
Color transparent = new Color(255, 0, 0, 0);
Color fill = Color.RED;
RadialGradientPaint rgp = new RadialGradientPaint(
                new Point2D.Double(955, 185),
                185,
                new float[]{0f, 0.75f, 1f},
                new Color[]{transparent, transparent, fill});
g2d.setPaint(rgp);
g2d.fill(new Rectangle(0, 0, mask.getWidth(), mask.getHeight()));
g2d.dispose();

接下来，我们使用AlphaComposite在原始（城市）图像上绘制蒙版......

BufferedImage masked = new BufferedImage(city.getWidth(), city.getHeight(), BufferedImage.TYPE_INT_ARGB);
g2d = masked.createGraphics();
g2d.setColor(Color.RED);
g2d.fillRect(0, 0, masked.getWidth(), masked.getHeight());
g2d.drawImage(city, 0, 0, null);
g2d.setComposite(AlphaComposite.DstAtop);
g2d.drawImage(mask, 0, 0, null);
g2d.dispose();

我们将masked图像与背景图像结合起来......

BufferedImage composite = new BufferedImage(city.getWidth(), city.getHeight(), BufferedImage.TYPE_INT_ARGB);
g2d = composite.createGraphics();
g2d.drawImage(background, city.getWidth() - background.getWidth(), 0, null);
g2d.drawImage(masked, 0, 0, null);
g2d.dispose();