Java获取透明，渐变叠加的像素颜色

Question

In my application I have an image (world map) as background picture. Over this background picture, there is a polygon with a color gradient and transparent filling effect.

Here you find a code snippet of the overlay:

public void paint(Graphics g) {

      //draw a polygon with a gradient filling effect
      Graphics2D g2 = (Graphics2D)g;
      GradientPaint gp = new GradientPaint(x1, y1, color1, x2, y2, color2, false);
      g2.setPaint(gp);
      g2.fill(polygon);

}

Does somebody know a method to get the color of one pixel of the overlay ? I don't need the color, which can be seen on the screen including the background picture - just the color of the overlay.

Best regards,

Michael

Answer 1

This is somewhat ugly, but works:

GradientPaint gp = new GradientPaint(0, 0, new Color(255, 0, 0, 50), 
                                   10, 10, new Color(128, 255, 0, 150));

ColorModel cm = ColorModel.getRGBdefault();
Rectangle r = new Rectangle(0, 0, 10, 10);
Raster raster = gp.createContext(cm, r, r, new AffineTransform(), null)
                  .getRaster(0, 0, 10, 10);

int[] rgba = raster.getPixel(5, 5, (int[])null);

Alternately, you could just paint the overlay into a BufferedImage (which you had first cleared to transparent).