graphics - Drawing a part of an image (Java)

Question

Here's my problem- I'm trying to draw a circular part of a single image.

I'm doing some work on a top-down dungeon crawler sort of game, and I'm attempting to make a light radius around the player. The floor is a single image, and I need to draw only a small, circular part of it. I've been looking at this method:

drawImage(Image img,
          int dx1, 
          int dy1,
          int dx2,
          int dy2,
          int sx1,
          int sy1,
          int sx2,
          int sy2,
          Color bgcolor, 
          ImageObserver observer) 

But, that looks like it would only draw a square subsection. Does anyone happen to know an easier method than drawing tons of little squares to give the illusion of a circle?

Thanks

Answer 1

The neatest effect for a light radius would be to use an overlay with a gradient in its alpha channel.

Something like this:

// do this once during setup
overlay = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGBA);
for (int x = 0; x < width; ++x)
{
    for (int y = 0; y < height; ++y)
    {
        double range = 100;
        double distance = Math.sqrt(Math.pow(x - width / 2, 2) + Math.pow(y - height / 2, 2));
        int value = Math.max(100, (int)Math.round(255 - 100 * distance / range));
        overlay.setRGB(x, y, new Color(0, 0, 0, value));
    }
}
....
// do this every frame
gfx.drawImage(overlay, 0, 0, null);

I did not compile this so it's probably full of errors!

If you want some "flicker" in it you can generate several maps, and add some noise to the alpha values. Or even tune the colors so you get warmer light.