Replace only the corners of a rotated image with a different color

Question

I am currently making a game that requires the rotating of an image. In order to rotate it, I am using the following code.

public ManipulableImage rotate(double degrees){
    BufferedImage rotatedImage = new BufferedImage(image.getWidth(), image.getHeight(), BufferedImage.TYPE_INT_RGB);
    Graphics2D g = rotatedImage.createGraphics();
    g.rotate(Math.toRadians(degrees), image.getWidth()/2, image.getHeight()/2);
    /*
    ManipulableImage is a custom class that makes it easier to manipulate
    an image code wise.
    */
    g.drawImage(image, 0, 0, null);
    return new ManipulableImage(rotatedImage, true).replace(0, -1);
}

The code does rotate the image, but it leaves the corners black which should be transparent. My renderer recognizes the rgb value -1 as the transparent value, and doesn't change a pixel when that value is present. So, I would like to change the rgb values of the corners from 0 (black) to -1 (transparent).

The only problem is, I can't simply iterate through the image and replace the black pixels because there are other pixels in the original image that are black. So my question is, how do I replace only the black pixels created by the rotation.

(Sorry I couldn't provide examples of the image, I'm not sure how to screenshot with this computer.)

Answer 1

The graphics object has no context to color these new pixels, so it simply colors them black.

BufferedImage rotatedImage = new BufferedImage(image.getWidth(), image.getHeight(), BufferedImage.TYPE_INT_RGB);

You should be using the following so the BufferedImage supports transparency:

BufferedImage.TYPE_INT_ARGB

Then in the painting code you can use:

g.setColor( new Color(0, 0, 0, 0) );
g.fillRect(0, 0, image.getWidth(), image.getHeight());
g.rotate(...);
g.drawImage(...);