import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import javax.imageio.ImageIO;
import org.lwjgl.util.vector.Vector2f;

public final class YourThing {

    int transformToInt(float vectorComponent) {
        return (int) ((vectorComponent + 1f) * 127.5f);
    }

    void main() {
        File file = new File("imageOut");
        String format = "PNG";
        int width = 512;
        int height = 512;

        BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB);
        Vector2f center = new Vector2f(width / 2 - 1, height / 2 - 1);

        // [0, 0] refers to the top left, I believe
        for (int x = 0; x < width; x++) {
            for (int y = 0; y < height; y++) {
                Vector2f vectorFromCenter = new Vector2f(x, y);
                Vector2f.sub(vectorFromCenter, center, vectorFromCenter);
                vectorFromCenter.x *= -1f;
                vectorFromCenter.normalise();
                // vectorFromCenter contains the direction vector from, you guessed it, the center of the image

                int red = transformToInt(vectorFromCenter.x);
                int green = transformToInt(vectorFromCenter.y);
                int blue = 0;
                int alpha = 255;
                image.setRGB(x, y, (alpha << 24) | (red << 16) | (green << 8) | blue);
            }
        }

        try {
            ImageIO.write(image, format, file);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}