File:Atan2-Red-Blue.png

void atanPlane()
{
        printf("P6\n%d %d 255\n", GridSize, GridSize);

        for(int y=0; y<GridSize; ++y)
        for(int x=0; x<GridSize; ++x)
        {
                const double dy = (GridSize/2)-y;
                const double dx = x - (GridSize/2);
                const double a = atan2(dy,dx)/M_PI;

                unsigned char rgb[4];

                if(a<0)
                {
                        rgb[0] = rgb[1] = 255 + 255*a;
                        rgb[2] = 255 + 127*a;
                }else{
                        rgb[0] = 255;
                        rgb[1] = rgb[2] = 255 - 255*a;
                }

                fwrite(rgb, 3, 1, stdout);
        }
        fflush(stdout);
}