Simple algorithm for drawing filled ellipse in C/C++

Question

On SO, found the following simple algorithm for drawing filled circles:

for(int y=-radius; y<=radius; y++)
    for(int x=-radius; x<=radius; x++)
        i         


        

Answer 1

An ellipse (about the origin) is a circle that has been linearly stretched along the x or y axes. So you can modify your loop like this:

for(int y=-height; y<=height; y++) {
    for(int x=-width; x<=width; x++) {
        double dx = (double)x / (double)width;
        double dy = (double)y / (double)height;
        if(dx*dx+dy*dy <= 1)
            setpixel(origin.x+x, origin.y+y);
    }
}

You can see that if width == height == radius, then this is equivalent to your code for drawing a circle.