Plot circles with centre and radius

Question

I am currently in the progress of using WritableRaster and it's setPixed method, and I need it to not set only one pixel, but a 'circle' with the radius of r. What I am thinking about is something like this:

for(int y = -r; y < r; y++)
{
    for(int x = -r; x < r; x++)
    {
         raster.setPixel(x,y,color);
 }}

The question is, would this work to make a circle, if so, how would I make it go through all the pixels inside?

Thanks in advance!

EDIT: Sorry I did not make this clear- I am making a rubber tool on a transparent canvas, thus, if I draw a circle with transparent color, it won't delete what was there before... This is why I am using setPixel.

EDIT EDIT: This is what the output of the code is (on g2d, using drawLine with same values so it only fills one pixel as in the method setPixel): https://i.sstatic.net/9ONWe.png

EDIT EDIT EDIT: If anyone wants to use this code for the same reason, I recommend using BufferedImage.setRGB() because it's much quicker. If you don't know what to do with the color (last parameter), use something like:

...
buffImg.setRGB(x,y,new Color(r,g,b,a).getRGB());
...

Answer 1

You would have to fill in each line individually as you are doing, but note that you have to adjust the bounds of x for the radius. This is somewhat similar to doing a 2D (discrete) integration. The basic idea is that x^2 + y^2 = r^2 at the outer bounds, and both y and r are fixed, so...:

for(int y = -r; y < r; y++)
{
    int bound = (int)(sqrt(r * r - y * y) + 0.5);
    for(int x = -bound; x < bound; x++)
    {
         raster.setPixel(x,y,color);
    }
}

... + 0.5 is a safe way to round to the nearest integer (instead of just taking the floor with casting) since bound will always be positive.