fast algorithm for drawing filled circles?

Question

I am using Bresenham's circle algorithm for fast circle drawing. However, I also want to (at the request of the user) draw a filled circle.

Is there a fast and efficient way of doing this? Something along the same lines of Bresenham?

The language I am using is C.

Answer 1

Here's a C# rough guide (shouldn't be that hard to get the right idea for C) - this is the "raw" form without using Bresenham to eliminate repeated square-roots.

Bitmap bmp = new Bitmap(200, 200);

int r = 50; // radius
int ox = 100, oy = 100; // origin

for (int x = -r; x < r ; x++)
{
    int height = (int)Math.Sqrt(r * r - x * x);

    for (int y = -height; y < height; y++)
        bmp.SetPixel(x + ox, y + oy, Color.Red);
}

bmp.Save(@"c:\users\dearwicker\Desktop\circle.bmp");

Answer 2

I would just generate a list of points and then use a polygon draw function for the rendering.

Answer 3

Having read the Wikipedia page on Bresenham's (also 'Midpoint') circle algorithm, it would appear that the easiest thing to do would be to modify its actions, such that instead of

setPixel(x0 + x, y0 + y);
setPixel(x0 - x, y0 + y);

and similar, each time you instead do

lineFrom(x0 - x, y0 + y, x0 + x, y0 + y);

That is, for each pair of points (with the same y) that Bresenham would you have you plot, you instead connect with a line.

Answer 4

Just use brute force. This method iterates over a few too many pixels, but it only uses integer multiplications and additions. You completely avoid the complexity of Bresenham and the possible bottleneck of sqrt.

for(int y=-radius; y<=radius; y++)
    for(int x=-radius; x<=radius; x++)
        if(x*x+y*y <= radius*radius)
            setpixel(origin.x+x, origin.y+y);