Circle fill

Does anyone know of a FAST circle fill algorithm?
In the form of:

void circleFill(float xCentre, float yCentre, float Radius)
???

You can use billboarding. Draw a square with a texture. For different radius, adjust the size of it’s width and height. The texture contain the image of circle. Inside the circle alpha is 1,outside 0.For better result, use a mipmap texture with filtering to reduce jagged edge.

Or a triangle fan.