#!/usr/bin/env python

import pygame
from pygame.locals import *


def circle_draw( x, y, radius, color, antialias, surf ):
    def draw_points( x0, y0, ox, oy ):
        surf.set_at( ( x0 + ox, y0 + oy ), color )
        surf.set_at( ( x0 + ox, y0 - oy ), color )
        surf.set_at( ( x0 - ox, y0 + oy ), color )
        surf.set_at( ( x0 - ox, y0 - oy ), color )

        surf.set_at( ( x0 + oy, y0 + ox ), color )
        surf.set_at( ( x0 + oy, y0 - ox ), color )
        surf.set_at( ( x0 - oy, y0 + ox ), color )
        surf.set_at( ( x0 - oy, y0 - ox ), color )
    # draw_points()

    def trivial( x, y, radius, color, surf ):
        """Uses floating point operations to calculate values"""
        from math import ceil, sqrt
        for ox in xrange( 0, int(ceil( float(radius) / sqrt(2) )) ):
            oy = sqrt( radius ** 2 - ox ** 2 )
            draw_points( x, y, int(ox), int(oy) )
    # trivial()


    def bresenham( x, y, radius, color, surf ):
        """Uses integer only operations to calculate values"""

        ox = 0
        oy = radius
        e = 1 - radius
        while ox <= oy:
            draw_points( x, y, ox, oy )
            e += 2 * ox + 3
            ox += 1
            if e > 0:
                e += 2 - 2 * oy
                oy -= 1
    # bresenham()

    ## Base (correct) circle
    #pygame.draw.circle( surf, Color( "gray50" ), ( x, y ), radius, 5 )
    #trivial( x, y, radius, color, surf )
    bresenham( x, y, radius, color, surf )
# circle_draw()


pygame.init()

screen = pygame.display.set_mode( ( 800, 600 ) )
screen.fill( Color( "black" ) )
circle_draw( 100, 100, 50, Color( "green" ), 0, screen )


run = True
clock = pygame.time.Clock()
while run:
    for e in pygame.event.get():
        if e.type == QUIT or \
               e.type == KEYDOWN and e.key == K_ESCAPE:
            run = False
    pygame.display.flip()
    clock.tick( 24 )