http://members.chello.at/~easyfilter/bresenham.html のPython版　直線と円

bresenham.py

# http://members.chello.at/~easyfilter/bresenham.html

import math

size(420, 420)
noSmooth()
background(0)
stroke(255)
        
def plotLine(x0, y0, x1, y1):
    dx =  math.fabs(x1-x0)
    dy = -math.fabs(y1-y0) 
    sx = 1 if x0 < x1 else -1
    sy = 1 if y0 < y1 else -1
    err = dx + dy
    
    while True:
        point(x0,y0)
        if x0 == x1 and y0 == y1: 
            break

        e2 = 2*err

        if e2 >= dy:
            err = err + dy
            x0 = x0 + sx
        
        if e2 <= dx:
            err = err + dx
            y0 = y0 + sy


def plotCircle(xm, ym, r):
    x = -r
    y = 0
    err = 2-2*r; # II. Quadrant 
    
    while True:
        point(xm-x, ym+y); #   I. Quadrant
        point(xm-y, ym-x); #  II. Quadrant
        point(xm+x, ym-y); # III. Quadrant
        point(xm+y, ym+x); #  IV. Quadrant
        r = err
        
        if r <= y:
            y += 1
            err += y*2+1   # e_xy+e_y < 0
      
        if r > x or err > y:
            x += 1
            err += x*2+1;  # e_xy+e_x > 0 or no 2nd y-step
        
        if x >= 0: 
            break
        
for th in range(0, 360, 30):
    x = math.cos(math.radians(th))*200
    y = math.sin(math.radians(th))*200
    plotLine(210, 210, int(210+x), int(210+y))

for r in range(50, 201, 50):
    plotCircle(210, 210, r)