#Bresenham Circle from "Jim Blinn's Corner" on "Graph Paper"
#Modified from program in Python/Tkinter by William Baker
#Emily Gunawan, Summer 2004, illiMath04 Program
#University of Illinois Urbana-Champaign Dept. of Math

import Tkinter
import math
import time

defaldelay=4 #default delay time

#******************************************************************************#
mag=10                  #magnification of the quadrille paper 
x0=400.0 ; y0=300.0    #(0,0) position on the x,y axis 

#******************************************************************************#
def pixset(x,y):         #set a blue box at (x,y)
    x=x0 + x*mag ; y= y0+y*mag
    canvas.create_rectangle(x,y,x+mag,y+mag,fill="blue")

#******************************************************************************#
def startAnimation(): #start animation when the start button is clicked
    ix=0
    iy=120/mag
    ie=0
    while abs(ix) <= iy:
        if (ie < 0):
            ie = ie + iy + iy -1
            iy = iy - 1
        ie = ie - ix - ix - 1
        ix = ix + 1
        pixset(ix,iy); pixset(iy,ix)
	pixset(-ix,iy); pixset(iy,-ix)
	pixset(ix,-iy); pixset(-iy,ix)
	pixset(-ix,-iy); pixset(-iy,-ix)
    	canvas.update()
    time.sleep(int(timedelay.get())/20.0)

#******************************************************************************#
def clear(): #clears the canvas when the clear button is clicked 
    canvas.delete("all")

#******************************************************************************#
window = Tkinter.Tk()
window.title("'Bresenham Circle on Graph Paper in Python/Tkinter")

clear_button = Tkinter.Button(window, text = "Clear", command = clear)

start = Tkinter.Button(window, text="Start", command=startAnimation)
delLabel=Tkinter.Label(window, width="15")
delLabel.configure(text="Time Delay= ")
timedelay=Tkinter.StringVar()
timedelay.set(`defaldelay`)
delentry = Tkinter.Entry(window, width="15", textvariable=timedelay)

canvas = Tkinter.Canvas(window, width=x0*2, height=2*y0)

canvas.pack(side="top")
delLabel.pack(side="left")
delentry.pack(side="left")
start.pack(side="right")
clear_button.pack(side = "right")
canvas.create_line(0,y0,2*x0,y0, fill="pink")   #x-axis
canvas.create_line(x0,0,x0,2*y0, fill="orange") #y-axis
window.mainloop() #start event loop