#########################
#                       #
#  Sierpinski triangle  #
#  Live coding demo     #
#  Roman Lossa          #
#  2011-10-06           #
#                       #
#########################


# import turtle module
from turtle import *


# speed up the turtle
speed(0)
delay(0)
hideturtle()


# triangle function
def triangle(dist=400, x="", y=""):
    # end of recursion
    if dist < 5:
        return

    # set start position at first call
    if x=="" or y=="":
        x = -dist/2
        y = -dist/2

    # move to start position
    penup()
    goto(x, y)
    pendown()

    # bottom line
    x1,y1 = position() # start pos of 1st sub triangle
    forward(dist/2)
    x2,y2 = position() # start pos of 2nd sub triangle
    forward(dist/2)
    left(120)
    # right line
    forward(dist)
    left(120)
    # left line
    forward(dist/2)
    x3,y3 = position() # start pos of 3rd sub triangle
    forward(dist/2)
    left(120)

    # draw sub triangles
    triangle(dist/2, x1, y1)
    triangle(dist/2, x2, y2)
    triangle(dist/2, x3, y3)


# speed up drawing
tracer(1000)

# execute
triangle()

# for usability reasons...
exitonclick()