#!/usr/bin/env python

from OpenGL.GL import *
from OpenGL.GLU import *
from OpenGL.GLUT import *

v = ((-1, -.58), (1, -.58), (0, 1.15))


def mid(a,b):
    return ((a[0]+b[0])*.5,
            (a[1]+b[1])*.5)

def divide_triangle(a,b,c,m):
    if m > 0:
        v0 = mid(a,b)
        v1 = mid(a,c)
        v2 = mid(b,c)
        divide_triangle(a, v0, v1, m-1)
        divide_triangle(c, v1, v2, m-1)
        divide_triangle(b, v2, v0, m-1)
    else:
        glVertexPointerf( [a,b,c] )
        glDrawArrays( GL_TRIANGLES, 0, 3 )
    
def init():
    glMatrixMode(GL_PROJECTION)
    glLoadIdentity()
    s = 1.2
    gluOrtho2D(-s,s,-s,s)
    glMatrixMode(GL_MODELVIEW)
    glClearColor(1,1,1,1) # white background
    glColor3f(0,0,0)      # draw in black
    glEnableClientState( GL_VERTEX_ARRAY )

def display():
    glClear(GL_COLOR_BUFFER_BIT)
    divide_triangle(v[0], v[1], v[2], n)
    glFlush()

    
if __name__ == '__main__':

    import sys, string

    try:
        n = string.atoi(sys.argv[1])
    except:
        n = 5

    glutInit([])
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB)
    glutInitWindowSize(700,700)
    glutCreateWindow('Sierpinski gasket -- Recursive')
    glutDisplayFunc(display)
    init()
    glutMainLoop()