#!/usr/bin/env python
#
# Use a random walk to produce an approximation to the Sierpinski Gasket.
# Graphics rendered in Cairo/GTK

import pygtk
pygtk.require('2.0')
import gtk
import math
import random

# how many iterations to do on each click
iters = 10

# work out sqrt(3) now, as we'll be using it later
sqrt3 = math.sqrt(3)
tan30 = math.tan(math.pi/6)

# the points of the main triangle
top    = 20
bottom = int(20+200*sqrt3)
left   = 20
right  = 420
triangle = [(left, bottom), ((left+right)/2, top), (right, bottom)]

def point_in_triangle(point):
    if point[1] == bottom:         # point is on bottom line, so
        return True                # guaranteed to be in triangle

    if point[0] == (left+right)/2: # point is on middle line, so
        return True                # guaranteed to be in triangle

    # calculate height up from bottom
    dist_up = bottom - point[1]

    # calculate how far in the sides are at the height relevant
    dist_in = dist_up * tan30

    if left+dist_in <= point[0] <= right-dist_in:
        return True

    # can't be in triangle
    return False

def midpoint(point1, point2):
    return ((point1[0]+point2[0])/2, (point1[1]+point2[1])/2)

class SierpinskiWin(object):
    point_list = [] # the list of points added already
    def __init__(self):
        window = gtk.Window(gtk.WINDOW_TOPLEVEL)
        window.set_title("Sierpinski's Gasket")
        window.connect("destroy", lambda w: gtk.main_quit())
        window.set_size_request(440, 400)

        self.area = gtk.DrawingArea()
        self.area.set_events(gtk.gdk.BUTTON_PRESS_MASK | gtk.gdk.EXPOSURE_MASK)
        self.area.set_size_request(220, 200)
        self.pangolayout = self.area.create_pango_layout("")

        window.add(self.area)

        self.area.connect("expose-event", self.area_expose_cb)
        self.area.connect("button_press_event", self.clicked_cb)
        self.area.show()
        window.show()

    def area_expose_cb(self, area, event):
        self.style = self.area.get_style()
        self.gc = self.style.fg_gc[gtk.STATE_NORMAL]
        self.gc.line_width = 2
        self.area.window.draw_polygon(self.gc, False, triangle)
        for point in self.point_list:
            self.area.window.draw_point(self.gc, *point)
        return True

    started = False # has the random walk started?
    next = (0, 0)
    def clicked_cb(self, area, event):
        if not self.started:
            self.next = int(event.x), int(event.y)
            if point_in_triangle(self.next):
                self.area.window.draw_point(self.gc, *self.next)
                self.point_list.append(self.next)
                self.started = True
        else:
            for i in range(10):
                self.next = midpoint(self.next, random.choice(triangle))
                self.point_list.append(self.next)
                self.area.window.draw_point(self.gc, *self.next)

    def main(self):
        gtk.main()
        return 0

if __name__ == "__main__":
    sw = SierpinskiWin()
    sw.main()