#!/usr/bin/env python

from __future__ import division
import gtk
import math

def B(x,y,z):
	return (1-y/2, x/2-1, 0)

def E(x,y,z):
	return (x/2-1, y/2-1, 0)

def repaint(widget, event):
	window = widget.window
	GC = window.new_gc()
	def get_a_angle(x1,y1,x2,y2):
		l = math.sqrt((x2-x1)**2+(y2-y1)**2)
		if l == 0:
			return None
		#(x2-y1,y2-y1) inproduct (1, 0)=(cos a)*l
		return math.acos((x2-x1)/l) * 360*64 / (math.pi * 2)

	def draw_line(x1,y1,x2,y2):
		window.draw_line(GC, x1 * 50,300 - y1 * 50,x2 * 50,300 - y2 * 50)

	def draw_arrow(x1,y1,x2,y2):
		draw_line(x1,y1,x2,y2)
		angle = get_a_angle(x1,y1,x2,y2)
		if angle is not None:
			start_angle = angle - 64 * 60
			end_angle = angle + 64 * 60
		else:
			start_angle = 0
			end_angle = 360 * 64
		window.draw_arc(GC, False, x2 * 50 - 5, 300 - y2 * 50 - 5, 10, 10, start_angle, end_angle)

	for x in [1,2,3]:
		GC.set_rgb_fg_color(gtk.gdk.Color(0, 0, 0xF000))
		draw_arrow(x, -5, x, +5)
		for y in [1,2,3]:
			GC.set_rgb_fg_color(gtk.gdk.Color(0, 0, 0xF000))
			draw_arrow(-5, y, 5, y)
			GC.set_rgb_fg_color(gtk.gdk.Color(0, 0, 0))
			B1 = B(x,y,0)
			E1 = E(x,y,0)
			GC.line_width = 2
			draw_arrow(x, y, x + E1[0], y + E1[1])
			GC.set_rgb_fg_color(gtk.gdk.Color(0x8000, 0, 0))
			draw_arrow(x, y, x + B1[0], y + B1[1])
			GC.line_width = 1

drawing_area = gtk.DrawingArea()
drawing_area.connect("expose-event", repaint)
drawing_area.show()

window = gtk.Window()
window.connect("delete-event", gtk.main_quit)
window.add(drawing_area)
window.show()

gtk.main()