# PyPredPrey.py

from OpenGL.GL import *
from OpenGL.GLU import *
from OpenGL.GLUT import *
from random import *
from numpy import *
import sys

#  Initial values of width and height
width = 250
height = 250
				
def init():
	# White background
	glClearColor(1.0, 1.0, 1.0, 0.0)
		
	#  Set the projection matrix... our "view"
	glMatrixMode(GL_PROJECTION)
	glLoadIdentity()
	
	#  Set the plot window range
	gluOrtho2D(0,10,0,6)
	
	#  Set the matrix for the object we are drawing
	glMatrixMode(GL_MODELVIEW)
	glLoadIdentity()

def plotFunc():
	
	# habitat and population parameters
	a = .7
	b = .5
	c = .3
	e = .2
	
	# time increment
	dt = .001
	
	# initial populations
	x = .5
	y = .5
	
	glClear(GL_COLOR_BUFFER_BIT)
	glBegin(GL_POINTS)
	for n in arange(0,10,.0001):
		
		# predator-prey equations
		x = x + (a*x - b*x*y)*dt
		y = y + (-c*y + e*x*y)*dt
		
		# parametric plot
		glColor3f(0.0,0.0,0.00)
		glVertex2f(x,y)
		
		# prey
		glColor3f(1.0, 0.0, 0.0)
		glVertex2f(n,x)
		
		# predator
		glColor3f(0.0, 0.0, 1.0)
		glVertex2f(n,y)
	
	glVertex2f(x,y)
	glEnd()
	glFlush()
		
def keyboard(key, x, y):
	#  Allows us to quit by pressing 'Esc' or 'q'
	if key == chr(27):
		sys.exit()
	if key == "q":
		sys.exit()

def main():
	
	glutInit(sys.argv)
	glutInitDisplayMode(GLUT_RGB|GLUT_SINGLE)
	glutInitWindowPosition(100,100)
	glutInitWindowSize(width,height)
	glutCreateWindow("Predator Prey Simulation")
	glutDisplayFunc(plotFunc)
	glutKeyboardFunc(keyboard)
	
	init()	
	glutMainLoop()

main()