#!/usr/local/bin/python

# This program zooms in & out - it allows the user to vary the orthographic
# projection (the "viewing area") by pressing the q & a keys.

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

halfWidth = 1.0
windowWidth = 500
windowHeight = 500

def draw():
	global halfWidth
	global windowWidth
	global windowHeight
	glMatrixMode(GL_PROJECTION)
	glLoadIdentity()
	gluOrtho2D(-halfWidth, halfWidth, -halfWidth * windowHeight/windowWidth, halfWidth * windowHeight/windowWidth)
	glMatrixMode(GL_MODELVIEW)
	glClear(GL_COLOR_BUFFER_BIT)
	glColor3f(1, 1, 0)
	glBegin(GL_TRIANGLES)
	glVertex2f(0.0, 0.0)
	glVertex2f(0.4, 0.0)
	glVertex2f(0.8, 0.8)
	glEnd()
	glFlush()

def keyboard(key, x, y):
	global halfWidth
	if key == chr(27):
		sys.exit(0)
	elif key == 'q':
		halfWidth = halfWidth / 2.0
		glutPostRedisplay()
	elif key == 'a':
		halfWidth = halfWidth * 2.0
		glutPostRedisplay()

def reshape(w, h):
    global windowWidth
    global windowHeight
    glViewport(0, 0, w, h)
    windowWidth = w
    windowHeight = h

print "Press 'q' to zoom in"
print "Press 'a' to zoom out"
glutInit([])
glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB)
glutInitWindowSize(500, 500)
glutInitWindowPosition(0,0)
glutCreateWindow(sys.argv[0])
glutDisplayFunc(draw)
glutKeyboardFunc(keyboard)
glutReshapeFunc(reshape)
glutMainLoop()