# This program draws a moving "car" with rotating wheel.s
# It demonstrates the use of the glPushMatrix and glPopMatrix to
# create a hierarchy of transformations.

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

angle = 0
carPosition = [-0.5, 0, 0]
carDirection = 1
prevTime = time.time()

def drawWheel():
	glBegin(GL_QUADS)
	glVertex2f(-0.08, -0.08)
	glVertex2f(0.08, -0.08)
	glVertex2f(0.08, 0.08)
	glVertex2f(-0.08, 0.08)
	glEnd()

def drawCar():
	glPushMatrix()
	glTranslatef(carPosition[0], carPosition[1], carPosition[2])
	glBegin(GL_QUADS)
	glVertex2f(-0.3, 0.0)
	glVertex2f(0.3, 0.0)
	glVertex2f(0.3, 0.2)
	glVertex2f(-0.3, 0.2)
	glEnd()

	glColor3f(1, 1, 0)

	glPushMatrix()
	glTranslatef(-0.2, 0.0, 0.0)

	glRotatef(angle, 0, 0, 1)
	drawWheel()

	glPopMatrix()

	glColor3f(1, 0, 0)

	glPushMatrix()
	glTranslatef(0.2, 0.0, 0.0)
	glRotatef(angle, 0, 0, 1)
	drawWheel()
	glPopMatrix()
	glPopMatrix()

def draw():
	global angle
	glLoadIdentity()
	glClear(GL_COLOR_BUFFER_BIT)

	glColor3f(0, 0, 1)

	drawCar()

	glutSwapBuffers()


def keyboard(key, x, y):
	if key == chr(27):
		sys.exit(0)

def update():
	global angle, carPosition, carDirection
	global prevTime
	currentTime = time.time()
	deltaTime = currentTime - prevTime
	prevTime = currentTime
	angle = angle - 180 * deltaTime * carDirection
	carPosition[0] = carPosition[0] + deltaTime * carDirection
	if carPosition[0] * carDirection > 1:
		carDirection = -carDirection
	glutPostRedisplay()

glutInit([])
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB)
glutInitWindowSize(300, 300)
glutInitWindowPosition(0,0)
glutCreateWindow(sys.argv[0])
glutDisplayFunc(draw)
glutKeyboardFunc(keyboard)
glutIdleFunc(update)
glutMainLoop()