# Demonstration of depth buffering
#
# This program takes the code from class 9's orbit3d demo, and adds depth
# buffering calls.  When depth buffering is active, the orbiting yellow
# planet will be properly hidden by the blue and red planets when it passes
# behind them.
# Depth buffering is toggled on & off by pressing the space bar.

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

useDepthBuffer = 0

angle0 = 0
angle1 = 90
angle2 = 0
prevTime = time.time()

def drawPlanet(radius, color):
	glColor3fv(color)
	glBegin(GL_QUADS)
	glVertex2f(-radius, -radius)
	glVertex2f(radius, -radius)
	glVertex2f(radius, radius)
	glVertex2f(-radius, radius)
	glEnd()
	
def draw():
	global angle0, angle1, angle2, useDepthBuffer

	if useDepthBuffer:
		glEnable(GL_DEPTH_TEST)
	else:
		glDisable(GL_DEPTH_TEST)

	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)
	glLoadIdentity()
#	glTranslatef(0, 0, -2)

	drawPlanet(0.2, [0, 0, 1])

	glPushMatrix()
	glRotatef(angle0, 1, 0, 0)
	glTranslatef(0.6, 0.0, 0.0)
	drawPlanet(0.1, [1, 0, 0])
	glPopMatrix()

	glPushMatrix()

	glRotatef(angle1, 0, 1, 0)
	glTranslatef(0.7, 0.0, 0.0)
	drawPlanet(0.08, [1, 1, 0])

	glPushMatrix()
	glRotatef(angle2, 0, 0, 1)
	glTranslatef(0.2, 0.0, 0.0)
	drawPlanet(0.03, [0.25, 1, 0.25])
	glPopMatrix()

	glPopMatrix()

	glutSwapBuffers()


def keyboard(key, x, y):
	if key == chr(27):
		sys.exit(0)
	elif key == ' ':
		global useDepthBuffer
		useDepthBuffer = not useDepthBuffer
		if useDepthBuffer:
			print "depth buffering on"
		else:
			print "depth buffering off"

def update():
	global angle0, angle1, angle2
	global prevTime
	currentTime = time.time()
	deltaTime = currentTime - prevTime
	prevTime = currentTime
	angle0 = angle0 + 120 * deltaTime
	angle1 = angle1 + 60 * deltaTime
	angle2 = angle2 + 270 * deltaTime
	glutPostRedisplay()

glutInit(sys.argv)
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH)
glutInitWindowSize(400, 400)
glutInitWindowPosition(0,0)
glutCreateWindow(sys.argv[0])
glutDisplayFunc(draw)
glutKeyboardFunc(keyboard)
print "Hit space bar to toggle depth buffering on or off"
print "Depth buffering is off to start with"
glutIdleFunc(update)
#glMatrixMode(GL_PROJECTION)
#gluPerspective(60, 1, 1, 100)
#glMatrixMode(GL_MODELVIEW)
glEnable(GL_DEPTH_TEST)
glutMainLoop()