FreeGLUT non-blocking drawing demo

freeglut_demo.py

#!/usr/bin/env python3

# Shows us to use non-blocking event loop from FreeGLUT. Original code from
# https://code.activestate.com/recipes/325391-open-a-glut-window-and-draw-a-sphere-using-pythono/

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

name = 'ball_glut'
closed = False

def on_close():
    global closed
    closed = True

def glut_init():
    print('Starting glut_init()')
    glutInit(sys.argv)
    glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH)
    glutInitWindowSize(400,400)
    glutCreateWindow(name)
    freeglut.glutSetOption(freeglut.GLUT_ACTION_ON_WINDOW_CLOSE,
                           freeglut.GLUT_ACTION_GLUTMAINLOOP_RETURNS)
    freeglut.glutCloseFunc(on_close)

    glClearColor(0.,0.,0.,1.)
    glShadeModel(GL_SMOOTH)
    glEnable(GL_CULL_FACE)
    glEnable(GL_DEPTH_TEST)
    glEnable(GL_LIGHTING)
    lightZeroPosition = [10.,4.,10.,1.]
    lightZeroColor = [0.8,1.0,0.8,1.0] #green tinged
    glLightfv(GL_LIGHT0, GL_POSITION, lightZeroPosition)
    glLightfv(GL_LIGHT0, GL_DIFFUSE, lightZeroColor)
    glLightf(GL_LIGHT0, GL_CONSTANT_ATTENUATION, 0.1)
    glLightf(GL_LIGHT0, GL_LINEAR_ATTENUATION, 0.05)
    glEnable(GL_LIGHT0)
    glutDisplayFunc(display)
    glMatrixMode(GL_PROJECTION)
    gluPerspective(40.,1.,1.,40.)
    glMatrixMode(GL_MODELVIEW)
    gluLookAt(0,0,10,
              0,0,0,
              0,1,0)
    glPushMatrix()

def display():
    glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT)
    glPushMatrix()
    color = [1.0,0.,0.,1.]
    glMaterialfv(GL_FRONT,GL_DIFFUSE,color)
    glutSolidSphere(2,20,20)
    glPopMatrix()
    glutSwapBuffers()

def main():
    glut_init()
    print('Starting to render stuff')
    try:
        while not closed:
            print('Running render')
            freeglut.glutMainLoopEvent()
            print('Waiting 0.1s')
            time.sleep(0.1)
    finally:
        print('Done, killing window')
        # Sometimes (e.g when ctrl+c-ing) this will lead to an illegal
        # instruction error, but I have no idea how to fix that.
        freeglut.glutLeaveMainLoop()
    print('Program will exit now (hopefully!)')

if __name__ == '__main__':
    main()