add: glutIdleFunc(display);
context: int setupGLUT(int *argc, char *argv[]){    glutInit(argc, argv);    glutInitDisplayMode(GLUT_RGB | GLUT_DEPTH | GLUT_DOUBLE);        int winid = glutCreateWindow("OpenSG");        glutReshapeFunc(reshape);    glutDisplayFunc(display);    glutMouseFunc(mouse);    glutMotionFunc(motion);    glutKeyboardFunc(keyboard);    return winid;}