GLUT_DEPTH
displayMode = GLUT_RGB | GLUT_SINGLE | GLUT_DEPTH;
if (gState.displayMode & GLUT_DEPTH)
#define GLUT_WIND_HAS_DEPTH(x) (((x) & GLUT_DEPTH) != 0)
glutInitDisplayMode(GLUT_RGB | GLUT_DEPTH | GLUT_DOUBLE);
glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGBA | GLUT_DEPTH);