case XK_Control_R: special = GLUT_KEY_CTRL_R; break;
case XK_Alt_L: special = GLUT_KEY_ALT_L; break;
case XK_Alt_R: special = GLUT_KEY_ALT_R; break;
case XK_Control_R: special = GLUT_KEY_CTRL_R; break;
case XK_Alt_L: special = GLUT_KEY_ALT_L; break;
case XK_Alt_R: special = GLUT_KEY_ALT_R; break;