glutPostRedisplay marks the current window as needing to be redisplayed.
Mark the normal plane of current window as needing to be redisplayed. The next iteration through glutMainLoop, the window's display callback will be called to redisplay the window's normal plane. Multiple calls to glutPostRedisplay before the next display callback opportunity generates only a single redisplay callback. glutPostRedisplay may be called within a window's display or overlay display callback to re-mark that window for redisplay.
Logically, normal plane damage notification for a window is treated as a glutPostRedisplay on the damaged window. Unlike damage reported by the window system, glutPostRedisplay will not set to true the normal plane's damaged status (returned by glutLayerGet(GLUT_NORMAL_DAMAGED).
Also, see glutPostOverlayRedisplay.