glutPostRedisplay

I am looking at this function, still need a way to post an external event to “main loop” and do not understand how / why this was posted elsewhere:

“put glutPostRedisplay in timer loop to be executed when timer expires”

Since the OpenGL process is “stuck” in glutMainLoop(); how it can run a (software) timer loop ?
Also putting glutPostRedisplay; inside callback function which does display already seems illogical / redundant.

I there something amiss here?

Sure looks as it is a time to ditch "glutMainLoop " “closed loop” concept - for my task.

There’s so much confusion in your message that it’s unclear what you are trying to accomplish. Could you spell that out for us?

If you’re just trying to time your full event loop to measure msec/frame, turn off VSync, and arrange for your display callback to be called continuously (e.g. call glutPostRedisplay() inside of your display callback).

Normally you wouldn’t do this though. You’d leave VSync enabled, and only call glutPostRedisplay when the content in your window needs to be redisplayed.