As noted in main, glutTimerFunc gives us the ability to call a function with a time delay prior to the call. The first parameter to glutTimerFunc is the amount of delay measured in milliseconds. When we set animation from main as our timer function, we wanted it to be called without delay and, in turn, we set the first parameter to 0. Since we now want a delay between frames, we pass the int value millisecondDelay as the first parameter.

We are using millisecondDelay = 50 as the delay value. This gives a frame rate of about 1000/50 = 20 frames per second.