i just started off using OpenGL and it seems it is not easy to understand the working of the glutMainLoop() what really happens there? Does it stay there doing nothing till any of the function calls responds?
It calls your display callback over and over, calling idle between so that it can maintain a specific framerate if possible, and others if necessary (such as if you resize the window or trigger an input event).
Essentially, within this function is the main program loop, where GLUT does most of the work for you and allows you to simply set up the specific program logic in these callbacks. It's been a while since I've worked with GLUT, and it is certainly confusing at first.
In your display callback should obviously be your main logic to draw whatever it is that should be going on. In the idle callback should be some very lightweight operations to determine what the change in state should be from the last time display was called to the next time. For example, if you're animating something, this would be where you change its position or orientation.
It is exactly as StrixVaria has stated.
glutMainLoop enters the GLUT event processing loop. This routine should be called at most once in a GLUT program. Once called, this routine will never return. It will call as necessary any callbacks that have been registered.
Taken from here
Using opengl and glut together means that you would be writing a 'glut' program that uses opengl commands in the callback functions. main contains glut functions. many glut functions need a callback function to be registered. Those callback functions usually contain opengl commands.
Coming to your question, now when it is clear that you are mainly writing a glut program, it should also be taken that glutMainLoop function call actually executes the callback functions as and when required, which in return executes the opengl commands.
Well glutMainLoop is the main function the keeps calling and calling the displaying functions and which also keeps your window actually opened. You''ll find out that opengl is not that scary.
来源：https://stackoverflow.com/questions/1862496/opengl-glutmainloop