is the main event loop of a glut OpenGL application; you just have to call it once.
You need to define a callback function (usually for the display) that will be called internally from the glutMainLoop function (with the
You will also need to define another callback function when the process is iddle, (use
It is in that function that you should update the radius of the sphere, and that radius will (should?) be used in the display function to redraw the sphere with the appropriate radius.
(mostly inspired from http://www.lighthouse3d.com/tutorials/glut-tutorial/