Routines beginning with the glutInit- prefix are used to initialize GLUT state. The primary initialization routine is glutInit that should only be called exactly once in a GLUT program. No non- glutInit- prefixed GLUT or OpenGL routines should be called before glutInit.
The other glutInit- routines may be called before glutInit. The reason is these routines can be used to set default window initialization state that might be modified by the command processing done in glutInit. For example, glutInitWindowSize(400, 400) can be called before glutInit to indicate 400 by 400 is the program's default window size. Setting the initial window size or position before glutInit allows the GLUT program user to specify the initial size or position using command line arguments.