glutMotionFunc man page
glutMotionFunc — Reports mouse-motion while a button is held.
OpenGLUT - input
glutMotionFunc(void( *callback )( int x, int y ));
Client hook for dragging mouse.
This function reports the mouse position when the mouse is dragged starting from within your window. (``Dragging'' occurs when you press one or more mouse buttons in one of your OpenGLUT windows, and then move the mouse around.)
This callback is bound to the
Events are reported until the mouse button is released, even if the mouse leaves the window.
Windows created via glutCreateMenuWindow() always cascade keyboard and mouse events to their parent.
glutCreateMenuWindow(3), glutMouseFunc(3), glutPassiveMotionFunc(3).