glutPassiveMotionFunc - Man Page
Sets the non-dragging (gliding?) mouse-motion callback.
OpenGLUT - input
glutPassiveMotionFunc(void( *callback )( int x, int y ));
Client mouse-glide hook.
If you set this callback on a window, then every time that OpenGLUT detects a change in the mouse position inside that window, with no buttons pressed on that mouse, OpenGLUT will invoke
with the window coordinates of the mouse.
This callback is bound to the
Windows created via glutCreateMenuWindow() always cascade keyboard and mouse events to their parent.
glutMotionFunc(3) glutMouseFunc(3) glutEntryFunc(3)
glutCreateMenuWindow(3), glutEntryFunc(3), glutMouseFunc(3).