glutOverlayDisplayFunc(3GLUT)        GLUT        glutOverlayDisplayFunc(3GLUT)

       glutOverlayDisplayFunc - sets the overlay display callback for the
       current window.

       void glutOverlayDisplayFunc(void (*func)(void));

       func      The new overlay display callback function.

       glutDisplayFunc sets the overlay display callback for the current
       window. The overlay display callback is functionally the same as the
       window's display callback except that the overlay display callback is
       used to redisplay the window's overlay.

       When GLUT determines that the overlay plane for the window needs to be
       redisplayed, the overlay display callback for the window is called.
       Before the callback, the current window is set to the window needing to
       be redisplayed and the layer in use is set to the overlay. The overlay
       display callback is called with no parameters. The entire overlay
       region should be redisplayed in response to the callback (this includes
       ancillary buffers if your program depends on their state).

       GLUT determines when the overlay display callback should be triggered
       based on the window's overlay redisplay state. The overlay redisplay
       state for a window can be either set explicitly by calling
       glutPostOverlayRedisplay or implicitly as the result of window damage
       reported by the window system. Multiple posted overlay redisplays for a
       window are coalesced by GLUT to minimize the number of overlay display
       callbacks called.

       Upon return from the overlay display callback, the overlay damaged
       state of the window (returned by calling
       glutLayerGet(GLUT_OVERLAY_DAMAGED) is cleared.

       The overlay display callback can be deregistered by passing NULL to
       glutOverlayDisplayFunc. The overlay display callback is initially NULL
       when an overlay is established. See glutDisplayFunc to understand how
       the display callback alone is used if an overlay display callback is
       not registered.

       glutDisplayFunc, glutPostOverlayRedisplay

       Mark J. Kilgard (

GLUT                                  3.7        glutOverlayDisplayFunc(3GLUT)