glutDisplayFunc  -  sets the display callback for the cur-
       rent window.

SYNTAX

       void glutDisplayFunc(void (*func)(void));

ARGUMENTS

       func      The new display callback function.

DESCRIPTION

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

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

       When an overlay is established for a window, but there  is
       no  overlay display callback registered, the display call-
       back is used for redisplaying both the overlay and  normal
       plane  (that is, it will be called if either the redisplay
       state or overlay redisplay state is set).  In  this  case,
       the layer in use is not implicitly changed on entry to the
       display callback.

       See  glutOverlayDisplayFunc  to  understand  how  distinct
       callbacks for the overlay and normal plane of a window may
       be established.

       When a window is created, no display callback  exists  for
       the  window. It is the responsibility of the programmer to
       install a display callback for the window before the  win-
       dow  is  shown.  A display callback must be registered for
       any window that is shown. If a  window  becomes  displayed
       without a display callback being registered, a fatal error
       occurs. Passing NULL to glutDisplayFunc is illegal  as  of
       GLUT  3.0;  there  is  no  way to ``deregister'' a display
       callback (though another callback routine  can  always  be
       registered).
       state  of  the  window  (returned  by  calling  glutLayer-
       Get(GLUT_NORMAL_DAMAGED)  is cleared. If there is no over-
       lay display callback registered the overlay damaged  state
       of the window (returned by calling glutLayerGet(GLUT_OVER-
       LAY_DAMAGED) is also cleared.

SEE ALSO

       glutCreateMenu, glutPostRedisplay, glutOverlayDisplayFunc

AUTHOR

       Mark J. Kilgard (mjk@nvidia.com)