glutIdleFunc - sets the global idle callback.

glutIdleFunc
	glutIdleFunc(func) -> None

void glutIdleFunc(void (*func)(void));

func      The new idle callback function.

glutIdleFunc sets the global idle callback to be func so a
GLUT program can perform background  processing  tasks  or
continuous  animation  when  window  system events are not
being received. If enabled, the idle callback is  continu-
ously called when events are not being received. The call-
back routine has no parameters.  The  current  window  and
current menu will not be changed before the idle callback.
Programs with multiple windows and/or menus should explic-
itly  set  the  current window and/or current menu and not
rely on its current setting.

The amount of computation and rendering done  in  an  idle
callback  should  be minimized to avoid affecting the pro-
gram's interactive response. In general, not more  than  a
single  frame of rendering should be done in an idle call-
back.

Passing NULL to glutIdleFunc disables  the  generation  of
the idle callback.

A  typical  idle  callback  to animate a window might look
like:

  void
  idle(void)
  {
    time += 0.05;
    glutSetWindow(window);
    glutPostRedisplay();
  }

Notice how the idle callback does not do any actual  draw-
ing;  it  only  advances the time scene state global vari-
able.  That is left to the window's display callback which
will be triggered by the call to glutPostRedisplay.

If  you use the idle callback for animation, you should be
sure to stop rendering when the  window  is  not  visible.
This  is  easy  to set up with a visibility callback.  For
example:

  void
  visible(int vis)

    if (vis == GLUT_VISIBLE)
      glutIdleFunc(idle);
    else
      glutIdleFunc(NULL);
  }

If you do use the idle callback for animation,  one  thing
you  should not do is setup the idle callback before call-
ing glutMainLoop.  It is much better to use the visibility
callback  to  install  idle callback when the window first
becomes visible on the screen.

glutTimerFunc, glutVisibilityFunc

Mark J. Kilgard (mjk@nvidia.com)