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       icetDrawFunc -- set a callback for drawing.


       #include <GL/ice-t.h>

       typedef void (*IceTCallback)(void);

       void icetDrawFunc(   IceTCallback   func  );


       The  icetDrawFunc  function  sets  a  callback that is used to draw the
       geometry from a given viewpoint.

       func should be a function that issues appropriate OpenGL calls to  draw
       geometry in the current OpenGL context. After func is called, the image
       left in the back frame buffer will be read back for compositing.

       func should not modify the GL_PROJECTION_MATRIX  as  this  would  cause
       IceT to place image data in the wrong location in the tiled display and
       improperly cull geometry. It is acceptable to  add  transformations  to
       GL_MODELVIEW_MATRIX,    but    the   bounding   vertices   given   with
       icetBoundingVertices or  icetBoundingBox  are  assumed  to  already  be
       transformed  by  any  such  changes  to  the  modelview  matrix.  Also,
       GL_MODELVIEW_MATRIX must be restored before the draw function  returns.
       Therefore,  any changes to GL_MODELVIEW_MATRIX are to be done with care
       and should be surrounded by a  pair  of  glPushMatrix  and  glPopMatrix

       It  is also important that func not attempt the change the clear color.
       In some composting modes, IceT needs to read, modify,  and  change  the
       background  color.  These  operations  will be lost if func changes the
       background color, and severe color blending artifacts may result.

       IceT may call func several times from within a call to icetDrawFrame or
       not  at  all  if  the current bounds lie outside the current viewpoint.
       This can have a subtle but important impact on the  behavior  of  func.
       For example, counting frames by incrementing a frame counter in func is
       obviously wrong (although you could  count  how  many  times  a  render
       occurs).  func should also leave OpenGL in a state such that it will be
       correct for a subsequent run  of  func.   Any  matrices  or  attributes
       pushed in func should be popped before func returns, and any state that
       is assumed to be true on entrance  to  func  should  also  be  true  on






       None known.


       func  is  tightly coupled with the bounds set with icetBoundingVertices
       or icetBoundingBox.  If the geometry drawn by func is dynamic  (changes
       from  frame  to frame), then the bounds may need to be changed as well.
       Incorrect bounds may cause the geometry  to  be  culled  in  surprising


       Copyright (C)2003 Sandia Corporation

       Under the terms of Contract DE-AC04-94AL85000, there is a non-exclusive
       license for use of this work by or on behalf of  the  U.S.  Government.
       Redistribution  and  use  in  source  and binary forms, with or without
       modification, are permitted provided that this Notice and any statement
       of authorship are reproduced on all copies.

See Also

       icetDrawFrame(3), icetBoundingVertices(3), icetBoundingBox(3)

IceT Reference                 January 31, 2007                icetDrawFunc(3)