icetGLDrawCallback -- set a callback for drawing with OpenGL .

       None known.

       Copyright (C)2003 Sandia Corporation

       Under  the  terms  of  Contract  DE-AC04-94AL85000  with  Sandia Corporation, the U.S. Government retains
       certain rights in this software.

       This source code is released under the New BSD License.

       The icetGLDrawCallback function sets a callback that is used to draw the geometry from a given viewpoint.
       It will be implicitly called from within icetGLDrawFrame.

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

       callback 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 functions.

       It is also important that callbacknot 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 callback changes
       the background color, and severe color blending artifacts may result.

       IceT  may  call callback several times from within a call to icetGLDrawFrame 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
       callback.   For  example,  counting frames by incrementing a frame counter in callback is obviously wrong
       (although you could count how many times a render occurs).  callback should also leave OpenGL in a  state
       such  that  it  will  be  correct for a subsequent run of callback.  Any matrices or attributes pushed in
       callback should be popped before callback returns, and any state that is assumed to be true  on  entrance
       to callback should also be true on return.

       The callback function pointer is placed in the ICET_GL_DRAW_FUNCTION state variable.

       icetGLDrawCallback  is  similar  to  icetDrawCallback.   The  difference  is  that  the  callback  set by
       icetGLDrawCallback is used by icetGLDrawFrame and  the  callback  set  by  icetDrawCallback  is  used  by
       icetDrawFrame.

ICET_INVALID_OPERATION
               Raised if the icetGLInitialize has not been called.

icetGLDrawCallback--setacallbackfordrawingwithOpenGL.

callback  is  tightly  coupled  with the bounds set with icetBoundingVertices or icetBoundingBox.  If the
       geometry drawn by callback 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 ways.

icetBoundingBox(3), icetBoundingVertices(3), icetDrawCallback(3), icetGLDrawFrame(3)

IceT Reference                                   August  9, 2010                           icetGLDrawCallback(3)

       #include <IceTGL.h>

       typedef void (* IceTGLDrawCallbackType)( void );

       void icetGLDrawCallback(   IceTGLDrawCallbackTypecallback  );

       None.