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.TH "icetGLDrawCallback" "3" "August  9, 2010" "\fBIceT \fPReference" "\fBIceT \fPReference"
.SH NAME

\fBicetGLDrawCallback \-\- set a callback for drawing with \fbOpenGL \fP\&.\fP
.PP
.SH Synopsis

.PP
#include <IceTGL.h>
.PP
typedef void (*
\fBIceTGLDrawCallbackType\fP)( void );
.PP
.TS H
l l l .
void \fBicetGLDrawCallback\fP(	\fBIceTGLDrawCallbackType\fP	\fIcallback\fP  );
.TE
.PP
.SH Description

.PP
The \fBicetGLDrawCallback\fP
function sets a callback that is used to
draw the geometry from a given viewpoint. It will be implicitly called
from within \fBicetGLDrawFrame\fP\&.
.PP
\fIcallback\fP
should be a function that issues appropriate \fbOpenGL \fP
calls to draw geometry in the current \fbOpenGL \fPcontext. After
\fIcallback\fP
is called, the image left in the frame buffer specified
by \fBicetGLSetReadBuffer\fP
will be read back for compositing.
.PP
\fIcallback\fP
should \fInot\fP
modify the
\fBGL_PROJECTION_MATRIX\fP
as this would cause \fBIceT \fPto place image
data in the wrong location in the tiled display and improperly cull
geometry. It is acceptable to add transformations to
\fBGL_MODELVIEW_MATRIX\fP,
but the bounding vertices given with
\fBicetBoundingVertices\fP
or \fBicetBoundingBox\fP
are assumed to
already be transformed by any such changes to the modelview matrix.
Also, \fBGL_MODELVIEW_MATRIX\fP
must be restored before the draw
function returns. Therefore, any changes to
\fBGL_MODELVIEW_MATRIX\fP
are to be done with care and should be
surrounded by a pair of glPushMatrix and glPopMatrix functions.
.PP
It is also important that \fIcallback\fP
\fInot\fP
attempt the change the
clear color. In some composting modes, \fBIceT \fPneeds to read, modify, and
change the background color. These operations will be lost if
\fIcallback\fP
changes the background color, and severe color blending
artifacts may result.
.PP
\fBIceT \fPmay call \fIcallback\fP
several times from within a call to
\fBicetGLDrawFrame\fP
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 \fIcallback\fP\&.
For example, counting frames by
incrementing a frame counter in \fIcallback\fP
is obviously wrong
(although you could count how many times a render occurs).
\fIcallback\fP
should also leave \fbOpenGL \fPin a state such that it will be
correct for a subsequent run of \fIcallback\fP\&.
Any matrices or
attributes pushed in \fIcallback\fP
should be popped before
\fIcallback\fP
returns, and any state that is assumed to be true on
entrance to \fIcallback\fP
should also be true on return.
.PP
The \fIcallback\fP
function pointer is placed in the
\fBICET_GL_DRAW_FUNCTION\fP
state variable.
.PP
\fBicetGLDrawCallback\fP
is similar to \fBicetDrawCallback\fP\&.
The
difference is that the callback set by \fBicetGLDrawCallback\fP
is used
by \fBicetGLDrawFrame\fP
and the callback set by
\fBicetDrawCallback\fP
is used by \fBicetDrawFrame\fP\&.
.PP
.SH Errors

.PP
.TP
\fBICET_INVALID_OPERATION\fP
 Raised if the \fBicetGLInitialize\fP
has not been called.
.PP
.SH Warnings

.PP
None.
.PP
.SH Bugs

.PP
None known.
.PP
.SH Notes

.PP
\fIcallback\fP
is tightly coupled with the bounds set with
\fBicetBoundingVertices\fP
or \fBicetBoundingBox\fP\&.
If the geometry
drawn by \fIcallback\fP
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.
.PP
.SH Copyright

Copyright (C)2003 Sandia Corporation
.PP
Under the terms of Contract DE\-AC04\-94AL85000 with Sandia Corporation, the
U.S. Government retains certain rights in this software.
.PP
This source code is released under the New BSD License.
.PP
.SH See Also

.PP
\fIicetBoundingBox\fP(3),
\fIicetBoundingVertices\fP(3),
\fIicetDrawCallback\fP(3),
\fIicetGLDrawFrame\fP(3)
.PP
.\" NOTE: This file is generated, DO NOT EDIT.