icetGLDrawCallback(3)

NAME
icetGLDrawCallback -- set a callback for drawing with OpenGL .

Synopsis

#include <IceTGL.h>

typedef void (* IceTGLDrawCallbackType)( void );

void icetGLDrawCallback( | IceTGLDrawCallbackType | callback );

Description

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 callback 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 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.

Errors

ICET_INVALID_OPERATION
     Raised if the icetGLInitialize has not been called.

Warnings

None.

Bugs

None known.

Notes

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.

Copyright
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.

See Also

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