icetCompositeOrder(3)

NAME
icetCompositeOrder - specify the order in which images are composited

SYNOPSIS
#include <GL/ice-t.h>

void icetCompositeOrder(const GLint *process_ranks);

DESCRIPTION
If ICET_ORDERED_COMPOSITE is enabled and the current strategy supports ordered composition, then the order which images are composited are specified with icetCompositeOrder. If compositing is done with z-buffer comparisons (i.e. the depth buffer is selected as an input with icetInputOutputBuffers), then the ordering does not matter, and ICET_ORDERED_COMPOSITE should probably be disabled. However, if compositing is done with color blending (i.e. the depth buffer is not selected as in input with icetInputOutputBuffers), then the order in which the images are composed can drastically change the output.

For ordered image compositing to work, the geometric objects rendered by processes must be arranged such that if the geometry of one process is ``in front'' of the geometry of another process for any camera ray, that ordering holds for all camera rays. It is the application's responsibility to ensure that such an ordering exists and to find that ordering. The easiest way to do this is to ensure that the geometry of each process falls cleanly into regions of an octree, k-d tree, or similar structure.

Once the geometry order is determined for a particular rendering viewpoint, it is given to ICE-T in the form of an array of ranks. The parameter process_ranks should have exactly ICET_NUM_PROCESSES entries, each with a unique, valid process rank. The first process should have the geometry that is ``in front'' of all others, the next directly behind that, and so on. It should be noted that the application may actually impose only a partial order on the geometry, but that can easily be converted to the linear ordering requird by ICE-T.

When ordering is on, it is accepted that icetCompositeOrder will be called in between every frame since the order of the geometry may change with the viewpoint.

If data replication is in effect (see icetDataReplicationGroup), all processes are still expected to be listed in process_ranks. Correct ordering can be achieved by ensuring that all processes in each group are listed in contiguous entries in process_ranks.

ERRORS

ICET_INVALID_VALUE
    Not every entry in the parameter process_ranks was a unique, valid process rank.

WARNINGS
None.

BUGS
If an ICET_INVALID_VALUE error is raised, internal arrays pertaining to the ordering of images may not be restored properly. If such an error is raised, the functions should be re-invoked with a valid ordering before preceding. Unpredictable results may occur otherwise.

COPYRIGHT
Copyright © 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
icetInputOutputBuffers, icetStrategy