David Luebke (luebke++at++cs.unc.edu)
Mon, 30 Oct 1995 18:01:18 -0500 (EST)
This is to announce the release of the pfPortals visibility software for
Performer 1.2. PfPortals is a FREE public domain library which provides
portal-based culling in Performer applications. The package can be downloaded
via anonymous ftp at:
ftp.cs.unc.edu:/pub/users/luebke/pfPortals.tar.Z
or over the World Wide Web at:
http://www.cs.unc.edu/~luebke/pfPortals/visibility.html.
Documentation is provided in html and postscript form. Here is an extract
from the introduction:
------
The library consists of a number of CULL and DRAW callbacks which are
attached to nodes in the Performer scene graph, and an interface for
controlling the behavior of those callbacks. The pfPortals library was
developed by David Luebke at the University of North Carolina during
the 1995 Spring semester.
The portal-based culling approach attempts to improve rendering performance
for large models by culling away portions of the model which are completely
occluded. It works best in scenarios such as architectural walkthroughs,
where most of the model is typically hidden from the viewer by walls,
floors and ceilings. Portal-based culling subdivides the model into
cells and portals. A cell is a polyhedral volume of space; a portal is
a transparent 2D region upon a cell boundary that connects adjacent cells.
Cells can only "see" other cells through the portals. In an architectural
model, the cell boundaries should follow the walls and partitions, so that
cells roughly correspond to the rooms of the building. The portals likewise
correspond to the doors and windows through which neighboring rooms can
view each other.
The pfPortals library implements the portal-based culling scheme described
in Portals and Mirrors: Simple, Fast Evaluation of Potentially Visible
Sets, by David Luebke and Chris Georges, in the Proceedings of the 1995
Symposium on Interactive 3-D Graphics (April 1995; ACM Press). Briefly,
this algorithm determines what cell contains the viewer, and what portals
of that cell are visible to the viewer. Next the code recursively determines
what portals of adjacent cells are visible through the portals already
determined to be visible. This approach accumulates a list of visible
cells without considering portions of the model far removed from the
visible set.
--Copyright--
The pfPortals library is a public domain software package and may be freely
used, modified, and distributed, provided certain conditions are met. The
following copyright appears in the source code and applies to this
documentation as well:
/***************************************************************************\
Copyright 1995 The University of North Carolina at Chapel Hill.
All Rights Reserved.
Permission to use, copy, modify and distribute this software and its
documentation without fee, and without a written agreement, is
hereby granted, provided that the above copyright notice and the
complete text of this comment appear in all copies, and provided that
the University of North Carolina and the original authors are
credited in any publications arising from the use of this software.
IN NO EVENT SHALL THE UNIVERSITY OF NORTH CAROLINA AT CHAPEL HILL
OR THE AUTHOR OF THIS SOFTWARE BE LIABLE TO ANY PARTY FOR DIRECT,
INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES, INCLUDING
LOST PROFITS, ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS
DOCUMENTATION, EVEN IF THE UNIVERSITY OF NORTH CAROLINA AND/OR THE
AUTHOR OF THIS SOFTWARE HAVE BEEN ADVISED OF THE POSSIBILITY OF
SUCH DAMAGES.
The author of the pfPortals1.2 software library may be contacted at:
US Mail: David Patrick Luebke
Department of Computer Science
Sitterson Hall, CB #3175
University of N. Carolina
Chapel Hill, NC 27599-3175
Phone: (919)962-1825
EMail: luebke++at++cs.unc.edu
\*****************************************************************************/
Enjoy!
Dave
-- David Luebke luebke++at++cs.unc.edu
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