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From: sbw@naucse.UUCP
Newsgroups: comp.graphics
Subject: Modified Liang-Barsky Polygon Clipping
Message-ID: <258@naucse.UUCP>
Date: Wed, 11-Mar-87 13:16:41 EST
Article-I.D.: naucse.258
Posted: Wed Mar 11 13:16:41 1987
Date-Received: Fri, 13-Mar-87 21:13:03 EST
Organization: Northern Arizona University, Flagstaff, Arizona
Lines: 23
Keywords: Polygon Clipping

I recently posted a query and a summary of responses concerning
the Liang-Barsky Polygon clipping algorithm as published in
CACM, VOL 26, Nov. 1983.

The corrigenda in CACM, VOL 27, April 1984 provided the fix
to the original algorithm.  It also led me to examine my
'patched' version more closely.  I now have a modified
version of the algorithm that, while based upon my patch,
appears (see below) to produce results identical to the
corrected Liang-Barsky algorithm.  The modified version is
both slightly simpler and slightly faster (it averages about 6%
faster over my test data) than the original.

Is anyone interested in this modified algorithm (in C)?  If so,
then I'll post the source to the net (about 150 lines - should
it go to net.sources?).

I have only done limited testing of the code, using 10 randomly
generated polygons (well 7 random and 3 'worst' case) with
from 4 to 200 vertices (counting first vertex twice).  In all
cases the output is exactly the same as the corrected Liang-Barsky
algorithm.  Anyone who wants to really test it out is welcome to.
Please mail me if it has problems.