NetNews Usenet Archive 1992 #27/NN_1992_27.iso/spool/comp/graphics/avs/912

Internet Message Format | 1992-11-16 | 1.6 KB

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From: [e-mail] (Larry Gelberg)
Subject: Re: Wanted: Information on the ASCII-geometry format from AVS
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Organization: Advanced Visual Systems Inc.
Date: Mon, 16 Nov 1992 15:34:05 GMT
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The example you posted seems to be two squares, not one.  One square
is at [[1,1,1], [1,1,-1], [1,-1,-1], [1,-1,1]], and the other is the
same but with X=-1.

The secret to understanding polytriangle strips is to realize that
vertices are doubled on either side of a "break" in the strip. This
creates two zero-area triangles (we call them "cobwebs") which are
culled in our renderer and ignored by many others.  If you wanted to
convert a polytriangle strip to disjoint triangles, you probably
want to skip over these zero-area triangles (easily identified by having
two of the vertices being identical).  Other than that, if the indexes
of the strip are [1,2,3,4,5,6], then the triangles are: [1,2,3], [2,3,4],
[3,4,5], [4,5,6]. I.e., there are N-2 triangles for a polytri strip
of N vertices.

Does this help?
larryg

--
=== Larry Gelberg ============================ [e-mail] =======
      Advanced Visual Systems Inc. (AVS Inc.)
      300 Fifth Ave, Waltham, MA 02154
===== Tel: [phone] = Fax: [phone] =========================