Re: What is the maximal triangle number in a pfGeoSet?

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From: Yair Kurzion (yair++at++polygon.engr.sgi.com)
Date: 12/15/2000 13:26:46

Hello Yigang !

> I met a problem, my program works well for small model, but it works
> incorrectly for big model. I put a big model into one pfGeoSet, the
> number of triangles is greater than 65536, then i want to pick one
> triangle. The pick is correct for small model, incorrect for big model.
> Is it the problem that i have too many triangles in one pfGeoSet? Is the
> maximal triangle number for a pfGeoSet is 2^16?

If you use indexed pfGeoSets then the number of vertices is limited
to 2^16 (unsigned short). This is an inherent limitation of pfGeoSet.

If your pfGeoSets are not indexed, then they can contain and draw up to 2^32
vertices. There is a bug in the intersection code so intersection works only
for up to 2^16 vertices (thanks for finding it). I will fix this bug for the
next maintenance release (2.4.1). If you have a small test program that fails
to intersect large pfGeoSets, please e-mail it to me. I'll be glad to test it
against my fix.

In general, running intersection on very large pfGeoSets is very wasteful.
Performer treats a pfGeoSet as an atom. If the pfGeoSet bounding volume
intersects your ISECT segments, Performer serially tests for intersection with
every triangle in the pfGeoSet.

It would be more efficient to break the pfGeoSet into smaller pfGeoSets - each
occupying a smaller bounding volume. The intersection code will run faster.

-yair 

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\_________  \_____  \__    \__  \_____         Yair Kurzion
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