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From: Steve Baker <sbaker@link.com>
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To: Multiple recipients of list OPENGL-GAMEDEV-L <OPENGL-GAMEDEV-L@fatcity.com>
Subject: Re: Strips vs Fans ...
Date: Sun, 12 Apr 1998 19:50:31 -0800

On Sat, 11 Apr 1998, Edward M Povazan wrote:

> I've been following threads here about auto strip generation, and am
> starting to wonder, why not do fans. I did a small paper test ... a regular
> triangle grid.
>   case : transforms per case : percentage less than seperate triangles
>   seperate triangles : 144 : 0
>   fans : 77 : 53%
>   strips : 56 : 39%
> 
> OK so strips win here. But on a general mesh (especially one optimized for
> rt3d) the strip runs are not as long. In fact, there are cases when fans
> produce less transforms than strips (this is the case in my landscape
> engine).
 
The other thing that leads me to get more excited about fans than
strips is that they tend to be more compact - spatially that is -
becuase they are all sharing that one vertex.

This is useful for pre-OpenGL culling since it greatly increases the
probablility that a fan will cleanly come out wither entirely inside
or entirely outside the view frustum. If (like me) you are using a
bounding sphere test to accept or reject entire strip/fan primitives
then it's easy to visualise how fans fit better into a neat sphere
than those long wandering strips.

I'm still struggling to convert an old terrain system which was based
around IRISGL primitives (alas, no fans) - and the wins for fans
seem pretty significant.

Steve Baker                (817)619-8776 (Vox/Vox-Mail)
Raytheon Systems Inc.      (817)619-4028 (Fax)
Work: SBaker@link.com      http://www.hti.com
Home: SJBaker1@airmail.net http://web2.airmail.net/sjbaker1

-- 
Author: Steve Baker
  INET: sbaker@link.com

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