Re: Occulting problems with polygon subfaces in Performer

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Andrew Walker (awalker++at++multigen.com)
Mon, 21 Oct 1996 10:48:47 -0700

John Wintle wrote:
> We are currently using ModelGen/Multigen II to create databases for use
> in Performer 2.0. The problem that we have is that subfaces (polygons
> attached to polygons) do occult properly. The child polygon is in the
> same plane as the parent, but still occasionally seems to get occulted
> by it. The subfaces also occult 3d items in the database, which are not
> attached to the parent polygon, i.e. a building on top of a concrete
> base.

Some things to think about when using subfaces.

1. They are very slow on the SGI. I would recommend acvoiding them.

2. Create your nested faces all at the same level in the hierarchy and offset them a
distance greater than one zbuffer unit. This depends upon your interoperability
range with the nested polygons. The problem with this aproach is that you are adding
depth complexity which also slows down a Z buffer system.

3. Use the cut subfaces tool in MultiGen. This will cut out the subfaces and place
them at the same level in the hierarchy allowing for longer T-strips and reduced
depth complexity. This tool is not completly bombproof but is improving.

4. Use a combination of 3 and 4. Use the offset face approach on your distant LOD's,
you won't be able to see that they are floating from a distance. And when you
require the most detail up close use cut in faces. your polygon count may be higher
but your t-strip length will be longer and your depth complexity will be lower which
will allow you to draw more polygons in your budgeted time.

If you have more modeling questions let me know.
  

-- 
Andrew R. Walker			awalker++at++multigen.com
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MultiGen Inc.				( 408 ) - 261 - 4100 MAIN
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