Occulting problems with polygon subfaces in Performer

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John Wintle (modellers++at++intersim.co.uk)
10/15/96 2:19 PM

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Message-ID: <3263AB75.41C6++at++intersim.co.uk>
Date: Tue, 15 Oct 1996 14:19:17 -0100
From: John Wintle <modellers++at++intersim.co.uk>
Organization: Intersim Limited
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To: Performer Group Submissions <info-performer++at++sgi.com>
Subject: Occulting problems with polygon subfaces in Performer
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     Ah, yes, the old z-fighting problem with coplanar polygons. On pure
     z-buffer systems (i.e. SGI's), roundoff errors in the rasterization
     process can cause subface pixels to be "behind" the parent face.
     Either elevate the subface slightly, use pfLayers, or don't use
     subfaces. The OpenFlight loader will create pfLayers for you, and by
     using pfdConverterMode_flt(), you can control the type of rendering it
     uses. Check the pfLayer man page and the OpenFlight loader docs for
     more info.
      
      
     Don Tidrow
     Visual Simulation Developer
     US Army TACOM

______________________________ Reply Separator _________________________________
Subject: Occulting problems with polygon subfaces in Performer
Author: John Wintle <modellers++at++intersim.co.uk> at TWLAN-SMTP
Date: 10/15/96 2:19 PM

Help Performer people,

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.
   We are using Performer 2.0 on High Impact machines with Irix6.2, and
we get the same problem whether we use our own app or perfly.

Does anyone have any idea what is going wrong here.

-- 


Regards,


John Wintle,
Principal Visual Modeller,
Intersim Limited, Units 7-8, Thorgate Road, Littlehampton. Sussex. UK
Tel: +44 (0)1903 733428
Fax: +44 (0)1903 730246
email: modellers++at++intersim.co.uk


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