Path: utzoo!attcan!uunet!samsung!zaphod.mps.ohio-state.edu!usc!snorkelwacker!mit-eddie!bu.edu!ouzo!tjh
From: tjh@ouzo.bu.edu (Tim Hall)
Newsgroups: comp.sys.sgi
Subject: Re: Two gl questions
Message-ID: <54012@bu.edu.bu.edu>
Date: 15 Mar 90 15:56:35 GMT
References: <9003150230.aa18653@SPARK.BRL.MIL>
Sender: news@bu.edu.bu.edu
Reply-To: tjh@ouzo.bu.edu (Tim Hall)
Organization: Boston University
Lines: 23

In article <9003150230.aa18653@SPARK.BRL.MIL> phil@BRL.MIL (Phil Dykstra) writes:
>
>1) Two sided polygons.
>
>just an ambient component on the back side.  The solution I have come
>up with is to draw every polygon twice, once CW, once CCW. Since they
>are coincident the Z buffer would yield unpredictable results, so I
>have turned backface culling on.
>

The other solution I use is to make two diametric light sources.  This
way no matter which side of the polygon the normal is pointing one of
the light sources will cause the polygon to be shaded.  This seems
faster than the above solution but this also only works for diffuse
shading, it doesn't work with specular shading.

>Something I would find very nice is
>a MATERIAL and/or LMODEL level selection of double sided polygons.

I second that.

-Tim Hall
tjh@bu-pub.bu.edu