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From: thant@horus.esd.sgi.com (Thant Tessman)
Newsgroups: comp.sys.sgi
Subject: Re: lmcolor and lighting a surface with a scalar field
Message-ID: <10853@odin.corp.sgi.com>
Date: 25 Jul 90 16:11:42 GMT
References: <2042@sparko.gwu.edu>
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Reply-To: thant@horus.esd.sgi.com (Thant Tessman)
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Organization: Silicon Graphics Inc.
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In article <2042@sparko.gwu.edu>, favre@seas.gwu.edu (Jean M. Favre) writes:

> The problem is that BOTH sides of the surface are shaded because the
material 
> properties are modified.
> 
> What I want is the side facing away from the normals to be shaded with a
> uniform gray color so that I can easily distinguish the inside and outside
> of the surface.

You can use backface(TRUE) if you are careful about the order 
you specify the vertices.

Turn on backface, and draw the lit object with the vertices defined
counter-clockwise.  Only polygons facing the eye will be drawn.  Then 
turn off lighting and specify a grey color and draw a version of the 
object with the vertices clockwise to draw only the polygons
facing away from the eye.

On the VGX you can specify two sided polygons using lmdef and lmbind.

thant