"Hidden" ambient light??

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Scott McMillan (scott++at++ht.com)
Tue, 19 Nov 1996 10:27:59 -0500 (EST)

I have been struggling with what I thought was a fog and then light
attenuation problem for a while now. I could never seem to get the
shading in the distance to go completely to black (until recently):

I am loading Alias/OBJ models with materials whose ambient, diffuse,
and specular components are non-zero. I have a single local
pfLightSource, and I am setting the quadratic attenuation term rather
high to get a significant effect. This light's ambient light has been
set to zero, and the diffuse is essentially white. But the geometry in the
distance was still slightly lit. Even when I turned the attenuation WAY up,
the geometry would dim to a certain point but never go black.

I finally fixed the problem, by setting the ambient components of the
materials to zero. Now if I understand what I read in the OpenGL manual last
night, this would seem to imply there is an ambient light source somewhere.
I haven't added one though, and pfPrint only shows the one light source I
added.

Is there a ambient light source that Performer/OpenGL sets up by default? If
so, how do I turn it off? If not, can anybody clue me in to what is
happening?

My system: High Impact, Irix 6.2, Performer 2.0.2

Thanks in advance,
scott

-- 
  Scott McMillan  |       HT Medical, Inc.      | Developing virtual environ-
   scott++at++ht.com   |      http://www.ht.com      | ment medical and surgical
 Ph: 301-984-3706 | 6001 Montrose Rd., Ste. 902 | simulations and surgery
Fax: 301-984-2104 |     Rockville, MD 20852     | simulation creation tools.


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