Problem with the lighting of a database

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Mario Veraart (rioj7++at++fel.tno.nl)
Thu, 29 Jan 1998 12:15:14 +0100 (MET)

I have a database that has coloured polygons that have to result on
screen to the exact color that was modeled on the polygon.

If you add a pfLightSource with full ambient term and no attenuation
you get a darkening factor of 179/255 = 0.70 (white [255] modelled will
result in grey [179]). If you set the lightsource to black (ambient
and diffuse) the scene has still some lighting, white will result in
approx grey level 76.

A scan of the OpenGL programmers manual showed that there is a global
ambient lighting term that is not caused by any lightsource, default
value .2. If I set the global ambient lighting in the draw callback I
have to set it's value to 1.427 (= 1/0.7) to get the result I want.
If I give a polygon a white (255) color it will give white (255) on
the screen.

What is the cause of the 0.7 attenuation factor?

Where can I find some information about the light calculation that
Performer uses?

Mario
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