Re: very bright lights

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Angus Dorbie (dorbie++at++bitch.reading.sgi.com)
Fri, 24 Jan 1997 15:24:47 +0000

The problem you describe is caused by OpenGL.

Pixel colours are clamped to 1.0 prior to texturing.

If you didn't do this you'd see all sorts of banding when you
applied dark textures to a bright surface because you simply
don't have the precision in the image.

The whole problem boils down to precision if you consider that
you could use colour tables to apply gain to the image on the
screen, so one solution might be to darken everything so that
colours are never actually clamped and then use a colour table
to apply gain.

But expect problems due to lack of sufficient precision.

Cheers,
Angus.

On Jan 23, 4:15pm, ken sartor wrote:
> Subject: very bright lights
>
> Greetings,
>
> For an effect that i am trying to achieve, it would be
> very nice to have *EXTREMELY* bright lights... But, when
> i just naively crank up the light, i do not get the
> effect i want. What happens is that all the geometry
> is affected in the way i want (when the light is sufficiently
> bright, it turns white) but the texture is clamped to some
> value (objects that are textured and already on white
> geometry are unaffected by brightning the light source
> above 1).
>
> The effect i want is for all objects to be brightened by
> the extremely bright light source and, if it is sufficiently
> bright, to turn white. Is there some way to achieve this
> effect? Note that i want a method that will do this generally
> for various databases (i.e., i don't want to depend on
> custom made databases).
>
> Thanks in advance!
>
> ken
>
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>-- End of excerpt from ken sartor

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