Re: [info-performer] Shadow ambient value is not supported on this platform

From: Jason Daly (jdaly++at++ist.ucf.edu)
Date: 12/20/2004 14:45:17

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On Mon, 2004-12-20 at 12:35, faculaganymede wrote:
> pfExperts,
>
> I am trying to run the Performer sample program
> projective.cxx on a PC (with Windows 2000). I don't
> understand why I am getting the following run-time
> message:
>
> Shadow ambient value is not supported on this platform
>
> Does anyone know why? What platform should I be
> running it in?

Probably because your platform supports programmable shading and/or
texture combining and you don't need it. If your platform supports
multitexturing and any of TexEnv combine, register combiners, or
programmable shading, then shadow ambient support is redundant.

ARB_shadow_ambient (the OpenGL extension that it's talking about)
was designed to allow a "default" ambient value when the depth map
test fails. If the platform doesn't support some way of combining
texture values, then ARB_shadow_ambient was the only way to control
what happens to that particular pixel when it is in shadow. Without
this, it can only be set to black.

You can read about it here:

http://oss.sgi.com/projects/ogl-sample/registry/ARB/shadow_ambient.txt

-- 
--"J"
"I'm a castaway stranded in a desolate land,
 I can see the footprints in the virtual sand."
	--Neil Peart

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