Re: White spot

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Angus Dorbie (dorbie++at++bitch.reading.sgi.com)
Fri, 21 Mar 1997 05:10:33 +0000

On Mar 20, 9:07pm, Angus Dorbie wrote:
> Subject: Re: White spot
> On Mar 20, 3:30pm, Yann Andenmatten wrote:
> > Subject: White spot
> > Hi,
> >
> > I'm trying to have an shiny textured object. I have set a pfMaterial with
> > specular light to (1.0,1.0,1.0) and shininess to 16.0. It's working, but
the
> > spot on the object isn't white (the color of the spot is defined by the
> > texture). The light has also a specular light to (1.0,1.0,1.0).
> >
> > How can I get a very saturated spot ?
> > Any idea ?
>
>
> It's the GL which is the problem here.
>
> To add the specular highlight after texture modulation you must
> render a second untextured pass with a black material and
> a (one, one) blendfunction, and polygon offset to avoid zfighting.

I should have mentioned here that the black material used on the second
pass should contain the shininess and specular material properties of
the material on the object. All other terms should be black unless you
have other aspects of the material which you don't want modulated by
texture, eg EMISSIVE. To be really accurate you should remove the terms
in this material from the material used in the first pass, ie blacken
them.

>
> As you can surmise, this type of approach can be expensive.
> The OpenGL ARB is currently exploring extensions to the API
> which may improve this situation on future implementations.
>
> I've been working on multipass shaders in Performer recently so
> if you want performer draw callbacks for the above email me and
> I can supply some code.
>
> Cheers,Angus.
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>-- End of excerpt from Angus Dorbie

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