Re: (originally no subject) Texturing modes

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Prakash Mahesh (prakash++at++drawcomp.com)
Tue, 09 Jun 1998 10:10:19 -0400

Hello all,
        I want to pose my previous question a different way, more
proactive then reactive. How would one utilize a 4 channel texture
(RGBA) so that the texture would appear on a surface as in decal mode,
but would be transparent as a function of its alpha channel? This
would allow a cookie-cutter decal based on the alpha channel (binary
with one designating stuff and 0 designating lack of stuff).

Thanks.
-Prakash

Moshe Nissim wrote:
>
> > No the original request said At for blend, in otherwords it doesn't want
> > to
> > use a constant alpha value I've isolated the relevant parts of the
> > email:
> >
> > "C = (1-At)Cf + At(Ct)"
> > "A = At"
> > "At is the alpha channel for the texel"
> >
> > I agree what you describe isn't as strange but it's not what was
> > requested.
> > Looks like you did have something else in mind.
>
> Agreed. I took only the point of blending fragment and texturecolors from the original post, changing the blend control as
> suited me :)
>
> > Agreed, this would be usefull, but so could lots of other fragment
> > operations.
> >
> > Right now most obviously and more usefully for me which the above
> > approach
> > could also give me.
> >
> > Cv=(1-Af)Cf+AfCt
>
> I would go with this as well.I have trouble combining the above paragraph and the subsequent fix
> message. Is the above formula feasible?
>
> >
> >
> > But 3D texture can handle this.
>
> > The permutations from extending current functionality rapidly explode,
> > everyone requires a different operation and the fragment operation
> > w.r.t.
> > the lighting equation (diffuse vs specular) is much more of an issue.
>
> But a different issue. The lighting equations are separate (at leasecurrently) from the texture-environment equations, and these in turn
> are separate from the blending equations. I guess this has to change
> when we'll move (hopefully!) to pixel-level lighting.
>
> > What's needed is something more powerfull than half a dozen pre canned
> > texture environments, but that requires another look at the glTexEnv.

-- 
  Prakash Mahesh                                     
  prakash++at++drawcomp.com
  	--or--
  prakash++at++openworlds.com
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