Re: Alpha and anti-aliasing...

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Angus Dorbie (dorbie++at++sgi.com)
Fri, 08 May 1998 14:57:50 -0700

Jan Barglowski wrote:
>
> Performers:
>
> This is probably a really easy question to answer. I have a cloud
> texture that is in rgba format. I texture it to a square and view
> the file in perfly. The texture looks to have 2 bits of alpha, unless
> I turn off anti-aliasing! Now, I don't want to turn off antialiasing
> for my main app, so how do I solve this?
>
> Vitals:
> - Onyx iR
> - Performer 2.2
> - MultiGen 15.4 (still using MultiGen loader that came with Performer 2.2)
>

You are using the sub pixel alpha mask mode for order
invariant transparency.

This gives you number of samples +1 values of alpha so you
get 5 discrete shades including 0.0 and 1.0.

You have the option of using blended transparency instead
which will introduce the classic zbuffer alpha occlusion
problems unless you sort in the cull process.

To do this set the pfTransparency to PFTR_HIGH_QUALITY or
PFTR_BLEND_ALPHA.

You could also use more multisamples to increase the
number of multisamples and therefore the number of
shades of alpha.

Cheers,Angus.

-- 
"Only the mediocre are always at their best." -- Jean Giraudoux 


For advanced 3D graphics Performer + OpenGL based examples and tutors:
http://www.dorbie.com/
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