Re: Blending between levels of detail for texture

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Angus Dorbie (dorbie++at++bitch.reading.sgi.com)
Wed, 12 Feb 1997 16:02:43 +0000

On Feb 12, 9:40am, WILLIAM_MARINELLI++at++ntsc.navy.mil wrote:
> Subject: Blending between levels of detail for texture
>
> I generated a little demo that does a hokey texture level of detail
> using a couple of polygons with vastly different texture patterns. The
> level of detail switching distances did not overlap - one would switch
> out at 200m and the othere would switch in at that same distance.
>
> MultiGen Marcus, my understanding is that to do this you have to use a
> separate polygon for each texture. Is that correct?
>

Yes that's correct, although you could use MIPmapping to perform a
transition like this on a single polygon, with code of your own to
load your own MIP level images.

What effect are you seeking?

> I ran it in perfly and the blending was excellent - no popping
> whatsoever.
>
> Angus et al, any idea how perfly does this? I tried grepping for this
> and that in the perfly source code directory and (uh, duh) found
> nothing.

Perfly can use fade lod if you have a multi-sample buffer
and are anti-aliasing.

This allows the RE or iR to mask writes to subpixels and perform the
fade for an entire portion of the scene graph without worrying
about order invariance or other GL state information.

The primary performer API calls to read up on are pfLODTransition and
pfChanLODAttr.

Cheers,
Angus.
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