Re: Double precision

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Angus Dorbie (dorbie++at++sgi.com)
Mon, 18 Oct 1999 12:15:48 -0700

The double precision coordinates is not the cause of most of the clip
texture issues. We are working to resolve all of the other issues. The
'wobble' problem is the large texture coordinate & clipping issue. This
is exactly analogous to large vertex coordinates and can be resolved the
same way, using a texture matrix to translate localized (tile space)
coordinates away from the eye while overriding the OpenGL clip center
near the origin in the draw process to compensate. The other issues like
jello can be worked around now by limiting the number of effective
levels on any set of geometry but it's not ideal.

The one fix which is not high on our list of priorities is double
precision texture coordinates, and infact the real hardware issue is
clipping interpolation precision. The feedback so far is that this can
be handled using the above methods, but things like jello impose more
serious performance constraints when the workarounds are in place.

It would help to understand what your specific problems are and what
you'd most like to see fixed. Feedback from anyone else on the list who
uses clip textures is very welcome. Please send any feedback direct to
me.

Cheers,ANgus.

Wayne Erchak wrote:
>
> Is SGI planning to implement double precision texture coordinates to eliminate
> all of the precision hacks and limitations of large cliptextures?
>
> --
> Wayne Erchak
> Naval Air Warfare Center
> wayne++at++setd-ctl.nawcad.navy.mil
> Phone: (301) 342-9713
> Fax: (301) 342-9708
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 no loss of enthusiasm."    -    Winston Churchill.


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