From: Klaus Otto (kotto++at++cae-gmbh.de)
Date: 10/12/2000 03:43:20
Hello Ian,
we were having a similar problem with a normal (non-clip) texture
overlayed with a detail texture for a ground vehicle application.
We could only eliminate the wobble by reducing the span of terrain covered
by the texture. We ended up with a span of about 400 m.
It did not matter which resolution of the base texture we choosed (2048x2048
or 512x512) nor which size the individual terrain polys had.
This is an excerpt from the answer we got from SGI support at that time:
The problem still is the magnification of the texture close to the
eyepoint. Making the polygons smaller only does not work, there is
still not enough texture resolution available for the first 5 to
10 metres.
The use of detail textures helps, but the choosen texture still
spans too big an area.
[..snip..]
Clipmapping only helps when high resolution textures are available.
End of excerpt.
So, it does not seem to be a problem of texture(vertex) coordinates but
of the (hardware/firmware) resolution the texel2pixel mapping inside the poly
is calculated with.
Hope this helps in your case,
Klaus
On 12 Oct 00, at 16:11, ihawkes2++at++csc.com.au wrote:
> Hi,
> I am having some problems curing a cliptexture of wobble/jello problems
> (Performer 2.2.8; Irix 6.5.8f on an Onyx2).
[ ... snip ...]
> So, my questions are ...
>
> 1) Examples of wobbly tex coords (before translation) include the area
> around (0.917722, 0.266216) and also (perhaps less severely) around
> (0.095587, 0.362692). Would you expect precision problems at these values?
>
> 2) Any ideas why neither reducing the num effective levels, nor translating
> the texcoords seems to improve things? Is it possible that the polygons
> involved are just too big?
>
> 3) Assuming that translating tex coords is the way to go, how should I
> incorporate it into my cliptexture strategy which tiles the cliptexture,
> and uses pre-cull node callbacks to set the virtual cliptexture params for
> each tile. Should I use the largest (_numEffectiveLevels+Offset) of all the
> tile callbacks in order to calculate the goodAreaSize and then do the
> translation and the applyCenter a frame later in the pre-cull (since it
> doesn't work postcull)?
>
> Any help would be most appreciated!
>
> Thanks,
> Ian Hawkes
>
>
>
>
>
>
> -----------------------------------------------------------------------
> List Archives, FAQ, FTP: http://www.sgi.com/software/performer/
> Submissions: info-performer++at++sgi.com
> Admin. requests: info-performer-request++at++sgi.com
>
------------------------------------------------------
| Klaus Otto | |
| CAE Elektronik GmbH | Email: kotto++at++cae-gmbh.de |
| Abt. Systemtechnik | |
| Steinfurt 11 | Tel. : +49-2402-106-456 |
| D-52222 Stolberg | Fax : +49-2402-106-270 |
| Germany | Web : http://www.cae.de |
------------------------------------------------------
This archive was generated by hypermail 2b29 : Thu Oct 12 2000 - 03:37:08 PDT