Re: [Algorithms] VIPM and UV texturing

[Mark W. <mwa...@to...>]

Thanks Tom,

The feature edges were what I am referring to ... what I'm trying to get at
is
that simple edge collapsing doesn't work _across_ a feature edge (yielding
the
undesired incorrect texture interpolation performed _by the card_, not me).

Fortunately you're a bit more eloquent (spelling?) than I :)

Your explanation is very much appreciated.

Thanks,

Mark

----- Original Message -----
From: "Tom Forsyth" <to...@mu...>
To: <gda...@li...>
Sent: Wednesday, August 09, 2000 7:19 PM
Subject: RE: [Algorithms] VIPM and UV texturing


> > From: Mark Wayland [mailto:mwa...@to...]
> [snip]
> > I cite different vertices because the actual UV coords are different
> > (eg. a vertex is NOT just gemoetry, as in the D3D definition)
> >
> > Doesn't anyone use large meshes that are textured using
> > multiple textures
> > with VIPM,
> > in that you would want the mesh as a whole to reduce, not the
> > similarly
> > textured "pieces" ?
>
> Ugh - no. Who would want to do that? :-)
>
> Actually, yes. Edges where two textures meet (or indeed any discontinuous
> data - colours, normals, etc) are what I call "feature" edges. The way I
> deal with them is that you find all your feature eges, and then only allow
> collapses _along_ edges and _onto_ edges. But I never allow collapses of a
> vertex on a feature edge onto a another vertex that isn't on the same edge
> (remember to disallow collapses of one feature vertex to another feature
> vertex that _isn't_ on the same edge, e.g. between two parallel feature
> edges).
>
> But the fewer feature edges you have on your model, the better VIPM can
cope
> with it, and the better it collapses.
>
> > What I'm tending to now assume is that most users of VIPM are
> > using it on
> > trivially textured
> > objects ... would this be a fair assumption, or once again
> > have I missed
> > something ?
>
> I dunno about "trivially" - mapping textures onto humanoid models (and
> indeed the not-so-humanoid - we have slugs, two-headed creatures and ones
> with four arms in Startopia) can get quite tricky.
>
> But yes, VIPM only works well when there are comparatively few feature
> edges.
>
> There are some schemes that try to perform collapses across feature edges.
> One is Jan Svarovsky's (follow the GDC link from the ultra-minimalist
> homepage: http://www.svarovsky.com/), which has a discussion of these
> collapses. But they're not pretty, and they complicate the collapse
process.
> By far the best way to proceed is to use friendly persuasion and Pavlovian
> conditioning (a big stick is handy for this) until the artists to create
> models with few feature edges.
>
> Tom Forsyth - Muckyfoot bloke.
> Whizzing and pasting and pooting through the day.
>
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