Re: [Algorithms] VIPM and UV texturing

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

Thanks for the response:

> Er... with the usual type of VIPM, you don't generate texture coords, or
> indeed any new vertices,  at all. All you do is throw one point away and
> collapse the edge onto the other one.
>
> There are variants where you generate some sort of new "average" midpoint,
> but (a) the quality improvement isn't very large and (b) it is quite a bit
> less efficient to render, because for a given LoD, you have vertices that
> are used by lower LoDs, but not the current one, which causes problems.

But if I have the scenario where one triangle is mapped with UVs : u1,v1,
u2,v2, u3,v3
and an adjacent triangle mapped with u6,v6, u7,v7, u8,v8; the adjacency is
along the edge
of (u1,v1 & u6,v6) - (u3,v3 & u8,v8), where u1,v1 and u6,v6 actual vertices
are coincident, as is the case with u3,v3 and u8,v8.

What happens when I drop out the edge ?

Wouldn't the texture coords will be interpolated from u2,v2 to u7,v7 which
may be totally screwed ?  I must be missing some fundamental stuff here ...

> A related question is how to calculate texture coords (and other
attributes)
> when creating subdiv surfaces. I just use linear - seems to work OK with
my
> data, but others prefer to use other methods, such as use the subdiv
surface
> method, but on the attributes data. This gives excellent results BUT it is
> possibly covered by a sneaky Pixar patent. It's still unclear exactly what
> this patent covers (as with all patents, it's extremely vague), but there
> may be some prior art that we can hide behind :-) In any case, simpler
> methods such as Loop subdivision is often perfectly acceptable for
> attributes, since perfect C1/G1 is not actually needed in most cases.

I've yet to look into subdiv surfs yet, but it'll no doubt arise ;)

Thanks again,

Mark