RE: [Algorithms] VIPM and UV texturing

[Tony C. <to...@mi...>]

>One particular problem I will share that comes up often is when texturing
characters.  My >system automatically will preserve vertices that have
texture coordinate discontinuities.  >However, artists will often model a
character with only half of the texture (particularly >in the face) then
just reflect the texture coords to save texture space.
>
>Now the problem as you would guess is you have the face with coordinates
like (1,0) -----  >(0,0) ---- (1,0).  Obviously more granular then that.
There are no texture coordinate 
>discontinuities so the algorithm says it is ok.  The surface of the face is
roughly flat 
>so the internal vertex and edges are good candidates for collapse.
However, you then get >the nice situation of  (1,0) ------ (1,0).  Doesn't
look so hot.  I have the artists tag 
>reflected seam vertices as uncollapsable until very late in the order.

Can you not algorithmically detect this situation as well? Compute the
tangent-normal basis for the polygon, and look at the derivative of the
texture coordinates w.r.t the tangent vector - if this changes sign you have
a seam.

More work, I grant you, and I admit not as flexible as having a tool that
lets the artists do the markup, but still possible.

Tony Cox - DirectX Luminary
Windows Gaming Developer Relations Group
http://msdn.microsoft.com/directx