[Bf-committers] [Bf-blender-cvs] SVN commit: /data/svn/bf-blender [51258] trunk/blender: Cycles: Anisotropic BSDF enabled, with tangents now computed from the active UV map.

[Morten Mikkelsen]

The problem is not the sphere. The problem is the general case which will
almost never work well with per vertex averaged tangents
in the context of aniso shading. The problem is of course that almost any
case of a discontinuity will give offensive discontinuities in the
lit results because it's anisotropic. You will consistently be presented
with two choices 1 is to average and one is to split
and you will be screwed whether you do or you don't. I promise you there is
no way you can get this to behave well in the majority of cases.
What will happen if you introduce a threshold is that some vertices will
pop and some will split.
If you follow a UV border down the seam at the surface of the mesh
(something organic such as a human head) this will basically
look horrendous.
You'll see it switching, going from vertex to vertex, between awful
distortions in the spec or hard discontinuities depending on whether or not
it averaged or split.
There will exist no global threshold that will give you a nice looking
result.




On Tue, Oct 16, 2012 at 11:56 AM, Brecht Van Lommel <
brechtvanlommel at pandora.be> wrote:

> Right, for a sphere you need a singularity at the poles, but you do
> not need a seam between them too.
>
> Brecht
>
> On Tue, Oct 16, 2012 at 8:34 PM, Morten Mikkelsen <mikkelsen7 at gmail.com>
> wrote:
> >>Ok, I'm still convinced we can do better than either, will try to figure
> > it out.
> >
> >
> > Can't blame a man for trying :)
> > Food for thought though:
> >
> > http://en.wikipedia.org/wiki/Hairy_ball_theorem
> >
> > The hairy ball theorem! It basically says that a tangent field on the
> > surface of a sphere in an odd dimensional vector space
> > must partition somewhere. Couldn't help bring it up since it's a classic
> :)
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