clipka <ano### [at] anonymousorg> wrote:
> Am 09.04.2015 um 12:33 schrieb Stephen:
> > On 09/04/2015 07:33, And wrote:
> >> ... this is what I rendered.
> >
> > That is the pattern I got when I used your original code. But something
> > looks wrong with the shading and shadows. So I did a series of renders
> > with a simpler material that is matt. I orbited the light around your
> > shape and included a couple of primitives (two spheres and a lathe)
> > using the same texture, for comparison. The Blue arrow points to the light.
> > Unless someone can explain it by the shape of the object. It looks like
> > a bug to me.
>
> Thanks for experimenting with this.
>
> Yes, this certainly is a bug. I haven't looked at the code yet, but
> judging from the effect I would assume that the surface normal at a
> given intersection point is computed as the (normalized) vector from the
> closest point on the "centroid circle" to the surface point; obviously
> this breaks down for the inner spindle of a spindle torus.

This ancient thread might be relevant:

Newsgroup: povray.binaries.images
From: Tor Olav Kristensen
Subject: Torus problem (69KB)
Date: 21st April 2000
http://news.povray.org/povray.binaries.images/thread/%3C38FFC5BF.757B1EBB%40hotmail.com%3E

--
Tor Olav
http://subcube.com

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