Wasn't it JWV who wrote:
>hello,
>
>30 minutes ago I started looking at the parametric object, and the result
>was a bit strange (and slow). I used the piece of code from the help files
>to make a sphere, and then changed it to make a half sphere and gave it a
>"pigment{White}". I was expecting to see a white half sphere, but what I
>saw, was a blackish/grey-ish kind of shape.
>This puzzeled me. So I made added a half white hollow sphere to the scene,
>to show you (the newsgroup) wat I was expecting, and what I was getting.
>But then it even became more puzzling. There were now 2
>half-white-hollow-spheres!
>
>Does anyone know what is happening here?
>
>The source will be posted in p.b.sf

It looks like it might be a bounding bug, and may have something to do
with shadow testing.

The default Bounding Threshold is 3. [When there are only a few objects
in a scene, the overheads involved in performing bounding tests are
often not worth while, so POV doesn't perform bounding when there are
less than this number of objects present.]

When there were only two objects in your scene (the parametric object
and the plane) bounding was disabled. Adding any third object caused the
bounding code to be activated. [You can force bounding to activate by
setting the Bounding Threshold to 0 with +MB0 in the command line.]

There are other weird things going on. Changing your "contained_by" to a
box causes the parametric to render correctly.

I suspect the shadow testing code, since some of my isosurface tutorial
examples have less than three objects in the scene and seem to render
correctly (I'll check them all properly under 3.6 tomorrow). The thing
that causes the difference in my example scenes is that my parametric
examples have "no_shadow".

-- 
Mike Williams
Gentleman of Leisure

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