"Jim Holsenback" <jho### [at] hotmailcom> wrote:
> > So your objects *do* intersect - not their surfaces, but their volumes.
>
> doesn't open (if applicable) and hollow keywords overcome that problem?

Uhm - no.

"Open" basically creates an object with an infinitely thin wall - but such an
object has no interior that an IOR would be applicable to. Or, seen from a
different perspective (and that's also POV's perspective), the interior does
*not* pertain to the wall (which is just an infinitely thin surface), but
rather to whatever is enclosed by it.

But obviously, with some of the surface removed, it is no longer possible to
clearly specify where the inside begins and the outside ends. So combining
"open" (or "clipped_by", for that matter) with an IOR other than 1.0 (or any
other different interior property than the air outside) messes with the object
in a fashion that has no real-world equivalent whatsoever. Unless someone
discovers a material in which the speed of light and the media density depend
on where the light entered the object.


All the while, "hollow" just specifies that the object itself is fit to contain
media. Which, as I just mentioned, doesn't mix well with "open"/"clipped_by"
either.


So what you need is either an "open" shape with a surface that models glass
sufficiently well without relying on IOR (which is difficult), or a CSG
difference of two sor objects defining a finitely thin wall. Or a single lathe
object comprised of a closed spline, or something alike.

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