Re: Shadow Volumes (was Re: Scenes with lots of simple objects)

Gavin Bell (
Wed, 8 Mar 1995 18:39:16 -0800

On Mar 8, 7:27pm, Linas Vepstas wrote:
> I beleive that (and I might be proven wrong) that this doesn't
> work when the objects stuffed into a separator node affect
> each-other's attributes in an order-dependent way. This is
> one reason I screamed last fall, when it became clear that the
> Inventor-VRML proposal had a strong order-dependence in it.
> (Clearly, the act of pre-pruning may cause you to accidentally
> prune away some item/attribute that affects how a visible part
> of the scene looks like. I don't know how to solve that
> problem.)

Just prune Separator (or Separator-like) nodes and you're fine; the
definition of a Separator is that no state "leaks out", so pruning the
Separator because it is outside the view volume or because it is inside a
shadow volume will cause absolutely no problems.

By the way... I'm familiar with Seth Teller's work on room-to-room visibility
algorithms. You seem to be describing something more general-- can you point
me to any references? I understand in theory, but it seems like
implementation and/or specification would be tricky (for example, how many
shadow planes are too many?).