On 25 Feb 2000 08:13:05 -0500, Nieminen Juha
<war### [at] sarakerttunencstutfi> wrote:

>: If a bounding object is smaller than what it bounds, the results are
>: unpredictable.
>
>  Nope. They are very predictable. Only a ray hitting the bounding object
>can hit the bounded object.
>
>  A bounding box is a bounding box, not a clipping box. The current
>implementation is the correct one. It should be documented better to
>avoid confusion, but it's correct.

Suppose the bounding box is smaller than the object itself. If and
only if a ray hits the box, it will look for the first intersection
with the object itself _along_the_ray_ and that intersection could
easily be outside the bounding box! So if you have a sphere bounded by
a smalled box, the result would look as if you've rendered the sphere
and then applied to the resulting image an alpha channel based on the
box. This, in my dictionary, is not correct.

Of course specifying a bounding box smaller than the bounded object is
incorrect in the first place :) but there are a few trick (besides
vampires and anti-vampires) that can be done with it.


Peter Popov
pet### [at] usanet
ICQ: 15002700

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