Le 2013-02-11 12:40, Warp a écrit :

>
> I haven't tested your scene, but I think you have a slight
> misunderstanding about what bounding objects do.
>
> A bounding object is *not* the same thing as an intersection with an
> "invisible" object. It cannot be used to "cut away" parts of an object
> because that's not how it works (nor is it intended for that purpose.)
>
> What happens is that when a ray is tested against the object, it will
> first be tested against its bounding object, and if it hits that, then
> it will be tested against the actual object. This test doesn't actually
> care where the bounding object is. Regardless of where it is, it just
> tests to see if the ray its hit, and proceeds with the actual intersection
> test only if that was so.
>
>  From this it follows that if the bounding object does not actually fully
> enclose the actual object, you'll get incorrect rendering (the visible
> parts of the object will depend on the orientation of the bounding object
> with respect the direction of the rays' origin.)
>
> If you want to actually clip the object with another, use clipped_by,
> which has been designed for that exact purpose.
>
> And in fact, given that wanting to both bound and clip with the same
> object, there's a handy shortcut, namely "clipped_by { bounded_by }"
>

What I've done is merely reproducing what I found to be causing some 
problem in an older scene from someone else that I rendered at a larger 
resolution and some added features.
Apparently, there was a time when this was commonly used.

I KNOW that bounded_by is not intended for that use.

One of the problems seems to be that, some shadow rays that /never 
reatch/ the bounding object /do/ generate shadows.
If you render the provided scene, you'll see shadows in areas that are 
visible far from the visible part.


Alain

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