Alain <ele### [at] netscapenet> wrote:
> statto nous illumina en ce 2008-12-10 07:22 -->
> > Is there a way to use a fog-like command to kill all rays over a certain length?
> >
> > Rather than the exponential decay with length with a normal fog, I would like
> > any ray over a certain length to be entirely eradicated, and any ray shorter
> > than that to be transmitted, possibly with a slight fuzziness between these two
> > extremes.
> >
> > Any ideas?
> >
> >
> There is no ready, automated, way to do that. I'm not sure why you want that.
>
> What you can do:
> Enclose your scene within a large sphere centered at the camera. That sphere's
> radius is set to the distance at whitch you want your rays terminated. Be sure
> to make it hollow, or use the "inverse" key word, if you want to use some fog.
>
> Use one of the background feature, and make sure that there are no object
> farther than the maximum distance you want. You may put your scene into an
> union, and intersect it with a large sphere. Anything outside that sphere will
> be removed.
>
>
> SarkD, bounding box don't work that way. Bounding boxes are used to make ray
> intersection tests with objects more efficient. You test against the list of
> bounding boxes, and, if you hit one, you test the object within.
>
> --
> Alain
> -------------------------------------------------
> A modest man is usually admired; if people ever hear of him.

Explaining why might make my question clearer: some friends and I were
discussing what it would look like if you could take a film with a camera so
fast that you could watch the progress of light across a room. I want the light
to ooze slowly out of the lights and over objects, and so I want to terminate
any ray which is longer than a distance ct, where c is the speed of light and t
the (short!) time since the start of the film.

If I understand your union-with-an-inverse-sphere suggestion correctly, it will
destroy all objects greater than a distance ct from the camera, which is not
quite the intended effect!

Perhaps my idea is impossible with POV-Ray...but I thought it would be easier to
make a computer model than try to do it in real life. ;)

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