On Mon, 23 Sep 2002 05:20:26 -0400, Tom Melly quoth:

> "Mark Wagner" <mar### [at] gtenet> wrote in message
> news:pan### [at] gtenet...
>> On Fri, 20 Sep 2002 12:06:19 -0400, Tom Melly quoth:
>>
>>
> <snip>
> 
> Thanks Mark - how about:
> 
> 1) changing image resolution
> 2) changing media density (if using media photons)
> 
> Also, I was surprised to read that changing the camera position was
> okay. This implies that photons are mapped to objects rather than
> positions. Is there an idiot's explanation as to how photons work in
> Pov?

Photons are mapped to positions, not objects.  The reason you can move
the camera around safely is because, unlike with radiosity, POV
calculates *all* photons in the scene, not just those that would be
visible from the current position.

Idiot's Guide:

When you specify that an object is to have photons shot at it, POV traces
rays at that object from each light source that casts photons.  It then
reflects and refracts each ray as it would during regular ray-tracing.
Whenever one of those rays hits an object, POV-Ray stores some data about
that ray-object intersection: where it took place, and what color the ray
was at that point.  This is a photon.

When you specify that an object is to have photons shot at it, POV-Ray
treats that object's texture as being opaque for the purpose of shadow
testing.  Additionally, if you've got any photons in the scene, then
whenever POV does lighting calculations for a point, it does an additional
check to see if any photons have been stored nearby.  The number of
photons it looks for, and how far it goes to find them, are set by your
photon settings.  In effect, it combines all the photons it has found for
the point and treats them as an additional light source illuminating that
point.

More advanced topics such as media photons I haven't figured out entirely
yet.

-- 
Mark

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