On Sat, 26 Jan 2002 11:41:25 +0100, Tim Nikias <tim### [at] gmxde>
wrote:

>So, I was wondering, what exactly are photons internally?

Internally, each photon has a location, a color, an intensity, and
also remembers the direction it came from (and some info for the
octree).

>Small lightsources or something like "glows" from MegaPOV,
>which only brighten up the places without actually doing
>lighting?

Lightsources are more like it.

>And are photons interpolated in 3D-Space, but
>wrapped onto surfaces, or what?

They reside in 3D space. They can even reside in media if you tell
them so. Lightmapping is used in pure radiosity (i.e. not monte carlo)
calculations and is a completely different beast.

>I was just wondering about a late image I made, and the strange
>speckle sizes the photons appeared to have. 

A case of parameter tuning, I believe.

>And while wondering about that, I though one could maybe create 
>a SDL Photon lightmapper using trace and lightsources...

Yes, it can be done. And it will be dreadfully slow, if POV doesn't
run out of memory building the light buffers.

I had the exact same idea quite some time ago (before I discovered
these newsgroups) - using virtual lightsources to model caustics. It
turned out that someone has invented the wheel already as this was how
Radiance (I think) included mirroring surfaces in radiosity
calculations. Alas, my programming skills were not sufficient by far
at the time so I only got to coding the parsing and put it off. I'm
glad I did as Nathan kame up with UVPOV soon after that and all my
efforts would have been in vain if I had not :)

Anyway, back to your question, you could simulate reflective photons
using point lights with a small fade_distance (although photons do not
fade themselves there's no other way to localize their effect). You'll
need some crazy light_grouping but it might as well work. I think
using spotlights will be a better choice, though, as you'll be able to
localize the effect in a more controllable fashion.

Hope I'm making some sense so early in the morning (1:15 pm :) ).


Peter Popov ICQ : 15002700
Personal e-mail : pet### [at] vipbg
TAG      e-mail : pet### [at] tagpovrayorg

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