In article <41bc6735$1@news.povray.org>,
 Andrew the Orchid <voi### [at] devnull> wrote:

> Right. But when I ment was, there's a keyword (roughness?) which 
> controls the angle at which light affects the surface. I was trying to 
> figure out whether the rad calculations take this into account.

You're asking whether the parameters controlling how lighting falls off 
as angle to the surface changes control the weighting of the radiosity 
samples? As far as I know, no...it uses a plain ol' Lambertian falloff, 
where the point weighting or distribution is done according to the 
cosine of the angle to the surface normal. That is, it assumes the 
surface is perfectly diffuse. This is usually a good enough 
approximation for things radiosity is used for.

The parameter you're thinking of is probably brilliance, which modifies 
the Lambertian falloff by raising it to a power...the falloff is 
pow(cos(angle), brilliance). As far as I know, the sample rays will 
"see" the effects of brilliance on other surfaces, but their weighting 
will be unaffected by it.
(Someone should probably check whether the "too bright" problem of 
highlights still applies...)


> Actually, I suppose you could program POV-Ray to try to illuminate an 
> entire scene with photon maps. I imagine that would go real slow, 
> compute a lot of photons you can't see, and generally not look so great. 

What you describe is "global photons". Possible, can very accurately 
simulate actual physical effects which are otherwise difficult or 
impossible, but extremely memory hungry and not really efficient. 
Multi-pass techniques might be useful...shoot a few million photons, do 
a render pass with the radius of effect of each photon limited (get a 
really dim, spotty picture), and continue to shoot photons and add the 
results together until you get a final picture. Jitter each pass 
slightly, and you get some antialiasing or focal blur in the bargain.


> (Does photon mapping work for a depth of more than 1?)

It wouldn't be very useful if it didn't. ;-)
You can actually specify separate max_trace_level and adc_bailout for 
photons. If you don't, the values specified for rendering are used.

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: <chr### [at] tagpovrayorg>
http://tag.povray.org/

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