Christoph Hormann wrote:

[lots]

Keep in minds that the following point may be moot...I haven't studied the
sources....

try {

Having spent most of my copious free time reading CG articles, dissecting
sources, coding some of mine and in general listening to any sources of
information, I feel that I have more of an adeguate understanding of ray
tracing to post the following question?:

1. How does Povray samples area lights?

Granted, Povray is no MC raytracer, but the problem should be similar.

2. Shouldn't it sample the solid angle subtended by the area light?

IIRC, illumination from an area light should be (in Kajiya's notation):
             /                                                dA'cos t'
L(x, psi) =  | g(x, x') rho(x, psi, psi') L(x' psi') cos(t) * --------
             / x' on S                                        ||x'-x||^2

where:
g is the blocking function, psi is the viewing vector, psi' the illumination
vector, rho is the BRDF L is the luminance function, t is the angle between
psi' and surface's normal at x, t' is the angle between psi' and x' and dA'
is the differential area of x'

3. How does Povray approximates this integral?

There is an interesting article in Graphics Gems III (ancient in terms of CG
time) which gives an unbiased probability function for a MC integration,
which should be applicable to distribution ray tracers.

4. Who is the author of the lighting code?

I would love an article from the guy (or guys) detailing the structure of
Povray's lighting engine and I daresay I'd buy a book on the innards of
Povray 3.5, which would make a splendid coursebook in CG.

I never had time to properly study Povray's sources and I'd love to plug in
some CG algorithms I've been reading in these years.

What I miss is an HOWTO (linux-style), detailing the functional units in
Povray.

Maybe...a book, or, better yet, an eBook.
}
catch(flames)
{
  // Exception dumb handler
  // Here we deal with people who can't stand a flame-bait

  // done.
}

Enough ranting...

Seriously, though: why not an eBook about Povray source?
The POV Team could write it (using docbook perhaps) and sell it through the
Povray site, making us tinkerer happy twice (we get to fully understand the
code and we *also* get to finance Povray development)
10$ or 20$ might be a reasonable price and without printing and distribution
costs, most of it would benefit the Povray team.

Just a thought,
Alex

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