Invisible <voi### [at] devnull> wrote:
> Does anybody, anywhere, have any details of how the algorithm actually 
> works? As in, how is this different to a normal ray tracer?

  A BRDF is a function between incoming light (from all possible directions)
and outcoming light (to all possible directions).

  In other words (in an ideal case), at each point light coming from all
possible directions are taken into account, and this light can be reflected
to all possible directions, with a factor given by the BRDF function.

  Naturally in order to calculate this you would have to shoot an infinite
number of rays from each point, and when those rays intersect other surfaces,
again an infinite amount of rays would have to be sent from those points,
ad infinitum.

  In practice this is, of course, impossible. However, brute force renderers
try to approximate this by simply sending rays at random directions, lots
and lots of them. The more rays are sent, the more the final results
approaches the optimal. This results in a very grainy image at first,
because the amount of samples is not even nearly enough. However, as more
and more rays are traced, the result starts slowly approaching the ideal.

  When the BRDFs are properly designed to simulate the behavior of
real-world materials, the results can be quite realistic.

  Or this is how I have understood it.

  POV-Ray's stochastic global illumination resembles this, although it's
quite limited (and doesn't use BRDFs).

-- 
                                                          - Warp

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