andrel <a_l### [at] hotmailcom> wrote:
> Just curious, why should it not be evenly distributed (or should I read
> that paper)?

The paper explains that there should be a bias and how it should be,
mathematically - but I guess it wouldn't get you much further about the "why".

The thing is simply that incident light coming in at a shallow angle illuminates
the surface less than light coming in steeper.

This could be modeled by multiplying each sampling ray with a correctional
weight term - but it is much more elegant to model it via a non-uniform
distribution of rays, because you can concentrate precious render time on rays
that really matter - and it may also save you some mathematical operations
during the sampling.

It would be some waste of time to run your random number generator output
through some trigonometric formulae first to get a uniform distribution, and
then run those co-ordinates again through more trigonometry to get your weight
- when maybe you can simply run your RNG output through some different trig
formulae to give you just the biased distribution you need to do without a
weight term and with a better overall "computing time per weight" ratio.

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