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On 29-Dec-08 14:40, clipka wrote:
> andrel <a_l### [at] hotmail com> 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".
Ok, I'll try to read it. If only I could find the link.
Could you post that again, I clicked through most of your posts here and
I cannot find it. :(
> The thing is simply that incident light coming in at a shallow angle illuminates
> the surface less than light coming in steeper.
Ok, that would be a fixed relation that does not depend on the material
used. I should be able to derive that myself. If only my brain would be
not so rusty.
> 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.
I'd be surprised if there is not already an efficient random generator
that does that all in one go, bypassing the need for trigonometry. Maybe
we only need the help of a resident google expert.
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