I've been working a bit on this with photon mapping.  If a global photon map
is created, the directional data can be used so that you only shoot sample
rays in directions where photons came from.  When doing this, you have to
use weights to compensate for the uneven distribution.  The code is in the
UVPov source in photons.c (but isn't very well commented and is not
currently used... but you can look at it if you like).  So, yes, this can
efficiently be done.

-Nathan

Margus Ramst <mar### [at] peakeduee> wrote...
> Perhaps something like this might work - if the calculation of weights can
be
> handled. The weight of a sample has to be proportional to the area of the
sky it
> represents (in the simplest case that the surface reflects only
diffusely). I am
> not sure how this can be efficiantly calculated with uneven distribution
of
> samples.
>
> Margus
>
> Nieminen Juha wrote:
> >
> >   Perhaps there could be a special keyword that you could apply to
objects
> > which tells povray "this object is very small and very bright, so send
more
> > radiosity rays here".
> >
> > --
> > main(i,_){for(_?--i,main(i+2,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[i]
> > ):5;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*-
Warp -*/

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