Gilles Tran wrote:
> 
> Jaime Vives Piqueres wrote:
> 
> >   But, if so, how Gilles radiosity scenes look so nice? I my self tried
> > just now pretrace start and end to 1 with my current irtc entry, and the
> > result is a 30% faster than with the recommended settings. And,
> > strangely, the result seems to be more "natural" although it has some
> > artifacts.
> 
> To be frank, it's very confusing. I just tested this and the truth is that I
> don't have a proper answer. In one little test scene, using Christoph's rad
> "IndoorHQ" settings, using pretrace values <1 is better than pretrace 1
> values : slightly lower rendering times, slightly less artifacts (but
> artifacts nonetheless).
> Now I'm sure to have experienced the same speed boost as you just noticed,
> which is why I've been using these settings for almost a year with no
> visible problems (I think that it was Xplo who found this trick). Note that
> this could also explain why I don't have artifacts when I stop and resume
> radiosity scenes (something I've been doing systematically to save memory,
> even with 640 Mb of RAM).
> I guess we should test this on full scenes. I just launched one of these
> (800*320) with pretrace activated, and will render it again without. I
> should have some answers on Saturday...

It's been a while since I actually messed with pretrace parameters, but
IIRC, error_bounds > .1 benefit visually from a really precise pretrace
(although above .4 or so, the benefit may not be worth the time anyway),
whereas smaller error_bounds don't, so pretrace should be set to 1 to
save time. Don't take this as absolute gospel, though; these are
approximations off the top of my head, and not based on extensive testing.

It's worth pointing out that the messier your scene naturally is (due to
texturing, or objects casting a lot of small shadows, or something), the
less perfect your radiosity has to be. Those of you who like making
radiosity scenes where everything is apparently made out of smooth gray
plastic might do well to keep that in mind...

-Xplo

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