POV-Ray : Newsgroups : povray.newusers : a given camera doesn't give expected object's shadow laying direction : Radiosity Server Time
21 Feb 2024 22:31:15 EST (-0500)
From: clipka
Date: 26 Sep 2018 08:51:16
Message: <5bab80c4$1@news.povray.org>
Am 26.09.2018 um 11:53 schrieb Warren:

> By the way... I'm looking for a tutorial that explains in details how radiosity
> works (Or is it to complicated ?).

Before I take a long deep breath and then exhale an excessively long
post - are you interested in details how to use it (i.e. which knob to
turn in which situation), or do you genuinely want to know the details
of what's going on under the hood?

> My current skills with the radiosity are the
> following:
> I render a radiosity scene in two pass, a first render with something like :
> +W80
> +H50
> +RFO
> +RF"radio_samp.rad"
> Output_To_File=Off
> Display=Off
> Then a render with
> +Wfinal width and +Hfinal height
> +RFI
> +RF"radio_samp.rad"
> Of course, I save lot of time by doing this.

Mmmm... um... nyyeeeh... I'm not so sure about that. As a matter of
fact, I doubt it.

If you're running the first pass once, and then the main render multiple
times for some reason - then yeah, that'll save time. But why would you
render a scene multiple times without changing the scene? And if you're
changing the scene, you need to re-run the first pass as well.

If however you're running the main render just once, all you're
effectively doing is going through POV-Ray's regular radiosity pre-trace

At best, this just compensates for a poor choice of pre-trace quality
settings. At worst, your pre-trace quality settings are good enough and
you're letting POV-Ray do pointless extra work.

In older versions (v3.6 and earlier) radiosity had some nasty conceptual
flaws causing artifacts that were difficult to eliminate, and IIRC the
save-restore approach helped avoid at least some of them, so it had its
use back then. But those flaws have been eliminated in v3.7, and from
both a quality and performance standpoint the save-restore approach is
pointless. It only makes sense if you do indeed save once and load
multiple times.

> I don't know much more about
> radiosity and I'd like to know the details of this technique :-D.

Let me know the general direction of your curiosity, and I guess I can
spew out some long-winded mix of useful and useless information about
it. I'm not the original author of the radiosity code, but I gave it a
thorough overhaul for v3.7, and although that's been a while now, I
might actually remember a thing or two about it ;)

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