On 15/01/2011 9:39 AM, Jaime Vives Piqueres wrote:
>    If I run two consecutive renders of this scene and difference the
> results, with 3.6 I get a totally black image (as it was expected). With
> 3.7 I get visible differences... Using the save/load mechanism only
> seems to make it worse and more noticeable.
>
>    I'm starting to think this is a problem with my build... something
> must have been gone wrong when compiling the RC2 sources, because I
> don't see anywhere mentioned that radiosity samples are now random for
> each run. Can anyone do a quick test?

Using pvengine.exe and pvengine-sse2.exe, RC2. I get identical results 
on consecutive renders, sorry.

-- 
Regards
     Stephen

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> This whole thing is a puzzler to me, too; unfortunately I haven't
> found the time to dig into it yet. My only idea is that something
> might get garbled during saving/loading of the pretrace data.

   Well, don't dig too deep...

   I think it all was a combination of (1) my ignorance about the
internals, (2) my abuse of pretrace, and (3) a curious coincidence.

   (1) After looking at the wiki and the code itself, I finally realized
that 3.7 radiosity, using SMP, cannot give the same exact results on two
consecutive renders... there was a "d'oh" moment when I learned about
the new +HR option. :)

   (2) After some tests, I confirmed that it is better and slighty faster
to use the same pretrace settings and "always_sample off" on the second
pass, as Clipka said. I seem to understand that even if I set
pretrace_start and pretrace_end to 1, POV-Ray is still taking some new
samples, and somehow this causes much bigger and more random artifacts
than using proper pretrace in some situations.

   (3) Anyhow, the thing is that I didn't notice any problem before
RC2... I have not used the betas extensively, but at least enough to be
sure that I would have noticed all this long time ago! So, I got back to
my finished 3.7 scenes, and realized that I never tried my "2-pass
radiosity" setup with the sort of scene where this issue would be
noticeable... I always used it with outdoor scenes, and this things
tends to be more noticeable on indoors.

   Well, mystery solved: at least now I know that I'm not crazy... just a
bit stupid. ;)


-- 
Jaime Vives Piqueres
		
La Persistencia de la Ignorancia
http://www.ignorancia.org

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