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Now here I am, brooding over various official and hacked versions of
POV-Ray, figuring out whether my latest changes broke anything - only to
find /this/:
Top left:
---------------------------------------------------------------
Persistence of Vision(tm) Ray Tracer Version 3.6.1 (g++ 3.4.1 @
i686-pc-linux-gnu)
This is an official version prepared by the POV-Ray Team. See the
documentation on how to contact the authors or visit us on the
internet at http://www.povray.org/.
---------------------------------------------------------------
Top right:
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Persistence of Vision(tm) Ray Tracer Version 3.6.1 (g++ 4.3.2 @
x86_64-unknown-linux-gnu)
This is an unofficial version compiled by:
Christoph Lipka
The POV-Ray Team(tm) is not responsible for supporting this version.
---------------------------------------------------------------
(Bottom left: Difference; bottom right: averaged grayscale with
differences highlighted)
Now this would not normally be too much of a surprise: You tamper with a
version, it behaves differently...
The thing is, the /only/ thing I changed in that particular 3.6.1
version - I swear! - was a constant that causes a slight shift in the
checker, cells and brick patterns.
And recompile, of course. With the same brand of compiler.
Optimized for a different CPU type.
Now what would you think which of these might have the strongest impact
on photon caustics?
The only conclusion I can draw from this is that POV-Ray is
fundamentally incapable of producing identical results on different
machines for some reason.
Well, maybe I should dig in the photons code to see whether it does some
bit magics somewhere, in the photons cache handling maybe. Might be
something that doesn't work as expected in a 64 bit environment - that
would explain something. With a bit of luck, maybe it's even related to
the segfaults I see with photons scenes when compiling POV-Ray with the
Intel compiler.
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