Lonnie nous apporta ses lumieres en ce 2005-07-22 08:19:

> I am quite certain that the strange disk of points in the orb's shadow is at
> least an artefact, it's suprising that there weren't more of them in a
> scene with millions of bouncing photons.   I got a warning that the
> max_trace_level had been reached, even though it had been set (in the
> global photon block) to what is to me an  incredible 41.  It would be nice
> if POV could pop up a dialog box when this happens, allowing you the option
> of increasing it.  While this was rendering, windows increased the size of
> my page file to over one gig, no suprise considering the huge photon map.
> What was a suprise at first was the erratic CPU usage.  While doing the
> area above the orb the CPU ran flat out, with a render speed well over 100
> PPS.  When it started on the orb, the speed slowly dropped, eventually to
> under 1 PPS near the center.  CPU usage dropped dramatically, often to just
> an idle with occasional spikes.  A friend pointed out that the hard disk
> was in constant use, even though no other major apps were running.  I would
> guess than in situations like this the speed of the CPU is not the
> bottleneck, hard disk access speed is.  A possible solution I'll try is
> relocating the swap file on a second hard drive.
> 
> A question that comes to mind is how random is dispersion without jitter?
> Suppose I am doing an animation (I truly am a cruel task master) where the
> orb spins.  The facets are 22.5 degrees apart.  If I use no anti-alias and
> no photon jitter the orb rotated 22.5 degrees should produce exactly the
> same scene as the orb with no rotation, but I have a sinking feeling this
> will not be true.  More tests on the way - I'll let you know.
>

When you start to swap, the CPU is always waiting for the drive. Spliting your swap on
2 physical 
drives may accelerate things some. It can be done with Windows 2000, and probably with
XP. Using a 
raid controler could help more.

Without jitter, dispersion is NOT random. The true random bits in POV Ray are: crand
and jitter, 
nothing else.

Alain

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