POV-Ray : Newsgroups : povray.general : Tracking down slow renders : Re: Tracking down slow renders Server Time
28 Nov 2023 14:18:12 EST (-0500)
  Re: Tracking down slow renders  
From: William F Pokorny
Date: 8 May 2023 18:09:41
Message: <64597325$1@news.povray.org>
On 5/8/23 10:53, Chris R wrote:
> I realized later that I had already increased my AA thresholds for the latest
> run, to no effect.  However, a combination of decreasing the max_trace_level
> from 30 to 10, as well as decreasing the block size from 32 to 8 seems to have
> markedly increased the over all speed, as well as eliminating the days-long
> rendering of the few problem blocks.

What version of POV-Ray are you using?

I'll mention a couple things I didn't note others bringing up.

1) If you have any transparency - and IIRC - since v3.7 rays transit 
through transparent surfaces, with an ior of 1.0, without increasing the 
max_trace count. This was done to avoid part of the old problem of black 
pixels on hitting max_trace_level.

What I've had happen, very occasionally since, is some smallish number 
of rays skimming a 'numerically bumpy' surface. The rays end up 
transiting in an out of the shape a large number of times. Alain taught 
me the trick of changing the ior to something like 1.0005 so those 
transitions through transparency count again toward the max_trace_level. 

2) With isosurfaces, using 'all_intersections' (really a max of 10) when 
you don't need them 'all' can be expensive. I usually start with 
max_trace at 2. Sometimes I cheat down to 1, if the object is simple, 
opaque and I don't see artefacts.

There is too the quality level. If of the radiosity, subsurface and 
media features all you use is radiosity, you can drop from 9 (=10 & =11) 
to 8 and check performance without radiosity. Dropping to 7 cuts out 
reflection, refraction and transparency(a). Plus, you can use start/end 
row start/end column settings to render only in regions running slow for 
performance testing.

Bill P.

(a) - Makes me wonder if different bucketing of some of those features 
relative to the quality level would be useful given we don't today use 
all the values? The internal cost of the conditionals would be similar 
(the same?), I think. It would make the quality setting different than 
what folks are used to using. Something to think about I guess.

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