POV-Ray : Newsgroups : povray.beta-test : v3.8+ crackle instability (facets?) with >1 uses per thread. : Re: v3.8+ crackle instability (facets?) with >1 uses per thread. Server Time
18 Jul 2024 06:55:40 EDT (-0400)
  Re: v3.8+ crackle instability (facets?) with >1 uses per thread.  
From: William F Pokorny
Date: 13 Jun 2024 19:26:02
Message: <666b800a$1@news.povray.org>
On 6/11/24 14:17, Thorsten wrote:
> It is impossible to predict the complexity with modern CPU, I think.

I agree. Today's hardware optimizations make performance tuning a tough 
trick - and make questionable a number of "rules of thumb" about which 
algorithms perform best.

> The benefit would be that the "texturing" would become a completely 
> separate task, and could actually be done (sans reflection and 
> refraction) after tracing, which, if nothing else, would lead to a cool 
> looking render preview. The other effect would be that at least bounding 
> optimisations and mesh intersection testing could be done on a GPU.
> Yet another benefit you get from separating the tracing and the 
> texturing is that you end up with a sort of frame buffer that contains 
> object data. An idea I never pursued to the end 20 or so years ago was 
> that this gives rise to the ability to edit a ray-traced scene on the 
> fly because you have access to the objects making up an individual pixel 
> and can separate objects in and out of the scene as long as the camera 
> doesn't move.

Cool ideas. :-) I can see how some parts might work, but far from all of 

Our ray tracing and texturing is today tangled in places (adc bailout, 
filtering/transparency, media, object modifiers). There is too how to 
handle anti-aliasing (AA) / camera focal blur.

Though our 'AA' approach today is expensive(a), it's a strength with 
respect to 'true result' that each sample ray considers the scene - 
including texturing - alongside all the ray tracing / branching in total.

Bill P.

(a) - With respect to performance, on my 'try it someday' list are 
cheaper AA / focal blur modes where the rays beyond some 'sampling 
depth/count' would terminate at a much shallower max_trace_level/sample 
count(*). Or maybe we gradually reduce the trace depth in opposition to 
the AA/blur sampling 'depth'. Results would be less true, but I 
'suspect' they'd often look good as a rule. (There is a tradeoff buried 
in the idea as the less accurate results due shallower ray trace depth 
would sometimes itself trigger additional sampling - and sometimes not 
where we would otherwise have shot more rays.)

(*) - Yes! I made trying the idea harder by implementing the forced min 
sampling AA in yuqk.

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