Am 13.04.2010 22:29, schrieb Kenneth:

>> But the approaches are not mutually exclusive: we could have
>> the default cutoff distance for each light source set based on
>> adc_bailout and intensity to speed up rendering without user
>> interaction...
>
> I vote YES to that one!  This is the way that I assumed POV-Ray already worked.
> :-(  It would speed up many things, to my way of thinking, cutting off
> unnecessary calculations for: shadows, IOR, photons and their target objects,
> etc. I'm rather clueless as to any problematic 'details' this might produce (or
> computational overhead) but on first glance, it seems like a winner.

It is done for *some* computations, but there's no shortcut yet to check 
the distance to a light source before testing for shadows (or even 
before computing the distance-attenuated brightness, for that matter).

> Here's another odd and clueless observation/question: In 32-bit POV-Ray, the
> default adc_bailout is 2^8. In the 64-bit version, is it 2^*higher power*?

You mean 1.0/2^8 for the 32-bit version, right?

In the 64-bit version, the default is still the same. It's a limit to 
cut short computations that would be unlikely to have any /noticeable/ 
influence on the resulting image; it has nothing to do with the internal 
precision of computations.

By the way, the major difference between the 64-bit and 32-bit versions 
is just the amount of memory POV-Ray can make use of, by using wider 
memory address words in the 64-bit version. While 64-bit processors do 
offer integer arithmetic with larger range than normally used on 32-bit 
processors, they do not offer any advantage in range or precision when 
it comes to floating point arithmetic, which is what POV-Ray really 
needs. Hence, all the constants are the same in both versions.

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