On Thu, 14 Feb 2002 05:53:36 -0500, "Timothy R. Cook"
<tim### [at] scifi-fantasycom> wrote:


>> Two ways to test: Either make both constructions and check the
>> end-render stats for each, or check how close the vista-buffers hug
>> the object.
>
>It's more of a general question, as I have a large number of instances
>wherein if discreet CSGs are faster, then the whole scene will be
>sped up, but if they're not, I don't want to spend the time changing
>everything just to check, then find out it's not...

I suggested that you test for yourself because it's been a long time
since I was current enough on the POV-Ray internals to answer the
question off the top of my head.

Difference is a tricky construction to autobound tightly, there's that
nasty INVERSE keyword involved. In general a difference can't be
bounded internally at lower levels than the whole object, if a ray
hits the 'outer' object all 'inner' objects will have to be evaluated.
As the number of 'inner' objects increase the total evaluation cost
increases as well. 

Look at your end-render statistics and look closely at the hit-rates.
If your hit-rate is below 10% or so you have a problem, if it's below
1% you have a big problem!!

In general differences with less than 5 inner objects shouldn't cause
problems, below 10 objects you shouldn't have big problems, but this
is just my ROT. YMMV.

/Erkki

Post a reply to this message