Larp nous illumina en ce 2008-08-07 14:21 -->
> Alain wrote:
> 
>> How are the holes made?
>> Transparent parts in the image_map, or actual holes made
>> with a diference? With the diference, you can try using a
>> merge of all the holes, it could be somewhat faster.
>  
> Holes are "real holes": rotated cylinders grouped in an
> union and then differenced with a can.
> 
> Should the merge be faster than the union? At least
> Documentation says opposite:
> 
> "Note: that in general merge is slower rendering than union
> when used with non transparent objects."
> (http://www.povray.org/documentation/view/3.6.1/307/)
> 
> Well, I gave merge a try and got rendering time 1:07:39 (no
> focal blur) which was even a bit more than with then
> previous render of original scene with no fb (about 1 h 5
> min. But I have to confess that tonight I surfed bit in the
> web while rendering, which could maybe alone explain
> difference of three minutes...
> 
> Probably the size of the picture I used in the etiquette --
> 5654x2724px -- is much more than needed when rendering
> scene at this size. I made the picture that big to make
> closeups with good quality possible. Maybe that explains
> significant part of the long render time?
> 
>    Larp
> 
Usualy, an union is faster than a merge due to a more efecient bounding and sub 
bounding: the usion is split into it's composants for the bounding. A merge 
can't be split that way. When using a diference or intersection, the bounding 
boxes of all components tend to enlarge to that of a merge of all components.

When you use a diference, all bounding boxes from all components tend to cover 
the whole object. That mean that every ray gets tested against every bounding 
boxes, and then, need to test against every components of the diference. Using a 
merge, you have to deal with lot less coincident bounding boxes.

You could also use a blob with a very small treshold value or a very large 
strenght value. This will minimize the rounding when two or more components touch.

-- 
Alain
-------------------------------------------------
   My wife likes to talk on the phone during sex; she called me from Chicago 
last night.
	Rodney Dangerfield

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