Warp nous illumina en ce 2008-05-26 04:17 -->
> Jan Dvorak <jan### [at] centrumcz> wrote:
>> Hello,
>> when using +am2 (recursive antialiasing), are the corner samples shared 
>> between their respective pixels, that is, is +am2 as fast as +am1 or is 
>> it four times slower if no antialiasing takes place? Are the edge 
>> samples reused?
> 
>   I actually don't know the exact details of the antialiasing algorithm
> used, but I have the impression that no samples are shared between pixels
> in either method. This is because antialiasing can be jittered, and if
> that's the case, most samples wouldn't be at pixel edges and thus difficult
> to share. (I have to admit, though, that I can think of variations where
> samples can be jittered *and* shared between pixels. However, I don't know
> exactly what POV-Ray is doing.)
> 
Acording to the documentation, there is a saving and reuse between adjacent 
pixels and subpixels:
"The advantage of this method is the reduced number of rays that have to be 
traced. Samples that are common among adjacent pixels and sub-pixels are stored 
and reused to avoid re-tracing of rays. The recursive character of this method 
makes the super-sampling concentrate on those parts of the pixel that are more 
likely to need super-sampling."

According to this, the first pixel traced takes 4 times as long (the 4 corners 
need to be evaluated). Those of the first line and column take twice as long 
(two corners have already been evaluated and saved), but the rest only take the 
same amount of time as non-antialiased if the differences are under the treshold 
value (3 of the corners comes from the previous line and the preceding pixel of 
the current line).

-- 
Alain
-------------------------------------------------
WARNING: The consumption of alcohol may make you think you are whispering when 
you are not.

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