On 1/26/23 14:40, Cousin Ricky wrote:
> On 2023-01-25 12:22 (-4), Alain Martel wrote:
>>
>> Any sampling array size between those values will be silently increased
>> to the following size of the list. A 4 x 4 adaptive is really 5 x 5, 6 x
>> 6 is promoted to 9 x 9 and 10 x 10 become 17 x 17.
> 
> Not according to my tests.  The attached images were rendered with
> area_illumination to reveal the internal array of lights.

Probable complications - as best my glitchy memory serves...  :-)

area_illumination essentially walks through each of the area light 
positions - more or less - as originally specified; tracing each are 
position in turn and coming up with a final, weight adjusted, result. 
Any adaptive bits (for shadow rays only) and circular bits run at each 
of the area light's effectively moving 'center' positions with 
area_illumination on.

The adaptive mechanism being discussed in this thread comes into play 
only during shadow ray tracing.

The circular option itself introduces some bias in the counts and 
position of the area lights as the rectangular specification gets mapped 
to a circular one.

--- Other misc.

There is an open github issue on the circular option occasionally 
introducing visible bias in lighting results.

https://github.com/POV-Ray/povray/issues/222

There is too this open github issue related specifically to 
area_illumination and adaptive/circular shadow calculations not playing 
well together:

https://github.com/POV-Ray/povray/issues/224

I believe these github issues still unsorted in any available POV-Ray or 
branch/patch release.

Bill P.

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