On 9/27/19 11:46 AM, Alain Martel wrote:

...
Thanks for the clarification on how the photon shooting parallelism works.
> 
> You can have a single polygon or triangle that is transparent and have 
> an ior. It will refract light.
> 
...
I was aware the disc had a defined inside and would support an interior, 
but wasn't aware single polygons or triangles were like this too. My 
original polygon concern was then not warranted.
...
>>
>> (3) - Spot lights / cylinder lights can still largely miss when doing 
>> this kind of thing. Gets complicated to optimize. 
...
>>
> 

OK... Some thinking aloud where I'm not completely sure what POV-Ray is 
doing today.

On splitting the cylinders (and perhaps tori too) into chunks. My 
footnote 2 & 3 sort of hinted at the issues I believe we might have with 
that approach. Norbert has spotlights and those, like cylinder lights, I 
believe define the spiral pattern with respect to the light source 
definition not to the target shape's bounding box. Meaning breaking 
those shapes up will increase the number of light-shape pairings during 
photon shooting without changing the end result.

In other words, my current understanding is if we changed spots to point 
lights we'd change to always centering the shooting spiral on each 
shape's bounding box. The splitting then would perhaps help more in that 
situation. Does my current understanding match what you (or others) 
think happens?

Also if right we could probably improve photon shooting performance 
quite a bit with a split_union off for that grille then splitting it 
into multiple unions where for some the whole sub-union might be outside 
the spot spirals.

Anyway, as an experiment I took the scene and changed back grille so it 
was not involved in the photon shooting to test the idea its mostly 
causing the graininess. Also changed photon spacing from 0.004 to 0.02. 
Attached is the result which took about 13 minutes (8 of it photon 
shooting) on my little 2 core i3.

The result I think lines up OK with how I think spot light photon 
shooting works and my suspicion the bursts of photons from the spirals 
crossing that back grille are involved in the graininess. There is still 
a little, but I suspect its coming mostly from the stem of that left sor.

Aside: Yep, a comparison to a render with the grille as a photon target 
would be ideal, but that render is still shooting photons after two 
hours and not sure I have the patience to let it finish...

Bill P.

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