On 12/7/25 10:34, Kenneth wrote:
> "jr" <cre### [at] gmailcom> wrote:
>>
>> "Kenneth" <kdw### [at] gmailcom> wrote:
>>>
>>> So there is some confusion here. I haven't yet looked at the online wiki
>>> docs to double-check...
>>
>> thank you.  (before changing/updating the docs) can someone looking at the
>> sources confirm the defaults, please ?
>>
> 
> In v3.8 beta 1, I've been running a series of tests (on just the photon
> 'refraction' defaults, not 'reflection' so far), using a modified version of the
> OP's code here-- and there seems to be a mixed-up interaction of on/off/default
> in the photons blocks of the light_source and the refracting object. In other
> words, the *default* behavior changes(!) when other changes are made in one or
> the other of the blocks. Sorry that I cannot be more specific yet, as I am still
> testing and trying to make sense of the results. But as it's off-topic here,
> I'll try to post a follow-up in a new thread.
> 
> I don't yet know if these odd results are specific to the 3.8 betas...and/or to
> the OP's specific cylinder light_source...
> 

I believe for the v3.7 / v3.8 versions, including yuqk, the 
documentation which is 'likely' wrong isn't with the light_source{} 
photon{} block, but the object's photon{} block - where the reflection 
and refraction defaults are 'on'.

---

What Kenneth is seeing is true too - there are some complicated 
dependencies and detail when dealing with photons.

For example, and using the updated scene I posted moving the beam light 
source outside the media box and using the photon mechanism for all 
light intensity calculations, if we set the beam light_source photon 
block's refraction to 'off' we get no photons deposited anywhere. The 
photon tracing stops at the first media box's transparent surface.

The same is true if we set the media box's photon block refraction 'off' 
while the light source's refraction is 'on' - no photons. The object's 
setting overrides the light's in that case.

However, if we turn the light source's photon refraction 'off' and the 
media box's refraction 'on', the light source's setting wins at the 
first media container's surface rather than the object's setting.

OK behavior I think, but not simple.

---

Secondary questions pop into my head: Does having an ior of other than 
one changes the specific behavior above? When we have transparent 
surfaces and ray reflection/fraction ray splitting, do the light's 
photon block's reflection/refraction settings continue to propagate in 
the same ways? What happens when we use, 'magic light transport', pass 
thru objects with light sources?

As Kenneth mentioned, there are too some differences in behavior 
depending upon the light source type. The cylindrical light working (at 
least sometimes) within objects containing media - bending our media 
light sources must be outside media containers rule.

Bill P.

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