Tim Attwood nous apporta ses lumieres en ce 2007/09/19 06:09:
> The docs are off a bit, but for clarification...
> 
> Docs: "The keyword pass_through causes
> photons to pass through the object unaffected
> on their way to a target object."
> 
> Docs: "Once a photon hits the target object,
> it will ignore the pass_through flag."
> Photons can still be deposited on objects
> with pass_through on.
> 
> When no_shadow is used in an object then
> photons are not deposited on it.
> 
> This is usually the effect that people notice
> and incorrectly equate with pass_through or
> collect on.
> 
> The docs suggest that you can set pass_through
> off on no_shadow objects to prevent photons
> from being cast thru it, but this isn't the case.
> If POV was actually this way the banded
> part of the caustics from the far water would
> disappear when pass_through was off in your
> test scenes, but the spots from the near water
> would remain on the rear box anyways.
> 
> There are ways to work-around this if you want
> such images.
> 
> Example 1: You can split the water into
> two objects and remove target from one of
> the sides to only have the near caustic on
> the rear wall.
> 
> Example 2: You can render the image with
> pass through set on the center wall with
> save_file set to catch the caustics, then
> re-render with load_file and no_shadow
> to let the spotlight hit the far water, but
> still have caustics on the no_shadow wall.
> 
> 
> suggested documentation change for 3.6...
> 3.6.3.2.2  Shooting Photons at an Object
> 
> remove old wording
> ---------------------
> If you use the no_shadow keyword, the object
> will be tagged as pass_through automatically.
> You can then turn off pass_through if necessary
> by simply using photons { pass_through off }.
> 
> replace with
> ------------
> If you use the no_shadow keyword, no photons
> will be deposited on the object, and photons
> will pass through the object.  When using the
> no_shadow keyword in an object the pass_through
> and collect keywords are ignored.
> 
> suggested code improvement
> -----------------------------
> Deposit photons on no_shadow objects. The old
> behavior can be preserved with collect off. 
> 
> 
It changed with the beta 3.7 22.

An object with no_shadow DOES collect photons and stops photons from reaching 
surfaces behind it.

An object with both no_shadow and pass_through does collect and stop reflected 
photons, but primary photons will reach surfaces behind the object.

-- 
Alain
-------------------------------------------------
BE ALERT!!!!  (The world needs more lerts ...)

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