Kenneth nous apporta ses lumieres en ce 2007/09/17 17:33:
> "Kenneth" <kdw### [at] earthlinknet> wrote:
>> I've just run into the same problem. The POV documentation is very clear
>> that no_shadow and pass_through *should* work together exactly as you
>> described.  But they don't.
>>
>> I think it's a bug.
>>
> 
> It's possible that I'm reading the photon documentation incorrectly.  But
> the problem is there, in one form or another.
> 
> I put together a small, simplified scene that is more in line with what the
> docs describe (or *seem* to describe): A single front light shining 45-deg.
> down at three objects: The "ground" (a thin, square horizontal box with some
> reflection and a normal pattern--the photon TARGET), and two thin, wide
> vertical boxes (slabs) standing on the ground, one behind the other,
> both facing the light source and separated from each other
> somewhat. NEITHER of which is a photon target.
> Normally, the front slab would shadow the rear slab, AND keep the light
> from reaching the ground "target" area inbetween the two slabs--
> blocking the ground there, so that no light can reach it and no photon
> caustics can reflect upward from that shadowed area onto the rear slab.
> 
> Running the scene as-is, the caustics work as expected: They show up on the
> front slab but not on the rear slab.
> 
> Adding photons{pass_through on} to the front slab has two effects:  Caustics
> still appear on that surface (kind of a surprise to me, since the docs don't
> mention that) AND the light source's light goes through it unimpeded, to
> strike the ground "target" area behind it, creating (reflecting) caustics
> from there upward onto the rear slab. The regular shadow, from the front
> slab, is still there.
> 
> So far, so good.
> 
> HOWEVER, adding no-shadow to the front slab is where the problem arises.
> The light source light goes through it completely unimpeded (no shadow, of
> course), but NO caustics show up on it now, yet caustics are still
> reflected onto the rear slab even when the front slab has
> photons{pass_through off}. It just doesn't seem to be working correctly.
> 
> Leaving no stone unturned, I tried this scene with different types of light
> sources; but the behavior is the same.
> 
> BTW, the photon docs in 3.6.3.2.3 seem to imply (to me at least) that a
> photon block is *required* in light sources.  That's not the case; they can
> be left out (unless you WANT to turn off reflection or refraction there.)
> 
> KW
> 
In the documentation, it is clearly said that pass_through only affect PRIMARY 
photons: those hiting the object directly, and never secondary photons: those 
that already have been reflected or been refracted by some ther object. The 
problem, is that it's buried, and easily missed, in a long explanation.
pass_trough object are only ignored between the light_source and a target.

-- 
Alain
-------------------------------------------------
Don't argue with an idiot; people watching may not be able to tell the difference.

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