"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

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