POV-Ray : Newsgroups : povray.newusers : projected_through as a light portal? : Re: projected_through as a light portal? Server Time
26 Feb 2024 07:07:05 EST (-0500)
  Re: projected_through as a light portal?  
From: Mr
Date: 29 Jul 2017 18:20:01
Message: <web.597d09c353698b6b61ea16670@news.povray.org>
Alain <kua### [at] videotronca> wrote:
> Le 17-07-28 à 02:51, Mr a écrit :
> > Hello. Suddenly the question occured to me: for an outside sunlight entering an
> > interior scene, can we use the projected through keyword to the window glass to
> > avoid wasting rays or photons oudoors? or os this not practically efficient?
> >
> >
> >
>
> projected_through can be viewed as a kind of negative shadow. Only the
> areas that would have been in the shadow of the projected_through object
> from a normal light are illuminated. Can be used to create some coloured
> shadows.
>
> If you use projected_through, you beed to add photons{pass_through} to
> the projected through object. Otherwise, it will intercept your photons.
> At least, that's what my tests show.
>
> If you don't see some areas, you don't shoot any rays at it. So you
> don't waste any. You shoot rays from the camera toward the scene. Then,
> you test if there is a clear path toward your light(s). That's called
> backward ray tracing.
>
> For the photons, they are ONLY shot toward objects that have a photon
> block that set them as target. That block can look as one of the 3 that
> follow :
> photons{target reflection on}
> photons{target refraction on}
> photons{target reflection on refraction on}
>
> For effeciency, don't stack several objects that are set as target. The
> first object will intercept, and block, all photons targetted at the
> objects behind it.
>
> The refraction and reflection switches apply ONLY to primary photons.
> Secondary photons from an object set as reflection on refraction off CAN
> get refracted by another object. That object DON'T need to have any
> photons block, just be transparent and have an ior.
>
> By the way, the full syntax for the target keyword is «target Float»,
> where Float specify a spacing multiplier.
> target 0.5 will cause the spacing for that object to be halved, causing
> the object to receive 4 times as many photons.

I tried with uberpov1.37.1.0.beta.10.msvc10.win64
and even with photons{passthrough},
the projected_through object seems to cast a shadow. Is this normal?


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