[Radiance-general] mirror and mixfunc

[Jan Wienold]

Hi Greg and Giulio,

thanks for your cool (kung foo:-) ) tips! And yes it totally makes 
sense! :-)

About the brightfunc I was already aware, but I couldn't find a solution 
to integrate a material for the interreflection calculation. I was 
already thinking of running two times with different material 
definitions, but this is a cool solution!

Jan




Am 12/1/15 um 5:56 PM schrieb Rob Guglielmetti:
> I love when Greg shares these kung foo tips and deep insights to 
> Radiance's underbelly, and then closes with "Does this make sense". 
> Yes, it makes sense, after reading it like five times. Thanks, Greg, 
> as always!
>
> On Tue, Dec 1, 2015 at 9:51 AM, Greg Ward <gregoryjward at gmail.com 
> <mailto:gregoryjward at gmail.com>> wrote:
>
>     Hi Jan,
>
>     As you discovered, the code isn't sophisticated enough to handle
>     virtual source materials (mirror, prism, prism2) through the
>     mixfunc interface.  (BTW, mixfunc also fails for light sources.) 
>     However, you can use the "alternate material" argument to the
>     mirror primitive to specify a different behavior for when the
>     mirror is not directly participating in the virtual source relay
>     calculation.  You could have a chain like this, which would work:
>
>     void metal mat1
>     [arguments]
>
>     void plastic mat2
>     [arguments]
>
>     void mixfunc mat1+2
>     4 mat1 mat2 mixing_var mixit.cal
>     0
>     0
>
>     void mirror mmat1+2
>     1 mat1+2
>     0
>     3 .5 .5 .5
>
>     ------
>     When the mirror material is participating in the virtual source
>     calculation, it reflects everything at 50%.  When it's
>     participating in the interreflection calculation, or you look at
>     it directly, then it switches to the mixfunc mat1+2's behavior.
>
>     If one of your goals is to have the mixfunc control the amount of
>     reflected light in the virtual calculation, I'm afraid you will
>     need to use a brightfunc modifier on the mirror material,
>     instead.  You can do this in conjunction with an alternate
>     material to make the behavior consistent if you like.  In the
>     example above, let's say that mat1 is mirror-like with 80%
>     reflectance and mat2 is diffusing.  You could use the same cal
>     file for your brightfunc, modifying the mirror primitive like so:
>
>     void brightfunc mir_amt
>     2 mixing_var mixit.cal
>     0
>     0
>
>     mir_amt mirror mmat1+2
>     1 mat1+2
>     0
>     3 .8 .8 .8
>
>     --------
>     Does this make sense?
>
>     -Greg
>
>     > From: Jan Wienold <jan.wienold at epfl.ch <mailto:jan.wienold at epfl.ch>>
>     > Subject: [Radiance-general] mirror and mixfunc
>     > Date: December 1, 2015 6:44:00 AM PST
>     >
>     > Hi all,
>     >
>     > I got stuck a bit applying mixfunc and mirror material. It seems
>     that the check for secondary light sources is partly disabled when
>     applying (at least I assume so).
>     >
>     > A simple example:
>     >
>     > lets assume an ideal mirror
>     >
>     > void mirror testmat1
>     > 0
>     > 0
>     > 3 1 1 1
>     >
>     > If I use just this  material on a surface and start an rtrace
>     sending to the surface, then I get the correct result for both
>     options - either rtrace or rtrace -I. So far so good.
>     >
>     > In case I use a (stupid, but simple) mixfunc:
>     >
>     > void mixfunc test_mix
>     > 4 testmat1 testmat1 0.5 .
>     > 0
>     > 0
>     >
>     > I should get the same result, since I'm mixing the same material
>     with a fixed value.
>     > But: rtrace -I delivers only 0, whereas rtrace delivers the
>     correct value. So it seems that mixfunc cannot be applied with
>     mirror, when the -I option is used. Or I did something wrong?
>     > I used -dr 2 and -dt 0 in both cases.
>     >
>     > Of course my ultimate goal is not mixing that simple but mixing
>     two different material types, also depending on the angle of
>     incidence, but this simple example shows the principle problem.
>     >
>     > Is there any solution using mixfunc and mirror when using rtrace
>     -I ?
>     >
>     > Jan
>
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-- 
Dr.-Ing.  Jan Wienold
Ecole Polytechnique Fédérale de Lausanne (EPFL)
EPFL ENAC IA LIPID

http://people.epfl.ch/jan.wienold
LE 1 111 (Office)
Phone    +41 21 69 30849

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