[Radiance-general] Strange behaviour with mixed material

[Santiago Torres]

Dear all,



I'm trying to define a mixfunc material to modify a mirror definition, so I can create holes (horizontal bands in this case) in the mirror. This was explained in an old tutorial by G. Antonutto, which now seems lost (at least I couldn't find it online... pillo?).



The complete definition is like this:



## metal

void metal metal_01

0

0

5 .8 .8 .8 .05 0



## mix the metal with void to create holes

void mixfunc strip

4 metal_01 void 'if(sin(Pz/10),0,1)' .

0

0



## alter the reflectance of mirror, reflectance is 0% for holes

void brightfunc band

2 'if(sin(Pz/10),0,1)' .

0

0



## mirror attached to the metal surface with holes

band mirror mix_01

1 strip

0

3 .9 .9 .9





If I create a cube with the "mix_01" material, it looks as expected. Horizontal bands of void in the mirror let the direct light through and the reflected light is also in matching stripes.



However, with the diffuse calculation, light doesn't seem to get through the void part. For example, if I measure irradiance inside the cube with only a glow source outside, I get zero.



The strangest part is that if I look at the model in rvu, it looks fine and there is diffuse light inside... unless I set -aa 0!!!



All other settings seem to make no difference (with ab > 0, of course).



Rpict behaves like rtrace, no diffuse light through.



I've tried setting all rtrace parameters to the rvu defaults (including dr 0), but the result is still nothing.



I'm sure there is an explanation, which is possibly that the material is just too weird, but I'm still confused by the strange difference in behaviour between rtrace/rpict and rvu...



Any ideas?

Thanks!

Santiago


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