[Radiance-general] Strange behaviour with mixed material

[Gregory J. Ward]

Just a quick follow-up.  This was indeed a bug in the m_mirror routine, which is now sorted out.  The next distribution should fix it.

Thanks, Santiago!

-Greg

> From: Greg Ward <gward at lmi.net>
> Date: June 3, 2016 1:38:53 PM PDT
> 
> Hi Santiago,
> 
> Giulio kindly shared his tutorials and I haven't gotten around to putting them onto radiance-online.org, mostly because I don't know how to modify the website anymore since it was updated.  However, I have uploaded this particular tutorial for you to:
> 
> 	http://www.anyhere.com/gward/pickup/giulio_mirror.tar.gz
> 
> However, this is really a situation that didn't occur to me, where you have indirect rays coming from the opposite side.  I see now that I should modify a test in the m_mirror.c routine to account for this case.  I will send you a modified version of this file in hopes that you can rebuild and test it for me.
> 
> Cheers,
> -Greg
> 
>> From: Santiago Torres <Santiago.Torres at arup.com>
>> Date: June 3, 2016 1:10:50 PM PDT
>> 
>> 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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