mixfunc for dichroic film?

Hi all,

I have a somewhat complex problem defining a material. With the introduction of "smart" materials (that are able to exhibit different behavior under different conditions) into the architectural context, I'd like to experiment with defining such a material. The mixfunc material seems promising in that it allows one surface to display two different behaviors. What I would like to achieve is to use an "if-then" condition to determine which of the two material properties should be exhibited in the rendering. More specifically, I'd like to define two different behaviors (rgb, reflectance, and transmittance), and use mixfunc to determine which one of the two behaviors will be used for the rendering (on a each pixel) along the surface depending on,
1. the angle of the light ray from the point of view to the surface normal; and
2. the angle of the light ray from the light source to the surface normal

If this is possible, then would it be possible to eventually define more than two behaviors (by modifying a mixfunc with another mixfunc) to get a more gradual gradient between the different behaviors?

Thanks.

John An

Hi John,

More likely you will want to look into the BRTDfunc material type which would allow for this type of control of material reflectance and transmittance. Also, it would be worth searching through the mailing list archives for "dicrhoic," I am pretty sure that this has been done in radiance before, so rather than starting from scratch it would obviously be better to see what has already been implemented.

-Jack

John An wrote:

···

Hi all,

I have a somewhat complex problem defining a material. With the introduction of "smart" materials (that are able to exhibit different behavior under different conditions) into the architectural context, I'd like to experiment with defining such a material. The mixfunc material seems promising in that it allows one surface to display two different behaviors. What I would like to achieve is to use an "if-then" condition to determine which of the two material properties should be exhibited in the rendering. More specifically, I'd like to define two different behaviors (rgb, reflectance, and transmittance), and use mixfunc to determine which one of the two behaviors will be used for the rendering (on a each pixel) along the surface depending on,
1. the angle of the light ray from the point of view to the surface normal; and
2. the angle of the light ray from the light source to the surface normal

If this is possible, then would it be possible to eventually define more than two behaviors (by modifying a mixfunc with another mixfunc) to get a more gradual gradient between the different behaviors?

Thanks.

John An

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# John E. de Valpine
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# visarc incorporated
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# channeling technology for superior design and construction

Jack,

Just the sound of BRDTfunc scared me off. I'll have to have a closer look at this material type.

I apologize for resurrecting a previously discussed topic. But my search ("dichroic," "multiple material," "materials with multiple properties," etc. on radiance-online, as well as "dichroic brtdfunc" on google ) resulted in no useful results (that I found). Do you have some suggestions as to other search terms to find this past discussion?

Thanks for always responding so quickly.

John

Hey John,

My apologies, although I seem to remember somebody somewhere talking about dichoic glazing in radiance (albeit a long time ago), after having followed my own advice to check in the archives, I have not been able to find anything. In any event, I think that something like BRTDfunc or perhaps transfunc will do what you want. Do you have any performance data that you can share so people can get a better sense of the performance characteristics of the material.

-Jack

John An wrote:

···

Jack,

Just the sound of BRDTfunc scared me off. I'll have to have a closer look at this material type.

I apologize for resurrecting a previously discussed topic. But my search ("dichroic," "multiple material," "materials with multiple properties," etc. on radiance-online, as well as "dichroic brtdfunc" on google ) resulted in no useful results (that I found). Do you have some suggestions as to other search terms to find this past discussion?

Thanks for always responding so quickly.

John

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.

--
# John E. de Valpine
# president
#
# visarc incorporated
# http://www.visarc.com
#
# channeling technology for superior design and construction

Hi John,

Another argument for using the BRTDfunc or transfunc types is that they don't require new ray evaluations for each new material type, which is a penalty you pay when you blend materials with a mixfunc. Although it is tempting, you really should avoid using mixfunc with materials unless there really is no other way. Originally, mixfunc would only blend patterns and textures, and this is still its primary purpose. However, using mixfunc as a this-or-that switch with materials doesn't incur the same penalty as smoothly blending them, because only one or the other material is ever evaluated. If one of the materials is "void," you can get a kind of selective absence of a surface, which can be useful for screen doors, gratings, etc.

I'm not familiar with dichroic materials in an architectural context. Can you be more specific as to the behavior you wish to simulate?

-Greg

I tried simulating caustics in Radiance classic (3.6a) by using mixfunc
(mirror + plastic with pattern)
I realized that Radiance does not look for virtual sources into mixed
definitions:
could you confirm that?

cheers,

giulio

PS sorry for the slightly different topic, it is just another mix-question
to add...

···

-----Original Message-----
From: [email protected]
[mailto:[email protected]]On Behalf Of Greg
Ward
Sent: 01 March 2004 17:10
To: Radiance general discussion
Subject: Re: [Radiance-general] mixfunc for dichroic film?

Hi John,

Another argument for using the BRTDfunc or transfunc types is that they
don't require new ray evaluations for each new material type, which is
a penalty you pay when you blend materials with a mixfunc. Although it
is tempting, you really should avoid using mixfunc with materials
unless there really is no other way. Originally, mixfunc would only
blend patterns and textures, and this is still its primary purpose.
However, using mixfunc as a this-or-that switch with materials doesn't
incur the same penalty as smoothly blending them, because only one or
the other material is ever evaluated. If one of the materials is
"void," you can get a kind of selective absence of a surface, which can
be useful for screen doors, gratings, etc.

I'm not familiar with dichroic materials in an architectural context.
Can you be more specific as to the behavior you wish to simulate?

-Greg

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Hi Guilio,

That is correct -- Radiance only finds virtual source objects using mirror or prism material types directly. It doesn't even look if you have a modifier in front of the material in the chain (e.g., you reference a pattern before the material).

I recently made a change that allows Radiance to find ordinary sources when the source material is further down the modifier chain or alias'ed, but I didn't do this for virtual source materials, whose surfaces must still be modified directly. Actually, I should make the change so aliases and intervening modifiers work properly with virtual source material types -- there's no reason not to. This still won't work for mixtures, in any case.

Mixtures don't make a lot of sense for sources or virtual source materials the way Radiance is designed, in my opinion.

-Greg

···

From: Giulio Antonutto <[email protected]>
Date: March 1, 2004 9:21:32 AM PST

I tried simulating caustics in Radiance classic (3.6a) by using mixfunc
(mirror + plastic with pattern)
I realized that Radiance does not look for virtual sources into mixed
definitions:
could you confirm that?

cheers,

giulio

PS sorry for the slightly different topic, it is just another mix-question
to add...

well...
the only reason for this mixtures is to create nice cups of tea:
patterns on the porcelain and caustics on the table ;-))
although this is not a main issue...

cheers again
giulio

···

-----Original Message-----
From: Greg Ward [mailto:[email protected]]
Sent: 01 March 2004 17:53
To: Radiance general discussion
Subject: Re: [Radiance-general] mixfunc for dichroic film?

Hi Guilio,

That is correct -- Radiance only finds virtual source objects using
mirror or prism material types directly. It doesn't even look if you
have a modifier in front of the material in the chain (e.g., you
reference a pattern before the material).

I recently made a change that allows Radiance to find ordinary sources
when the source material is further down the modifier chain or
alias'ed, but I didn't do this for virtual source materials, whose
surfaces must still be modified directly. Actually, I should make the
change so aliases and intervening modifiers work properly with virtual
source material types -- there's no reason not to. This still won't
work for mixtures, in any case.

Mixtures don't make a lot of sense for sources or virtual source
materials the way Radiance is designed, in my opinion.

-Greg

From: Giulio Antonutto <[email protected]>
Date: March 1, 2004 9:21:32 AM PST

I tried simulating caustics in Radiance classic (3.6a) by using mixfunc
(mirror + plastic with pattern)
I realized that Radiance does not look for virtual sources into mixed
definitions:
could you confirm that?

cheers,

giulio

PS sorry for the slightly different topic, it is just another
mix-question
to add...

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Radiance-general mailing list
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general

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