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Fresnel channel
Posted: Thu Jan 10, 2013 8:35 pm
by noldo
I wanted to ask a question. It 'correct to use the fresnel channel as a channel of specularity? In other words, it is appropriate to use a specularity texture in the fresnel channel to control the amount of specularity? Thank you.
Re: Fresnel channel
Posted: Thu Jan 10, 2013 9:02 pm
by Zom-B
Actually there is no fresnel channel in Indigo, only a fresnel scale for phong materials, and that isn't controllable by a map afaik!
Maybe you should explain your needs a little detailed, and also tell what Exporter you work with
Re: Fresnel channel
Posted: Thu Jan 10, 2013 9:38 pm
by noldo
Ok, I'm sorry but my English is not very good.
With fresnel channel, i mean fresnel scale, as you specify.
I use skindigo exporter, but for the moment the plug-in dont'have the fresnel scale control, then i add the fresnel scale in indigo rt application.
It is possible to apply a map in the fresnel scale channel (why not?).
I noticed that a black value of map, cause no specularity (diffuse channel only), while a white value mean full fresnel value (1.0?), so I thought that the specularity was driveable with the fresnel scale value (with a map).
Thanks.
Re: Fresnel channel
Posted: Thu Jan 10, 2013 9:40 pm
by noldo
In other words:
- exponent channel control the roughness;
- fresnel scale control the specularity (reflection);
Re: Fresnel channel
Posted: Thu Jan 10, 2013 9:47 pm
by Zom-B
The "roughness" of a reflective Phong material (and also Glossy Transparent!) IS possible my using a texture.
Its the exponent you define by that, so the controle where the material is rough, and where it is shiney.
B controls the spectrum of glossiness and brighter pixels on the texture set the glossiness to more reflective on the defined spectrum of B.
Fresnel Scale is afaik a 0 to 1 value that most exporters still haven't included yet :/
If unchanged the value is at 1 as default (afaik).
Re: Fresnel channel
Posted: Thu Jan 10, 2013 9:54 pm
by noldo
Zom-B wrote:The "roughness" of a reflective Phong material (and also Glossy Transparent!) IS possible my using a texture.
Its the exponent you define by that, so the controle where the material is rough, and where it is shiney.
B controls the spectrum of glossiness and brighter pixels on the texture set the glossiness to more reflective on the defined spectrum of B.
Exactly, but in this channel (exponent), a lower value mean more rough, while a higher value mean more shiny.
In the fresnel scale channel (with a bitmap applied, for example a black & white checkerboard), the black value mean NO reflection (someone like lambertian material), the white value mean normal reflection value (1.0) in according with the glossiness in the exponent map.
Re: Fresnel channel
Posted: Fri Jan 11, 2013 2:56 am
by PureSpider
As I understand it, he pretty much wants an "IOR Map" for Phong materials, something I'd also love a lot!
Re: Fresnel channel
Posted: Fri Jan 11, 2013 3:25 am
by OnoSendai
Zom-B wrote:only a fresnel scale for phong materials, and that isn't controllable by a map afaik!
It is in 3.6.x.
Re: Fresnel channel
Posted: Fri Jan 11, 2013 3:28 am
by FakeShamus
noldo wrote:
In the fresnel scale channel (with a bitmap applied, for example a black & white checkerboard), the black value mean NO reflection (someone like lambertian material), the white value mean normal reflection value (1.0) in according with the glossiness in the exponent map.
this is possible, are you using the newest version, 3.6.4?
Re: Fresnel channel
Posted: Fri Jan 11, 2013 3:39 am
by Zom-B
OnoSendai wrote:Zom-B wrote:only a fresnel scale for phong materials, and that isn't controllable by a map afaik!
It is in 3.6.x.
Seems I totally missed that -.-'
Re: Fresnel channel
Posted: Fri Jan 11, 2013 6:09 am
by CTZn
Zom-B wrote:OnoSendai wrote:Zom-B wrote:only a fresnel scale for phong materials, and that isn't controllable by a map afaik!
It is in 3.6.x.
Seems I totally missed that -.-'
Me too. Worse in fact, I noticed the feature . But I didn't integrate the fact, and was nearly going to explain why it wasn't implemented yet early today
Re: Fresnel channel
Posted: Fri Jan 11, 2013 7:04 am
by galinette
OnoSendai wrote:Zom-B wrote:only a fresnel scale for phong materials, and that isn't controllable by a map afaik!
It is in 3.6.x.
By the way, why not making it spectral, and by this way make the "specular color" parameter obsolete? As it removes the diffuse color, it is quite useless as it is.
Etienne
Re: Fresnel channel
Posted: Sat Jan 12, 2013 10:14 am
by FakeShamus
OnoSendai wrote:Zom-B wrote:only a fresnel scale for phong materials, and that isn't controllable by a map afaik!
It is in 3.6.x.
is ISL working as expected in the Fresnel channel? I was trying something similar to what I've used previously within a Blend shader, using a normalWS check to return somewhere from 0.0 to 1.0 for the Fresnel Scale, but I get an error, saying that it "failed to find function eval(vec3)"?
I'm trying the exact same code that I used for the "Snowy Rock" blend - actually your code, Ono:
Code: Select all
def eval() real :
if(dot(normalWS(), vec3(0.0, 0.0, 1.0)) > 0.3,
1.0,
0.0)
shouldn't the above "eval() real" work in Fresnel, just as in the Blend channel? also looks like this doesn't work as a shader for Exponent, but I would expect it to (correct me if I'm wrong, cause I only have the most amateur understanding of what's going on in these functions...)
Re: Fresnel channel
Posted: Sat Jan 12, 2013 11:24 am
by CTZn
It is working as expected, yes. Indigo is certainly registering the blend and fresnel scale as different data types, wich explains the different respective signatures.
You can see on a new phong material that by default the fresnel scale shader uses the signature:
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In general you can trust and just abide by the ISL debugger.
Now, why the blend parameter could not, even as a ratio, be 'pos dependent', this is above my head yet and again
Re: Fresnel channel
Posted: Thu Jan 17, 2013 2:59 am
by OnoSendai
galinette wrote:OnoSendai wrote:Zom-B wrote:only a fresnel scale for phong materials, and that isn't controllable by a map afaik!
It is in 3.6.x.
By the way, why not making it spectral, and by this way make the "specular color" parameter obsolete? As it removes the diffuse color, it is quite useless as it is.
Etienne
This is an interesting idea.
It's a bit tricky to change fresnel_scale to be spectral, as it is tied up with energy conservation and sampling.
What I could do is to introduce a new (optional) fresnel_colour parameter, that would multiply the specular part of the BRDF. Having non-unity fresnel colour what model some kind of absorption happening during specular scatters.