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23 Dec 2024 07:12:41 EST (-0500)
  Specular & Fresnel (Message 1 to 5 of 5)  
From: Tek
Subject: Specular & Fresnel
Date: 10 Dec 2010 12:55:01
Message: <web.4d026937920e2f25caa39c860@news.povray.org>
This may have been asked before, but is there any way to make specular fade off
with fresnel (or reflection falloff)?

The reason I ask is because of these rather interesting demonstrations of
real-world specular & fresnel:
Everything is Shiny: http://filmicgames.com/archives/547
Everything has Fresnel: http://filmicgames.com/archives/557

Clearly materials in the real world have specular that fades with fresnel. But
the only way I can think to achieve that in POV (3.7 beta) is to use an aoi
texture to blend between 2 different finishes. Which then means I can't use a
normal map (since the aoi uses the true shape of the surface).

Any ideas?

--
Tek
evilsuperbrain.com


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From: clipka
Subject: Re: Specular & Fresnel
Date: 10 Dec 2010 13:18:50
Message: <4d026f0a$1@news.povray.org>
Am 10.12.2010 18:53, schrieb Tek:
> This may have been asked before, but is there any way to make specular fade off
> with fresnel (or reflection falloff)?
>
> The reason I ask is because of these rather interesting demonstrations of
> real-world specular&  fresnel:
> Everything is Shiny: http://filmicgames.com/archives/547
> Everything has Fresnel: http://filmicgames.com/archives/557
>
> Clearly materials in the real world have specular that fades with fresnel. But
> the only way I can think to achieve that in POV (3.7 beta) is to use an aoi
> texture to blend between 2 different finishes. Which then means I can't use a
> normal map (since the aoi uses the true shape of the surface).
>
> Any ideas?

POV-Ray uses a fresnel term in the metallic version of specular. Using 
an rgbt <0,0,0,1> top texture layer with "metallic" directly in the 
finish statement might do the trick. I'm not exactly sure though - it 
might have just the opposite effect of what's desired.

Another one for my personal To-Do list...


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From: Tek
Subject: Re: Specular & Fresnel
Date: 10 Dec 2010 13:30:00
Message: <web.4d02713375743386caa39c860@news.povray.org>
clipka <ano### [at] anonymousorg> wrote:
>
> POV-Ray uses a fresnel term in the metallic version of specular. Using
> an rgbt <0,0,0,1> top texture layer with "metallic" directly in the
> finish statement might do the trick. I'm not exactly sure though - it
> might have just the opposite effect of what's desired.
>

Of course!
I did actually think of that the other day but then completely forgot about it
when I got around to implementing it. I'll give it a try now...

It works!

Cheers,
Tek


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From: Alain
Subject: Re: Specular & Fresnel
Date: 11 Dec 2010 18:39:50
Message: <4d040bc6$1@news.povray.org>

> This may have been asked before, but is there any way to make specular fade off
> with fresnel (or reflection falloff)?
>
> The reason I ask is because of these rather interesting demonstrations of
> real-world specular&  fresnel:
> Everything is Shiny: http://filmicgames.com/archives/547
> Everything has Fresnel: http://filmicgames.com/archives/557
>
> Clearly materials in the real world have specular that fades with fresnel. But
> the only way I can think to achieve that in POV (3.7 beta) is to use an aoi
> texture to blend between 2 different finishes. Which then means I can't use a
> normal map (since the aoi uses the true shape of the surface).
>
> Any ideas?
>
> --
> Tek
> evilsuperbrain.com
>
>
>

As a starting point, you can give an ior to your objects, even if they 
are opaque.
interior{ior IOR}

You can add metallic with a small value.

You can use variable reflection with the fresnel keyword.

I don't think that it will exactly reproduce the real world, as at least 
part of the effect is related to polarisation.




Alain


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From: clipka
Subject: Re: Specular & Fresnel
Date: 11 Dec 2010 18:48:20
Message: <4d040dc4@news.povray.org>
Am 12.12.2010 00:39, schrieb Alain:

> I don't think that it will exactly reproduce the real world, as at least
> part of the effect is related to polarisation.

The fresnel formulae used in POV-Ray already take into account that 
differently polarized light is reflected at different intensity. They 
should be ok, under the presumption that the incoming light is 
non-polarized.


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