POV-Ray : Newsgroups : povray.unofficial.patches : UberPOV is back : Re: UberPOV is back Server Time
21 Apr 2024 07:08:45 EDT (-0400)
  Re: UberPOV is back  
From: clipka
Date: 1 Sep 2016 12:35:14
Message: <57c858c2$1@news.povray.org>
Am 01.09.2016 um 16:06 schrieb Mr:

>>> -Minnaert?
>>
>> Nope. Again, to the contrary: Minnaert also makes the diffuse component
>> fall off at shallower angles.
> 
> Blender's implementation can also do the opposite: lightening faces as their
> normals get perpendicular to the viewing direction, kind of like oren Nayer also
> does , but orders of magnitude stronger.  (" if Dark is 1 you get exactly the
> Lambertian result. Higher darkness values will darken the center of an object
> (where it points towards the viewer). Lower darkness values will lighten the
> edges of the object, making it look somewhat velvet")

I must confess that I'm digging into the Minnaert model only just now.
And yes, it seems indeed to be capable of doing something like the
Oren-Nayar and Lommel-Seeliger models.

> So maybe we could say that Lommel-Seeliger  is a good model to emulate all
> darkness values of Blender Minnaert below 1 wile values above could switch to a
> darkening slope_map/aoi pattern ?

If you want to emulate Blender's Minnaert in POV-Ray, wait for a couple
of hours until the next UberPOV release ;)

> And Brilliance parameter would be better to emulate Fresnel as it's more light
> dependant than viewing angle dependant???

The Brilliance parameter is primarily a poor hack with no physical
legitimation. I suspect the best way to emulate it would be with
something like an aoi pattern. While it might indeed have been used as a
poor man's attempt at approximating a fresnel term, it would have
succeeded in that only for the outgoing light, ingoing that there should
be a symmetric term for the incoming light.

(After some research, I have a hunch that the brilliance parameter
/might/ actually have originated as a failed attempt to implement the
Minnaert model. But that's just speculation, and it's probably far too
late to find out the truth about it.)

> Anyway, at the moment I meet a bigger issue, as I see no variation when trying
> to use the two new models in pov, are they confirmed to work in your Windows 64
> build?

They should be working fine in UberPOV 1.37.1.1-alpha.8756754, but I'll
check again.

> The Minnaert shader in POV was the topic of this work:
>
http://news.povray.org/povray.binaries.images/thread/%3C3f6ccdf7%40news.povray.org%3E/
> 
> Has it been used for this feature or can it still be added to all the options?

I didn't even know about Kevin's work until right now that you've
mentioned it (and I'm not sure whether I would be able to dig up his
code on the Internet). I had even started on my own Minnaert
implementation already.


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