Martin,
Wow! You have been quietly hard at work on these shaders. I'm looking
forward to seeing them. I get "warm shader fuzzies" I have not felt
since back in 2006 when /Tim/ Borgmann posted his various rope and
string shaders he used in many of his outstanding pictures:
http://www.realsoft.com/productinfo/kpics/Macversion5.jpg
Thank you in advance for your hard work and contributions.
Regards,
Brandon
On 1/6/2011 10:45 PM, mengil...@gmx.net wrote:
First of all: Thanks! =D
It was so quiet that I had even thought my mails would perhaps for some strange
reason have not been received.
So, regarding the shader(s):
The Ashikhmin-Shirley BRDF is something like a mixture of a
Ward-anisotropic-like specular reflection component and a limb-darkening
diffuse reflection component.
Meaning that it enables isotropic (simple point-shaped) and anisotropic
(streched along a direction of the surface) highlights.
Pictures and explanation will follow when I got it working right, though I´m a
bit tired of working this out.
I´ve worked on some shaders for RS3D for the last two months, to an extent
where I hardly did anything else in my free time.
So, several other shaders will follow.
I´ve already made two Oren-Nayar Diffuse shaders, one simple and one complete,
am working on a Oren-Nayar-Wolff Diffuse shader (like the previous plus some
refinements), two Hapke-Lommel-Seeliger shaders, one simple and one complex,
two Minnaert Shaders, an Asperity Scattering shader, plus several other
components.
The Oren-Nayar Shader is a diffuse shader suitable for rough diffuse surface
(like clay/pottery), the Hapke-Lommel-Seeliger Shader is a shader for powdery
surfaces like the surface of the moon, the Minnaert Shader was an early try on
the same matter, the Asperity Scattering Shader is for simulating fuzzy
surfaces (like peach).
The latter two are very similar to the "simple fur" and "custom fur" materials
already in RS3D.
So, really quite a lot.
And honestly I´m more than a bit proud of myself because I had NEVER done
something even remotely familiar to this before.
But, every time I think the shaders are ready for release, I see some new
problems.
One general problem seems to be that I often don´t know how to handle the
values obtained through the shading algorithms.
My understanding of the matter is still rudimentary, but as I see it, a BRDF
(bidirectional reflectance distribution function) like the previously mentioned
simply works different to how RS3D handles things.
Especially the Ashikhmin-Shirley BRDF seems to be made for a rendering engine
that supports pathtracing. The paper which describes the BRDF gives methods to
obtain blurred reflections that depend on the parameters of the shader - a
highly anisotropic setting would produce highly anisotropicly blurred
reflections.
I don´t know how to simulate this in RS3D.
And I get the feeling that it isn´t possible at all, as long as RS3D doesn´t
implement pathtracing or the likes.
This kinda makes me sad because I´ve now seen a great bunch of shading
algorithms that could pretty simply be implemented into RS3D to simulate a wide
variety of phenomena very realistically, if RS3D supported pathtracing and
wavelength-dependency.
When even I as a former total noob can get a glimpse of what is needed to do
that, it shouldn´t be that hard to implement things like diffraction,
dispersion, blurred reflections and refractions, subsurface scattering, Mie
scattering for clouds and Rayleigh scattering for atmospheric effects.
The papers are out there, some aren´t even two years old with models that seem
to top the models that are in use by other packages.
But perhaps RS3D already offers possibilities to incorporate these things
effectively, and I just haven´t come to know them; documentation is just too
sparse in this area.
And it makes me sad that there is no dialog between Realsoft and us users
regarding these matters.
Many of these things (subsurface scattering, pathtracing/GI, etc.) have been
talked about and demanded by users over and over again, for years.
I can only say it again - almost every other render-engine, be it freeware or
commercial, be it standalone or part of a suite, has outrun RS3D in this
respect.
And then it becomes clear that Realsoft already works on V8 - and still there is no talk
about any of this, no "What do you users want most in V8?", not even a hint at
what will be the new features of V8.
*sigh*
Well, however.
I will post pictures and documentation for the shader, plus the other shaders,
when I have gotten them to a degree that you can rely on them working.
Thanks for reading. :)
Martin
