[Bf-cycles] Need testers for the Disney BSDF implementation

Brecht Van Lommel brechtvanlommel at pandora.be
Sun Jul 24 15:29:21 CEST 2016

Hi Pascal,

I haven't found the time yet to look deeply into this. Some general
questions for now:

* There seems to be quite a bit of code duplication between the
microfacet BSDFs, any plans to solve avoid that?
* With a separate refraction roughness, it might be difficult to fit
in multiple scattering GGX eventually? In general a different
refraction and reflection roughness seems like it's difficult to make
energy conserving. Why doesn't a sharp clearcloat with a rough
reflection/refraction layer below work for your case?
* Maybe the thing you're really trying to approximate with that
refraction roughness is some forward scattering medium? We would need
some brute force subsurface scattering implementation to handle that
properly I guess.
* Any ideas in general about using the multiple scattering GGX for the
Disney BSDF? As I understand it sheen exists partly to compensate for
the energy loss that we can now properly solve, though it is also used
for cloth shaders so probably we would keep it regardless.


On Wed, Jul 20, 2016 at 11:38 AM, "Pascal Schön" <pascal_schoen at gmx.net> wrote:
> Hey guys,
> after some weeks where I spent only little amount of time on the
> implementation of the Disney BSDF/BSSRDF (my master thesis had to be forced
> a little bit ;-) ), I now need some testers for the shader. At this point it
> implements the current version of the Disney BSDF/BSSRDF that was introduced
> here:
> http://blog.selfshadow.com/publications/s2015-shading-course/burley/s2015_pbs_disney_bsdf_notes.pdf
> I would be very pleased if you would take some time and try out the shader
> and mail me your feedback on the usability and correctness! You can also
> write me if you have questions on the implementation.
> Some notes:
> - I added a roughness parameter for the refractions because I wanted to be
> able to create translucent materials with a smooth surface and a milky look
> inside. The two roughness values are correlated for refractions because if
> you have a rough surface it scatters the incoming rays while entering the
> surface and is then scattered further within the object. For reflections
> only the surface roughness value is used.
> - For the subsurface scattering I simply use the already implemented version
> of the Burley/Christensen SSS.
> Pascal
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