Is it that simple ? Everything else uses either simplified (Unreal4) or more complex version of GGX (Vray's GTR) and looks right. Octane uses some arbitrary crap, and still looks rather correct (but I see it can't do fully rough either).
This probably doesn't have anything to do with the shading BRDF but with how Corona uses the Fresnel. I've seen renderers that with simple Blinn and Schlick approximation produce correct specular brightness with rough materials.
There really is something completely else behind this.
Here is former incorrect
Fresnel in Cycles Renderer and corrected. Look at the difference, this is exactly what is Corona doing. Of course, the gamma control for specular lobe spread (GTR in Vray) is also nice...but, at least the correct dimming would be first step.
Wrong:CorrectSource :
https://www.blender.org/forum/viewtopic.php?t=27455The Oren-Nayar vs Lambertian is just something that (diffuse) fresnel roughness solves, I think it's completely different, detached issue. Vray has this parameter but I think nobody ever used it except for some moon render :- ).
Surprisingly the popular alSurface Shader also has it, but it has the abominable programmer controls that are something halfway between specular and PBR convention. Like Redshift...I hate those...
Here is how roughness looks in current (2015+) Disney shader. (Extended Disney principled PBR shader //
http://blog.selfshadow.com/publications/s2015-shading-course/burley/s2015_pbs_disney_bsdf_slides.pdf &
http://blog.selfshadow.com/publications/s2012-shading-course/burley/s2012_pbs_disney_brdf_notes_v3.pdf both of these are
must read)
No crazy rim effect. This shader is such a thing of beauty. So much want. Sheen, retro-grazing reflection, artist controls... double specular lobe as default (gamma 1 and 2, see Vray ? It can be done artist-friendly too).
« Last Edit: 2016-06-28, 22:45:53 by Juraj_Talcik »
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