GGX for FastSSS2

[LudvikKoutny]

Seems like FastSSS2 still uses some primitive BRDF. Would be good to have it use GGX

[^Lele^]

blend with an additive coat after setting specular level to 0.

[LudvikKoutny]

blend with an additive coat after setting specular level to 0.

Tried it, but it is much slower than single material. My entire scene is covered in snow, and this effectively doubles the rendertime :/

[^Lele^]

It's got to be something with your setup.
As the attached image show, the performance is higher in any of the combination of specular BRDFs through a blend than it is using the (likely very very old) fastsss2 Phong code alone (the slowest rendering of them all.).
Nowhere a doubling of the rendertimes is to be found, inherent to the setup proposed (rather, the exact setup proposed renders in half the time of the sss2 with its phong.), and while it isn't for free, it was never a case of additive rendertime per coat layer, since its inception a decade ago, so you must be confused with some other renderer, or be bending your shader well backwards, compared to the original request you put forward in this thread.

[LudvikKoutny]

You may be right, in trivial scene, difference in performance is next to none. My scene, though, is quite complex. It's large environment with snow covered ground, and that snow has this FastSSS2 materials. There's lots of trees, scattered debris, shrubs, etc... Even if I isolate the snow itself, the difference is there, in favor of native FastSSS2 blinn shading, rather than layered one, but it's much smaller, just a few %, definitely not twice. Once I render full scene together though, it starts to slow down rapidly. But it may indeed be some secondary problem, which using GGX reflection layer just amplifies.

[Bigguns]

Why not using Alsurface Mtl instead of sss2 ?? Even for snow, the Alsurface would work wayyyyyyy better since the sss has much more translucency plus you have control over each layers , etc. Just put white in the diffuse, crank up the sss mix to 1 and put a bluish color in one sss layer , I owuld trun off the 2 other one, you won't need I guess, not tried to do snow with it, but that's how I would start it, and play with the sss weight and radius to make it deeper, stronger etc . to fit your need, plus the alsurface has a WAY better backscatter then sss2 .. and it has 2 refleciton layers, wich can be set to GGX or Beckmann .

[^Lele^]

native FastSSS2 blinn shading

It's actually phong, a wee bit slower than Blinn (by virtue of a concatenated dot product and one more multiplication. A dot product and a multiplication more than Blinn, in total, which cheats with the half-vector.).

[LudvikKoutny]

Why not using Alsurface Mtl instead of sss2 ?? Even for snow, the Alsurface would work wayyyyyyy better since the sss has much more translucency plus you have control over each layers , etc. Just put white in the diffuse, crank up the sss mix to 1 and put a bluish color in one sss layer , I owuld trun off the 2 other one, you won't need I guess, not tried to do snow with it, but that's how I would start it, and play with the sss weight and radius to make it deeper, stronger etc . to fit your need, plus the alsurface has a WAY better backscatter then sss2 .. and it has 2 refleciton layers, wich can be set to GGX or Beckmann .

Because: http://forums.chaosgroup.com/showthr...ace-super-slow

[Bigguns]

yeah for sure Alsurface is wayyy slower then sss2, especially with crips detailed displacement.. without displacement not too much difference but with detailed displacement it's slowww... but beautifull haha. if it's for an animation , yeah you can be screwed up by rendertime.

Any idea Vlado why Alsurface is so slow with detailed displacement map ? like me I use 8k maps .. and many maps.

Recon442, have you tried with a volumetric sss combined with a vray mtl via a blend mtl, mayby you can get something cool with that for snow .

[vlado]

It shouldn't be that much slower actually. I have some scenes so I'll profile them to see what's going on.

Best regards,
Vlado