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Best BTDF Options In Mantra ?


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Hi guys ,


I would be curious to know what are all the BTDF available in Mantra ?

When using the PBR specular Mantra reduce the option to Cone and Phong Only ?


First i would like to be sure what vex function they use

Phong is phonglobe(tnN, tnR, uexp, vexp, tanu, tanv, "label", "refract"); ?

Cone   is cone(tnN, tnR, newangle, "label", "refract"); ?


I find that the glossy refraction BTDF in Phong and Cone is not very nice


Do you know if other alternative are possible ?

What about a GGX BTDF is this possible to use GGX as a BTDF by default ?


What about ashikimin ?


is there any exemple where people use more recent model for transmission ?


Thanks for your time !





Edited by sebkaine
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after double check the only bsdf that allow to compute transmission along a vector direction are

bsdf phonglobe(vector nml, vector dir, float exponent);
bsdf specular(vector dir);
bsdf cone(vector dir, float angle);

GGX and Ashikmin which look to be the most modern bsdf only work in BRDF mode and not BTDF

So this mean you can't have a coherent roughness who behave similarly for reflection and refraction.

Edited by sebkaine
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  • 6 months later...

I ressurect this topic from the grave.


each time i need to use blurred refraction with mantra i find that they looks really bad.

either Phong or Cone are directly very rough , you don't have this smooth gradual roughness progression,


I have try to do some glass by mixing 2 phongs + mario dispersion code



it was good enough. But each time i need to do blur refraction it just look average.

I would like to know if some Mantra expert have some tricks / solution ?


My biggest problem is that in glass the reflected ray and the refracted ray should follow the exact same model,

your roughness should be the same value. By combining GGX / phong you don't respect that.


The not so bad option is combining 2 phong but either for reflection and refraction you are using very old school stuff ?

At the moment this the only major problem i have in Mantra. Arnold do MUCH better in this area ...

I have not seen any enhancement in H 15 regarding this , and it's quite a bad news because they have rebuild all !


The only news is that now the PBR specular is able to compute GGX transmission, but you can't disable the fresnel mask.

It's not even use in any of the new shader that still rely on the old PHONG !  (cf attach)


Any help on how to do Ligue-1 blur transmission in H would be great !






ps : sorry if this topic is complete monologue at the moment :)



Edited by sebkaine
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