VraySamplerInfo - Normal Vector & Single face objects

[pingus]

Hello,

We are experiencing a few issues with objects that have no thickness, like leaves in trees.
(3dsmax 2020.3, Vray 4.30.01)

I have reproduce it on a simple scene :

A plane vs a plan + shell, both rotating 360°.
Rendering with grey material + a VraySamplerInfo render element ( type Normal vector, coord system World)

- in front view, both objects share the same values. (image #1)
- in back view, now the left plane has a different value for its back face. (image #2)
- strangely, the VraySamplerInfo in type Normal vector with Bump works has i want (image #3) but only works if the original material is a VrayMtl, doesn't work with light material. (witch is my goal)


Does anyone have any idea why single face object has a different value on back face ?
Image #4 is what we want, #5 is what we have.

Thanks
-p-

[hermit.crab]

The 'Normal vector' type shows the direction of the surface normal. For a single plane object, this means that the backside and frontside will be the same color since its normals are facing the same direction. The 'Normal vector with bump mapping', however, considers the two-sidedness of materials, hence why it works as it does with a VRayMtl and not with a VRayLightMtl (turning off the 'double-sided' of the VRayMtl would end in matching results). Try applying a VRay2SidedMtl, in which you plug a VRayLightMtl and set a black translucency and see if that works out for you.