Front/Back Map?

V-Ray V-Ray for 3ds Max General
1

Is there some map that will give me black and white for front or back faces (e.g. White for front faces black for back faces) or similar?

I would like to use with with a VRayExtraTex render element, so a map is idea. I could render a separate pass if I had to, but was trying to do it in one.

Thanks in advance.

2

By back faces, do you mean flipped faces or faces facing away from the camera?

If you mean flipped - you can use a VRay2SidedMtl and bake the result onto a texture.
If you mean facing away - a Solid Gradient Ramp mapped with a Falloff (Towards/Away)

3

I mean backfaces in the old school sense of the back side of a polygon. So every polygon has a normal facing a certain direction, and the backface would be the opposite side from the normal.

Basically I just want a different map for side A and side B of the polygons.

I ended up solving it with an additional pass with a VRay2SidedMtl set to do VRayColors. But would still like to know if there is an easy way to get that with a map.

Not sure how VRay would handle it, but back in the LightWave days you would duplicate your polys and flip them so you had a copy facing each way. It shaded free of artifacts because the coplanar polys were identical except for their normals (and because LIghtWave was designed to work like this). I wonder can VRay shade such things without issues? I suppose it could. And then each side could have its own material ID I suppose. But in my case I already have a bunch of polys with different IDs. Maybe an ID offset…

4

You can use a standard 2-sided material…maybe similar to a Vray2sided but simpler at least.

5

Good call. Still doesn’t give me a map, though (and the VRay2SidedMtl rendered fast with solid colors and no translucency).

6

Check my edited post (didn’t refresh, sorry).

7

Ah, baking the VRay2sidedMtl is a good idea! I think that would actually do it. Thanks.

8

I usually use this simple OSL map - OSL-Shaders/FrontBack.osl at master · gkmotu/OSL-Shaders · GitHub

9

Excellent. I was looking through the included OSL files, but didn’t do a web search. Also, OSL is pretty simple code sometimes. That is sweet. Thanks.