Using Yeti and Vray for maya I’m trying to colour the fur based on the underlying surface’s facing ratio.
If I use the sampler info into a ramp the facing ratio is worked out on a per hair basis (see image).
I posted this on the yeti page an Colin responded with:
‘I’m not too sure how the best way to handle this with VRay shading, we do have surf_n and pass that into all
the renderman shaders - but I don’t think there’s a way of passing that into VRay so the samplerInfo node picks it up. If there is a way we can do this I’d be happy to add it.’
Colin is right that it cannot be done for the moment. We could try to figure out something, but in any case it wont work with a samplerInfo node - you’d still have to use something like VRayHairSampler to extract the original surface normal.
Did you guys get a solution to this problem? I am currently trying to find a way around this very situation. I have seen the shader node in Yeti can give out a normals value and the Vray help documentation mentions using yeti channels in textures with the Vray user colour. Perhaps there is a workflow to combine them?
Vlado also mentions the Vray hair sampler and using that to sample a normal - could also be something that could work.
If you can get Yeti to store the surface normal in an extra channel, you can use VRayUserColor to read that channel, and then maybe use some math nodes to get the dot product between that and the forward direction of the camera.
Okay I got a setup for this (Thanks to a talented TD at my work - Shout out JeroenH). It works pretty much as you stated…
Using the Yeti shader node you set the diffuse colour to $N (the normal). You then setup your shader taking the matrix eye to world and using a vector product and a dot product. The clamp gets rid of the normals facing away from camera and the multiply simply multiplies it to get it a positive number again.
The maths is a bit on the heavy side - but the results are great. You can obviously use the ramp to drive anything you want. We are currently using it to fake a velvet-ey falloff on some furry fabric. I’ll post the results when the commercial is on TV.
The remaining question would be how to get this working on normal Vray fur? I dont know how I can get the same normal value (which I am using from yeti) from Maya/Vray? If you know of a way to do this I would be really happy as I still use Vray fur for a lot of things.
But…
