4.11+ Hair material documentation + questions

Development Rendering
, , , ,
1

What is the ETA on exhaustive official documentation on the hair material’s specifics and best practices (model and texture) for achieving Paragon-grade results? The content example material isn’t sufficient enough for genuinely understanding how to work with it for the best visual outcome. I could see in the hair feature preview video that the Backlit feature, which has been assumed broken, was being used with some kind of a specific parameter configuration beyond just plugging in a Scalar value, for example. Since the material is really performance heavy, it would be great to know how to make the most bang for our buck with it.

I also really need to know if there is a specific map lighting or model setting configuration needed to get the proper shadow mapping showcased in the preview videos. Copying the sample material only got me vague indistinct shadows and barely any self-shadowing or occlusion at all, total lack of a sense of depth and volume. Additionally, pixel depth offset seems to just mess up my hair model and expose the bald scalp underneath even with low values instead of creating the organic hair card intersections advertised.
I unfortunately can’t share screenshots or assets because of NDA.

Additonally:

1280×720 79 KB

I can see that the Paragon hair cards are using averaged vertex normals (as opposed to smoothing the normals across cards with a normal steal from a blob mesh) and the material seems to blend away the card edge transitions for a smooth, soft look. I can’t find a solution for getting this effect even when I’m layering a lot of flyaway cards over my main cards to try and blend them out - the lighting exposes the card geometry no matter what I do. How was this effect achieved in the mesh, material and/or lighting?

2

We really need answers here, for the moment I found noone beeing able to make correct hair in ue4 exept paragon team and ninja theory … please share some docs for us amateurs.

3

I haven’t looked at paragon models, but hair shader parameters are pretty similar to the ones used in other applications.
In addition to common material parameters, you have these two:

  • Backlit: Controls intensity of light that refracts into the hair and
    refracts out again toward the viewer.
  • Tangent: Used to control orientation of anisotropic specular
    stretching Typically, this should be
    a unifrom value, if you hair strands
    are unwrapped and arranged, following
    the same direction along either U or
    V in your texture sheet. Otherwise,
    it can take a flowmap input, to
    determine strand direction vs tangent
    space.

Blending between hair strands is most likely achieved by using some sort of dither pattern with pixel depth offset, I think this technique was briefly described on a stream, that was devoted to Parallax Occlusion Mapping and Procedural foliage in Paragon stream.

Hiding obvious transition between head and hair strand cards can probably be achieved by modified vertex normals. All after all, hair strands are not much different from foliage, and all techniques, that apply to it, are also applicable for hair.