Updated:
08/21/2010 – fixed some problems with the shadowMap texture and AO texture and vertex color code.
This one is pretty cool – I’ve been reading some of the papers coming out of Siggraph and one by the Uncharted 2 Team referenced an old 2004 paper called “Practical Real-Time Hair Rendering and Shading” by Thorsten Scheuermann. Its a really great paper and I decided to make a cgfx implementation of its hair technique for Maya. The paper is interesting because it offers a single purpose anisotropic highlight function that is specially designed for hair – using no normal maps, the only real required map is a specular map to jitter the highlight and create the ‘strands’ effect.
My Maya shader is much expanded and has a lot of functions from my previous shaders as well as some new things. Its a very versatile hair shader – although it tends to lend itself more to stylized looks than photorealism.
NOTE: Hair UV shells should all be aligned vertically – highlight orientation is based on the UV shell alignment.
There are a ton of attributes, but some of the more interesting ones are:
Main UV Texture Tiling – tiling is useful on main diffuse and specular textures to sort of set the size of the hair strands – normal map can be excluded from tiling
Hair Color – Multiplied by diffuse map – diffuse map can be B&W or colorized if you set hair color to white.
Spec Edge Sharpness – hardens the specular highlight to make it look shinier/slicker
Specular Highlight Shift – moves the highlight up and down the surface
Specular Noise Map Scale – controls the intensity of the specular jitter effect
AO in vertex color – you can bake AO into the vertex color – multiplies by the Ambient and Diffuse
Shadow Map – r is shadow for light 1, g is shadow for light 2, b is shadow for light 3, a (alpha) is AO
Texture Examples:
diffuse (multiply by hair color) – alpha is hair transparency
normal map (for big waves)
specular highlight jitter (this is normal map alpha channel)
