AshikhminShirley roughness¶
The AshikminShirley roughness model is an anisotropic generalization of the Phong roughness model, based on the paper An Anisotropic Phong BRDF Model.
It uses two roughness parameters, nu and nv. They control the roughness along u and v directions, thus allowing anisotropy when different values are used. The u and v directions are defined by the UV coordinate parametrization of the surface, therefore, the results are undefined when this roughness model is used on a geometry without UV coordinates.
nu and nv have exactly the same behavior than the exponent parameter of the Phong roughness. They may vary from zero (maximum roughness) to infinity (perfectly smooth surface). For high values, they are equivalent to 2/α², where α is the standard deviation (RMS) of the surface slope along each U and V axis.
Children nodes¶
The roughness exponent along u axis 

The roughness exponent along v axis 
Parameters¶
none
Ocean XML 3.0 example¶
<roughness name="roughness" type="ashikhminshirley">
<scalarshader name="nu" type="uniform" value="1"/>
<scalarshader name="nv" type="uniform" value="10"/>
</roughness>