[How-To] use Minnaert diffuse reflectance for UE3 materials

Minnaert's model is a pure diffuse reflectance model which does not affect the specular reflectance. Therefore it can be combined with any specular model, like phong, blinn, cook-torrance etc.
The special feature about the minnaert model is that it can provide a velvet look by darkening the model along it edges.


Material Setup

The UE3/UDK implementation requires a material with custom lighting:

The amount of darkening is controlled by a paramter which I named as darkening paramter in the screenshot above. This one can have any value equal or bigger than zero. A value of zero means there is no darkening at all and will result in lamberts diffuse reflectance (UDK default).



Comparison

The following screenshots show the affect of different parameter values.