如下是幫助里提供的定義 %p}_4+[;
BRDF：Bi-directional Reflectance Distribution Function. It is the scattered radiance from a surface (reflective scattering) per unit incident Irradiance, and thus has units of inverse steradians (1/sr). The BRDF is defined as the differential scattered radiance per unit incident Irradiance. bGvALz' BSDF：Bi-directional Scattering Distribution Function and is a generic term which is used to refer to BRDF and BTDF. 9&=~_,wJd BTDF：Bi-directional Transmittance Distribution Function. It is the scattered radiance through a surface per unit incident Irradiance. .,pGW8Js $-$^r; 具體參數(shù)怎么選取需要自己去多嘗試，手冊里雖然有公式，但很抽象。