specularbrdf

float  specularBRDF(vector L, vector N, vector V, float rough)

specularBRDF、phongBRDF、blinnBRDF和diffuseBRDF函数用于返回VEX着色中不同光照模型计算的BRDF值。您可以在自定义的illuminance循环中使用这些函数，以复现对应VEX光照函数的光照模型。

vector nn = normalize(frontface(N, I));
vector ii = normalize(-I);
Cf = 0;
illuminance(P, nn)
{
    vector ll = normalize(L);
    Cf += Cl * (specularBRDF(ll, nn, ii, rough) + diffuseBRDF(ll, nn));
}