Where can I get metal and sheen implementations

[FeiLongXu]

Because I want to use this standard material in cycles, but cycles does not provide the implementation of metal and sheen

[iliyang]

I'm afraid we currently don't provide reference implementations of the basic closures. We are planning to expand our reference implementations, however. But here's some guidance:

1. The metal closure is a standard GGX microfacet conductor closure whose complex IOR parameters eta and kappa are computed using Gulbrandsen's mapping (see white paper for details).
2. The sheen closure is the one by Estevez and Kulla [2017] as discussed in the white paper.