sample_bsdf VEX function

Samples a bsdf.

Contexts: displace, fog, light, shadow, surface

See also: eval_bsdf, emission_bsdf

sample_bsdf(bsdf b, vector viewer, vector geo_normal, vector &out_vector, vector &eval, int &type, float sx, float sy, int mask)

`viewer`	Vector toward viewer.
`geo_normal`	Geometric normal.
`sx` and `sy`	Random values, such as generated by nextsample. Different values of `sx` and `sy` translate into different random directions to sample.
`mask`	A bitmask indicating which types of bounces to evaluate. The following bitmask constants are defined in `pbr.h`: `PBR_DIFFUSE_MASK` - diffuse component `PBR_GLOSSY_MASK` - glossy component `PBR_SPECULAR_MASK` - mirror specular component `PBR_EMISSION_MASK` - emission component

The function modifies the values of the following arguments:

`out_vector`	The sampled outgoing vector.
`eval`	The color of the evaluated component.
`type`	The type of component sampled. This uses the same constants as in the `mask` argument.