Shaders

misss_physical

The misss_physical shader performs three kinds of calculations which can be used together or independently, as described here:

Multiple-scattering estimation, the most accurate, uses a strictly deterministic simulation of photon tracing to record sites in an internal photon map. These sites are looked up at render time and an optimized ray marching technique estimates multiple scatter irradiance.
Single-scattering approximation is based on light intensities, which is independent from photon mapping.
Diffusion theory is applied to evaluate the contribution of photons in the deep layer.

This is the shader declaration:

    declare shader
        "misss_physical" (
            color   "material",
            color   "transmission",
            scalar  "ior",
            vector  "absorption_coeff",
            vector  "scattering_coeff",     
            scalar  "scale_conversion",
            scalar  "scattering_anisotropy",
            scalar  "depth",
            integer "max_samples",
            integer "max_photons",
            scalar  "max_radius",
            boolean "approx_diffusion",
            boolean "approx_single_scatter",
            boolean "approx_multiple_scatter",
            array light "lights"
        )
        version 3
        apply material, photon
    end declare

This shader integrates subsurface scattering seamlessly into mental ray, and supports these features:

Simulate subsurface scattering materials both in still images and animations (although the misss_fast_* shaders are more suitable for animation).
Receive and continue subsurface scattering media caustics from the outside world.
Cast caustics from the subsurface scattering media to the outside world.
Specify both absorption and scattering coefficients. The resulting image will simulate correctly areas of absorption and areas of scattering. This is very important to get subtle color changes for example in milk from blue to yellow.
Perform scattering along the geometry.

The shader must be used both as material and photon shader. Otherwise use the following phenomenon.

misss_physical_phen

This is a Phenomenon that allows the user to avoid setting up shading graph connections both to the material and photon slots. It has the same characteristics of the misss_physical.