Physically Correct Subsurface Scattering

The misss_physical shader simulates subsurface scattering in a physically correct way, attempting to simulate reality trough the same (but simplified) mechanism which happens in the natural world. Its goal is to provide subsurface scattering simulation in the situations where the misss_fast_* shaders might encounter difficulties, for instance when photon tracing comes into play: consider a situation where photons from the environment need to interact with an object with subsurface scattering, as well as when photons coming out from such an object and need to interact with the surroundings. Another example is light scattering trough geometry, as in a fiber channel.

One of the design goals of the misss_fast_* shaders is to provide a way to efficiently render human skin. They are most suitable for shallow (near surface) scattering. While they do support "through" scattering it is not truly volumetric and most suitable for translucency of relatively thin objects such as ears. For true volumetric results the physical shader is recommended.

The Physical shader is recommended for:

jade, emerald, and other highly translucent minerals.
milk, blood, ketchup, ivory soap.
thick slabs of translucent materials.
anything where light scatters deeply.
when rendering accuracy is important.
users that have experience with setting up scenes for global illumination.

The Fast shader is recommended for:

leaves, grass, plastic, wax, butter.
human skin, such as backlit ears.
when rendering speed is important.
when memory is important.
materials into which light does not penetrate deeply.

The shader library exports a shader which must be used both in the material shader and photon shader slots of a material. In addition, a material Phenomenon is provided. It internally connects the miss_physical shader both to material and photon slots.

Type	name	page
Shader	misss_physical	_misss_physical_shader
Phenomenon	misss_physical_phen	misss_physical_phen