This material is analogous to the settings for the MIE phase function of the Dali Volumetric material. But unlike Dali Volumetric, which works with voxel volumes, the MIE material is designed for particle systems. The important feature of the material is that it is one-sided. This means that when the beam meets the reverse side, the beam passes without collision.
The material is very slow for standard settings, it does physically correct scattering on large particles using long calculations in accordance with Mie's theory of electromagnetic scattering.
The parameters are the same as those of the Dali Volumetric material.
Additionally, you can mix in an arbitrary second material and assign transparency.
Diameter
Particle diameter in microns. A good rain rainbow requires particle sizes of 100-300 microns.
IOR
Refractive index (real part) for particle material. Spectral effects require specifying a spectral spline.
IOR-K
The imaginary part of the refractive index is responsible for the conductive properties of the particles.
Gain
A non-physical parameter that enhances the brightness of the rainbow. If the rainbow hits a bright background, then its visibility can be improved by this factor.
Spread
In nature, it does not happen that all drops have exactly the same size. In the laboratory, this can be done and get rings of secondary rainbows. In nature, it is difficult to notice even a second rainbow, although up to 15 rings were obtained in the laboratory.
This setting brings chaos to the size of the particles and makes the rainbow look more natural.
Bias
Shifts the particle size distribution up or down from the Diameter value.
Resample
Improves the signal-to-noise ratio by resampling a random sample. It slows down the calculations. Whether or not to use this option depends on the particular scene.
Filter color
Additional coloring for reflection
Mixing material
Additionally mixes arbitrary material. The second material must not be a volumetric dielectric as the Dali MIE is one sided.
Opacity
Material transparency.
Faked shadow rays
This material will not cast a shadow.
Nesting priority
The priority value for a system of nested dielectrics. For example, you can turn off those particles that have fallen under the surface of the water.
