This is a complex material for setting up volumetric effects. The interface consists of two parts:
Base
Basic absorption settings, optimizations, etc.
Open VDB
Specialized settings for reading OpenVDB and AUR files (PhoenixFD).
The material adds volumetric scattering. If a child material is defined, it acts as the border material.
Dali Renderer uses a full stochastic Monte Carlo calculation (an improved version of the Decomposition Spectral Tracking algorithm is used). Each Dali Volumetric material must be bounded by a closed mesh. All texture maps are sampled inside the volume and require 3D coordinates to do so.
Dali Volumetric boundaries can be nested. Internal materials can replace or extend external ones, their parameters will be replaced or combined. The material works in the concept of Nested Dielectrics, where materials are prioritized over others. Dali Volumetric may combine its parameters with other Nested Dielectrics materials, not necessarily Dali Volumetric.
If the material is emissive, then it can be converted to a light emitter. This will result in less noise in scenes, especially for small volumes (such as a bright candle flame).
The ability to combine gives more freedom for modeling. You can download just one VDB cloud template and use its Instances to form an extended cloud cover.
Uniform (without texture maps and VDB files) Dali Volumetric is optimized for Path guiding and REDS technology and their combination. Non-uniform (using texture maps or VDB files) Dali Volumetric does not work well with REDS if Grid Depth is enabled; the problem, however, is that without the Grid Depth the noise is so great that REDS is useless. This issue should be fixed in future versions.
The basic principle of light propagation in a material:
It is assumed that the material consists of a large number of small particles. A beam of light flies between particles until it collides with one of them. This distance on average determines the depth of penetration of the beam into the material. After a collision, the light can be absorbed by the particle (absorption), or it can be re-emitted in a new direction (scattering). In addition, a particle can emit its own light (emission). If a beam of light (many photons) goes through the material, then some of them will fly through, and some will not. For a beam of light that has passed through, this will be a change in its hue. Therefore, it is appropriate to speak of absorption in terms of hue and the distance at which that hue will be obtained from initially white light.
