Heterogeneous Volumes

How to create a VDB volume object

This feature enables path-traced volume rendering of both VDB files (internally converted to NanoVDB, a faster and more compact GPU-friendly volume representation) and procedural MDL based volumes. VDB files can either contain a SDF (signed distance field/level set) or density volume. Currently, the VDB volume material can only be applied to a cube mesh, while procedural volume materials can be applied to any kind of mesh (cube, sphere, torus, etc). Volumes can also overlap with other volumes. The maximum number of overlaps between the volumes is currently limited to four.

Create a cube mesh
In the cube's Property tab, check is Volume
Assign VDBTestMaterial.mdl to the cube
In the Property tab of the VDBTestMaterial, assign a VDB file to the volume_density_texture

Create a cube mesh
In the cube's Property tab, check is Volume
Assign either perlinNoise.mdl or worleyNoise.mdl to the cube

Setting	Description
Heterogeneous Volumes	The number of bounces is controlled by Max Heterogeneous Volume Scattering Bounces (under the Path-Tracing section in Path-Traced Mode Settings). • When set to 1: perform single scattering. Fast, suitable for lowly scattering volumes like fog. • When set to a value greater than 1: perform multi-scattering. Slower, suitable for highly scattering volumes like clouds. Important: Make sure to increase the number of bounces to avoid darkening artifacts.
Transmittance Method	Choose between Biased Ray Marching, Ratio Tracking or Brute-Force Ray Marching. Biased ray marching is the ideal option in all cases
Max Collision Count	Maximum delta tracking iterations. Increase to more than 32 for highly scattering volumes like clouds. Important: if set too low, parts of the volume will disappear
Max Light Collision Count	Maximum ratio tracking iterations. Increase to more than 32 for highly scattering volumes like clouds. Important: if set too low, parts of the volume will disappear
Max Density	Upper bound of the density of the volume (called Global Majorant in volume rendering).Important: if set too low, the volume will appear overly transparent
Fast VDB	Accelerates volume rendering of VDB files by 3-6x at the same accuracy. This setting does not work with MDL based volumes