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Heterogeneous Volumes & Sparse Volume Textures

UE 5.3+ introduced Sparse Volume Textures (SVT) and the HeterogeneousVolume actor — real-time volumetric rendering for clouds, smoke, fluid sims, nebulae. The plumbing that finally makes OpenVDB content first-class in UE.

Components

Asset / Actor Purpose
SparseVolumeTexture 3D voxel asset; can be loaded from .vdb
HeterogeneousVolume actor Places an SVT in the world; provides bounds + material
Volumetric materials Material Domain = Volume

Importing OpenVDB

  1. Enable OpenVDB Importer plugin
  2. Drag a .vdb from Houdini/Embergen/EmberGen/SideFX Solaris into the Content Browser
  3. Choose Sparse Volume Texture during import
  4. UE compresses grids into BCn-style volume textures

Sequence (animated SVT)

OpenVDB files can be sequences — UE imports them as a SparseVolumeTextureFrame array. Set the Frame Number on the HeterogeneousVolume to animate, or hook into Sequencer for keyframed playback.

Materials

Material Domain = Volume. Inputs:

  • Albedo (volumetric color)
  • Extinction (density × extinction coefficient)
  • Emissive
  • AmbientOcclusion

Sample the SVT via Volume Texture Sample. The renderer ray-marches the volume against the scene.

Performance

Lever Effect
Voxel resolution Linear cost
Step count (CVar r.HeterogeneousVolumes.MaxStepCount) Sample density along rays
Sparse mode Only allocates voxels with content
Mip levels LOD across distance

Lighting

HeterogeneousVolumes are lit by:

  • Lumen (real-time, approximate)
  • Path Tracer (offline, accurate scattering)
  • Directional lights cast self-shadows automatically

Gotchas

  • Lumen reflections off heterogeneous volumes look correct in HW RT, fuzzy in SW.
  • Translucent post-process ordering matters — set r.HeterogeneousVolumes.RenderBeforeTransparent if blending issues appear.
  • Editor playback of animated VDB can be expensive — reduce voxel grid resolution or set a smaller bounding box.

Use cases

  • Real-time cloudscapes (combined with VolumetricCloud)
  • Smoke plumes
  • Magical fog / energy fields
  • Holographic projections (low-density emissive volumes)