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Geometry Cache

Asset class: UGeometryCache Component: UGeometryCacheComponent Plugin (built-in): Alembic Importer Status: stable since UE 4.21, production-ready in 5.7

Geometry Cache is Unreal's playback system for pre-baked, per-vertex-per-frame animated meshes. Where Skeletal Mesh deforms via a bone hierarchy, Geometry Cache replays the exact vertex positions captured in a DCC simulation — frame by frame, optionally interpolated.

What it's for

Use case Why Geometry Cache
Cloth & soft-body simulations from Houdini / Marvelous Designer No skeleton needed; topology can change
Fluid / pyro / FLIP simulations Vertex count changes per frame are allowed
Destruction baked in Houdini Captures the exact sim output
MetaHuman facial mocap (legacy path) High vertex count, low-bone replay
Crowd cache replays Cheaper than skel mesh per-instance

For real-time simulations, use Niagara Fluids, Chaos, or Cloth Asset (Dataflow). Geometry Cache is for pre-baked content.

Pipeline

graph LR
  H[Houdini / Blender / Maya] -->|Alembic .abc| A[Project/Content folder]
  A -->|drag into editor| I[Import dialog]
  I --> G[UGeometryCache asset]
  G --> C[UGeometryCacheComponent on actor]
  C --> S[Sequencer or Blueprint playback]
# In a ROP_Alembic1 node:
# - Build Hierarchy From Attribute: path
# - Use Object Path Hierarchy: off
# - Frame Range: timeline
# - Pack Transform: World Space
# - Format: Ogawa
# - Face Sets: name

Export from Blender

File → Export → Alembic (.abc)
  - Selected Objects: on
  - Flatten Hierarchy: on
  - Apply Subdivision Surface: as needed
  - UV Write / Normals: on
  - Frame Start / End: scene range

Import to UE

  1. Drag the .abc into the Content Browser.
  2. In the import dialog choose Geometry Cache (not Static or Skeletal).
  3. Key options:
  4. Material Slot: auto from per-face-set or single
  5. Force Single Mesh: for high-perf playback
  6. Compression: Zlib for size, none for speed
  7. Flatten Tracks: merges multi-object Alembics into one cache
  8. Optimize Index Buffer: on for static topology, off if topology changes per frame

Placing in a level

  1. Drag the UGeometryCache asset into the viewport — it creates an AGeometryCacheActor.
  2. Inspect the GeometryCache component for:
  3. Start Time Offset
  4. Playback Speed
  5. Looping
  6. Override Wireframe Color
  7. Motion Vector Scale (for TSR / motion blur)

Sequencer integration

Geometry Cache is a first-class Sequencer track:

  1. Add the actor to your Level Sequence
  2. + Track → Geometry Cache
  3. Keyframe Start Time Offset, Playback Speed, or use the Geometry Cache Section for scrub-frame control

Materials

  • Per-face-set Alembic exports become per-slot materials automatically.
  • For changing topology, use two-sided + disable lightmaps; baked GI is impossible with topology change.
  • Lumen GI handles dynamic Geometry Cache transparently in UE 5.x.

Performance

Lever Effect
Compression Trades disk size for CPU decode cost
Force Single Mesh One draw call per frame instead of N
Motion Vectors Required for TSR/TAA — small cost
Stream from Disk Off-loads memory; needs SSD
GPU Skinning Auto for fixed-topology caches

Memory: ~vertices × 12 bytes × frames uncompressed. A 100k-vertex 240-frame cache ≈ 280 MB before compression, ~50 MB Zlib.

API examples

#include "GeometryCacheComponent.h"
#include "GeometryCache.h"

UGeometryCacheComponent* Comp = NewObject<UGeometryCacheComponent>(this);
Comp->SetGeometryCache(LoadObject<UGeometryCache>(nullptr,
    TEXT("/Game/FX/MyCache.MyCache")));
Comp->SetStartTimeOffset(0.f);
Comp->SetLooping(true);
Comp->Play();

import unreal
asset = unreal.load_asset('/Game/FX/MyCache')
actor = unreal.EditorLevelLibrary.spawn_actor_from_object(asset,
    unreal.Vector(0,0,0))

Gotchas

  • Vertex count differences per frame disable GPU skinning; CPU path is much slower.
  • Lightmaps are not supported. Use Lumen.
  • Collision is per-frame trace against bounds only. For collidable destruction use Chaos Destruction instead.
  • Editor scrubbing can be slow on large caches — toggle "Disable Editor Preview" on the component while editing other things.
  • Niagara cannot read Geometry Cache vertex data directly — bake to a Vertex Animation Texture (VAT) via the Animation Asset toolkit if you need particle attachment.

Modern alternatives

Need Use instead
Real-time cloth Cloth Asset (Dataflow) in UE 5.7
Real-time fluids Niagara Fluids
Real-time destruction Chaos Destruction
Film-grade huge scenes USD with UsdStageActor
Per-particle baked motion Vertex Animation Texture (VAT)