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Performance and Baking

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What a structure costs

The Stats section in the Details panel shows the result of the last build: how many instanced components, how many instances in total, how many Spline Mesh components and how many procedural meshes (polygons). Look there when a structure starts to feel heavy.

Line vs Curve

  • Line — all meshes go into an InstancedStaticMeshComponent, one component per unique mesh. Cheap, and the whole structure stays editable. Fine for most scenes.
  • Curve — each element of each span becomes its own SplineMeshComponent. The component count climbs fast: a second section on a 50-point spline is another ~50 components. Turn Curve on only where the mesh really must bend along the curve, and watch Stats.

Large static structures: build and bake

For long fences, railings, roads and tracks — once the parameters are final — the recommended path is Merge to Static Mesh:

  1. Fully configure the structure.
  2. Run the merge — all the geometry becomes one StaticMesh asset.
  3. Enable Nanite on it.

After that the engine treats the structure as an ordinary static mesh with Nanite: per-cluster culling and level of detail at any distance, no manual LODs and no instancing cost. This is almost always a better result than trying to keep thousands of Spline Mesh components alive.

The downside is that the structure "freezes": to change it you bring the SplineCraft actor back and merge again.

A note on the number of unique meshes

In Line mode components are keyed by "mesh + materials". The fewer different meshes and materials in a structure, the fewer components and draw calls. Random meshes from a large list multiply the number of ISM components.

Lighting and baking

  • Mobility = Static — required for components to take part in static lighting bakes.
  • The Build Scenario step child actors are forced Movable — they will not receive baked static light. For a "frozen" result use a normal actor without a scenario, or Merge to Static Mesh.
  • For the final build of large structures, Merge to Static Mesh plus baked lighting gives the most predictable result.

See also