Splines

Ownership boundary

This skill owns path math, spline queries, spline-mesh deformation, distance travel, and rigid placement along a path. Route terrain deformation/paint to unreal-landscape, procedural population to unreal-pcg, and streamed-cell/Data Layer/HLOD ownership to unreal-world-partition.

Select the system

Read references/use-cases.md before implementation.

• Use USplineComponent for path data, transforms, distance queries, and movement.
• Use one USplineMeshComponent per segment to deform a mesh between two endpoints.
• Use Landscape Splines when the path must deform or paint Landscape terrain.
• Use PCG spline tools when the spline is an authoring input for procedural placement.
• Use ISM/HISM placement instead of spline meshes when repeated objects must remain rigid.

Do not substitute one system for another merely because each contains “Spline” in its name.

Execute

1. Classify the job: query path, move actor, deform continuous mesh, place rigid instances, edit Landscape, or drive PCG.
2. Declare coordinate space for every query. Prefer World for actor placement and Local when feeding start/end data into a Spline Mesh Component owned by the same actor.
3. Use distance along spline for constant-speed travel and uniform spacing. Do not assume spline point index or input key is proportional to physical distance.
4. Put editor-generated geometry in the Construction Script. Put runtime mutation in explicit runtime functions. Make both paths idempotent.
5. Batch point edits, then update the spline once. Avoid rebuilding components every tick.
6. Validate start, midpoint, end, tightest bend, closed-loop seam, reverse travel, collision, and cooked build behavior.

Read references/action-patterns.md for exact patterns. Read references/troubleshooting.md when output twists, stretches, bunches, duplicates, or moves at inconsistent speed.

Hard rules

• Treat a Spline Component as a path, not rendered geometry.
• Treat a Spline Mesh Component as a two-point deformation, not a multi-point path.
• Derive repeated counts and spacing from Get Spline Length.
• Scale motion by delta time.
• Preserve an explicit mesh forward axis and up-vector convention.
• Clean up previously generated components before regenerating them.
• Keep spline mutation authoritative in networked gameplay; replicate state or results, not divergent per-client construction.
• Profile dense spline meshes and collision. Prefer instancing for large rigid repeats.

See references/sources.md for the UE 5.8 source trail.