Action patterns

Constant-speed actor movement

Variables:

• DistanceCm — float
• SpeedCmPerSec — float
• Direction — 1.0 or -1.0
• Loop — bool
• OrientToSpline — bool

Per update:

1. Length = Spline -> Get Spline Length.
2. DistanceCm += SpeedCmPerSec * Direction * DeltaSeconds.
3. Loop: wrap into [0, Length); non-loop: clamp into [0, Length].
4. Get Transform at Distance Along Spline in World space.
5. If orientation is disabled, use only returned location.
6. Apply with Set Actor Transform or move the intended component.
7. Define end behavior explicitly: stop, loop, reverse, fire event, or dwell.

Do not drive constant speed with Get Location at Spline Input Key plus a linearly increasing key. Parametric distance is not guaranteed to be uniform.

Closest progress to an actor

1. Read actor world location.
2. Use Get Distance Along Spline at Location with World coordinate space.
3. Use the returned distance for progress, ordering, or a subsequent transform query.
4. If the spline crosses itself, retain previous progress and constrain how far the result may jump between updates.

Rigid objects at uniform intervals

1. Get spline length.
2. Choose either:
   • fixed maximum spacing: count = ceil(length / maxSpacing);
   • approximately target spacing with even end fit: count = round(length / targetSpacing).
3. Compute actualSpacing = length / max(1, count).
4. Iterate 0..count when both endpoints need objects; otherwise 0..count-1.
5. Query transform at index * actualSpacing.
6. Add an ISM/HISM instance for repeated meshes; spawn actors only when each instance needs independent behavior.
7. Apply lateral offset in the sampled transform's right-vector direction.

Continuous deformed mesh

For each consecutive pair of spline points:

1. Create or reuse one Spline Mesh Component.
2. Query start/end locations and tangents in the spline owner's Local space.
3. Assign the static mesh and Forward Axis.
4. Call Set Start and End with start position/tangent and end position/tangent.
5. Apply start/end scale or roll only if required by the design.
6. Register the component when created at runtime.
7. Store generated components in an array. Destroy/clear them before regeneration.

For a closed loop, include the last-to-first segment.

Editable Blueprint generator

Recommended layout:

• Actor root
• Spline Component
• Exposed mesh/material/spacing/width/collision variables
• GeneratedComponents array
• Rebuild function used by Construction Script and explicit runtime updates

Rebuild:

1. Destroy or clear previously generated components/instances.
2. Validate spline point count and assets.
3. Generate deterministically from current spline data.
4. Do not modify the designer's control points unless that is the tool's explicit job.

Landscape road

1. Enter Landscape Manage mode and select Spline.
2. Create/join/split control points and segments.
3. Add a dedicated Spline Edit Layer before expecting heightmap deformation.
4. Set segment mesh, width, side falloff, layer name, and raise/lower behavior.
5. Snap points to Landscape where appropriate.
6. Inspect intersections, steep grades, tangents, and material paint transitions.

PCG spline authoring in UE 5.8

• Enable and enter PCG Editor Mode.
• Use Draw Spline for roads, fences, and line placement.
• Use Draw Spline Surface for closed fields or bounded scattering.
• Use graph refresh-rate controls when interactive generation is expensive.
• Use Apply Spline to Component when PCG must update an existing Spline Component.
• Mark the workflow experimental in production documentation and provide a fallback.