ue5-pcg-building

Quick Start

• Define generation target: blockout towers, modular facades, or lot-based building sets.
• Define deterministic inputs: lot splines/points, district tags, style preset, and seed.
• Define runtime mode: static bake, on-demand, or runtime scheduled generation.
• Define output mode: Static Mesh instances first, Spawn Actor only for interactive/stateful parts.

API Anchors (UE5.6-UE5.8)

• Runtime trigger and radii live on UPCGComponent:
  • EPCGComponentGenerationTrigger::GenerateAtRuntime
  • bOverrideGenerationRadii, GenerationRadii, SchedulingPolicyClass, SchedulingPolicy
  • GenerateLocal(...), Cleanup(...)
• Runtime scheduler refresh lives on UPCGSubsystem:
  • UE5.6/UE5.7: RefreshRuntimeGenComponent(...), RefreshAllRuntimeGenComponents(...)
  • UE5.8: RefreshRuntimeGenExecutionSource(...), RefreshAllRuntimeGenExecutionSources(...)
  • UE5.8 deferred refresh: DirtyRuntimeGenExecutionSources(...)
  • Shared cleanup API: CleanupLocalComponentsImmediate(...)
• Output selection anchor classes:
  • UPCGStaticMeshSpawnerSettings for high-count rendering
  • UPCGSpawnActorSettings for interactive/stateful outputs
• Shape Grammar anchor classes:
  • UPCGSubdivisionBaseSettings::GrammarSelection
  • Do not rely on deprecated grammar fields (bGrammarAsAttribute_DEPRECATED, Grammar_DEPRECATED)

Graph Stage Contract

• Every stage must explicitly declare:
  • Input data type (EPCGDataType or asset source)
  • Core node/classes (minimum two)
  • Required parameters (seed, tags, ranges, radii, or style keys)
  • Output data type
  • Debug method (node-level checks, debug node, or log/assert path)
• If a stage cannot satisfy these five items, treat the graph design as incomplete.

Workflow

1) Input

• Input data type: actor/spline/point sources.
• Core node/classes: UPCGDataFromActorSettings, UPCGGetActorPropertySettings, UPCGCreatePointsSettings.
• Required parameters: lot tag filters, district/style tags, seed source, source bounds.
• Output: normalized lot point or spline data with stable ordering.
• Debug method: run UPCGDebugSettings after input stage and verify point count and bounds.

2) Filter

• Input data type: point/spline data from Input stage.
• Core node/classes: UPCGAttributeFilteringSettings, UPCGDensityFilterSettings, UPCGFilterByTagSettings.
• Required parameters: slope range, exclusion tags, min lot area/width, occupancy constraints.
• Output: only buildable lots/candidates.
• Debug method: compare candidate count before/after filter and inspect rejected tag distribution.

3) Transform

• Input data type: filtered buildable candidates.
• Core node/classes: UPCGCopyPointsSettings, UPCGCreateSplineSettings, UPCGApplyScaleToBoundsSettings.
• Required parameters: floor height, pivot convention, facade orientation basis, local axes.
• Output: footprint transforms and per-floor transforms.
• Debug method: inspect transform axes and floor index attributes on output points.

4) Grammar

• Input data type: segment/spline/point data from Transform stage.
• Core node/classes: UPCGSubdivideSplineSettings, UPCGSubdivideSegmentSettings, UPCGSelectGrammarSettings.
• Required parameters: GrammarSelection, module size limits, style-based grammar key mapping.
• Output: grammar-resolved module placements/attributes.
• Debug method: use UPCGPrintGrammarSettings for grammar parse and token validation.
• Rule: use GrammarSelection only; avoid deprecated grammar fields.

5) Output

• Input data type: grammar-resolved placements.
• Core node/classes: UPCGStaticMeshSpawnerSettings, UPCGSpawnActorSettings, UPCGCreateTargetActor.
• Required parameters:
  • Static path: mesh selector, instance packer, ISM/HISM policy.
  • Actor path: actor class, spawn attributes, state/interaction requirements.
• Output: rendered buildings and optional interactive building elements.
• Debug method: split output by layer/tag and validate per-layer counts.
• Default policy: prefer Static Mesh Spawner; use Spawn Actor only when stateful behavior is required.

6) Validate

• Input data type: final spawned result and runtime generation state.
• Core node/classes: UPCGDebugSettings, UPCGComponent, UPCGSubsystem.
• Required parameters: expected cell bounds, max per-update spawn budget, nav/collision expectations.
• Output: pass/fail signals and fix actions.
• Debug method: run staged checks for overlap, navigation impact, per-cell generation time, and deterministic replay.

Constraints

• Keep the main pipeline compatible with UE5.6-UE5.8 unless a version-specific note is required.
• Runtime generation must explicitly set:
  • GenerationTrigger = GenerateAtRuntime
  • explicit GenerationRadii (do not rely on implicit defaults)
  • explicit SchedulingPolicyClass for predictable scheduler behavior
• Prefer ISM/HISM style output for large counts; avoid spawning heavyweight actors for each small part.
• Keep runtime generation bounds explicit to avoid uncontrolled world-wide regeneration.
• Avoid hidden dependency on editor-only data when runtime generation is expected.
• Treat World Partition boundaries as hard constraints for runtime scopes.

Failure Handling

• Symptom: no buildings spawn.
  • Locate: Input stage output count, source bounds, lot tags.
  • Fix: verify source actor/spline ingestion and lot filter tags; confirm non-empty candidate set.
• Symptom: output exists in editor preview but not runtime.
  • Locate: GenerationTrigger and runtime radii/scheduling settings.
  • Fix: set GenerateAtRuntime, radii override, and valid scheduling policy.
• Symptom: runtime update regenerates too wide an area.
  • Locate: runtime radii and generation source movement.
  • Fix: reduce generation/cleanup radii and tighten source bounds.
• Symptom: stale generated pieces remain after rules shrink.
  • Locate: cleanup path and local component lifecycle.
  • Fix: trigger cleanup with remove-components behavior and force local cleanup when needed.
• Symptom: heavy hitching during runtime generation.
  • Locate: points-per-cell, actor spawn count, per-update workload.
  • Fix: reduce per-cell complexity, cap actor spawns, move non-interactive parts to static mesh instances.
• Symptom: deterministic replay mismatch with same seed.
  • Locate: unstable upstream point ordering or non-seeded random branch.
  • Fix: normalize ordering before random selection and bind every stochastic path to explicit seed inputs.
• Symptom: facade grammar fails or produces empty modules.
  • Locate: grammar parse logs and module token mapping.
  • Fix: validate grammar string, module dictionary, and segment size constraints.
• Symptom: overlap and collision issues.
  • Locate: filter thresholds and final placement constraints.
  • Fix: add clearance/slope filters and occupancy rejection before output stage.
• Symptom: navmesh degradation around generated buildings.
  • Locate: collision profile and nav-affecting flags on spawned outputs.
  • Fix: split nav-affecting vs non-nav-affecting outputs and rebuild nav only where required.
• Symptom: runtime changes do not apply after parameter edits.
  • Locate: scheduler refresh flow.
  • Fix: request runtime scheduler refresh for the modified component or all runtime components.

Runtime Scheduler Ops

• Use component refresh when one runtime component changed style/radii/scheduling inputs.
• Use global refresh when style/global rules changed for many runtime components.
• Use immediate local cleanup when bounds shrink or partition ownership changed.
• After cleanup, trigger local regeneration only for affected runtime scope.

UE5.6-UE5.8 Compatibility Notes

• Core runtime trigger and grammar APIs above are stable in UE5.6-UE5.8.
• UE5.8 adds non-destructive manual editing and complex metadata attribute values; treat these as optional 5.8 capabilities rather than requirements for cross-version graphs.
• Header path difference for subsystem:
  • UE5.6 commonly uses Public/PCGSubsystem.h
  • UE5.7/UE5.8 use Public/Subsystems/PCGSubsystem.h and include Subsystems/PCGSubsystem.h
• UE5.8 deprecates component-named scheduler refresh calls. Use the IPCGGraphExecutionSource-based APIs in 5.8 code; retain the component-based calls only for 5.6/5.7 branches.

Escalation

• Escalate when architecture requires custom C++ PCG elements or engine plugin extension.
• Escalate when city-scale generation must be integrated with World Partition streaming policy.
• Escalate when generated layout must be synchronized with save/load or multiplayer authority rules.