Use this skill when working with procedural generation in Unreal Engine: PCG framework, ProceduralMesh, instanced mesh, HISM, spline, runtime mesh, noise, terrain generation, or dungeon generation. See references/pcg-node-reference.md for PCG node types and references/procedural-mesh-patterns.md for

ue procedural generation You are an expert in Unreal Engine's procedural generation systems, including the PCG framework, ProceduralMeshComponent, instanced static meshes, noise functions, and spline based generation. Context Check Before advising, read .agents/ue project context.md to determine: Whether the PCG plugin is enabled (plugins list) Target generation type: world layout, terrain, dungeon, vegetation, runtime mesh Performance constraints (mobile, console, Nanite enabled) Multiplayer requirements (server authority vs. deterministic seeding) Information Gathering Ask for clarification on: 1. Generation type : world population (PCG), runtime mesh (ProceduralMeshComponent), instanced geometry (ISM/HISM), or spline driven? 2. Timing : editor time baked result or runtime dynamic generation? 3. Instance count : hundreds (ISM) or tens of thousands (HISM)? 4. Collision : does generated geometry need physics collision? 5. Determinism : same seed must produce same result across sessions or network clients? 1. PCG Framework (UE 5.2+) Node based rule driven world generation. Operates on point clouds with transform, density, color, seed, and metadata attributes. Plugin Setup Core Classes Class Header Purpose UPCGComponent PCGComponent.h Actor component driving generation UPCGGraph PCGGraph.h Asset: nodes + edges UPCGGraphInstance PCGGraph.h Graph instance with parameter overrides UPCGPointData Data/PCGPointData.h Point cloud between nodes UPCGSettings PCGSettings.h Node settings base class UPCGBlueprintBaseElement Elements/Blueprint/PCGBlueprintBaseElement.h Custom Blueprint node base UPCGComponent Key API (from PCGComponent.h ) Generation triggers ( EPCGComponentGenerationTrigger ): GenerateOnLoad — one shot on BeginPlay GenerateOnDemand — explicit Generate() call only GenerateAtRuntime — budget scheduled by UPCGSubsystem UPCGGraph Node API (from PCGGraph.h ) Custom Blueprint PCG Node Derive from UPCGBlueprintBaseElement : Key UPCGBlueprintBaseElement properties: bIsCacheable = false — when node spawns actors or components bRequiresGameThread = true — for actor spawn, component add CustomInputPins / CustomOutputPins — extra typed pins PCG Determinism PCG graphs are deterministic by default — the same seed produces identical output. Each node receives a seeded random stream via GetRandomStreamWithContext() . To vary output across instances, set the PCG component's Seed property. For multiplayer, ensure all clients use the same seed (replicate via GameState or pass as spawn parameter). PCG Data Types Type Contains Use for FPCGPoint / Point Data Position, rotation, scale, density, color Scatter placement, foliage, instance positioning UPCGSplineData Spline points + tangents Roads, rivers, paths, boundary definitions UPCGLandscapeData Height + layer weight sampling Terrain aware placement, biome queries UPCGVolumeData 3D bounds Volume based filtering and generation Point data is the most common — most PCG nodes consume and produce point collections. Also available: UPCGTextureData , UPCGPrimitiveData , UPCGDynamicMeshData . See references/pcg node reference.md for all node types, settings fields, and pin labels. 2. ProceduralMeshComponent Core API Terrain Grid Example Performance Notes One draw call per CreateMeshSection . Keep vertex count < 65K per section. UpdateMeshSection updates vertex positions and collision (if enabled) but cannot change topology — call CreateMeshSection for new triangles. ProceduralMesh does not support Nanite. Compute vertex data on background thread; call CreateMeshSection on game thread only. Async Mesh Generation Generate vertices on a background thread, then apply on the game thread: Collision on Procedural Meshes Set UProceduralMeshComponent::bUseComplexAsSimpleCollision = true to use the rendered triangles directly for collision. This is accurate but expensive — only use for static geometry. For dynamic or high poly meshes, generate simplified convex hulls instead. 3. Instanced Static Meshes (ISM / HISM) Feature ISM ( InstancedStaticMeshComponent.h ) HISM ( HierarchicalInstancedStaticMeshComponent.h ) Best for < 1,000 dynamic instances 1,000 mostly static Culling Distance only Hierarchical BVH + distance LOD GPU selection Built in transitions Remove cost O(n) async BVH rebuild Key ISM API (from InstancedStaticMeshComponent.h ) Culling properties: InstanceStartCullDistance , InstanceEndCullDistance , InstanceLODDistanceScale , bUseGpuLodSelection . Vegetation Scatter (HISM + Terrain Trace) Foliage System The editor's Foliage paint mode uses AInstancedFoliageActor which internally wraps UHierarchicalInstancedStaticMeshComponent . For procedural foliage at scale, use UProceduralFoliageComponent with UProceduralFoliageSpawner — it distributes foliage via simulation (species competition, shade tolerance) rather than manual painting. Per instance collision : Enable bUseDefaultCollision on the ISM component. Each instance inherits the static mesh's collision. For custom per instance collision shapes, use separate actors — ISM does not support unique collision per instance. Platform limits : HISM GPU buffer caps vary by platform (~1M on desktop, ~100K on mobile). Monitor with stat Foliage . Split large populations across multiple HISM components. 4. Noise and Math Height/density maps : Sample UTexture2D pixel data via FTexturePlatformData to drive terrain height or placement density. Lock with BulkData.Lock(LOCK READ ONLY) , read, then unlock. Poisson disc sampling (minimum separation scatter for natural placement) — full Bridson algorithm implementation in references/procedural mesh patterns.md . 5. Spline Components USplineComponent API (from SplineComponent.h ) Point types: Linear , Curve , Constant , CurveClamped , CurveCustomTangent . FindInputKeyClosestToWorldLocation(WorldLocation) — returns the spline key nearest to a world position (useful for snapping actors to splines). Runtime modification : Call AddSplinePoint() , RemoveSplinePoint() , or SetLocationAtSplinePoint() then UpdateSpline() to rebuild. Batch modifications before calling UpdateSpline() — each call recalculates the entire spline. Spline Placement Example USplineMeshComponent (Mesh Deformation) 6. Runtime Mesh Generation Patterns See references/procedural mesh patterns.md for full implementations: Marching Cubes — isosurface from 3D density scalar field Dungeon BSP — BSP partition into rooms, L corridor carving, tile to mesh L System — string rewriting + turtle interpreter to HISM branches Wave Function Collapse — constraint propagation tile grid layout Async mesh generation — background thread vertex computation, game thread CreateMeshSection Spline road extrusion — cross section profile swept along USplineComponent Common Mistakes and Anti Patterns PCG Calling GenerateLocal() in Tick — generation is not free; use GenerateOnDemand and regenerate only on data change. Using GenerateLocal() in multiplayer — it is NOT replicated; use Generate(bForce) (NetMulticast). Heavy custom nodes with bIsCacheable = true — only cache if output depends solely on inputs + seed. Graphs with bIsEditorOnly = true fail to cook into packaged builds. ProceduralMeshComponent Passing bCreateCollision=false to CreateMeshSection — characters fall through the mesh. Calling UpdateMeshSection expecting topology to change — vertex count must match; use CreateMeshSection for new triangles. Using ProceduralMesh for Nanite scale terrain — not supported; use Landscape or PCG + ISM. Wrong triangle winding (CW instead of CCW) — polygons are invisible due to back face culling. ISM / HISM Using ISM above ~500 instances — switch to HISM for BVH culling. Setting bMarkRenderStateDirty=true on every UpdateInstanceTransform in a loop — only set true on the last call. Skipping PreAllocateInstancesMemory before bulk add — repeated realloc degrades performance. Splines Calling AddSplinePoint(bUpdateSpline=true) in a loop — rebuilds reparameterization table every call; use false and call UpdateSpline() once. Using spline input key (not distance) for even spacing — key is NOT proportional to arc length. Multiplayer Procedural content must be deterministic (same seed) or server authoritative. GenerateLocal() does not replicate; Generate(bool) is NetMulticast, Reliable . Related Skills ue actor component architecture — component lifecycle, registration, replication ue physics collision — collision profiles, complex vs. simple on generated geometry ue cpp foundations — NewObject , TSubclassOf , TArray , memory management Reference Files references/pcg node reference.md — all PCG node types, pin labels, settings fields, determinism checklist references/procedural mesh patterns.md — quad grid, marching cubes, dungeon BSP, L system, WFC, spline road

ue-procedural-generation