Procedural Placement Tool

The Procedural Placement Tool automates the placement of static mesh instances and Blueprint actors across terrain using configurable rules for density, slope filtering, height ranges, biome zones, exclusion volumes, landscape layer sampling, clustering, and spacing constraints. It uses Hierarchical Instanced Static Mesh Components (HISM) for efficient rendering of hundreds of thousands of instances.

Version: 2.0.0 | Engine: UE 5.7 | Author: StraySpark

Core Features

• Multi-layer scatter -- Configure independent placement layers, each with its own mesh set, density, and filter rules
• Density modes -- Uniform, Perlin noise modulation, radial falloff, or texture mask sampling
• Surface filtering -- Filter by slope angle range and world height range
• Weighted mesh selection -- Assign probability weights to multiple meshes per layer
• Surface alignment -- Align instances to world up, surface normal, or random rotation
• Minimum spacing -- O(1) spatial hash grid enforces distance between placed instances
• Deterministic generation -- Seed-based random stream for reproducible results
• Reusable rule assets -- Save placement configurations as UDataAsset for sharing across actors
• Per-layer seed override -- Independent randomization per layer

V2.0 Features

• Exclusion zone volumes -- Box volumes that prevent placement, with optional soft falloff edges
• Spline scatter -- Scatter along spline paths for roads, rivers, fences, and trails
• Blueprint actor spawning -- Spawn full Blueprint actors (not just meshes) with proper cleanup
• Texture density masks -- Use grayscale textures to modulate density with contrast control
• Landscape layer sampling -- Filter placement based on landscape paint layer weights
• Cluster/grouping system -- Generate natural-looking clumps with configurable count, radius, and spacing
• Object-aware collision -- Sphere overlap test prevents placement where existing actors are present
• Non-uniform scale -- Independent per-axis scale ranges (X, Y, Z)
• Debug visualization -- 6 modes: None, PointCloud, DensityHeatmap, SlopeOverlay, RejectedPoints, AllPoints
• Undo/redo support -- FScopedTransaction wraps all editor operations
• Generation statistics -- Per-layer breakdown of placed/filtered instances with timing data
• Progress feedback -- FScopedSlowTask progress bar with cancellation support
• 10 themed presets -- Dense Forest, Desert, Snowy Forest, Urban Park, Swamp, Roadside, River Bank, Cliff Face, Tropical Beach, Mixed Biome Transition

Plugin Structure

Plugins/ProceduralPlacement/
  ProceduralPlacement.uplugin
  Source/
    ProceduralPlacementRuntime/     Core placement logic (12 source files)
      Public/
        ProceduralPlacementTypes.h       Enums, structs, delegates
        ProceduralPlacementRule.h         Reusable rule data asset
        ProceduralScatterActor.h         Main box-based scatter actor
        SplineScatterActor.h             Spline-based scatter actor
        BiomeZoneVolume.h                Biome zone definition volume
        ExclusionZoneVolume.h            Exclusion zone volume
        PlacementQuerySubsystem.h        World subsystem for queries
        PlacementPresets.h               10 themed preset factories
        SpatialHashGrid.h               O(1) proximity utility (header-only)
        ProceduralPlacementRuntimeModule.h
      Private/
        (matching .cpp files)
    ProceduralPlacementEditor/     Detail panel customization (4 source files)
      Public/
        ProceduralScatterDetailCustomization.h
        ProceduralPlacementEditorModule.h
      Private/
        (matching .cpp files)

Runtime Classes

Class	Type	Purpose
AProceduralScatterActor	Actor	Main scatter actor -- box bounds, layers, HISM + actor spawning, debug viz
ASplineScatterActor	Actor	Spline-based scatter -- scatter along/around spline paths
UProceduralPlacementRule	DataAsset	Reusable rule set containing an array of placement layers
ABiomeZoneVolume	Actor	Box volume defining a biome region with type, priority, and blend radius
AExclusionZoneVolume	Actor	Box volume preventing placement with optional falloff edge
UPlacementQuerySubsystem	WorldSubsystem	Surface traces, biome detection, exclusion checks, landscape layers, collision
UPlacementPresets	FunctionLibrary	10 preset factory functions for common placement scenarios
FSpatialHashGrid	Utility	Header-only O(1) spatial hash grid for min-spacing enforcement

Key Types

Type	Description
FPlacementLayer	Full layer config: meshes/actors, density, filters, spacing, scale, alignment, biome, clustering, seed
FWeightedMeshEntry	Mesh soft reference with probability weight
FSurfaceQueryResult	Hit location, surface normal, slope degrees, biome type
FScatterResult	Generation stats: placed, filtered, time, per-layer breakdown
FLayerScatterStats	Per-layer filter breakdown (surface, slope, height, biome, spacing, exclusion, collision, landscape)
EBiomeType	Default, Forest, Desert, Grassland, Mountain, Swamp, Snow, Urban, Custom
EDensityMode	Uniform, PerlinNoise, RadialFalloff, TextureMask
ESurfaceAlignMode	AlignToWorldUp, AlignToSurfaceNormal, RandomRotation
EPlacementObjectType	StaticMesh (HISM), BlueprintActor (SpawnActor)
EDebugVisMode	None, PointCloud, DensityHeatmap, SlopeOverlay, RejectedPoints, AllPoints

Generation Pipeline

The scatter algorithm follows this sequence for each generation pass:

1. Collect active layers from the rule asset or inline configuration
2. Initialize spatial hash grid and refresh biome/exclusion caches
3. For each layer:
   • Generate sample points within bounds (box or spline band) using density mode
   • For clustered layers, generate cluster centers first, then scatter within each cluster
   • For each sample point: raycast downward to find the surface, filter by slope angle range, filter by world height range, check biome zone compatibility, check exclusion zone volumes, check landscape layer weight threshold, check actor collision (sphere overlap), enforce minimum spacing via spatial hash, calculate transform (position + height offset, rotation with alignment, scale), spawn mesh instance (HISM) or Blueprint actor
   • Record per-layer statistics
4. Broadcast OnScatterComplete delegate with results

Editor Features

Custom details panel on AProceduralScatterActor with:

• Generate button -- Run the scatter algorithm (with undo support)
• Clear button -- Remove all generated instances (with undo support)
• Randomize Seed button -- Set a new random seed and regenerate
• Generation Statistics -- Total placed/filtered, generation time, per-layer breakdown with filter reasons

Requirements

• Unreal Engine 5.7
• DX12 / SM6
• Windows (Win64)

Dependencies

• Runtime: Core, CoreUObject, Engine, Foliage, Landscape, RenderCore
• Editor: UnrealEd, PropertyEditor, InputCore, LevelEditor, LandscapeEditor
• No third-party dependencies

Next Steps

• Getting Started -- Installation and first scatter tutorial
• Configuration -- All placement layer settings
• Density Modes -- Uniform, Perlin, Radial, Texture
• Biome Zones -- Regional vegetation control
• Spline Scatter -- Scatter along paths
• Exclusion Zones -- Prevent placement in areas
• Presets -- 10 built-in placement presets
• Examples -- Practical recipes and patterns
• API Reference -- Complete API documentation
• Changelog -- Version history