CHEXAUMODULE

Overview

The CHEXAUMODULE is a multi-threaded procedural runtime spawner for repeatable meshes (foliage, trees, rocks, etc.) based on hexagonal or square grid patterns. It generates HierarchicalInstancedStaticMeshComponent instances around the player in real-time, with probabilistic mesh selection, biome filtering, slope filtering, altitude filtering and room-type filtering.

Depends on CCOREUMODULE.

Architecture

The generation pipeline works as follows:

1. ACHexaSpawner is placed in the level with a reference to a DataTable row (FCHexaSpawnerDataStruct) and a pawn to track.
2. On tick, the spawner delegates to UCHexamaker::buildASync which computes tile UV coordinates around the pawn asynchronously.
3. Tiles are calculated in parallel (ParallelFor) with probabilistic mesh selection and multi-criteria filtering (biome, slope, altitude, room).
4. Mesh data is queued and processed on the game thread (updateISM_sync), creating UHierarchicalInstancedStaticMeshComponent instances.
5. Each FCHexaMakerStruct defines an independent placement layer (e.g. trees, rocks, grass) with its own parameters.
6. The system supports banned areas (bannedArea) to exclude regions from placement.

Placement Patterns

The module supports two grid patterns via the HexaPattern enum.

HEXAGONE — Hexagonal grid (flat-top)

Uses the axial coordinate system (q, r) with cube conversion (q, r, s = -q-r). The spawn area around the player forms a hexagon.

Each hexagonal cell is defined by 6 vertices around the center, with size = radius from center to vertex.

Axial-to-pixel conversion: pixel.X = tileSize × (√3 × q + √3/2 × r), pixel.Y = tileSize × 1.5 × r.

The spawn zone is bounded by the cubic condition q² + r² + s² ≤ nbHexaAround², producing a hexagonal shape around the player.

SQUARE — Square grid

Uses a regular grid layout. The spawn area forms a square around the player. Direct conversion: pixel.X = q × tileSize, pixel.Y = r × tileSize.

Placement Variations

Within each cell (hexagonal or square), the module offers several variations controlled by FCHexaMakerStruct:

Jitter (dispersion)

jitterForce randomly offsets the mesh from the cell center, avoiding a too-regular appearance. The offset is computed as a random value between minJitterForce × tileSize and maxJitterForce × tileSize, applied independently on X and Y with a random sign.

Random rotation

If rotate = true, each mesh receives a random Y rotation [0°, 360°].

Random scale

Each mesh receives a uniform random scale between minScalePercent and maxScalePercent.

Align to slope (alignToSlope)

When enabled, mesh rotation is adapted to follow the terrain slope via WorldUtility::bendRotatorOnSlope.

Altitude filter (withBound)

Restricts placement between above and below Z values.

Normal filter (withNormal)

Restricts placement based on terrain slope (zMinNornal → zMaxNornal, 0=vertical, 0.5=45°, 1=horizontal).

Biome selection

The biomeNoise singleton (UCNoisator) provides a noise value per position. Placement is filtered between biomeSelectLowerBound and biomeSelectUpperBound. When both bounds are equal (default 0=0), the filter is disabled.

Room type filter (roomType)

With CROOMUMODULE, placement can be restricted to:

• ROOM: inside rooms only (with distance-to-center filtering via meshSelectRateDistanceToRoomLowerBound/UpperBound)
• CORRIDOR: inside corridors only (with distance-to-edge filtering via meshSelectRateDistanceToEdgeLowerBound/UpperBound)
• WALL: outside rooms and corridors only
• UNSET: no room filtering (default)