Terrain System

The terrain system generates procedural 3D terrain using multi-layer Perlin noise with support for flat zones under stations and buildings. The system uses worker-based computation for height and normal calculations to maximize performance.

Location: packages/shared/src/systems/shared/world/TerrainSystem.ts

Architecture

Worker-Based Computation

The terrain system offloads height and normal calculations to a Web Worker for optimal performance:

// From TerrainSystem.ts
// Height and normal computation happens in TerrainWorker
// Main thread only recomputes for tiles overlapping flat zones
private async generateTileGeometry(tileX: number, tileZ: number): Promise<void> {
  // Request worker computation
  const workerResult = await this.terrainWorker.computeTile(tileX, tileZ);
  
  // Use worker heights + normals directly for tiles without flat zones
  if (!this.tileOverlapsFlatZone(tileX, tileZ)) {
    this.applyWorkerResults(workerResult);
    return;
  }
  
  // Fall back to main-thread recomputation only for flat zone tiles
  this.recomputeWithFlatZones(tileX, tileZ);
}

Performance Benefits:

Zero noise calls on main thread for non-flat-zone tiles
Parallel computation across multiple tiles
Normals computed in worker with centered finite differences
Main thread only handles flat zone blending

Height Parameter Synchronization

All terrain generation constants are centralized in TerrainHeightParams.ts to prevent parameter drift between main thread and worker:

// From TerrainHeightParams.ts
export interface NoiseLayerDef {
  scale: number;
  weight: number;
  octaves?: number;
  persistence?: number;
  lacunarity?: number;
  iterations?: number;  // For erosion noise
}

export const CONTINENT_LAYER: NoiseLayerDef = {
  scale: 0.0008,
  octaves: 5,
  persistence: 0.7,
  lacunarity: 2.0,
  weight: 0.35,
};

export const HILL_LAYER: NoiseLayerDef = {
  scale: 0.02,
  octaves: 4,
  persistence: 0.6,
  lacunarity: 2.2,
  weight: 0.25,
};

// Island configuration
export const ISLAND_RADIUS = 350;
export const ISLAND_FALLOFF = 100;
export const BASE_ELEVATION = 0.42;
export const OCEAN_FLOOR_HEIGHT = 0.05;

// Pond configuration
export const POND_RADIUS = 50;
export const POND_DEPTH = 0.55;
export const POND_CENTER_X = -80;
export const POND_CENTER_Z = 60;

// Coastline noise for irregular shorelines
export const COASTLINE_CIRCLE_SAMPLE_RADIUS = 2;
export const COAST_LARGE = {
  octaves: 3,
  persistence: 0.5,
  lacunarity: 2.0,
  weight: 0.2,
};

// Mountain boost
export const MOUNTAIN_BOOST_MAX_NORM_DIST = 2.5;
export const MOUNTAIN_BOOST_GAUSSIAN_COEFF = 0.3;

// Worker code generation
export function buildGetBaseHeightAtJS(): string {
  // Injects all constants into worker string
  return `function getBaseHeightAt(worldX, worldZ) { ... }`;
}

Implementation:

TerrainSystem imports params as TypeScript constants
TerrainWorker receives params via buildGetBaseHeightAtJS() injection
Single source of truth prevents parameter drift
Worker and main thread produce identical heights
All numeric constants baked into worker code at runtime

Worker Height Computation

The worker computes fully correct heights including shoreline adjustments:

// From TerrainWorker (injected into worker string)
function getBaseHeightAt(x: number, z: number): number {
  // 1. Multi-layer Perlin noise
  let height = 0;
  height += perlin(x * continentScale, z * continentScale) * continentWeight;
  height += perlin(x * ridgeScale, z * ridgeScale) * ridgeWeight;
  height += perlin(x * hillScale, z * hillScale) * hillWeight;
  height += perlin(x * erosionScale, z * erosionScale) * erosionWeight;
  height += perlin(x * detailScale, z * detailScale) * detailWeight;
  
  // 2. Island mask
  const islandMask = calculateIslandMask(x, z);
  height *= islandMask;
  
  // 3. Pond depression
  const pondMask = calculatePondMask(x, z);
  height -= pondMask;
  
  // 4. Shoreline adjustment
  const slope = calculateBaseSlopeAt(x, z);
  height = adjustHeightForShoreline(height, slope);
  
  // 5. Mountain boost
  if (height > mountainBoostThreshold) {
    height = mountainBoostThreshold + 
      (height - mountainBoostThreshold) * mountainBoostMultiplier;
  }
  
  return height * MAX_HEIGHT;
}

Normal Computation in Worker

Normals are computed in the worker using centered finite differences on an overflow grid:

// Worker computes (resolution+2)² grid with 1-tile border
// Allows centered finite differences at all vertices
const gridSize = resolution + 2;
const heights = new Float32Array(gridSize * gridSize);

// Sample heights with overflow
for (let z = -1; z <= resolution; z++) {
  for (let x = -1; x <= resolution; x++) {
    const worldX = tileWorldX + x * step;
    const worldZ = tileWorldZ + z * step;
    heights[(z + 1) * gridSize + (x + 1)] = getBaseHeightAt(worldX, worldZ);
  }
}

// Compute normals with centered finite differences
for (let z = 0; z < resolution; z++) {
  for (let x = 0; x < resolution; x++) {
    const hL = heights[(z + 1) * gridSize + x];
    const hR = heights[(z + 1) * gridSize + (x + 2)];
    const hD = heights[z * gridSize + (x + 1)];
    const hU = heights[(z + 2) * gridSize + (x + 1)];
    
    const nx = (hL - hR) / (2 * step);
    const nz = (hD - hU) / (2 * step);
    const ny = 1.0;
    
    // Normalize
    const len = Math.sqrt(nx * nx + ny * ny + nz * nz);
    normals[idx] = nx / len;
    normals[idx + 1] = ny / len;
    normals[idx + 2] = nz / len;
  }
}

Benefits:

Accurate normals at tile boundaries (no edge artifacts)
Centered differences produce smoother lighting
Worker handles all computation (zero main thread cost)

World Specs

// From TerrainSystem.ts CONFIG
const CONFIG = {
  TILE_SIZE: 100,           // 100m × 100m tiles
  WORLD_SIZE: 100,          // 100×100 grid = 10km × 10km world
  TILE_RESOLUTION: 64,      // 64×64 vertices per tile
  MAX_HEIGHT: 50,           // 50m max height variation
  WATER_THRESHOLD: 9.0,     // Water appears below 9m
  CAMERA_FAR: 400,          // Draw distance
};

Noise Layers

Terrain height is generated from multiple Perlin noise layers defined in TerrainHeightParams.ts:

Layer	Scale	Weight	Octaves	Persistence	Lacunarity	Purpose
Continent	0.0008	0.35	5	0.7	2.0	Large-scale landmasses
Ridge	0.003	0.15	-	-	-	Mountain ridges
Hill	0.02	0.25	4	0.6	2.2	Rolling hills
Erosion	0.005	0.1	3 iterations	-	-	Weathering patterns
Detail	0.04	0.08	2	0.3	2.5	Local bumps and variation

Combined height is normalized to [0, 1], raised to power curve (1.1), then scaled by MAX_HEIGHT (50m). Coastline Variation: Natural irregular shorelines created by sampling noise on a circle around the island:

Large-scale: 3 octaves, weight 0.2
Medium-scale: 3x frequency, 2 octaves, weight 0.08
Small-scale: 8x frequency, weight 0.02
Varies island radius by ±20% for organic coastlines

Flat Zones

Flat zones create level terrain under stations and buildings with smooth blending to procedural terrain.

How It Works

Height Calculation Priority:

Flat zones checked before procedural terrain
Core Flat Area: Inside the zone, terrain returns exact height value
Blend Area: Within blendRadius of zone edge, smoothstep interpolation blends to procedural terrain
Spatial Indexing: Terrain tiles (100m) used for O(1) lookup
Manifest-Driven: Stations with flattenGround: true automatically create flat zones

Blend Formula:

// Smoothstep interpolation from flat to procedural
const t = smoothstep(0, blendRadius, distanceFromEdge);
const blendedHeight = flatHeight * (1 - t) + proceduralHeight * t;

Flat Zone Registration

When a station spawns, TerrainSystem registers a flat zone: Dimensions calculated from:

Station footprint (from model bounds)
flattenPadding (extra space around footprint)
flattenBlendRadius (smooth transition zone)

Height sampled from:

Procedural terrain at station center
Ensures flat zone matches surrounding terrain elevation

// From StationSpawnerSystem.ts
terrainSystem.registerFlatZone({
  id: `station_${stationId}`,
  centerX: position.x,
  centerZ: position.z,
  width: footprint.width + flattenPadding * 2,
  depth: footprint.depth + flattenPadding * 2,
  height: terrainSystem.getHeightAt(position.x, position.z),
  blendRadius: flattenBlendRadius,
});

Height Calculation

When terrain height is requested, flat zones are checked first:

getHeightAt(worldX: number, worldZ: number): number {
  // 1. Check flat zones (O(1) via spatial index)
  const flatHeight = getFlatZoneHeight(worldX, worldZ);
  if (flatHeight !== null) {
    return flatHeight;
  }
  
  // 2. Fall back to procedural height
  return getProceduralHeightWithBoost(worldX, worldZ);
}

TerrainSystem API

// Register a flat zone (for dynamic structures)
terrainSystem.registerFlatZone({
  id: "player_house_1",
  centerX: 50.0,
  centerZ: 50.0,
  width: 10.0,
  depth: 10.0,
  height: 42.5,
  blendRadius: 1.0,
});

// Remove a flat zone
terrainSystem.unregisterFlatZone("player_house_1");

// Query flat zone at position
const zone = terrainSystem.getFlatZoneAt(worldX, worldZ);
if (zone) {
  console.log(`Standing on flat zone: ${zone.id}`);
}

Duel Arena Floor Fix (commits b8f56e81, 7a60135e, 51453da)

Players and agents were sinking ~0.4m into duel arena floors because flat zones were not being registered with the terrain system. This caused getHeightAt() to return raw procedural terrain height instead of floor-level height, and also allowed grass to grow through floor surfaces. Problem:

Flat zones were not registered for duel arena floors
getHeightAt() returned procedural terrain height (~0.4m below arena floors)
Players/agents spawned at procedural height, sinking into visual floor meshes
Grass system used procedural heights, rendering grass through floors
Terrain mesh rendered at procedural height, creating z-fighting with floor geometry

Solution: Flat zones are now registered programmatically from DuelArenaVisualsSystem for all 8 floor areas (6 arenas + lobby + hospital):

// From DuelArenaVisualsSystem.ts
// Register flat zones during system initialization
private registerArenaFlatZones(): void {
  const FLAT_ZONE_HEIGHT_OFFSET = 0.4; // Where players stand above procedural terrain
  const BLEND_RADIUS = 1.0;
  const CARVE_INSET = 1.0;

  // Register flat zones for all 6 arenas
  for (let i = 0; i < ARENA_COUNT; i++) {
    const row = Math.floor(i / 2);
    const col = i % 2;
    const centerX = ARENA_BASE_X + col * (ARENA_WIDTH + ARENA_GAP) + ARENA_WIDTH / 2;
    const centerZ = ARENA_BASE_Z + row * (ARENA_LENGTH + ARENA_GAP) + ARENA_LENGTH / 2;

    const proceduralHeight = this.getProceduralTerrainHeight(centerX, centerZ);
    const zone: FlatZone = {
      id: `duel_arena_floor_${i + 1}`,
      centerX,
      centerZ,
      width: ARENA_WIDTH,
      depth: ARENA_LENGTH,
      height: proceduralHeight + FLAT_ZONE_HEIGHT_OFFSET,
      blendRadius: BLEND_RADIUS,
      carveInset: CARVE_INSET,
    };

    this.terrainSystem.registerFlatZone(zone);
    this.flatZoneIds.push(zone.id);
  }

  // Register lobby and hospital floors (similar logic)
  // ...
}

Key Implementation Details:

Procedural Height Sampling: Uses getProceduralTerrainHeight() to get the raw terrain height at each arena center, then adds 0.4m offset for player standing height
Flat Zone Parameters:
- height: Procedural terrain height + 0.4m (where players stand)
- blendRadius: 1.0m smooth transition to surrounding terrain
- carveInset: 1.0m inset from zone edges to preserve blend padding
Registration Timing: Flat zones are registered in DuelArenaVisualsSystem.start() after terrain system is initialized but before arena meshes are created
Cleanup: Flat zones are unregistered in DuelArenaVisualsSystem.destroy() to prevent memory leaks

Affected Areas:

6 duel arenas (20m × 24m each)
Lobby floor (40m × 25m)
Hospital floor (30m × 25m)

Impact:

Terrain height queries now return correct floor-level values (procedural + 0.4m)
Players/agents spawn at proper height (no sinking)
Grass system respects flat zones (no grass through floors)
Terrain mesh is carved under floor areas to prevent overdraw
Visual floor meshes positioned 2cm above terrain mesh to prevent z-fighting
Terrain tiles are automatically regenerated when flat zones are registered after initial tile generation

Terrain Mesh Regeneration: When flat zones are registered after terrain tiles have already been generated, the terrain system automatically regenerates affected tiles to reflect the flat zone heights:

// From TerrainSystem.ts
// Regenerate any existing terrain tiles to apply flat zone heights
if (tilesToRegenerate.length > 0) {
  console.log(
    `[TerrainSystem] Regenerating ${tilesToRegenerate.length} terrain tiles for flat zone "${zone.id}"`
  );
  for (const tile of filteredTiles) {
    this.queueTerrainTileRegeneration(tile.x, tile.z, \"flat_zone\");
  }
}

This ensures terrain meshes always reflect flat zone heights, even when buildings or arenas are added after terrain initialization. Console Output:

[DuelArenaVisualsSystem] Registered 8 flat zones (6 arenas + lobby + hospital)
[DuelArenaVisualsSystem] Created floor 1 at (70.0, 0.67, 92.0) - terrain=0.27
[TerrainSystem] Flat zone stats: 8 zones registered, 24 tile keys in spatial index
[TerrainSystem] Regenerating 2 terrain tiles for flat zone "duel_arena_floor_1"

Console Logging

TerrainSystem logs flat zone activity:

[TerrainSystem] Registered flat zone "station_bank_lumbridge_1" -> tile keys: [0_-1, 0_0]
[TerrainSystem] FLAT ZONE HIT: "station_bank_lumbridge_1" at (2.5, -24.8) -> height=42.15
[TerrainSystem] Flat zone stats: 5 zones registered, 12 tile keys in spatial index, 1247 height lookups used flat zones
[TerrainSystem] Regenerating 2 terrain tiles for flat zone "duel_arena_0"

Performance Characteristics

Worker-Based Computation:

Height calculation: ~0ms on main thread (worker handles all noise)
Normal calculation: ~0ms on main thread (worker computes with overflow grid)
Tile generation: ~5-10ms total (worker + transfer + geometry build)
Flat zone tiles: ~15-20ms (requires main thread recomputation)

Spatial Indexing:

Flat zone lookup: O(1) via tile-based spatial index
Typical world: 5-10 flat zones, 10-20 tile keys
Negligible memory overhead (~1KB per zone)

Movement System - Uses terrain heights for collision
Collision System - Integrates with flat zones
World Generation - Terrain is part of world initialization

Overview

Engine Architecture

Client Application

Game Systems

AI Agents

Data Manifests

Technical Reference

Terrain System

Terrain System

Architecture

Worker-Based Computation

Height Parameter Synchronization

Worker Height Computation

Normal Computation in Worker

World Specs

Noise Layers

Flat Zones

How It Works

Flat Zone Registration

Height Calculation

TerrainSystem API

Duel Arena Floor Fix (commits b8f56e81, 7a60135e, 51453da)

Console Logging

Performance Characteristics

Overview

Engine Architecture

Client Application

Game Systems

AI Agents

Data Manifests

Technical Reference

​Terrain System

​Architecture

​Worker-Based Computation

​Height Parameter Synchronization

​Worker Height Computation

​Normal Computation in Worker

​World Specs

​Noise Layers

​Flat Zones

​How It Works

​Flat Zone Registration

​Height Calculation

​TerrainSystem API

​Duel Arena Floor Fix (commits b8f56e81, 7a60135e, 51453da)

​Console Logging

​Performance Characteristics

​Related Systems

Terrain System

Architecture

Worker-Based Computation

Height Parameter Synchronization

Worker Height Computation

Normal Computation in Worker

World Specs

Noise Layers

Flat Zones

How It Works

Flat Zone Registration

Height Calculation

TerrainSystem API

Duel Arena Floor Fix (commits b8f56e81, 7a60135e, 51453da)

Console Logging

Performance Characteristics

Related Systems