dcl-regenesislabs/optimize-scene

Optimizing Decentraland Scenes

Authoring split

The patterns in this skill — object pools, LOD, asset preloading, system throttling — are all runtime mechanics and live in src/index.ts. The static layout (chairs, walls, lamps, the props that get LOD'd) should still be declared in main-entities.ts; the optimization code reads those entities by name (engine.getEntityOrNullByName) or by component query (engine.getEntitiesWith(Transform)).

The parenting optimization (a static container with many children) is best expressed in main-entities.ts using Transform.parent: 'parent_name' — that way the editor can move the entire group as a unit.

Scene Limits (Per Parcel Count)

All limits scale with parcel count n. Triangles, entities, and bodies scale linearly. Materials, textures, and height scale logarithmically. Except for hard MB size limits on deploy, all other limits CAN be exceeded — scenes won't crash, but performance degrades and the scene may become unusable on lower-end devices. Treat the numbers as guidelines, not enforcement.

| Resource | Formula | 1 parcel | 2 parcels | 4 parcels | 9 parcels | 16 parcels | |---|---|---|---|---|---|---| | Triangles | n x 10,000 | 10,000 | 20,000 | 40,000 | 90,000 | 160,000 | | Entities | n x 200 | 200 | 400 | 800 | 1,800 | 3,200 | | Physics bodies | n x 300 | 300 | 600 | 1,200 | 2,700 | 4,800 | | Materials | log2(n+1) x 20 | 20 | 31 | 46 | 66 | 81 | | Textures | log2(n+1) x 10 | 10 | 15 | 23 | 33 | 40 | | Height limit | log2(n+1) x 20m | 20m | 31m | 46m | 66m | 81m |

File limits: 15 MB per parcel, 300 MB max total, 200 files per parcel, 50 MB max per individual file.

Entity Count Optimization

Reuse Entities

// BAD: Creating new entity each time
function spawnBullet() {
  const bullet = engine.addEntity() // Creates entity every call
  // ...
}

// GOOD: Object pooling
const bulletPool: Entity[] = []
function getBullet(): Entity {
  const existing = bulletPool.find(e => !ActiveBullet.has(e))
  if (existing) return existing
  const newBullet = engine.addEntity()
  bulletPool.push(newBullet)
  return newBullet
}

Remove Unused Entities

engine.removeEntity(entity) // Frees the entity slot

Use Parenting

Instead of separate transforms for each child, use entity hierarchy:

const parent = engine.addEntity()
Transform.create(parent, { position: Vector3.create(8, 0, 8) })

// Children inherit parent transform
const child1 = engine.addEntity()
Transform.create(child1, { position: Vector3.create(0, 1, 0), parent })

const child2 = engine.addEntity()
Transform.create(child2, { position: Vector3.create(1, 1, 0), parent })

Triangle Count Optimization

Use Lower-Poly Models

• Small props: 100-500 triangles
• Medium objects: 500-1,500 triangles
• Large buildings: 1,500-5,000 triangles
• Hero pieces: Up to 10,000 triangles

Use LOD (Level of Detail)

Show simpler models at distance:

engine.addSystem(() => {
  // Check distance to player and swap models
  const playerPos = Transform.get(engine.PlayerEntity).position
  const objPos = Transform.get(myEntity).position
  const distance = Vector3.distance(playerPos, objPos)

  const gltf = GltfContainer.getMutable(myEntity)
  if (distance > 30) {
    gltf.src = 'models/building_lod2.glb' // Low poly
  } else if (distance > 15) {
    gltf.src = 'models/building_lod1.glb' // Medium poly
  } else {
    gltf.src = 'models/building_lod0.glb' // High poly
  }
})

Use Primitives Instead of Models

For simple shapes, MeshRenderer is lighter than loading a .glb:

MeshRenderer.setBox(entity)    // Very cheap
MeshRenderer.setSphere(entity) // Cheap
MeshRenderer.setPlane(entity)  // Very cheap

Texture Optimization

• Dimensions must be power-of-two: 256, 512, 1024, 2048
• Recommended sizes: 512x512 for most objects, 1024x1024 max for hero pieces
• Use .png for UI/sprites with transparency
• Use .jpg for photos and textures without transparency
• Prefer compressed formats (WebP) over raw PNG where possible
• Use texture atlases (combine multiple textures into one image) to reduce draw calls and material count
• Share texture references across materials — do not duplicate texture files
• Reuse materials across entities:

// GOOD: Define material once, apply to many
Material.setPbrMaterial(entity1, { texture: Material.Texture.Common({ src: 'images/wall.jpg' }) })
Material.setPbrMaterial(entity2, { texture: Material.Texture.Common({ src: 'images/wall.jpg' }) })
// Same texture URL = shared in memory

System Optimization

Avoid Per-Frame Allocations

// BAD: Creates new Vector3 every frame
engine.addSystem(() => {
  const target = Vector3.create(8, 1, 8) // Allocation!
})

// GOOD: Reuse constants
const TARGET = Vector3.create(8, 1, 8)
engine.addSystem(() => {
  // Use TARGET
})

Throttle Expensive Operations

let lastCheck = 0
engine.addSystem((dt) => {
  lastCheck += dt
  if (lastCheck < 0.5) return // Only run every 0.5 seconds
  lastCheck = 0
  // Expensive operation here
})

Remove Systems When Not Needed

const systemFn = (dt: number) => { /* ... */ }
engine.addSystem(systemFn)

// When no longer needed:
engine.removeSystem(systemFn)

Asset Preloading (AssetLoad Component)

For large assets that would cause visible pop-in, use AssetLoad to pre-download before rendering:

import { engine, AssetLoad, LoadingState, GltfContainer, Transform } from '@dcl/sdk/ecs'
import { Vector3 } from '@dcl/sdk/math'

// Create a preload entity at scene startup
const preloadEntity = engine.addEntity()
AssetLoad.create(preloadEntity, { src: 'models/large-model.glb' })

// System to track loading progress
function assetLoadingSystem(dt: number) {
  for (const [entity] of engine.getEntitiesWith(AssetLoad)) {
    const state = AssetLoad.get(entity)
    if (state.loadingState === LoadingState.FINISHED) {
      // Asset is cached — now safe to create the visible entity
      GltfContainer.create(entity, { src: 'models/large-model.glb' })
      Transform.create(entity, { position: Vector3.create(8, 0, 8) })
      AssetLoad.deleteFrom(entity) // Remove preload component
    }
  }
}
engine.addSystem(assetLoadingSystem)

Use this pattern for any model over ~1 MB or for assets that should be ready before a game phase begins.

Loading Time Optimization

• Lazy-load 3D models (load on demand, not all at scene start)
• Use compressed .glb files (Draco compression)
• Minimize total asset size
• Use CDN URLs for large shared assets when possible
• Preload critical assets with AssetLoad, defer non-essential ones

Common Performance Pitfalls

1. Too many systems: Each system runs every frame. Combine related logic.
2. Unnecessary component queries: Cache engine.getEntitiesWith() results when the set doesn't change.
3. Large GLTF files: Optimize in Blender before export (decimate, remove hidden faces).
4. Uncompressed audio: Use .mp3 instead of .wav for music (10x smaller).
5. Continuous raycasting: Set continuous: false unless you need per-frame raycasting.
6. Text rendering: TextShape is expensive. Use Label (UI) for text that doesn't need to be in 3D space.

Cross-References

• add-3d-models — model loading, colliders, and file organization
• game-design — performance budgets, design patterns, and MVP planning
• advanced-rendering — texture modes, material reuse, and LOD with VisibilityComponent