Threejs Game

Three.js Game Development

You are an expert Three.js game developer. Follow these opinionated patterns when building 3D browser games.

Reference: See reference/llms.txt (quick guide) and reference/llms-full.txt (full API + TSL) for official Three.js LLM documentation. Prefer patterns from those files when they conflict with this skill.

Performance Notes

• Take your time with each step. Quality is more important than speed.
• Do not skip validation steps — they catch issues early.
• Read the full context of each file before making changes.
• Profile before optimizing. The bottleneck is rarely where you think.

Reference Files

For detailed reference, see companion files in this directory:

• core-patterns.md — Full EventBus, GameState, Constants, and Game.js orchestrator code
• tsl-guide.md — Three.js Shading Language reference (NodeMaterial classes, when to use TSL)
• input-patterns.md — Gyroscope input, virtual joystick, unified analog InputSystem, input priority system

For performance optimization patterns with measured before/after evidence, see the threejs-perf skill (skills/threejs-perf/SKILL.md).

Tech Stack

• Renderer: Three.js (three@0.183.0+, ESM imports)
• Build Tool: Vite
• Language: JavaScript (not TypeScript) for game templates — TypeScript optional
• Package Manager: npm

Project Setup

When scaffolding a new Three.js game:

mkdir <game-name> && cd <game-name>
npm init -y
npm install three@^0.183.0
npm install -D vite

Create vite.config.js:

import { defineConfig } from 'vite';

export default defineConfig({
  root: '.',
  publicDir: 'public',
  server: { port: 3000, open: true },
  build: { outDir: 'dist' },
});

Add to package.json scripts:

{
  "type": "module",
  "scripts": {
    "dev": "vite",
    "build": "vite build",
    "preview": "vite preview"
  }
}

Modern Import Patterns

Vite / npm (default — used in our templates)

import * as THREE from 'three';
import { OrbitControls } from 'three/addons/controls/OrbitControls.js';
import { GLTFLoader } from 'three/addons/loaders/GLTFLoader.js';

Import Maps / CDN (standalone HTML games, no build step)

<script type="importmap">
{
  "imports": {
    "three": "https://cdn.jsdelivr.net/npm/three@0.183.0/build/three.module.js",
    "three/addons/": "https://cdn.jsdelivr.net/npm/three@0.183.0/examples/jsm/"
  }
}
</script>
<script type="module">
import * as THREE from 'three';
import { OrbitControls } from 'three/addons/controls/OrbitControls.js';
</script>

Use import maps when shipping a single HTML file with no build tooling. Pin the version in the import map URL.

Required Architecture

Every Three.js game MUST use this directory structure:

src/
├── core/
│   ├── Game.js          # Main orchestrator - init systems, render loop
│   ├── EventBus.js      # Singleton pub/sub for all module communication
│   ├── GameState.js     # Centralized state singleton
│   └── Constants.js     # ALL config values, balance numbers, asset paths
├── systems/             # Low-level engine systems
│   ├── InputSystem.js   # Keyboard/mouse/gamepad input
│   ├── PhysicsSystem.js # Collision detection
│   └── ...              # Audio, particles, etc.
├── gameplay/            # Game mechanics
│   └── ...              # Player, enemies, weapons, etc.
├── level/               # Level/world building
│   ├── LevelBuilder.js  # Constructs the game world
│   └── AssetLoader.js   # Loads models, textures, audio
├── ui/                  # User interface
│   └── ...              # Game over, overlays
└── main.js              # Entry point - creates Game instance

Core Principles

1. Core loop first — Implement one camera, one scene, one gameplay loop. Add player input and a terminal condition (win/lose) before adding visual polish. Keep initial scope small: 1 mechanic, 1 fail condition, 1 scoring system.
2. Gameplay clarity > visual complexity — Treat 3D as a style choice, not a complexity mandate. A readable game with simple materials beats a visually complex but confusing one.
3. Restart-safe — Gameplay must be fully restart-safe. GameState.reset() must restore a clean slate. Dispose geometries/materials/textures on cleanup. No stale references or leaked listeners across restarts.

Core Patterns (Non-Negotiable)

Every Three.js game requires these four core modules. Full implementation code is in core-patterns.md.

1. EventBus Singleton

ALL inter-module communication goes through an EventBus (core/EventBus.js). Modules never import each other directly for communication. Provides on, once, off, emit, and clear methods. Events use domain:action naming (e.g., player:hit, game:over). See core-patterns.md for the full implementation.

2. Centralized GameState

One singleton (core/GameState.js) holds ALL game state. Systems read from it, events update it. Must include a reset() method that restores a clean slate for restarts. See core-patterns.md for the full implementation.

3. Constants File

Every magic number, balance value, asset path, and configuration goes in core/Constants.js. Never hardcode values in game logic. Organize by domain: PLAYER_CONFIG, ENEMY_CONFIG, WORLD, CAMERA, COLORS, ASSET_PATHS. See core-patterns.md for the full implementation.

4. Game.js Orchestrator

The Game class (core/Game.js) initializes everything and runs the render loop. Uses renderer.setAnimationLoop() -- the official Three.js pattern (handles WebGPU async correctly and pauses when the tab is hidden). Sets up renderer, scene, camera, systems, UI, and event listeners in init(). See core-patterns.md for the full implementation.

Renderer Selection

WebGLRenderer (default — use for all game templates)

Maximum browser compatibility. Well-established, most examples and tutorials use this. Our templates default to WebGLRenderer.

import * as THREE from 'three';
const renderer = new THREE.WebGLRenderer({ antialias: true });

WebGPURenderer (when you need TSL or compute shaders)

Required for custom node-based materials (TSL), compute shaders, and advanced rendering. Note: import path changes to 'three/webgpu' and init is async.

import * as THREE from 'three/webgpu';
const renderer = new THREE.WebGPURenderer({ antialias: true });
await renderer.init();

When to pick WebGPU: You need TSL custom shaders, compute shaders, or node-based materials. Otherwise, stick with WebGL. See tsl-guide.md for TSL details.

Play.fun Safe Zone

When games run inside the Play.fun dashboard on mobile Safari, the SDK sets CSS custom properties on the game iframe's document.documentElement:

• --ogp-safe-top-inset — space below the Play.fun header bubbles (~68px on mobile)
• --ogp-safe-bottom-inset — space above Safari bottom controls (~148px on mobile)

Both default to 0px when not running inside the dashboard (desktop, standalone).

Constants

// In Constants.js — reads SDK CSS vars with static fallbacks
function _readSafeInsets() {
  const s = getComputedStyle(document.documentElement);
  return {
    top: parseInt(s.getPropertyValue('--ogp-safe-top-inset')) || 0,
    bottom: parseInt(s.getPropertyValue('--ogp-safe-bottom-inset')) || 0,
  };
}
const _insets = _readSafeInsets();

export const SAFE_ZONE = {
  TOP_PX: Math.max(75, _insets.top),
  BOTTOM_PX: _insets.bottom,
  TOP_PERCENT: 8,
};

CSS Rule

All .overlay elements (game-over, pause, menus) must use the CSS variables for padding:

.overlay {
  padding-top: max(20px, 8vh, var(--ogp-safe-top-inset, 0px));
  padding-bottom: var(--ogp-safe-bottom-inset, 0px);
}

Bottom-positioned UI (joysticks, action buttons) must also respect the bottom inset:

#joystick-zone {
  bottom: max(20px, 3vh, var(--ogp-safe-bottom-inset, 0px));
}
.bottom-hud {
  margin-bottom: var(--ogp-safe-bottom-inset, 0px);
}

What to Check

• No text, buttons, or interactive elements in the top or bottom inset areas
• Game-over overlays center content in the usable area (between both insets), not the full viewport
• Score displays, titles, and restart buttons are all visible and not hidden behind browser chrome
• Bottom-positioned controls (joysticks, action buttons) are not clipped by Safari bottom bar

Note: The 3D canvas itself renders behind the chrome, which is fine — the game should bleed to fill the full viewport. Only HTML overlay UI needs the safe zone offset. In-world 3D elements (HUD textures, floating text) should avoid the top 8% and bottom inset of screen space.

Performance Rules

• Use renderer.setAnimationLoop() instead of manual requestAnimationFrame. It pauses when the tab is hidden and handles WebGPU async correctly.
• Cap delta time: Math.min(clock.getDelta(), 0.1) to prevent death spirals
• Cap pixel ratio: renderer.setPixelRatio(Math.min(window.devicePixelRatio, 2)) — avoids GPU overload on high-DPI screens
• Object pooling: Reuse Vector3, Box3, temp objects in hot loops to minimize GC. Avoid per-frame allocations — preallocate and reuse.
• Disable shadows on first pass — Only enable shadow maps when specifically needed and tested on mobile. Dynamic shadows are the single most expensive rendering feature.
• Keep draw calls low — Fewer unique materials and geometries = fewer draw calls. Merge static geometry where possible. Use instanced meshes for repeated objects. See skills/threejs-perf/ for InstancedMesh patterns (~9,000× fewer draw calls, ~57× faster render CPU).
• Prefer simple materials — Use MeshBasicMaterial or MeshStandardMaterial. Avoid MeshPhysicalMaterial, custom shaders, or complex material setups unless specifically needed.
• No postprocessing by default — Skip bloom, SSAO, motion blur, and other postprocessing passes on first implementation. These tank mobile performance. Add only after gameplay is solid and perf budget allows.
• Keep geometry/material count small — A game with 10 unique materials renders faster than one with 100. Reuse materials across objects with the same appearance.
• Use powerPreference: 'high-performance' on the renderer
• Dispose properly: Call .dispose() on geometries, materials, textures when removing objects
• Frustum culling: Let Three.js handle it (enabled by default) but set bounding spheres on custom geometry

Asset Loading

• Place static assets in /public/ for Vite
• Use GLB format for 3D models (smaller, single file)
• Use THREE.TextureLoader, GLTFLoader from three/addons
• Show loading progress via callbacks to UI

import { GLTFLoader } from 'three/addons/loaders/GLTFLoader.js';

const loader = new GLTFLoader();

function loadModel(path) {
  return new Promise((resolve, reject) => {
    loader.load(
      path,
      (gltf) => resolve(gltf.scene),
      undefined,
      (error) => reject(error),
    );
  });
}

Input Handling (Mobile-First)

All games MUST work on desktop AND mobile unless explicitly specified otherwise. Allocate 60% effort to mobile / 40% desktop when making tradeoffs. Choose the best mobile input for each game concept:

Unified Analog InputSystem

Use a dedicated InputSystem that merges keyboard, gyroscope, and touch into a single analog interface. Game logic reads moveX/moveZ (-1..1) and never knows the source. Keyboard input is always active as an override; on mobile, the system initializes gyroscope (with iOS 13+ permission request) or falls back to a virtual joystick. See input-patterns.md for the full implementation, including GyroscopeInput, VirtualJoystick, and input priority patterns.

When Adding Features

1. Create a new module in the appropriate src/ subdirectory
2. Define new events in EventBus.js Events object using domain:action naming
3. Add configuration to Constants.js
4. Add state to GameState.js if needed
5. Wire it up in Game.js orchestrator
6. Communicate with other systems ONLY through EventBus

Pre-Ship Validation Checklist

Before considering a game complete, verify:

• Core loop works — Player can start, play, lose/win, and see the result
• Restart works cleanly — GameState.reset() restores a clean slate, all Three.js resources disposed
• Touch + keyboard input — Game works on mobile (gyro/joystick/tap) and desktop (keyboard/mouse)
• Responsive canvas — Renderer resizes on window resize, camera aspect updated
• All values in Constants — Zero hardcoded magic numbers in game logic
• EventBus only — No direct cross-module imports for communication
• Resource cleanup — Geometries, materials, textures disposed when removed from scene
• No postprocessing — Unless explicitly needed and tested on mobile
• Shadows disabled — Unless explicitly needed and budget allows
• Delta-capped movement — Math.min(clock.getDelta(), 0.1) on every frame
• Mute toggle — Audio can be muted/unmuted; isMuted state is respected
• Safe zone respected — All HTML overlay UI uses var(--ogp-safe-top-inset) / var(--ogp-safe-bottom-inset) for Play.fun safe area; bottom controls offset above the bottom inset
• Build passes — npm run build succeeds with no errors
• No console errors — Game runs without uncaught exceptions or WebGL failures