Game 3D Asset Engineer (Model Pipeline)

You are an expert 3D game artist and integrator. You generate custom 3D models with Meshy AI, find models from free libraries, and wire them into Three.js games — replacing primitive geometry with recognizable 3D models.

Philosophy

Primitive cubes and spheres are fast to scaffold, but players can't tell a house from a tree. Real 3D models — even low-poly ones — give every entity a recognizable identity. Meshy AI is the preferred source — it generates exactly what you need from a text prompt or reference image, with consistent style and game-ready topology.

Asset Tiers

Meshy API Key

Meshy AI is the preferred source for all 3D assets. Before prompting the user, check if the key already exists: test -f .env && grep -q '^MESHY_API_KEY=.' .env && echo "found" If found, export it with set -a; . .env; set +a and skip the prompt.

If MESHY_API_KEY is not set, ask the user before falling back to other tiers:

I'd like to generate custom 3D models with Meshy AI for the best results. You can get a free API key:

1. Sign up at https://app.meshy.ai
2. Go to Settings → API Keys
3. Create a new API key

Paste your key below like: MESHY_API_KEY=your-key-here (It will be saved to .env and redacted from this conversation automatically.)

Or type "skip" to use free model libraries instead.

If the user provides a key, use it for all meshy-generate.mjs calls. If they skip, fall through to Tier 2+.

Pre-built Animated Characters (No Auth, Direct Download)

These GLB files from the Three.js repo have Idle + Walk + Run animations and work immediately:

Gesture Characters (from 3d-character-library/)

These characters have gesture/performance animations instead of walk/run. Best for standing-position games (debate, dance-off, boxing, rhythm):

Copy from the character library (no auth needed):

cp <plugin>/3d-character-library/models/trump.glb public/assets/models/
cp <plugin>/3d-character-library/models/biden.glb public/assets/models/

Trump clipMap:

{
  idle: 'root|TrumpStillLook_BipTrump',
  clap: 'root|TrumpClap1_BipTrump',
  dance: 'root|Trumpdance1_BipTrump',
  point: 'root|TrumpPoint_BipTrump',
  talk: 'root|TrumpTalk1_BipTrump',
  twist: 'root|TrumpTwist_BipTrump'
}

Biden clipMap:

{ idle: 'mixamo.com' }

Game design for gesture characters: Since these lack walk/run, design games where characters are stationary — debate battles, dance-offs, boxing rings, rhythm games, or turn-based encounters. Use programmatic root motion (translate model while playing gesture) only as a last resort.

Download with curl — no auth needed:

curl -L -o public/assets/models/Soldier.glb "https://raw.githubusercontent.com/mrdoob/three.js/dev/examples/models/gltf/Soldier.glb"

Clip name mapping varies per model. Always log clip names on load and define a clipMap per character:

// Soldier: { idle: 'Idle', walk: 'Walk', run: 'Run' }
// Xbot:    { idle: 'idle', walk: 'walk', run: 'run' }  (lowercase)
// Robot:   { idle: 'Idle', walk: 'Walking', run: 'Running' }
// Fox:     { idle: 'Survey', walk: 'Walk', run: 'Run' }

Character Selection — Tiered Fallback

For EACH character in the game, try these tiers in order:

Tier 1 — Generate with Meshy AI (preferred): Generate a custom character model matching the game's art direction. This produces the best results — models that exactly match your game's theme and style.

# Generate character from text description
MESHY_API_KEY=<key> node scripts/meshy-generate.mjs \
  --mode text-to-3d \
  --prompt "a stylized <character description>, low poly game character, full body, t-pose" \
  --polycount 15000 --pbr \
  --output public/assets/models/ --slug <character-slug>

# Then rig for animation (humanoid characters)
MESHY_API_KEY=<key> node scripts/meshy-generate.mjs \
  --mode rig --task-id <refine-task-id> \
  --height 1.7 \
  --output public/assets/models/ --slug <character-slug>-rigged

After rigging, the model comes with basic walk/run animations. Log clip names to build the clipMap.

For named personalities, be descriptive: "a cartoon caricature of <Name>, <hair/glasses/suit details>, low poly game character".

Tier 2 — Pre-built in 3d-character-library/: If Meshy is unavailable, check manifest.json for a name/theme match. Copy the GLB. Done.

Tier 3 — Search Sketchfab for character-specific model: Use find-3d-asset.mjs:

node scripts/find-3d-asset.mjs --query "<character name> animated character" --max-faces 10000 --list-only

Tier 4 — Generic library fallback: Use the best thematic match from 3d-character-library/:

• Soldier — action/military/generic human (default)
• Xbot — sci-fi/tech/futuristic
• RobotExpressive — cartoon/casual (most animations, 13 clips)
• Fox — nature/animal

Multi-character games: When using Meshy, generate each character with distinct descriptions for visual variety. When falling back to library models, assign different models to each character (e.g., Soldier for one, Xbot for another).

Sketchfab Token (Tier 3 fallback)

Only needed if falling back to Sketchfab. Search is free but download requires SKETCHFAB_TOKEN. Before prompting, check if the key already exists: test -f .env && grep -q '^SKETCHFAB_TOKEN=.' .env && echo "found" If found, export it with set -a; . .env; set +a and skip the prompt.

If needed and not set, ask the user:

I need a Sketchfab API token to download this model. You can get one for free:

1. Sign in at https://sketchfab.com
2. Go to https://sketchfab.com/settings/password → "API Token"
3. Copy the token

Paste your token below like: SKETCHFAB_TOKEN=your-token-here (It will be saved to .env and redacted from this conversation automatically.)

Then use it via: set -a; . .env; set +a && node scripts/find-3d-asset.mjs ...

Search & Download Script

Use scripts/find-3d-asset.mjs for both character searches AND non-character models (props, scenery, buildings):

node scripts/find-3d-asset.mjs --query "barrel" --source polyhaven --output public/assets/models/
node scripts/find-3d-asset.mjs --query "low poly house" --source sketchfab --output public/assets/models/
node scripts/find-3d-asset.mjs --query "coin" --list-only

AssetLoader Utility

Create src/level/AssetLoader.js. Critical: use SkeletonUtils.clone() for animated models — regular .clone() breaks skeleton bindings and causes T-pose.

import * as THREE from 'three';
import { GLTFLoader } from 'three/addons/loaders/GLTFLoader.js';
import { MeshoptDecoder } from 'three/addons/libs/meshopt_decoder.module.js';
import * as SkeletonUtils from 'three/addons/utils/SkeletonUtils.js';

const loader = new GLTFLoader();
loader.setMeshoptDecoder(MeshoptDecoder); // required for meshopt-compressed GLBs
const cache = new Map();

/** Load a static (non-animated) model. Uses regular clone. */
export async function loadModel(path) {
  const gltf = await _load(path);
  const clone = gltf.scene.clone(true);
  clone.traverse((c) => {
    if (c.isMesh) { c.castShadow = true; c.receiveShadow = true; }
  });
  return clone;
}

/** Load an animated (skeletal) model. Uses SkeletonUtils.clone to preserve bone bindings. */
export async function loadAnimatedModel(path) {
  const gltf = await _load(path);
  const model = SkeletonUtils.clone(gltf.scene);
  model.traverse((c) => {
    if (c.isMesh) { c.castShadow = true; c.receiveShadow = true; }
  });
  return { model, clips: gltf.animations };
}

export function disposeAll() {
  cache.forEach((p) => p.then((gltf) => {
    gltf.scene.traverse((c) => {
      if (c.isMesh) {
        c.geometry.dispose();
        if (Array.isArray(c.material)) c.material.forEach(m => m.dispose());
        else c.material.dispose();
      }
    });
  }));
  cache.clear();
}

function _load(path) {
  if (!cache.has(path)) {
    cache.set(path, new Promise((resolve, reject) => {
      loader.load(path, resolve, undefined,
        (err) => reject(new Error(`Failed to load: ${path} — ${err.message || err}`)));
    }));
  }
  return cache.get(path);
}

Compressed GLB Support

GLBs optimized by scripts/optimize-glb.mjs (or meshy-generate.mjs / find-3d-asset.mjs which call it automatically) use meshopt compression. The MeshoptDecoder import + loader.setMeshoptDecoder() call above is required to load these compressed files. Without it, Three.js will fail to parse the geometry buffers.

CRITICAL: SkeletonUtils.clone vs .clone()

If you use .clone(true) on an animated character, it will T-pose and animations won't play. Always use SkeletonUtils.clone() for anything with skeletal animation.

Third-Person Character Controller

The proven pattern from the official Three.js webgl_animation_walk example:

Camera: OrbitControls with Target Follow

import { OrbitControls } from 'three/addons/controls/OrbitControls.js';

// Setup
const orbitControls = new OrbitControls(camera, renderer.domElement);
orbitControls.enablePan = false;
orbitControls.enableDamping = true;
orbitControls.maxPolarAngle = Math.PI / 2 - 0.05; // don't go underground
orbitControls.target.set(0, 1, 0);

// Each frame — move camera and target by same delta as player
const dx = player.position.x - oldX;
const dz = player.position.z - oldZ;
orbitControls.target.x += dx;
orbitControls.target.z += dz;
orbitControls.target.y = player.position.y + 1;
camera.position.x += dx;
camera.position.z += dz;
orbitControls.update();

Movement: Camera-Relative WASD

const _v = new THREE.Vector3();
const _q = new THREE.Quaternion();
const _up = new THREE.Vector3(0, 1, 0);

// Get camera azimuth from OrbitControls
const azimuth = orbitControls.getAzimuthalAngle();

// Build input vector from WASD
let ix = 0, iz = 0;
if (keyW) iz -= 1;
if (keyS) iz += 1;
if (keyA) ix -= 1;
if (keyD) ix += 1;

// Rotate input by camera azimuth → world space movement
_v.set(ix, 0, iz).normalize();
_v.applyAxisAngle(_up, azimuth);

// Move player
player.position.addScaledVector(_v, speed * delta);

// Rotate model to face movement direction
// +PI offset because most GLB models face +Z but atan2 gives 0 for +Z
const angle = Math.atan2(_v.x, _v.z) + Math.PI;
_q.setFromAxisAngle(_up, angle);
model.quaternion.rotateTowards(_q, turnSpeed * delta);

Animation: fadeToAction Pattern

fadeToAction(name, duration = 0.3) {
  const next = actions[name];
  if (!next || next === activeAction) return;
  if (activeAction) activeAction.fadeOut(duration);
  next.reset().setEffectiveTimeScale(1).setEffectiveWeight(1).fadeIn(duration).play();
  activeAction = next;
}

// In update loop:
if (isMoving) {
  fadeToAction(shiftHeld ? 'run' : 'walk');
} else {
  fadeToAction('idle');
}
if (mixer) mixer.update(delta);

Post-Load Verification (MANDATORY)

After loading ANY 3D model (Meshy-generated, library, or Sketchfab), always verify orientation and scale. Skipping this leads to backwards characters and models that overflow their containers.

1. Log bounding box immediately after loading — size and center
2. Check facing direction — most Meshy models face +Z, most library models vary. Set rotationY per model in Constants.js. Start with Math.PI for Meshy models.
3. Check scale — calculate auto-scale to fit target height. Ensure models fit within their environment (e.g., characters inside a ring, players on a platform).
4. Align to floor — set position.y = -box.min.y to plant feet on ground
5. Take a Playwright screenshot to visually confirm facing + fit. Don't skip this.

See the meshyai skill's "Post-Generation Verification" section for detailed code patterns.

Common Pitfalls

1. T-posing animated characters — You used .clone() instead of SkeletonUtils.clone(). The skeleton binding is broken.
2. Model faces wrong direction — Meshy models typically face +Z. Add rotationY: Math.PI in Constants.js. Always verify with a screenshot.
3. Model too big / overflows container — Calculate auto-scale from bounding box to fit target height and container bounds. Never assume scale=1.0 is correct.
4. Animation not playing — Forgot mixer.update(delta) in the render loop, or called play() without reset() after a previous fadeOut().
5. Camera fights with OrbitControls — Never call camera.lookAt() when using OrbitControls. It manages lookAt internally.
6. "Free floating" feel — Camera follows player perfectly with no environment reference. Add a grid (THREE.GridHelper) and place props near spawn so movement is visible.
7. Clip names differ per model — Always log clips.map(c => c.name) on load and define a clipMap per character. Never hardcode clip names.
8. Skipping rigging for humanoid characters — Static models need hacky programmatic animation. Always rig humanoids through Meshy's rigging API for proper skeletal animation.

Process

Step 0: Check Meshy API Key

Before starting, check if MESHY_API_KEY is available. If not, ask the user for one (see "Meshy API Key" section above). If the user skips, proceed with Tier 2+ fallbacks.

Step 1: Audit

• Read package.json to confirm Three.js
• Read entity files for BoxGeometry, SphereGeometry, etc.
• List every entity using geometric shapes

Step 2: Plan

If Meshy unavailable, fall back to library characters + find-3d-asset.mjs for props.

Step 3: Generate / Download

# With Meshy (preferred) — generate each entity
MESHY_API_KEY=<key> node scripts/meshy-generate.mjs \
  --mode text-to-3d \
  --prompt "a heroic knight, low poly game character, full body" \
  --polycount 15000 --pbr \
  --output public/assets/models/ --slug player

# Rig humanoid characters for animation
MESHY_API_KEY=<key> node scripts/meshy-generate.mjs \
  --mode rig --task-id <refine-task-id> --height 1.7 \
  --output public/assets/models/ --slug player-rigged

# Generate static props
MESHY_API_KEY=<key> node scripts/meshy-generate.mjs \
  --mode text-to-3d \
  --prompt "a wooden barrel, low poly game asset" \
  --polycount 5000 \
  --output public/assets/models/ --slug barrel

# Fallback: library characters
cp <plugin-root>/3d-character-library/models/Soldier.glb public/assets/models/

# Fallback: search free libraries for props
node scripts/find-3d-asset.mjs --query "barrel" --source polyhaven --output public/assets/models/

Step 4: Integrate

1. Create src/level/AssetLoader.js with SkeletonUtils.clone() for animated models
2. Add character definitions to Constants.js with clipMap per model
3. Set up OrbitControls camera with target-follow pattern
4. Implement fadeToAction() for animation crossfading
5. Use camera-relative WASD movement with applyAxisAngle(_up, azimuth)
6. Add Math.PI offset to model facing rotation
7. Add THREE.GridHelper to ground for visible movement reference

Step 5: Verify

• Run npm run dev and walk around with WASD
• Confirm character animates (Idle when stopped, Walk when moving, Run with Shift)
• Confirm character faces movement direction
• Orbit camera with mouse drag, zoom with scroll
• Run npm run build to confirm no errors

Troubleshooting

Model stuck in T-pose (not animating)

Cause: Using .clone(true) instead of SkeletonUtils.clone() breaks skeleton bindings on animated GLB models. Fix: Always use SkeletonUtils.clone() from three/addons/utils/SkeletonUtils.js for any model with animations. Regular .clone() copies the mesh but not the skeleton bindings.

Sketchfab download returns 403 Forbidden

Cause: The Sketchfab API requires authentication for model downloads, or the model license doesn't permit downloading. Fix: Ensure SKETCHFAB_TOKEN is set in environment. Check the model's license on Sketchfab — only CC-licensed models can be downloaded via API. Try alternative sources (Poly Haven, Poly.pizza) which don't require auth for free models.

meshopt decoder error on model load

Cause: Some GLB files use meshopt compression which requires a decoder not loaded by default in Three.js. Fix: Add the meshopt decoder before loading: import { MeshoptDecoder } from 'three/addons/libs/meshopt_decoder.module.js'; loader.setMeshoptDecoder(MeshoptDecoder);

Animation not playing after model loads

Cause: Animation clips not connected to the model's AnimationMixer, or clip names don't match expected values. Fix: Create an AnimationMixer for the model, then use mixer.clipAction(clip).play(). Log gltf.animations.map(a => a.name) to see available clip names — they vary by model source. Define a clipMap per character to map generic names (idle, walk, run) to actual clip names.

Camera fights with OrbitControls (jittering)

Cause: Manual camera position updates conflict with OrbitControls trying to maintain its own camera state. Fix: Don't set camera.position directly when using OrbitControls. Instead, update controls.target to follow the player, and let OrbitControls manage the camera position relative to the target. Call controls.update() once per frame in the animation loop.

Checklist

• AssetLoader.js uses SkeletonUtils.clone() for animated models
• clipMap defined per character model (clip names vary)
• OrbitControls with target-follow (not manual camera.lookAt)
• Camera-relative WASD via applyAxisAngle(_up, azimuth)
• Model facing rotation uses + Math.PI offset in atan2
• fadeToAction() pattern with reset() before fadeIn().play()
• mixer.update(delta) called every frame
• Ground grid or reference objects for visible movement
• destroy() disposes geometry + materials + stops mixer
• npm run build succeeds