Game Asset Generator Skill

Overview

This skill generates game-ready assets (3D models, Gaussian Splat environments, 2D sprites, images/textures) using AI APIs and free asset sources. It follows a three-phase workflow: DETECT the asset type -> GENERATE via the appropriate API or source -> INTEGRATE into the game. Only the relevant reference is loaded per task -- do not load all references upfront.

Scope: Use for AI-generated 3D models, world environments, pixel art sprites, concept art, textures, and sourcing free pre-built assets. Keep game engine scripting, physics, game loop logic, and shader authoring in threejs-builder after asset generation.

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Phase 1: DETECT

Goal: Identify the asset type from the request and load the single corresponding reference.

Step 1: Classify the request

Signal in request	Asset Type	Reference to load
"3D model", "character model", "generate model", GLB, mesh, rig, animate, humanoid	3D Model	references/meshyai.md
"environment", "world", "scene background", "gaussian splat", "splat", volumetric	Environment	references/worldlabs.md
"sprite", "pixel art", "2D character", "tile", "tileset", canvas sprite	2D Sprite	references/pixel-art-sprites.md
"image", "texture", "concept art", "icon", "generate image", chroma key	Image / Texture	references/fal-ai-image.md
No API key available, "free asset", "find model", "download asset", generation failed	Existing Assets	references/asset-sources.md

If the request is ambiguous between 3D Model and Image, ask: "Do you need a 3D mesh (GLB file for a Three.js scene) or a 2D image/texture?"

Step 2: Check API key availability

Before calling any paid API, verify the required key exists:

grep -E "MESHY_API_KEY|WLT_API_KEY|FAL_KEY" ~/.env 2>/dev/null

If the required key is missing, the fallback chain applies -- load references/asset-sources.md alongside the primary reference.

Fallback chain: Meshy API -> Sketchfab search -> Poly Haven -> Poly.pizza -> BoxGeometry placeholder. All sources output GLB into the same path so game loading code does not change.

Gate: Asset type identified, relevant reference loaded. Proceed to Phase 2 only when gate passes.

---

Phase 2: GENERATE

Goal: Call the API or source to produce the asset. Follow the loaded reference exactly -- it is the authoritative guide for its API.

Core constraints (all asset types):

• Download immediately -- Meshy retains assets only 3 days; World Labs SPZ files expire similarly. Never assume a URL will be valid tomorrow.
• Output to a stable path -- write assets to public/assets/ or an equivalent game-accessible directory so integration code does not need path changes per asset.
• Save the .meta.json sidecar -- every generated asset gets a .meta.json recording the prompt, model, generation timestamp, and asset ID. Required for regeneration and auditing.
• Validate the output file -- after download, confirm file size > 0 and extension matches expected type (GLB, SPZ, PNG, etc.) before proceeding.

Per-type generation summary (read the reference for full API details):

3D Model (Meshy): Two-step pipeline -- preview (fast, low quality, confirms prompt works) -> refine (full quality). Auto-rig only for humanoids meeting all criteria: bipedal, textured, clearly defined limbs. Animate rigged models with walk/run/idle presets. Post-process with scripts/optimize-glb.mjs for 80-95% size reduction before integration.

Environment (World Labs): Upload reference image (preferred over text-only) -> poll 3-8 minutes -> download SPZ + GLB collider + panorama JPG. Y-axis flip (rotation.x = Math.PI) required after loading into Three.js scene.

2D Sprite (code-only): Canvas-based generation -- no API call. Load references/pixel-art-sprites.md and generate sprites from the palette and matrix system defined there. Works without any API key.

Image / Texture (fal.ai): Queue-based API -- submit job -> poll for result. Choose model endpoint based on need (GPT Image 1.5 for transparency, Nano Banana 2 for speed). Use #00FF00 chroma-key background when the asset needs transparency extraction.

Gate: Asset file downloaded and validated (size > 0, correct extension). .meta.json saved. Proceed to Phase 3 only when gate passes.

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Phase 3: INTEGRATE

Goal: Load the generated asset into the game scene correctly.

Core constraint: Use SkeletonUtils.clone() -- never .clone() -- for animated models. Regular .clone() breaks skeleton bindings and leaves the model in a permanent T-pose. This is the single most common integration failure with rigged GLBs.

import { SkeletonUtils } from 'three/addons/utils/SkeletonUtils.js';

// Load once, clone for each instance
loader.load('/assets/character.glb', (gltf) => {
  const instance = SkeletonUtils.clone(gltf.scene);
  scene.add(instance);
});

GLB loading (Three.js):

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

const dracoLoader = new DRACOLoader();
dracoLoader.setDecoderPath('https://www.gstatic.com/draco/versioned/decoders/1.5.6/');

const loader = new GLTFLoader();
loader.setDRACOLoader(dracoLoader); // Required for Draco-compressed GLBs from Meshy optimizer
loader.load('/assets/model.glb', (gltf) => {
  const model = gltf.scene;
  const box = new THREE.Box3().setFromObject(model);
  const center = box.getCenter(new THREE.Vector3());
  model.position.sub(center);
  scene.add(model);
});

Gaussian Splat (World Labs) -- see references/worldlabs.md for the @sparkjsdev/spark SplatMesh integration. The Y-axis flip and raycast direction inversion are required, not optional.

Animation playback:

const mixer = new THREE.AnimationMixer(model);
const action = mixer.clipAction(gltf.animations[0]); // walk/run/idle from Meshy
action.play();

// In animation loop:
mixer.update(deltaTime);

Gate: Asset visible in scene. No console errors. Animations play if applicable.

---

Reference Loading Table

Signal	Load These Files	Why
"3D model", "character model", "generate model", GLB, mesh, rig, animate, humanoid	meshyai.md	3D Model
"environment", "world", "scene background", "gaussian splat", "splat", volumetric	worldlabs.md	Environment
"sprite", "pixel art", "2D character", "tile", "tileset", canvas sprite	pixel-art-sprites.md	2D Sprite
"image", "texture", "concept art", "icon", "generate image", chroma key	fal-ai-image.md	Image / Texture
No API key available, "free asset", "find model", "download asset", generation failed	asset-sources.md	Existing Assets
references/meshyai.md	meshyai.md	3D model generation request
references/worldlabs.md	worldlabs.md	Environment / Gaussian Splat request
references/fal-ai-image.md	fal-ai-image.md	Image, texture, or concept art request
references/asset-sources.md	asset-sources.md	No API key, fallback chain, or "find free asset"
references/pixel-art-sprites.md	pixel-art-sprites.md	2D sprite or pixel art request

Error Handling

Error: "GLB loads but model is in T-pose"

Cause: Used .clone() instead of SkeletonUtils.clone() on a rigged model. Solution: Replace gltf.scene.clone() with SkeletonUtils.clone(gltf.scene). Import from three/addons/utils/SkeletonUtils.js.

Error: "Meshy task stuck in PENDING"

Cause: API key invalid, quota exceeded, or Meshy service issue. Solution:

1. Verify MESHY_API_KEY is set in ~/.env and the value is current
2. Check quota at app.meshy.ai
3. If quota exhausted, fall through to references/asset-sources.md fallback chain
4. Use status mode: node scripts/meshy-generate.mjs status <task_id>

Error: "Downloaded GLB is 0 bytes or corrupt"

Cause: URL expired (Meshy 3-day limit) or network error during download. Solution: Regenerate -- do not attempt to repair a corrupt GLB. Resubmit using the prompt saved in .meta.json.

Error: "Gaussian Splat renders but objects fall through floor"

Cause: Raycast direction inverted after Y-axis flip on the SplatMesh. Solution: Load references/worldlabs.md -- the fix is in the raycast inversion section.

Error: "fal.ai request returns 401"

Cause: FAL_KEY missing or incorrectly formatted. fal.ai uses Key $FAL_KEY format (not Bearer). Solution: Confirm FAL_KEY is in ~/.env. Authorization header must be Key <your-key> -- not Bearer <your-key>.

Error: "gltf-transform command not found"

Cause: @gltf-transform/cli not installed globally. Solution: npm install -g @gltf-transform/cli

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References

Reference	When to load	Content
references/meshyai.md	3D model generation request	Meshy API: text-to-3D, image-to-3D, rig, animate, status polling, optimize-glb
references/worldlabs.md	Environment / Gaussian Splat request	World Labs Marble API: SPZ generation, SplatMesh renderer, Y-flip gotcha
references/fal-ai-image.md	Image, texture, or concept art request	fal.ai: 8 model endpoints, queue API, cost tracking, chroma-key
references/asset-sources.md	No API key, fallback chain, or "find free asset"	Sketchfab, Poly Haven, Poly.pizza search and download workflows
references/pixel-art-sprites.md	2D sprite or pixel art request	Canvas sprite matrices, palette system, animation frames (no API needed)