How to safely backup and restore a Babylon.js scene while validating data integrity?

Answer Overview

To preserve a Babylon.js scene across sessions or devices you can serialize the scene to JSON, store the payload, and later deserialize it while verifying that the data hasn’t been altered. The core steps are: export, hash, store, restore, validate.

1. Export the Scene

const serialized = BABYLON.SceneSerializer.Serialize(scene, {
    // Include only what you need – e.g., meshes, materials, lights
    // Default options cover most built‑in properties
});
// serialized is a JSON string

If you added custom properties or metadata, pass options.metadata = true or manually attach them before serialization.

2. Compute a Cryptographic Hash

// Simple example using the SubtleCrypto API
async function computeHash(str) {
    const buffer = new TextEncoder().encode(str);
    const digest = await crypto.subtle.digest('SHA-256', buffer);
    return Array.from(new Uint8Array(digest)).map(b => b.toString(16).padStart(2, '0')).join('');
}
const hash = await computeHash(serialized);

Store this hash alongside the JSON payload. It serves as a tamper‑evidence checkpoint.

3. Persist the Backup

• LocalStorage – simple key/value; suitable for small scenes (< 5 MB). localStorage.setItem('sceneBackup', serialized); localStorage.setItem('sceneHash', hash);
• IndexedDB – better for larger scenes; store the JSON string and hash as separate records.
• Remote Server – upload via fetch or axios. Ensure Content-Type: application/json and handle CORS (set the server’s Access‑Control‑Allow‑Origin header).
• Optionally compress the JSON with pako (gzip) before upload to save bandwidth.

4. Restore the Scene

// Retrieve the stored payload
const restoredJson = /* fetch from storage */;
// Re‑compute the hash
const restoredHash = await computeHash(restoredJson);
if (restoredHash !== storedHash) {
    throw new Error('Scene backup corrupted or tampered');
}
// Deserialize into a new scene
const restoredScene = BABYLON.SceneSerializer.Parse(restoredJson, engine);

5. Verify Integrity After Restore

• Compare the number of meshes, materials, and lights: restoredScene.meshes.length === originalScene.meshes.length.
• Optionally re‑serialize the restored scene and compare the new hash to the original hash. A match guarantees a bit‑exact round‑trip.
• For visual confirmation, render the scene to an off‑screen canvas and compare pixel data against a baseline screenshot using canvas.toBlob() and an image‑diff library.

Environment & Assumptions

• Browser support for crypto.subtle.digest (modern browsers). Polyfills are available for older browsers.
• IndexedDB is available in all major browsers; fallback to localStorage if needed.
• When uploading to a remote server, CORS must allow your origin or you must proxy the request.
• Large scenes (>10 MB) may hit memory limits; consider chunking or using a server‑side storage service that supports streaming uploads.
• Custom user data added via mesh.metadata or dynamic properties is not serialized by default; include it explicitly or handle it separately.

Optional Third‑Party Validation Libraries

• Use js-sha256 for quick hash calculation if you prefer a pure JS implementation.
• For schema validation, ajv can validate the JSON against a JSON Schema that describes the expected scene structure.
• To detect accidental data loss, diff libraries (e.g., deep-diff) can show differences between the original and restored JSON.

Next Step

Which Babylon.js version are you targeting? The exact method names and option flags differ between 4.x, 5.x, and newer releases, which could affect the serialization options you need to pass.