babylon-mcp/examples/scene/getMeshById_with_mcp.md

* **Wall Time** 30s
* **tokens** Unclear, didn't output
* **tool usages** 4
```
explain how Scene.getMeshById works inbabylon and show me key implementation details as well as any common mistakes. 
```
⏺ How Scene.getMeshById Works in Babylon.js

Implementation

From scene.ts:3889, here's the actual implementation:

public getMeshById(id: string): Nullable<AbstractMesh> {
for (let index = 0; index < this.meshes.length; index++) {
if (this.meshes[index].id === id) {
return this.meshes[index];
}
}
return null;
}

Key Details

1. Linear Search Algorithm
- Iterates through the entire scene.meshes array sequentially
- Uses simple string equality (===) to compare IDs
- Returns the first match only
- Time complexity: O(n) where n is the number of meshes

2. Return Type
- Returns Nullable<AbstractMesh> (can be null)
- Always returns the first mesh found with matching ID
- Returns null if no mesh with that ID exists

3. ID vs Name vs UniqueId
   Babylon.js has three different identifiers:
- id: String identifier you can set manually (not guaranteed unique)
- name: String identifier for human-readable references
- uniqueId: Auto-generated numeric ID (guaranteed unique per scene)

Common Mistakes

1. Assuming IDs are Unique
   // WRONG - Multiple meshes can share the same ID!
   const mesh1 = new Mesh("myMesh", scene);
   mesh1.id = "player";
   const mesh2 = new Mesh("otherMesh", scene);
   mesh2.id = "player";  // ID collision!

scene.getMeshById("player");  // Returns mesh1 (first one added)

Fix: Use getMeshesById() (plural) if you expect multiple matches, or use uniqueId instead.

2. Confusing id with name
   const mesh = new Mesh("spaceship", scene);  // This sets the NAME, not ID
   scene.getMeshById("spaceship");  // Returns null! ❌

// By default, id === name initially, but they're separate properties
console.log(mesh.name);  // "spaceship"
console.log(mesh.id);    // "spaceship" (copied from name at creation)

Fix: Use getMeshByName() for name-based lookups, or explicitly set the id property.

3. Not Null-Checking
   // WRONG - Can cause runtime errors
   const mesh = scene.getMeshById("nonexistent");
   mesh.position.x = 10;  // TypeError: Cannot read property 'position' of null

Fix: Always null-check:
const mesh = scene.getMeshById("player");
if (mesh) {
mesh.position.x = 10;
}

4. Performance with Large Scenes
   // WRONG - Calling in render loop with many meshes
   scene.onBeforeRenderObservable.add(() => {
   const mesh = scene.getMeshById("player");  // O(n) lookup every frame!
   mesh?.position.x += 0.1;
   });

Fix: Cache the reference:
const playerMesh = scene.getMeshById("player");
scene.onBeforeRenderObservable.add(() => {
playerMesh?.position.x += 0.1;
});

5. Using Deprecated getMeshByID() (uppercase D)
   scene.getMeshByID("player");  // Deprecated! Works but discouraged

Fix: Use getMeshById() (lowercase 'd') instead.

Better Alternatives

For Unique Lookups:
// Store uniqueId at creation
const mesh = new Mesh("player", scene);
const meshId = mesh.uniqueId;

// Later lookup (faster, guaranteed unique)
const found = scene.getMeshByUniqueId(meshId);

For Multiple Meshes with Same ID:
// Get all meshes with this ID
const allEnemies = scene.getMeshesById("enemy");
allEnemies.forEach(enemy => {
enemy.dispose();
});

For Name-Based Lookup:
const mesh = scene.getMeshByName("spaceship");  // Uses the 'name' property

Related Methods

- getMeshesById(id) - Returns array of all meshes with matching ID
- getMeshByName(name) - Searches by name property instead
- getMeshByUniqueId(uniqueId) - Uses auto-generated numeric ID (guaranteed unique)