threejs-math

## When to use this skill

**ALWAYS use this skill when the user mentions:**

- Vector/matrix math order, `applyQuaternion`, `lookAt`, world vs local transforms
- Bounding volumes `Box3`/`Sphere`, containment/intersection tests
- `Ray` vs `Plane` vs `Frustum` tests (without full picking pipeline)

**IMPORTANT: math vs objects vs animation**

| Need | Skill |
|------|--------|
| Raw math types | **threejs-math** |
| `Raycaster` + layers picking | **threejs-objects** |
| QuaternionKeyframeTrack playback | **threejs-animation** |

**Trigger phrases include:**

- "Vector3", "Matrix4", "Quaternion", "Box3", "Ray", "Frustum"
- "向量", "矩阵", "四元数", "包围盒"

## How to use this skill

1. **Conventions**: multiply vectors by matrices on the left as three.js examples show; call `updateMatrixWorld` before world-space queries (**threejs-objects**).
2. **Bounding**: `Box3().setFromObject(object)` for rough bounds; refine per need.
3. **Collision-ish checks**: `ray.intersectBox`, `sphere.containsPoint`, etc., per docs.
4. **Addon structures**: `Octree`/`OBB` for games—cite addon pages, avoid copying full API tables here.
5. **Color**: `Color` conversions relate to materials/textures—cross-link.
6. **Random sampling**: `MeshSurfaceSampler` for distributing points on meshes.

### Example: Ray-AABB intersection test

```javascript
import * as THREE from 'three';

const ray = new THREE.Ray(
  new THREE.Vector3(0, 1, 0),  // origin
  new THREE.Vector3(0, 0, -1)  // direction
);
const box = new THREE.Box3(
  new THREE.Vector3(-1, -1, -5),
  new THREE.Vector3(1, 1, -3)
);

const hit = ray.intersectBox(box, new THREE.Vector3());
if (hit) {
  console.log('Intersection at:', hit);
}
```

See [examples/workflow-ray-aabb.md](examples/workflow-ray-aabb.md).

## Doc map (official)

| Docs section | Representative links |
|--------------|----------------------|
| Math | https://threejs.org/docs/Vector3.html |
| Math | https://threejs.org/docs/Matrix4.html |
| Math | https://threejs.org/docs/Quaternion.html |
| Math | https://threejs.org/docs/Ray.html |

## Scope

- **In scope:** Core Math types; addon math entries as pointers.
- **Out of scope:** Keyframe track evaluation beyond type references (animation skill).

## Common pitfalls and best practices

- Euler gimbal lock—prefer quaternions for arbitrary rotations.
- Reusing temporary vectors reduces GC thrash in hot loops.
- Frustum culling helpers vary—verify against your three version.

## Documentation and version

Core math types are listed under [Math](https://threejs.org/docs/#Math); addon utilities (`Octree`, `OBB`, …) appear under **Addons → Math** in [three.js docs](https://threejs.org/docs/). [Global](https://threejs.org/docs/#Global) also lists constants (e.g. wrapping, blending) sometimes needed alongside materials.

## Agent response checklist

When answering under this skill, prefer responses that:

1. Link the concrete type (`Vector3`, `Matrix4`, `Quaternion`, …) from the docs.
2. Send `AnimationMixer` / track math to **threejs-animation** when time-sampled.
3. Send `Raycaster` picking flows to **threejs-objects** when interaction is the goal.
4. Mention numeric stability (epsilon) where comparisons matter.
5. Point to **Addons → Math** for game-oriented structures when users need spatial acceleration.

## References

- https://threejs.org/docs/#Math
- https://threejs.org/docs/MathUtils.html
- https://threejs.org/docs/Ray.html

## Keywords

**English:** vector, matrix, quaternion, euler, box3, sphere, ray, frustum, three.js

**中文：** 向量、矩阵、四元数、欧拉角、包围盒、射线、three.js