threejs-helpers

## When to use this skill

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

- Visualizing axes, grids, camera frusta, shadow cameras, light directions
- Showing skeleton bones, bounding boxes, normals/tangents for mesh inspection
- Light probe or rect area visualization via helper classes

**IMPORTANT: helpers vs production meshes**

- Helpers are **debug** objects; do not use as final scene geometry.

**Trigger phrases include:**

- "AxesHelper", "GridHelper", "CameraHelper", "SkeletonHelper", "VertexNormalsHelper"
- "辅助线", "法线显示", "包围盒调试"

## How to use this skill

1. **Attach** helper to the object it describes (e.g., `CameraHelper(light.shadow.camera)`).
2. **Update** when targets move — some helpers need per-frame refresh.
3. **Gate behind debug flags** — remove helpers in production builds to save draw calls.
4. **Performance** — helpers add draw calls; disable when profiling performance issues.
5. **Addons** — import from `three/addons/helpers/...` paths per **threejs-dev-setup**.

### Example: Debug flag pattern for conditional helpers

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

const DEBUG = import.meta.env.DEV; // Vite-style; adapt for your bundler
const debugGroup = new THREE.Group();
debugGroup.visible = DEBUG;
scene.add(debugGroup);

// Add helpers only in development
if (DEBUG) {
  debugGroup.add(new THREE.AxesHelper(5));
  debugGroup.add(new THREE.GridHelper(10, 10));

  // Shadow camera helper for directional light
  const shadowHelper = new THREE.CameraHelper(directionalLight.shadow.camera);
  debugGroup.add(shadowHelper);
}

// Toggle helpers at runtime via console or GUI
// debugGroup.visible = !debugGroup.visible;
```

See [examples/workflow-light-camera-helpers.md](examples/workflow-light-camera-helpers.md).

## Doc map (official)

| Docs section | Representative links |
|--------------|----------------------|
| Helpers | https://threejs.org/docs/AxesHelper.html |
| Helpers | https://threejs.org/docs/GridHelper.html |
| Helpers | https://threejs.org/docs/CameraHelper.html |
| Helpers | https://threejs.org/docs/SkeletonHelper.html |

## Scope

- **In scope:** Core + Addons helpers for visualization.
- **Out of scope:** Production meshes or shipping art (**threejs-geometries**, **threejs-lights**); orbit/transform gizmo behavior (**threejs-controls**); editor UX parity with DCC tools; physics debug beyond helper stubs.

## Common pitfalls and best practices

- Too many helpers obscures view—toggle per subsystem.
- Wrong attachment parent misaligns helper transforms.
- Helpers inherit scene graph transforms—parent under a debug group to batch hide/show.
- Some helpers duplicate geometry cost; strip in production or use `#ifdef DEBUG` style flags.
- `CameraHelper` for shadow cameras must reference `light.shadow.camera`, not the main view camera.

## Documentation and version

Helpers are listed under [Helpers](https://threejs.org/docs/#Helpers) (core) and **Addons → Helpers** in [three.js docs](https://threejs.org/docs/). They are for **debug** only; production meshes and lighting should use real geometry/lights (**threejs-geometries**, **threejs-lights**).

## Agent response checklist

When answering under this skill, prefer responses that:

1. Link the helper class (`AxesHelper`, `CameraHelper`, …) being used.
2. State that helpers are not shipping art—strip or gate behind debug flags.
3. Pair shadow/light helpers with **threejs-lights** tuning workflows.
4. Mention performance cost when many helpers are enabled.
5. Import paths follow **threejs-dev-setup** addon conventions.

## References

- Manual (debug workflow context): https://threejs.org/manual/
- Docs index (Helpers group): https://threejs.org/docs/#Helpers
- Examples: https://threejs.org/docs/DirectionalLightHelper.html

## Keywords

**English:** helper, debug, axes, grid, skeleton, normals, light helper, three.js

**中文：** 辅助、调试、坐标轴、网格、骨架、法线、Helper、three.js