threejs-scenes

## When to use this skill

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

- `Scene` as root, `scene.background`, environment or skyball setup at scene level
- `Fog` or `FogExp2` parameters (`near`, `far`, `color`, density) and interaction with camera far plane
- Organizing render lists conceptually (children of scene)

**IMPORTANT: scenes vs textures vs loaders**

| Concern | Skill |
|---------|--------|
| Scene + fog API | **threejs-scenes** |
| Texture sampling, PMREM generator usage | **threejs-textures** |
| Fetching HDR/glTF | **threejs-loaders** |

**Trigger phrases include:**

- "Scene", "Fog", "FogExp2", "background", "雾"
- "场景根节点", "线性雾", "指数雾"

## How to use this skill

1. Instantiate `Scene` and add lights/meshes/cameras as children per graph rules (**threejs-objects**).
2. Choose fog: linear `Fog` vs exponential `FogExp2` for outdoor/horizon feel.
3. Tune fog `near`/`far` alongside camera `far` to avoid clipping artifacts.
4. Set `scene.background` to `Color`, `Texture`, or cube map per docs; env lighting still needs matching renderer/material settings.
5. When user wants IBL from HDR file, point to loaders → textures → materials pipeline explicitly.
6. Document that fog does not replace frustum culling for performance.

### Example: Scene with fog and background

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

const scene = new THREE.Scene();
scene.background = new THREE.Color(0xa0a0a0);

// Linear fog — match color with background to hide horizon seam
scene.fog = new THREE.Fog(0xa0a0a0, 10, 50);

// Ensure camera far plane covers fog range
camera.far = 60; // slightly beyond fog far
camera.updateProjectionMatrix();
```

See [examples/workflow-fog-background.md](examples/workflow-fog-background.md).

## Doc map (official)

| Docs section | Representative links |
|--------------|----------------------|
| Scenes | https://threejs.org/docs/Scene.html |
| Fog | https://threejs.org/docs/Fog.html |
| FogExp2 | https://threejs.org/docs/FogExp2.html |

## Scope

- **In scope:** `Scene`, fog types, background field semantics at API level.
- **Out of scope:** HDR / glTF file fetch (**threejs-loaders**); PMREM and texture sampling (**threejs-textures**); tone mapping / output color space defaults (**threejs-renderers**); full-screen fog-only post stack (**threejs-postprocessing**) unless tying to scene `Fog`; custom atmospheric scattering shaders beyond core fog API.

## Common pitfalls and best practices

- Fog color should harmonize with background to hide the horizon seam.
- Very large `far` on camera with fog still needs scene scale consistency.
- `background` rotation/intensity features depend on renderer version—cite current docs.

## Documentation and version

`Scene`, `Fog`, and background fields are documented under [Scenes](https://threejs.org/docs/#Scenes) in [three.js docs](https://threejs.org/docs/). Environment-related visuals often combine this skill with **threejs-textures** (PMREM) and **threejs-loaders** (HDR files) — link those pages when the user moves from “fog color” to “HDR sky”.

## Agent response checklist

When answering under this skill, prefer responses that:

1. Link `Scene`, `Fog`, or `FogExp2` official pages.
2. Relate fog distances to **threejs-camera** `far` plane and world scale.
3. Defer PMREM/HDR file steps to **threejs-textures** / **threejs-loaders** with one sentence each.
4. Avoid duplicating full color-management tutorials — point to renderer + textures skills.

## Keywords

**English:** scene, fog, fogexp2, background, environment, three.js

**中文：** 场景、雾、Fog、背景、环境、three.js