threejs-geometries

## When to use this skill **ALWAYS use this skill when the user mentions:** - Building or modifying `BufferGeometry`, attributes, index buffers, draw ranges - Instancing via `InstancedBufferAttribute` / `InstancedMesh` geometry side (**threejs-objects** for mesh wrapper) - Extruding `Shape` along paths, `TubeGeometry`, `LatheGeometry`, `ExtrudeGeometry` - Text or decal addon geometries **IMPORTANT: geometries vs math** - **threejs-geometries** = GPU-ready triangle data. - **threejs-math** = `Box3`, `Sphere`, `Ray` tests without mesh topology. **Trigger phrases include:** - "BufferGeometry", "BufferAttribute", "ExtrudeGeometry", "Shape", "Curve" - "几何体", "缓冲几何", "挤出", "文字几何" ## How to use this skill 1. Prefer built-in primitives when they fit before custom buffers. 2. For custom meshes: create `BufferGeometry`, set `position`, `normal`, `uv`, optional `index`; compute bounding volumes for culling. 3. For instancing attributes, align divisor/count with `InstancedMesh` patterns in **threejs-objects**. 4. For 2D profiles: build `Shape`/`Path`, extrude or lathe per docs; consult Extras **Curve** family for path sampling. 5. For addon NURBS knots, follow Addons **Curves** pages sparingly—cite docs instead of copying full APIs. 6. Dispose geometries when replacing meshes to avoid leaks. See [examples/workflow-extrude-shape.md](examples/workflow-extrude-shape.md). ## Doc map (official) | Docs section | Representative links | |--------------|----------------------| | Core | https://threejs.org/docs/BufferGeometry.html | | Geometries | https://threejs.org/docs/BoxGeometry.html | | Extrude | https://threejs.org/docs/ExtrudeGeometry.html | | Shape | https://threejs.org/docs/Shape.html | ## Scope - **In scope:** Core geometries, buffer core, curve/shape/extrusion workflows, selected addon geometries. - **Out of scope:** Physics collision mesh baking; full CAD import pipelines. ## Common pitfalls and best practices - Missing normals break lighting; compute or import consistently. - Wrong winding order flips faces—check side/culling. - Huge attribute counts need LOD or simplification (modifiers in addons—mention only if user asks). ## Documentation and version Primitives and `BufferGeometry` live under [Geometries](https://threejs.org/docs/#Geometries) and [BufferGeometry](https://threejs.org/docs/BufferGeometry.html) in [three.js docs](https://threejs.org/docs/). Curve, `Shape`, and extrusion APIs appear under **Extras** and **Geometries**—Addons **Curves** / **Geometries** document NURBS and text meshes; link those instead of copying long signatures. ## Agent response checklist When answering under this skill, prefer responses that: 1. Link `BufferGeometry`, a primitive, or `ExtrudeGeometry` / `Shape` as appropriate. 2. Point **instancing** usage to **threejs-objects** for `InstancedMesh` patterns. 3. Point morph targets and tracks to **threejs-animation** when deformation is time-driven. 4. Reference `BufferGeometryUtils` (Addons **Utils**) only by name + docs link when merging/splitting. 5. Emphasize `dispose()` when replacing large custom buffers. ## References - https://threejs.org/docs/#Geometries - https://threejs.org/docs/BufferGeometry.html - https://threejs.org/docs/ExtrudeGeometry.html ## Keywords **English:** buffergeometry, extrude, shape, path, curve, primitives, instancing, three.js **中文：** 几何体、BufferGeometry、挤出、Shape、曲线、实例化、three.js