2nd/10_Wiki/Topics/DevOps_and_Security/BufferGeometry.md

---
id: wiki-2026-0508-buffergeometry
title: BufferGeometry
category: 10_Wiki/Topics
status: verified
canonical_id: self
aliases: [P-Reinforce-AUTO-2887C6, Three.js BufferGeometry]
duplicate_of: none
source_trust_level: A
confidence_score: 0.9
verification_status: applied
tags: [graphics, threejs, webgl, performance]
raw_sources: []
last_reinforced: 2026-05-10
github_commit: pending
tech_stack:
  language: javascript
  framework: three.js
---

# BufferGeometry

## 매 한 줄
> **"매 Three.js 의 GPU-resident geometry container — 매 modern Three 의 only geometry class."**. BufferGeometry 는 typed-array 기반 attribute (position, normal, uv, index) 의 GPU upload 를 직접 관리하며, 매 Geometry class deprecation (r125) 이후 표준 — instancing/batching/morph 의 backbone.

## 매 핵심

### 매 Attribute
- **Position** (Float32Array, itemSize=3): vertex coords.
- **Normal** (Float32Array, itemSize=3).
- **UV** (Float32Array, itemSize=2).
- **Index** (Uint16/Uint32Array): triangle list.
- **Custom**: any vertex attribute (color, tangent, instance data).

### 매 Update Strategy
- **Static**: upload once, never modify (default).
- **Dynamic** (`setUsage(DynamicDrawUsage)`): frequent CPU update.
- **Stream**: per-frame update (rare).

### 매 응용
1. Custom shaders with custom attributes.
2. GPU instancing (InstancedBufferAttribute).
3. Procedural geometry generation.
4. Mesh deformation / morphing.
5. GPGPU particle systems.

## 💻 패턴

### Manual Triangle
```javascript
import * as THREE from "three";

const geo = new THREE.BufferGeometry();
const positions = new Float32Array([
  0,  1, 0,
 -1, -1, 0,
  1, -1, 0,
]);
geo.setAttribute("position", new THREE.BufferAttribute(positions, 3));
geo.computeVertexNormals();
```

### Indexed Quad
```javascript
const positions = new Float32Array([-1,-1,0,  1,-1,0,  1,1,0,  -1,1,0]);
const indices = new Uint16Array([0, 1, 2,  0, 2, 3]);
const geo = new THREE.BufferGeometry();
geo.setAttribute("position", new THREE.BufferAttribute(positions, 3));
geo.setIndex(new THREE.BufferAttribute(indices, 1));
```

### Dynamic Vertex Update
```javascript
const attr = geo.attributes.position;
attr.setUsage(THREE.DynamicDrawUsage);

function tick(t) {
  for (let i = 0; i < attr.count; i++) {
    attr.setY(i, Math.sin(t + i * 0.1));
  }
  attr.needsUpdate = true;
}
```

### Custom Shader Attribute
```javascript
const aRandom = new Float32Array(geo.attributes.position.count);
for (let i = 0; i < aRandom.length; i++) aRandom[i] = Math.random();
geo.setAttribute("aRandom", new THREE.BufferAttribute(aRandom, 1));

const mat = new THREE.ShaderMaterial({
  vertexShader: `attribute float aRandom; varying float vR;
    void main(){ vR=aRandom; gl_Position=projectionMatrix*modelViewMatrix*vec4(position,1.); }`,
  fragmentShader: `varying float vR; void main(){ gl_FragColor=vec4(vR,vR,vR,1.); }`,
});
```

### Instanced Attribute
```javascript
const N = 10000;
const offsets = new Float32Array(N * 3);
for (let i = 0; i < N; i++) {
  offsets[i*3] = (Math.random()-0.5)*100;
  offsets[i*3+1] = (Math.random()-0.5)*100;
  offsets[i*3+2] = (Math.random()-0.5)*100;
}
const igeo = new THREE.InstancedBufferGeometry().copy(geo);
igeo.instanceCount = N;
igeo.setAttribute("aOffset", new THREE.InstancedBufferAttribute(offsets, 3));
```

### Merge Geometries
```javascript
import { mergeGeometries } from "three/addons/utils/BufferGeometryUtils.js";

const merged = mergeGeometries([geoA, geoB, geoC], false);
// single draw call instead of three
```

### Bounding Volume Recompute
```javascript
geo.computeBoundingBox();
geo.computeBoundingSphere();   // required for frustum culling after vertex moves
```

## 매 결정 기준
| 상황 | Approach |
|---|---|
| Static mesh | StaticDrawUsage (default) |
| Per-frame deform | DynamicDrawUsage + needsUpdate |
| Many copies | InstancedBufferGeometry |
| Many distinct meshes | mergeGeometries or BatchedMesh |
| Massive points | BufferGeometry + Points + custom shader |

**기본값**: static indexed BufferGeometry; switch to instanced/merged for >100 copies.

## 🔗 Graph
- 부모: [[Three.js]]
- 변형: [[BatchedMesh]]
- Adjacent: [[BufferAttribute]]

## 🤖 LLM 활용
**언제**: generate procedural geometry boilerplate, debug attribute layout.
**언제 X**: micro-optimization of custom shaders without profiling.

## ❌ 안티패턴
- **Forgetting `needsUpdate = true`**: GPU never re-uploads.
- **Recreating BufferGeometry per frame**: GC pressure — mutate in place.
- **Float32 indices**: not supported — use Uint16/Uint32.
- **No bounding sphere recompute**: frustum-culled erroneously after deform.

## 🧪 검증 / 중복
- Verified (three.js r170 docs, threejs-journey).
- 신뢰도 A.

## 🕓 Changelog
| 날짜 | 변경 |
|---|---|
| 2026-05-08 | Phase 1 |
| 2026-05-10 | Manual cleanup — attributes, dynamic update, instancing patterns |