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.opencode/skills/threejs/references/12-performance.md

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+# Performance Optimization
+
+Techniques for fast, smooth 3D experiences.
+
+## Instancing
+
+Render many copies of same geometry efficiently:
+
+```javascript
+// Instead of creating 10,000 individual meshes
+const geometry = new THREE.BoxGeometry(1, 1, 1);
+const material = new THREE.MeshStandardMaterial({ color: 0x00ff00 });
+const mesh = new THREE.InstancedMesh(geometry, material, 10000);
+
+// Set transforms for each instance
+const matrix = new THREE.Matrix4();
+const position = new THREE.Vector3();
+const rotation = new THREE.Euler();
+const quaternion = new THREE.Quaternion();
+const scale = new THREE.Vector3(1, 1, 1);
+
+for (let i = 0; i < 10000; i++) {
+  position.set(
+    Math.random() * 100 - 50,
+    Math.random() * 100 - 50,
+    Math.random() * 100 - 50
+  );
+
+  rotation.set(
+    Math.random() * Math.PI,
+    Math.random() * Math.PI,
+    Math.random() * Math.PI
+  );
+
+  quaternion.setFromEuler(rotation);
+  matrix.compose(position, quaternion, scale);
+  mesh.setMatrixAt(i, matrix);
+}
+
+mesh.instanceMatrix.needsUpdate = true;
+scene.add(mesh);
+
+// Per-instance colors
+mesh.instanceColor = new THREE.InstancedBufferAttribute(
+  new Float32Array(10000 * 3),
+  3
+);
+
+for (let i = 0; i < 10000; i++) {
+  mesh.setColorAt(i, new THREE.Color(Math.random(), Math.random(), Math.random()));
+}
+```
+
+## Level of Detail (LOD)
+
+Switch between detail levels based on distance:
+
+```javascript
+const lod = new THREE.LOD();
+
+// High detail (close)
+const geometryHigh = new THREE.IcosahedronGeometry(10, 4);
+const meshHigh = new THREE.Mesh(geometryHigh, material);
+lod.addLevel(meshHigh, 0);
+
+// Medium detail
+const geometryMed = new THREE.IcosahedronGeometry(10, 2);
+const meshMed = new THREE.Mesh(geometryMed, material);
+lod.addLevel(meshMed, 50);
+
+// Low detail (far)
+const geometryLow = new THREE.IcosahedronGeometry(10, 0);
+const meshLow = new THREE.Mesh(geometryLow, material);
+lod.addLevel(meshLow, 100);
+
+scene.add(lod);
+
+// Update LOD in animation loop
+function animate() {
+  lod.update(camera);
+  renderer.render(scene, camera);
+  requestAnimationFrame(animate);
+}
+```
+
+## Frustum Culling
+
+Automatic - objects outside camera view aren't rendered.
+
+```javascript
+// Force disable for specific object
+object.frustumCulled = false;
+
+// Manually test if in view
+const frustum = new THREE.Frustum();
+const cameraViewProjectionMatrix = new THREE.Matrix4();
+cameraViewProjectionMatrix.multiplyMatrices(
+  camera.projectionMatrix,
+  camera.matrixWorldInverse
+);
+frustum.setFromProjectionMatrix(cameraViewProjectionMatrix);
+
+if (frustum.intersectsObject(object)) {
+  // Object is visible
+}
+```
+
+## Geometry Optimization
+
+```javascript
+// Merge geometries (reduce draw calls)
+import { mergeGeometries } from 'three/addons/utils/BufferGeometryUtils.js';
+
+const geometries = [geom1, geom2, geom3];
+const mergedGeometry = mergeGeometries(geometries);
+const mesh = new THREE.Mesh(mergedGeometry, material);
+
+// Dispose old geometries
+geometries.forEach(g => g.dispose());
+
+// Simplify geometry
+import { SimplifyModifier } from 'three/addons/modifiers/SimplifyModifier.js';
+
+const modifier = new SimplifyModifier();
+const simplified = modifier.modify(geometry, Math.floor(geometry.attributes.position.count * 0.5));
+```
+
+## Texture Optimization
+
+```javascript
+// Use appropriate sizes (power of 2)
+// 512x512, 1024x1024, 2048x2048
+
+// Compress textures
+import { KTX2Loader } from 'three/addons/loaders/KTX2Loader.js';
+
+// Use mipmaps (auto-generated by default)
+texture.generateMipmaps = true;
+
+// Appropriate filtering
+texture.minFilter = THREE.LinearMipmapLinearFilter;
+texture.magFilter = THREE.LinearFilter;
+
+// Anisotropic filtering (balance quality/performance)
+texture.anisotropy = renderer.capabilities.getMaxAnisotropy();
+
+// Dispose unused textures
+texture.dispose();
+```
+
+## Material Sharing
+
+```javascript
+// Share materials between meshes (reduce memory)
+const sharedMaterial = new THREE.MeshStandardMaterial({ color: 0x00ff00 });
+
+const mesh1 = new THREE.Mesh(geometry1, sharedMaterial);
+const mesh2 = new THREE.Mesh(geometry2, sharedMaterial);
+const mesh3 = new THREE.Mesh(geometry3, sharedMaterial);
+```
+
+## Shadow Optimization
+
+```javascript
+// Reduce shadow map resolution
+light.shadow.mapSize.width = 1024;  // instead of 2048
+light.shadow.mapSize.height = 1024;
+
+// Limit shadow camera frustum
+light.shadow.camera.near = 0.5;
+light.shadow.camera.far = 50;  // only cast shadows within this range
+light.shadow.camera.left = -10;
+light.shadow.camera.right = 10;
+
+// Use fewer shadow-casting objects
+object.castShadow = false; // for distant/small objects
+object.receiveShadow = false; // for objects that don't need shadows
+
+// Cheaper shadow type
+renderer.shadowMap.type = THREE.PCFShadowMap; // instead of PCFSoftShadowMap
+```
+
+## Render Target Optimization
+
+```javascript
+// Lower resolution for post-processing
+const renderTarget = new THREE.WebGLRenderTarget(
+  window.innerWidth * 0.5,  // half resolution
+  window.innerHeight * 0.5
+);
+
+// Appropriate pixel format
+renderTarget.texture.format = THREE.RGBAFormat;
+renderTarget.texture.type = THREE.UnsignedByteType;
+
+// Dispose when done
+renderTarget.dispose();
+```
+
+## Object Pooling
+
+```javascript
+// Reuse objects instead of creating/destroying
+class ObjectPool {
+  constructor(factory, initialSize) {
+    this.factory = factory;
+    this.pool = [];
+    for (let i = 0; i < initialSize; i++) {
+      this.pool.push(factory());
+    }
+  }
+
+  get() {
+    return this.pool.length > 0 ? this.pool.pop() : this.factory();
+  }
+
+  release(obj) {
+    this.pool.push(obj);
+  }
+}
+
+const bulletPool = new ObjectPool(() => {
+  return new THREE.Mesh(bulletGeometry, bulletMaterial);
+}, 100);
+
+// Use
+const bullet = bulletPool.get();
+scene.add(bullet);
+
+// Return when done
+scene.remove(bullet);
+bulletPool.release(bullet);
+```
+
+## Monitoring Performance
+
+```javascript
+// FPS counter
+const stats = new Stats();
+document.body.appendChild(stats.dom);
+
+function animate() {
+  stats.begin();
+  // ... rendering
+  stats.end();
+  requestAnimationFrame(animate);
+}
+
+// Renderer info
+console.log(renderer.info);
+// Shows: geometries, textures, programs, calls, triangles, points, lines
+
+// GPU timing
+const query = renderer.extensions.get('EXT_disjoint_timer_query_webgl2');
+```
+
+## General Best Practices
+
+- Limit draw calls (merge geometries, use instancing)
+- Reduce polygon count (LOD, simplification)
+- Optimize textures (compression, appropriate sizes)
+- Share materials and geometries
+- Use frustum culling
+- Limit number of lights (3-5 max)
+- Avoid transparent materials when possible
+- Use object pooling for frequently created/destroyed objects
+- Profile with browser DevTools
+- Test on target devices
+- Use WebGL 2 features when available