# Three.js Post-Processing

## Quick Start

```javascript
import * as THREE from "three";
import { EffectComposer } from "three/addons/postprocessing/EffectComposer.js";
import { RenderPass } from "three/addons/postprocessing/RenderPass.js";
import { UnrealBloomPass } from "three/addons/postprocessing/UnrealBloomPass.js";

// Setup composer
const composer = new EffectComposer(renderer);

// Render scene
const renderPass = new RenderPass(scene, camera);
composer.addPass(renderPass);

// Add bloom
const bloomPass = new UnrealBloomPass(
  new THREE.Vector2(window.innerWidth, window.innerHeight),
  1.5, // strength
  0.4, // radius
  0.85, // threshold
);
composer.addPass(bloomPass);

// Animation loop - use composer instead of renderer
function animate() {
  requestAnimationFrame(animate);
  composer.render(); // NOT renderer.render()
}
```

## EffectComposer Setup

```javascript
import { EffectComposer } from "three/addons/postprocessing/EffectComposer.js";
import { RenderPass } from "three/addons/postprocessing/RenderPass.js";

const composer = new EffectComposer(renderer);

// First pass: render scene
const renderPass = new RenderPass(scene, camera);
composer.addPass(renderPass);

// Add more passes...
composer.addPass(effectPass);

// Last pass should render to screen
effectPass.renderToScreen = true; // Default for last pass

// Handle resize
function onResize() {
  const width = window.innerWidth;
  const height = window.innerHeight;

  camera.aspect = width / height;
  camera.updateProjectionMatrix();

  renderer.setSize(width, height);
  composer.setSize(width, height);
}
```

## Common Effects

### Bloom (Glow)

```javascript
import { UnrealBloomPass } from "three/addons/postprocessing/UnrealBloomPass.js";

const bloomPass = new UnrealBloomPass(
  new THREE.Vector2(window.innerWidth, window.innerHeight),
  1.5, // strength - intensity of glow
  0.4, // radius - spread of glow
  0.85, // threshold - brightness threshold
);

composer.addPass(bloomPass);

// Adjust at runtime
bloomPass.strength = 2.0;
bloomPass.threshold = 0.5;
bloomPass.radius = 0.8;
```

### Selective Bloom

Apply bloom only to specific objects.

```javascript
import { UnrealBloomPass } from "three/addons/postprocessing/UnrealBloomPass.js";
import { ShaderPass } from "three/addons/postprocessing/ShaderPass.js";

// Layer setup
const BLOOM_LAYER = 1;
const bloomLayer = new THREE.Layers();
bloomLayer.set(BLOOM_LAYER);

// Mark objects to bloom
glowingMesh.layers.enable(BLOOM_LAYER);

// Dark material for non-blooming objects
const darkMaterial = new THREE.MeshBasicMaterial({ color: 0x000000 });
const materials = {};

function darkenNonBloomed(obj) {
  if (obj.isMesh && !bloomLayer.test(obj.layers)) {
    materials[obj.uuid] = obj.material;
    obj.material = darkMaterial;
  }
}

function restoreMaterial(obj) {
  if (materials[obj.uuid]) {
    obj.material = materials[obj.uuid];
    delete materials[obj.uuid];
  }
}

// Custom render loop
function render() {
  // Render bloom pass
  scene.traverse(darkenNonBloomed);
  composer.render();
  scene.traverse(restoreMaterial);

  // Render final scene over bloom
  renderer.render(scene, camera);
}
```

### FXAA (Anti-Aliasing)

```javascript
import { ShaderPass } from "three/addons/postprocessing/ShaderPass.js";
import { FXAAShader } from "three/addons/shaders/FXAAShader.js";

const fxaaPass = new ShaderPass(FXAAShader);
fxaaPass.material.uniforms["resolution"].value.set(
  1 / window.innerWidth,
  1 / window.innerHeight,
);

composer.addPass(fxaaPass);

// Update on resize
function onResize() {
  fxaaPass.material.uniforms["resolution"].value.set(
    1 / window.innerWidth,
    1 / window.innerHeight,
  );
}
```

### SMAA (Better Anti-Aliasing)

```javascript
import { SMAAPass } from "three/addons/postprocessing/SMAAPass.js";

const smaaPass = new SMAAPass(
  window.innerWidth * renderer.getPixelRatio(),
  window.innerHeight * renderer.getPixelRatio(),
);

composer.addPass(smaaPass);
```

### SSAO (Ambient Occlusion)

```javascript
import { SSAOPass } from "three/addons/postprocessing/SSAOPass.js";

const ssaoPass = new SSAOPass(
  scene,
  camera,
  window.innerWidth,
  window.innerHeight,
);
ssaoPass.kernelRadius = 16;
ssaoPass.minDistance = 0.005;
ssaoPass.maxDistance = 0.1;

composer.addPass(ssaoPass);

// Output modes
ssaoPass.output = SSAOPass.OUTPUT.Default;
// SSAOPass.OUTPUT.Default - Final composited output
// SSAOPass.OUTPUT.SSAO - Just the AO
// SSAOPass.OUTPUT.Blur - Blurred AO
// SSAOPass.OUTPUT.Depth - Depth buffer
// SSAOPass.OUTPUT.Normal - Normal buffer
```

### Depth of Field (DOF)

```javascript
import { BokehPass } from "three/addons/postprocessing/BokehPass.js";

const bokehPass = new BokehPass(scene, camera, {
  focus: 10.0, // Focus distance
  aperture: 0.025, // Aperture (smaller = more DOF)
  maxblur: 0.01, // Max blur amount
});

composer.addPass(bokehPass);

// Update focus dynamically
bokehPass.uniforms["focus"].value = distanceToTarget;
```

### Film Grain

```jav

…