Implement SMAAPass Anti-Aliasing in Three.js

When utilizing the EffectComposer for post-processing in Three.js, the browser’s default hardware anti-aliasing (MSAA) is automatically disabled, resulting in jagged edges on 3D meshes. To resolve this visual degradation without sacrificing performance, you can implement Subpixel Morphological Anti-Aliasing (SMAA) via the SMAAPass. This article provides a direct, step-by-step guide to integrating SMAAPass into your Three.js post-processing pipeline to restore smooth, high-quality edges.

Why Use SMAAPass?

By default, the WebGLRenderer handles anti-aliasing. However, once rendering is redirected to an off-screen frame buffer for post-processing effects, this built-in anti-aliasing no longer functions. SMAAPass is an efficient, screen-space anti-aliasing filter that reconstructs sharp details and smooths aliased edges during the post-processing pass with a minimal performance footprint, making it ideal for web-based 3D applications.

Step 1: Import the Required Modules

First, import the core Three.js library alongside the necessary post-processing classes. You will need EffectComposer, RenderPass, and SMAAPass from the Three.js examples directory.

import * as THREE from 'three';
import { EffectComposer } from 'three/examples/jsm/postprocessing/EffectComposer.js';
import { RenderPass } from 'three/examples/jsm/postprocessing/RenderPass.js';
import { SMAAPass } from 'three/examples/jsm/postprocessing/SMAAPass.js';

Step 2: Initialize the Renderer and Composer

When initializing your WebGLRenderer, set antialias to false. Since the built-in MSAA does not work with post-processing, disabling it saves rendering performance.

// Initialize WebGLRenderer without hardware anti-aliasing
const renderer = new THREE.WebGLRenderer({ antialias: false });
renderer.setSize(window.innerWidth, window.innerHeight);
renderer.setPixelRatio(Math.min(window.devicePixelRatio, 2));
document.body.appendChild(renderer.domElement);

// Create the main Scene and Camera
const scene = new THREE.Scene();
const camera = new THREE.PerspectiveCamera(75, window.innerWidth / window.innerHeight, 0.1, 1000);

// Set up the EffectComposer
const composer = new EffectComposer(renderer);

Step 3: Add the Passes to the Composer

You must first pass the scene and camera through a RenderPass to generate the initial image. After the RenderPass, append the SMAAPass to apply the anti-aliasing filter.

// 1. Add the base RenderPass
const renderPass = new RenderPass(scene, camera);
composer.addPass(renderPass);

// 2. Add the SMAAPass
const pixelRatio = renderer.getPixelRatio();
const smaaPass = new SMAAPass(
    window.innerWidth * pixelRatio, 
    window.innerHeight * pixelRatio
);
composer.addPass(smaaPass);

Note: Passing the correct pixel-ratio-adjusted width and height to the SMAAPass constructor ensures that the post-processing textures match the rendering resolution perfectly.

Step 4: Handle Window Resizing

If the browser window resizes, both the EffectComposer and the SMAAPass must be updated with the new viewport dimensions to prevent rendering distortions or blurred artifacts.

```window.addEventListener(‘resize’, () => { const width = window.innerWidth; const height = window.innerHeight; const pixelRatio = renderer.getPixelRatio();

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

// Update Renderer and Composer
renderer.setSize(width, height);
composer.setSize(width, height);

// Update SMAAPass dimensions
smaaPass.setSize(width * pixelRatio, height * pixelRatio);

});

## Step 5: Update the Render Loop

To output the anti-aliased frame, replace your standard `renderer.render(scene, camera)` call inside your animation loop with `composer.render()`.

```javascript
function animate() {
    requestAnimationFrame(animate);

    // Perform animations or physics updates here

    // Render the scene through the post-processing pipeline
    composer.render();
}

animate();