How to Use Three.js StereoCamera for Anaglyph 3D

This article provides a comprehensive guide on how the StereoCamera works in Three.js and how it can be implemented to create immersive, red-cyan anaglyph 3D effects. You will learn the underlying principles of stereoscopic vision in web graphics and how to easily integrate this effect into your 3D web applications using the built-in Three.js tools.

Understanding the Three.js StereoCamera

In Three.js, THREE.StereoCamera is a utility class designed to mimic human binocular vision. Humans perceive depth because our eyes are separated by a small distance (interpupillary distance), allowing each eye to view the world from a slightly different angle. The brain combines these two distinct images into a single 3D scene.

The StereoCamera replicates this by managing two internal PerspectiveCamera instances—one for the left eye and one for the right eye. When configured, it calculates the correct offset and projection matrices for both cameras based on a defined eye separation (stereoscopic focus) and the aspect ratio of the viewport.

How StereoCamera Generates Anaglyph 3D Effects

Anaglyph 3D is a technique where the left-eye image and right-eye image are filtered with chromatically opposite colors (usually red for the left eye and cyan for the right eye). When viewed through matching color-filtered glasses, each eye only sees its intended image, resulting in a perceived 3D depth.

While StereoCamera handles the math of positioning the two virtual eyes, Three.js uses the AnaglyphEffect class to handle the rendering and color-filtering process. The AnaglyphEffect wraps around your standard renderer and uses StereoCamera under the hood to perform the following steps:

  1. Left Eye Render: It renders the scene from the perspective of the left camera, filtering the output to a red color channel.
  2. Right Eye Render: It renders the scene from the perspective of the right camera, filtering the output to a cyan (blue and green) color channel.
  3. Composite: It overlays these two renders onto the screen.

Implementing Anaglyph 3D in Three.js

To implement anaglyph 3D, you do not need to manually configure the StereoCamera. Instead, you use the AnaglyphEffect helper, which is available in the Three.js addons repository.

Step 1: Import the AnaglyphEffect

First, ensure you import the necessary module alongside the standard Three.js library:

import * as THREE from 'three';
import { AnaglyphEffect } from 'three/addons/effects/AnaglyphEffect.js';

Step 2: Set Up the Effect

Create your standard scene, perspective camera, and WebGLRenderer. Then, instantiate the AnaglyphEffect by passing the renderer and the viewport dimensions to it:

const renderer = new THREE.WebGLRenderer();
renderer.setSize(window.innerWidth, window.innerHeight);
document.body.appendChild(renderer.domElement);

const width = window.innerWidth;
const height = window.innerHeight;
const effect = new AnaglyphEffect(renderer, width, height);

Step 3: Render Using the Effect

Instead of calling renderer.render(scene, camera) in your animation loop, call the render method of the AnaglyphEffect instance:

function animate() {
    requestAnimationFrame(animate);

    // Update your animations or controls here

    // Render the scene using the 3D effect
    effect.render(scene, camera);
}
animate();

Step 4: Handle Window Resizing

When the window is resized, you must update both the camera aspect ratio and the size of the anaglyph effect:

window.addEventListener('resize', () => {
    camera.aspect = window.innerWidth / window.innerHeight;
    camera.updateProjectionMatrix();

    effect.setSize(window.innerWidth, window.innerHeight);
});

By wrapping the standard WebGLRenderer with the AnaglyphEffect, the StereoCamera handles the dual-camera offset automatically, giving your users an instant retro 3D experience with standard red-cyan glasses.