Basic Three.js Scrollbar Animation

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Some of the most visually impressive websites use scroll animations with Three.js. The following snippet configures a Three.js scene to animate when the user moves the scrollbar.

Scene

Setup a basic fullscreen scene using the example from the official docs:

file_type_js_official app.js 
import * as THREE from 'three';

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

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

Make the canvas stay fixed to screen as an animated background.

file_type_css style.css 
  canvas {
    position: fixed;
    top: 0;
    left: 0;
  }

Overlaying Content

Overlay the main content with abosolute positioning. It is given an artifically large height value to make it scroll without content.

file_type_css style.css 
main {
    width: 100vw;
    height: 500vh;
    z-index: 99;
    position: absolute;
  }
file_type_html index.html 
<body>
    <main></main>
</body>

Animate on Scroll

Finally, add a cube to the scene and animate it. Listen to the onscroll on the body to trigger a change or calculate the next animation position.

file_type_js_official app.js 
const geometry = new THREE.BoxGeometry();
const material = new THREE.MeshBasicMaterial( { color: 0x00ff00 } );
const cube = new THREE.Mesh( geometry, material );
scene.add( cube );

camera.position.z = 5;

function animate() {
  cube.rotation.x += 0.01;
  cube.rotation.y += 0.01;
  cube.rotation.z += 0.01;

  renderer.render( scene, camera );
}

document.body.onscroll = () => { 
  animate()
  console.log(document.body.offsetTop)
}

Questions?

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