Three.js Instanced Mesh Field

:root {
  --bg: #03060d;
  --text: #edf4ff;
  --muted: #c2d0e7;
  --accent: #8de8ff;
}
* {
  box-sizing: border-box;
}
body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: "Avenir Next", "Segoe UI", sans-serif;
}
#scene {
  position: fixed;
  inset: 0;
}
.topbar {
  position: fixed;
  inset: 0 0 auto 0;
  z-index: 20;
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: .75rem 1rem;
  background: rgba(0, 0, 0, 0.28);
  backdrop-filter: blur(8px);
}
.topbar a {
  color: var(--accent);
  text-decoration: none;
  font-weight: 700;
}
button {
  border: 1px solid rgba(255, 255, 255, 0.25);
  border-radius: 999px;
  padding: .45rem .8rem;
  background: rgba(255, 255, 255, 0.07);
  color: var(--text);
  cursor: pointer;
}
.overlay {
  position: relative;
  z-index: 10;
  min-height: 100vh;
  width: min(900px, 92%);
  margin: 0 auto;
  display: grid;
  align-content: center;
  text-align: center;
  gap: .7rem;
}
.label {
  margin: 0;
  color: var(--accent);
  letter-spacing: .1em;
  text-transform: uppercase;
}
h1,
p {
  margin: 0;
}
h1 {
  font-size: clamp(2rem, 7vw, 4rem);
}
p {
  color: var(--muted);
}

if (!window.MotionPreference) {
  const __mql = window.matchMedia("(prefers-reduced-motion: reduce)");
  const __listeners = new Set();

  const MotionPreference = {
    prefersReducedMotion() {
      return __mql.matches;
    },
    setOverride(value) {
      const reduced = Boolean(value);
      document.documentElement.classList.toggle("reduced-motion", reduced);
      window.dispatchEvent(new CustomEvent("motion-preference", { detail: { reduced } }));
      for (const listener of __listeners) {
        try {
          listener({ reduced, override: reduced, systemReduced: __mql.matches });
        } catch {}
      }
    },
    onChange(listener) {
      __listeners.add(listener);
      try {
        listener({
          reduced: __mql.matches,
          override: null,
          systemReduced: __mql.matches,
        });
      } catch {}
      return () => __listeners.delete(listener);
    },
    getState() {
      return { reduced: __mql.matches, override: null, systemReduced: __mql.matches };
    },
  };

  window.MotionPreference = MotionPreference;
}

import * as THREE from "three";

const host = document.getElementById("scene");
const toggle = document.getElementById("toggleMotion");
let motionEnabled = !window.MotionPreference.prefersReducedMotion();

const scene = new THREE.Scene();
scene.background = new THREE.Color(0x02040a);
scene.fog = new THREE.Fog(0x02040a, 8, 70);

const camera = new THREE.PerspectiveCamera(62, window.innerWidth / window.innerHeight, 0.1, 120);
camera.position.set(0, 0, 18);

const renderer = new THREE.WebGLRenderer({ antialias: true });
renderer.setPixelRatio(Math.min(window.devicePixelRatio || 1, 2));
renderer.setSize(window.innerWidth, window.innerHeight);
host.appendChild(renderer.domElement);

const count = 1800;
const geometry = new THREE.IcosahedronGeometry(0.11, 0);
const material = new THREE.MeshStandardMaterial({
  color: 0x88dcff,
  emissive: 0x2f6782,
  emissiveIntensity: 0.35,
  roughness: 0.35,
  metalness: 0.25,
});
const instanced = new THREE.InstancedMesh(geometry, material, count);
scene.add(instanced);

const dummy = new THREE.Object3D();
const data = [];
for (let i = 0; i < count; i += 1) {
  data.push({
    x: (Math.random() - 0.5) * 28,
    y: (Math.random() - 0.5) * 16,
    z: -Math.random() * 80,
    speed: 0.08 + Math.random() * 0.16,
    rot: Math.random() * Math.PI,
  });
}

scene.add(new THREE.AmbientLight(0x9abfff, 0.42));
const key = new THREE.PointLight(0x9fe1ff, 1.2, 55);
key.position.set(8, 8, 10);
scene.add(key);

function setLabel() {
  toggle.textContent = motionEnabled ? "Disable motion" : "Enable motion";
}

function animate() {
  requestAnimationFrame(animate);

  for (let i = 0; i < count; i += 1) {
    const d = data[i];
    if (motionEnabled) {
      d.z += d.speed;
      d.rot += 0.015;
      if (d.z > 8) d.z = -80;
    }

    dummy.position.set(d.x, d.y, d.z);
    dummy.rotation.set(d.rot, d.rot * 0.6, d.rot * 1.1);
    dummy.updateMatrix();
    instanced.setMatrixAt(i, dummy.matrix);
  }

  instanced.instanceMatrix.needsUpdate = true;
  renderer.render(scene, camera);
}

function onResize() {
  camera.aspect = window.innerWidth / window.innerHeight;
  camera.updateProjectionMatrix();
  renderer.setSize(window.innerWidth, window.innerHeight);
}

toggle.addEventListener("click", () => {
  motionEnabled = !motionEnabled;
  setLabel();
});

window.addEventListener("resize", onResize);
setLabel();
animate();

<!doctype html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Demo 15 - Instanced Mesh Field</title>
    <link rel="stylesheet" href="style.css" />
    <script type="importmap">{"imports":{"gsap":"https://esm.sh/gsap@3.13.0","gsap/ScrollTrigger":"https://esm.sh/gsap@3.13.0/ScrollTrigger","gsap/SplitText":"https://esm.sh/gsap@3.13.0/SplitText","gsap/Flip":"https://esm.sh/gsap@3.13.0/Flip","gsap/ScrambleTextPlugin":"https://esm.sh/gsap@3.13.0/ScrambleTextPlugin","gsap/TextPlugin":"https://esm.sh/gsap@3.13.0/TextPlugin","gsap/all":"https://esm.sh/gsap@3.13.0/all","gsap/":"https://esm.sh/gsap@3.13.0/","lenis":"https://esm.sh/lenis@1.1.13/dist/lenis.mjs","three":"https://esm.sh/three@0.171.0","three/addons/":"https://esm.sh/three@0.171.0/examples/jsm/"}}</script>
</head>
  <body>
    <header class="topbar">
      <a href="../">Back to demos</a>
      <button id="toggleMotion"></button>
    </header>

    <div id="scene"></div>
    <section class="overlay">
      <p class="label">Demo 15</p>
      <h1>Instanced Mesh Field</h1>
      <p>High object count field using GPU instancing.</p>
    </section>

    <script type="module" src="script.js"></script>
      </body>
</html>