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Add dolly zoom demo #13

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9b7005e
Add dolly zoom demo
claude Apr 29, 2026
c739930
Vendor Three.js and tune scene for clearer dolly zoom
claude Apr 29, 2026
1444bfe
Add preview assets for the dolly zoom demo
claude May 6, 2026
73d31dd
Add self-contained standalone.html for Claude.ai artifact use
claude May 7, 2026
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367 changes: 367 additions & 0 deletions dolly-zoom/index.html
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<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Dolly Zoom Demo</title>
<style>
html, body {
margin: 0;
padding: 0;
overflow: hidden;
font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Helvetica, Arial, sans-serif;
background: #87ceeb;
color: #fff;
}
canvas { display: block; }

#info {
position: absolute;
top: 16px;
left: 16px;
background: rgba(0, 0, 0, 0.55);
padding: 12px 14px;
border-radius: 10px;
font-size: 13px;
line-height: 1.45;
max-width: 320px;
pointer-events: none;
}
#info strong { font-size: 14px; }

#controls {
position: absolute;
bottom: 24px;
left: 50%;
transform: translateX(-50%);
background: rgba(0, 0, 0, 0.6);
padding: 14px 22px;
border-radius: 14px;
display: flex;
align-items: center;
gap: 14px;
min-width: 360px;
box-shadow: 0 8px 24px rgba(0, 0, 0, 0.25);
}
#controls label {
font-size: 13px;
letter-spacing: 0.04em;
text-transform: uppercase;
opacity: 0.85;
}
#zoom { flex: 1; accent-color: #ff7043; }
#zoomVal {
font-variant-numeric: tabular-nums;
min-width: 56px;
text-align: right;
font-size: 15px;
font-weight: 600;
}

#stats {
position: absolute;
top: 16px;
right: 16px;
background: rgba(0, 0, 0, 0.55);
padding: 10px 14px;
border-radius: 10px;
font-family: ui-monospace, SFMono-Regular, Menlo, monospace;
font-size: 12px;
line-height: 1.6;
pointer-events: none;
}
#stats span { color: #ffd180; }
</style>
</head>
<body>
<div id="info">
<strong>Dolly Zoom Demo</strong><br>
The foreground person stays the same size on screen.<br>
As you zoom in, the camera dollies back to compensate.<br>
Watch the second person — 100&nbsp;m behind — appear to grow,
and the surroundings compress.
</div>

<div id="stats">
FOV:&nbsp;&nbsp;&nbsp;&nbsp;<span id="fovVal">60.0°</span><br>
Cam&nbsp;dist:&nbsp;<span id="distVal">5.0 m</span><br>
To&nbsp;person&nbsp;2:&nbsp;<span id="dist2Val">105.0 m</span>
</div>

<div id="controls">
<label for="zoom">Zoom</label>
<input id="zoom" type="range" min="1" max="20" step="0.05" value="1">
<span id="zoomVal">1.00×</span>
</div>

<script type="importmap">
{
"imports": {
"three": "./three.module.js"
}
}
</script>
<script type="module">
import * as THREE from 'three';

const BASE_FOV = 60; // degrees, at zoom = 1
const BASE_DISTANCE = 5; // metres from camera to subject at zoom = 1
const CAM_HEIGHT = 1.65; // eye height
const PERSON2_OFFSET = 100; // metres behind subject

const scene = new THREE.Scene();
scene.background = new THREE.Color(0x9bd3ee);
scene.fog = new THREE.Fog(0xb8dff0, 220, 900);

const camera = new THREE.PerspectiveCamera(BASE_FOV, innerWidth / innerHeight, 0.1, 2000);
camera.position.set(0, CAM_HEIGHT, BASE_DISTANCE);
camera.lookAt(0, CAM_HEIGHT, 0);

const renderer = new THREE.WebGLRenderer({ antialias: true });
renderer.setPixelRatio(Math.min(devicePixelRatio, 2));
renderer.setSize(innerWidth, innerHeight);
renderer.shadowMap.enabled = true;
renderer.shadowMap.type = THREE.PCFSoftShadowMap;
document.body.appendChild(renderer.domElement);

// --- Lighting -----------------------------------------------------------
const sun = new THREE.DirectionalLight(0xfff2d6, 1.15);
sun.position.set(60, 100, 40);
sun.castShadow = true;
sun.shadow.mapSize.set(2048, 2048);
const s = sun.shadow.camera;
s.left = -120; s.right = 120; s.top = 120; s.bottom = -120;
s.near = 1; s.far = 400;
scene.add(sun);
scene.add(new THREE.AmbientLight(0xffffff, 0.45));
scene.add(new THREE.HemisphereLight(0x9bd3ee, 0x4a6b2a, 0.45));

// --- Ground -------------------------------------------------------------
const ground = new THREE.Mesh(
new THREE.PlaneGeometry(2000, 2000),
new THREE.MeshLambertMaterial({ color: 0x6fa84a })
);
ground.rotation.x = -Math.PI / 2;
ground.receiveShadow = true;
scene.add(ground);

// Dirt path running from in front of subject far back past person 2
const path = new THREE.Mesh(
new THREE.PlaneGeometry(3.2, 320),
new THREE.MeshLambertMaterial({ color: 0x927043 })
);
path.rotation.x = -Math.PI / 2;
path.position.set(0, 0.01, -150);
path.receiveShadow = true;
scene.add(path);

// --- Helpers ------------------------------------------------------------
const rand = (a, b) => a + Math.random() * (b - a);

function makePerson(shirtColor, pantsColor = 0x223366, hatColor = null) {
const g = new THREE.Group();
const skin = new THREE.MeshLambertMaterial({ color: 0xf2c79c });
const shirt = new THREE.MeshLambertMaterial({ color: shirtColor });
const pants = new THREE.MeshLambertMaterial({ color: pantsColor });

const lLeg = new THREE.Mesh(new THREE.CylinderGeometry(0.12, 0.12, 0.85, 12), pants);
lLeg.position.set(-0.13, 0.43, 0);
const rLeg = lLeg.clone(); rLeg.position.x = 0.13;
g.add(lLeg, rLeg);

const body = new THREE.Mesh(new THREE.CylinderGeometry(0.28, 0.32, 0.78, 16), shirt);
body.position.y = 1.24;
g.add(body);

const lArm = new THREE.Mesh(new THREE.CylinderGeometry(0.09, 0.09, 0.72, 12), shirt);
lArm.position.set(-0.37, 1.24, 0);
const rArm = lArm.clone(); rArm.position.x = 0.37;
g.add(lArm, rArm);

const head = new THREE.Mesh(new THREE.SphereGeometry(0.18, 16, 16), skin);
head.position.y = 1.81;
g.add(head);

if (hatColor !== null) {
const hat = new THREE.Mesh(
new THREE.ConeGeometry(0.22, 0.26, 16),
new THREE.MeshLambertMaterial({ color: hatColor })
);
hat.position.y = 2.04;
g.add(hat);
}

g.traverse(o => { if (o.isMesh) { o.castShadow = true; o.receiveShadow = true; } });
return g;
}

function makeTree(scale = 1) {
const g = new THREE.Group();
const trunk = new THREE.Mesh(
new THREE.CylinderGeometry(0.28 * scale, 0.38 * scale, 2.4 * scale, 8),
new THREE.MeshLambertMaterial({ color: 0x5a3a1e })
);
trunk.position.y = 1.2 * scale;
g.add(trunk);

const greens = [0x2e7d32, 0x388e3c, 0x4a8b3a, 0x356b29, 0x4f9b48];
const foliage = new THREE.Mesh(
new THREE.ConeGeometry(2 * scale, 5 * scale, 12),
new THREE.MeshLambertMaterial({ color: greens[Math.floor(Math.random() * greens.length)] })
);
foliage.position.y = (2.4 + 5 / 2) * scale;
g.add(foliage);

g.traverse(o => { if (o.isMesh) { o.castShadow = true; o.receiveShadow = true; } });
return g;
}

function makeHouse() {
const g = new THREE.Group();
const w = rand(5, 8);
const d = rand(5, 8);
const h = rand(3, 4.5);
const wallColor = new THREE.Color().setHSL(0.07 + Math.random() * 0.08, 0.45, 0.7);
const walls = new THREE.Mesh(
new THREE.BoxGeometry(w, h, d),
new THREE.MeshLambertMaterial({ color: wallColor })
);
walls.position.y = h / 2;
g.add(walls);

const roofColors = [0x8a3324, 0x5d4037, 0x6d4c41, 0x7b3f00];
const roof = new THREE.Mesh(
new THREE.ConeGeometry(Math.max(w, d) * 0.78, h * 0.75, 4),
new THREE.MeshLambertMaterial({ color: roofColors[Math.floor(Math.random() * roofColors.length)] })
);
roof.position.y = h + h * 0.375;
roof.rotation.y = Math.PI / 4;
g.add(roof);

// Door
const door = new THREE.Mesh(
new THREE.PlaneGeometry(0.9, 1.6),
new THREE.MeshLambertMaterial({ color: 0x3e2a14 })
);
door.position.set(0, 0.8, d / 2 + 0.01);
g.add(door);

// Windows
const winMat = new THREE.MeshLambertMaterial({ color: 0xfff7c2, emissive: 0x222200 });
const w1 = new THREE.Mesh(new THREE.PlaneGeometry(0.8, 0.8), winMat);
w1.position.set(-w / 3, h / 2 + 0.2, d / 2 + 0.01);
const w2 = w1.clone(); w2.position.x = w / 3;
g.add(w1, w2);

g.traverse(o => { if (o.isMesh) { o.castShadow = true; o.receiveShadow = true; } });
return g;
}

// --- Scene populating ---------------------------------------------------
// Subject (foreground person), facing camera
const subject = makePerson(0xd24343, 0x223366);
subject.position.set(0, 0, 0);
subject.rotation.y = Math.PI; // face +z (towards camera)
scene.add(subject);

// Second person, 100 m behind subject, offset slightly to one side so
// they're never fully occluded by the foreground person, and facing camera.
const person2 = makePerson(0x3d6cb4, 0x222222, 0xf6c84c);
person2.position.set(1.4, 0, -PERSON2_OFFSET);
person2.rotation.y = Math.PI;
scene.add(person2);

// Trees scattered along both sides, well behind the subject
// (kept out of the immediate space between camera and subject)
// Keep a clear corridor on the path centerline so person 2 stays visible
// even at the narrow FOVs reached at high zoom.
for (let i = 0; i < 90; i++) {
const t = makeTree(0.85 + Math.random() * 0.6);
const side = Math.random() < 0.5 ? -1 : 1;
const xOff = side * rand(8, 70);
const z = rand(-220, -2);
t.position.set(xOff, 0, z);
t.rotation.y = Math.random() * Math.PI * 2;
scene.add(t);
}

// Distant tree line
for (let i = 0; i < 80; i++) {
const t = makeTree(1 + Math.random() * 0.9);
t.position.set(rand(-260, 260), 0, rand(-320, -230));
scene.add(t);
}

// Houses scattered along the sides
const housePositions = [
[-18, -12], [22, -25], [-30, -55], [28, -68], [-24, -90],
[32, -105], [-38, -130], [26, -148], [-20, -170], [34, -190],
[-44, -210], [40, -40], [-15, -78], [18, -125]
];
housePositions.forEach(([x, z]) => {
const h = makeHouse();
h.position.set(x, 0, z);
h.rotation.y = (x > 0 ? -1 : 1) * (Math.PI / 2 + rand(-0.4, 0.4));
scene.add(h);
});

// A few fence posts along the path for extra depth cue
const fenceMat = new THREE.MeshLambertMaterial({ color: 0x8a6a3c });
for (let z = -10; z >= -210; z -= 6) {
for (const side of [-1, 1]) {
const post = new THREE.Mesh(
new THREE.BoxGeometry(0.12, 1.1, 0.12),
fenceMat
);
post.position.set(side * 2.4, 0.55, z);
post.castShadow = true;
scene.add(post);
}
}

// --- Resize -------------------------------------------------------------
addEventListener('resize', () => {
camera.aspect = innerWidth / innerHeight;
camera.updateProjectionMatrix();
renderer.setSize(innerWidth, innerHeight);
});

// --- Dolly zoom ---------------------------------------------------------
// Keep subject screen size constant: d * tan(fov/2) = const
// Increasing zoom -> narrower fov + camera moves back proportionally.
const baseHalfTan = Math.tan(THREE.MathUtils.degToRad(BASE_FOV) / 2);

const slider = document.getElementById('zoom');
const zoomVal = document.getElementById('zoomVal');
const fovVal = document.getElementById('fovVal');
const distVal = document.getElementById('distVal');
const dist2Val = document.getElementById('dist2Val');

function applyZoom(z) {
const halfFovRad = Math.atan(baseHalfTan / z);
const fovDeg = THREE.MathUtils.radToDeg(halfFovRad * 2);
const distance = BASE_DISTANCE * z;

camera.fov = fovDeg;
camera.position.set(0, CAM_HEIGHT, distance);
camera.lookAt(0, CAM_HEIGHT, 0);
camera.updateProjectionMatrix();

zoomVal.textContent = z.toFixed(2) + '×';
fovVal.textContent = fovDeg.toFixed(1) + '°';
distVal.textContent = distance.toFixed(1) + ' m';
dist2Val.textContent = (distance + PERSON2_OFFSET).toFixed(1) + ' m';
}

slider.addEventListener('input', () => applyZoom(parseFloat(slider.value)));
applyZoom(1);

// --- Render loop --------------------------------------------------------
function tick() {
requestAnimationFrame(tick);
renderer.render(scene, camera);
}
tick();
</script>
</body>
</html>
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