<html>
<head>
<title>Epicyclic Circles</title>
<style>
body { margin: 0; }
canvas { width: 100%; height: 100% }
</style>
</head>
<body>
<script src="https://rawgit.com/mrdoob/three.js/dev/build/three.js"></script>
<script src="https://rawgit.com/mrdoob/three.js/dev/examples/js/controls/OrbitControls.js"></script>
<script>
// Set up the basic scene, camera, and lights.
var scene = new THREE.Scene();
scene.background = new THREE.Color( 0xf0f0f0 );
var camera = new THREE.PerspectiveCamera( 75, window.innerWidth/window.innerHeight, 0.1, 1000 );
scene.add(camera)
var light = new THREE.PointLight( 0xffffff, 0.8 );
camera.add( light );
camera.position.z = 200;
var renderer = new THREE.WebGLRenderer();
renderer.setSize( window.innerWidth, window.innerHeight );
document.body.appendChild( renderer.domElement );
// Add the orbit controls to permit viewing the scene from different angles via the mouse.
controls = new THREE.OrbitControls( camera, renderer.domElement );
controls.enableDamping = true; // an animation loop is required when either damping or auto-rotation are enabled
controls.dampingFactor = 0.25;
controls.screenSpacePanning = false;
controls.minDistance = 0;
controls.maxDistance = 500;
function createCircleMesh(plane, radius, depth, meshColor, meshOpacity) {
let extrudeSettings = { depth: depth, bevelEnabled: true, bevelSegments: 2, steps: 2, bevelSize: .25, bevelThickness: .25 };
let arcShape = new THREE.Shape();
arcShape.moveTo( 0, 0 );
arcShape.absarc( 0, 0, radius, 0, Math.PI * 2, false );
let holePath = new THREE.Path();
holePath.moveTo( 0, radius * 0.75 );
holePath.absarc( 0, radius * 0.75, radius * 0.20, 0, Math.PI * 2, true );
arcShape.holes.push( holePath );
var geometry = new THREE.ExtrudeBufferGeometry( arcShape, extrudeSettings );
var mesh = new THREE.Mesh( geometry, new THREE.MeshStandardMaterial({color: meshColor, roughness: 1, metalness: 0, transparent: meshOpacity !== 1, opacity: meshOpacity}) );
scene.add( mesh );
if (plane === "XZ") {
mesh.rotateX(Math.PI / 2);
} else if (plane === "YZ") {
mesh.rotateY(Math.PI / 2);
}
return mesh;
}
// Create an array of circles and their meshes.
circle = [];
for (let i = 0; i < 5; i++) {
let r = 5 - i;
circle[i] = {
radius: r*10 + Math.random() * r * 10,
rotationRate: (Math.random() * 2 * Math.PI - Math.PI) / 100
};
// RenderOrder is stepped to reduce dithering.
circle[i].mesh = createCircleMesh("XY", circle[i].radius, 5, 0xff0000, 0.5);
circle[i].mesh.renderOrder = i;
circle[i].centerMesh = createCircleMesh("XY", 5, 2, 0xff0000, 1);
if (i === 0) {
circle[i].centerX = circle[i].radius;
circle[i].centerY = circle[i].radius;
circle[i].centerZ = i; // Offset the meshes to reduce dithering.
} else {
circle[i].centerX = circle[i-1].centerX + circle[i-1].radius;
circle[i].centerY = circle[i-1].centerY;
circle[i].centerZ = i; // Offset the meshes to reduce dithering.
}
circle[i].rotated = 0;
}
// Set up "viewing" planes.
var plane = new THREE.Plane( new THREE.Vector3( 1, 0, 0 ), 0 );
var helper = new THREE.PlaneHelper( plane, 500, 0x696969 );
scene.add( helper );
var plane2 = new THREE.Plane( new THREE.Vector3( 0, 1, 0 ), 0 );
var helper2 = new THREE.PlaneHelper( plane2, 500, 0xE06666 );
scene.add( helper2 );
var plane3 = new THREE.Plane( new THREE.Vector3( 0, 0, 1 ), 0 );
var helper3 = new THREE.PlaneHelper( plane3, 500, 0xD85C6 );
scene.add( helper3 );
var size = 250;
var divisions = 10;
var gridHelper = new THREE.GridHelper( size, divisions );
scene.add( gridHelper );
var animate = function () {
requestAnimationFrame( animate );
// During each animation frame, let's rotate the objects.
for (let i = 0; i < 5; i++) {
let c = circle[i];
c.rotated += c.rotationRate;
if (0 < i) {
c.centerX = circle[i-1].centerX + circle[i-1].radius * Math.cos(circle[i-1].rotated);
c.centerY = circle[i-1].centerY + circle[i-1].radius * Math.sin(circle[i-1].rotated);
}
// Note that due to the stepping of the meshes to reduce dithering, it is necessary
// to alter the step (via Math.sign(camera.position.z)) if we're looking via the backside.
c.mesh.rotateZ(c.rotationRate);
c.mesh.position.set(c.centerX, c.centerY, c.centerZ * Math.sign(camera.position.z));
c.centerMesh.position.set(c.centerX, c.centerY, c.centerZ * Math.sign(camera.position.z));
}
renderer.render( scene, camera );
};
animate();
</script>
</body>
</html>