RandomCode/Double Pendulum.html at main · GaMaDeCa/RandomCode · GitHub

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<!doctype html>
<!--Randomized Arms Double Pendulum-->
<html lang="en">
<head>
  <meta charset="utf-8" />
  <meta name="viewport" content="width=device-width, initial-scale=1" />
  <title>Chaos Pendulum</title>
  <style>
    html,body { margin:0; padding:0; height:100%; background:#fff; overflow:hidden; }
    canvas { display:block; width:100%; height:100%; background:#fff; }
  </style>
</head>
<body>
  <canvas id="canvas"></canvas>
  <script>
    const canvas = document.getElementById('canvas');
    const ctx = canvas.getContext('2d');

function resize() {
  canvas.width = window.innerWidth;
  canvas.height = window.innerHeight;
}
function getRandomIntInclusive(min, max) {
  min = Math.ceil(min);
  max = Math.floor(max);
  return Math.floor(Math.random() * (max - min + 1)) + min;
}
window.addEventListener('resize', resize);
resize();

// Parameters
let L1 = getRandomIntInclusive(50, 110);// length of first arm
let L2 = getRandomIntInclusive(50, 110); // length of second arm
let m1 = 10;  // mass 1
let m2 = 10;  // mass 2
let g = 1;    // gravity

let a1 = Math.PI/2; // angle 1
let a2 = Math.PI/2; // angle 2
let a1_v = 0;       // angular velocity 1
let a2_v = 0;       // angular velocity 2

// Tracking path
const pathCanvas = document.createElement('canvas');
const pathCtx = pathCanvas.getContext('2d');
function resizePathCanvas() {
  pathCanvas.width = canvas.width;
  pathCanvas.height = canvas.height;
}
resizePathCanvas();

window.addEventListener('resize', resizePathCanvas);

function update() {
  // Equations of motion for a double pendulum (simplified)
  let num1 = -g*(2*m1+m2)*Math.sin(a1);
  let num2 = -m2*g*Math.sin(a1-2*a2);
  let num3 = -2*Math.sin(a1-a2)*m2*(a2_v*a2_v*L2 + a1_v*a1_v*L1*Math.cos(a1-a2));
  let den = L1*(2*m1+m2 - m2*Math.cos(2*a1-2*a2));
  let a1_a = (num1 + num2 + num3) / den;

  num1 = 2*Math.sin(a1-a2)*(a1_v*a1_v*L1*(m1+m2) + g*(m1+m2)*Math.cos(a1) + a2_v*a2_v*L2*m2*Math.cos(a1-a2));
  den = L2*(2*m1+m2 - m2*Math.cos(2*a1-2*a2));
  let a2_a = num1 / den;

  a1_v += a1_a;
  a2_v += a2_a;
  a1_v *= 0.999; // damping
  a2_v *= 0.999;
  a1 += a1_v;
  a2 += a2_v;
}

function draw() {
  ctx.clearRect(0, 0, canvas.width, canvas.height);
  const originX = canvas.width/2;
  const originY = canvas.height/4;

  const x1 = originX + L1*Math.sin(a1);
  const y1 = originY + L1*Math.cos(a1);
  const x2 = x1 + L2*Math.sin(a2);
  const y2 = y1 + L2*Math.cos(a2);

  // Draw tracking path (red line)
  pathCtx.strokeStyle = 'red';
  pathCtx.lineWidth = 2;
  pathCtx.lineCap = 'round';
  pathCtx.beginPath();
  pathCtx.moveTo(x2, y2);
  pathCtx.lineTo(x2, y2);
  pathCtx.stroke();

  // Merge tracking path onto main canvas
  ctx.drawImage(pathCanvas, 0, 0);

  // Draw pendulum arms (black lines)
  ctx.strokeStyle = 'black';
  ctx.lineWidth = 2;
  ctx.beginPath();
  ctx.moveTo(originX, originY);
  ctx.lineTo(x1, y1);
  ctx.lineTo(x2, y2);
  ctx.stroke();

  // Draw points (dark blue)
  ctx.fillStyle = '#002b8f';
  ctx.beginPath();
  ctx.arc(x1, y1, m1/2, 0, 2*Math.PI);
  ctx.arc(x2, y2, m2/2, 0, 2*Math.PI);
  ctx.fill();
}

function loop() {
  update();
  draw();
  requestAnimationFrame(loop);
}

loop();

  </script>
</body>
</html>