​

var positions = [];

var velocities = [];

var isChild = [];

​

var numLinks = 50;

var linkLength = 6;

var chainStart = 100;

​

var gravity;

​

constrainIterations = 20;

var simSpeed = 1;

​

​

function setup() {

  createCanvas(480, 640);

  gravity = createVector(0, 2);

  // create links

  var offset = createVector(width/2, chainStart);

  for(var i = 0; i < numLinks; i++) {

    var offsetX = random(-linkLength, +linkLength);

    var offsetY = sqrt(linkLength**2 - offsetX**2);

    positions.push(offset.copy());

    velocities.push(createVector());

    isChild.push(true);

    offset.x += offsetX;

    offset.y += offsetY;

  }

}

​

function draw() {

  background(240);

  var pendingVelocities = [];

  for(var i = 1; i < numLinks; i++) {

    var pos1 = positions[i];

    // draw

    var pos2 = positions[i-1];

    line(pos1.x, pos1.y, pos2.x, pos2.y);

  }

  for(var it = 0; it < constrainIterations; it++) {

    for(var i = 1; i < numLinks; i++) {

      // simulate gravity

      velocities[i].add(p5.Vector.div(gravity, constrainIterations/simSpeed));

      // mouse force

      var mouseVector = positions[i].copy();

      mouseVector.sub(createVector(mouseX, mouseY));

      mouseVector.setMag((mouseVector.mag() ** (-2))*5000);

      if(mouseIsPressed) {

        velocities[i].add(p5.Vector.div(mouseVector, constrainIterations/simSpeed));

      }

      // forces between links

      // backward

      var backward = p5.Vector.sub(positions[i], positions[i-1])

      backward.normalize();

      var dot = velocities[i].dot(backward);

      backward.mult(dot);

      velocities[i].sub(p5.Vector.div(backward, constrainIterations/simSpeed));

      velocities[i-1].add(p5.Vector.div(backward, constrainIterations/simSpeed));

      // forward

      if(i < numLinks-1 && false) {

        var forward = p5.Vector.sub(positions[i+1], positions[i])

        backward.normalize();

        var dot = velocities[i].dot(backward);

        backward.mult(dot);

        velocities[i].add(p5.Vector.div(backward, constrainIterations/simSpeed*2));

        velocities[i+1].sub(p5.Vector.div(backward, constrainIterations/simSpeed*2));

      }

      // integrate

      positions[i].add(p5.Vector.div(velocities[i], constrainIterations/simSpeed));

      // constrain links

      positions[i].sub(positions[i-1]);

      positions[i].setMag(linkLength);

      positions[i].add(positions[i-1]);

    }

  }

  velocities[0].setMag(0);

}

​