var Particle = function Particle() {

  this.px = 0;

  this.py = 0;

  this.vx = 0;

  this.vy = 0;

  this.mass = 1.0;

  this.damping = 0.96;

​

  this.bFixed = false;

  this.bLimitVelocities = true;

  this.bPeriodicBoundaries = false;

  this.bHardBoundaries = false;

​

  // Initializer for the Particle

  this.set = function (x, y) {

    this.px = x;

    this.py = y;

    this.vx = 0;

    this.vy = 0;

    this.damping = 0.96;

    this.mass = 1.0;

  };

​

  // Add a force in. One step of Euler integration.

  this.addForce = function (fx, fy) {

    var ax = fx / this.mass;

    var ay = fy / this.mass;

    this.vx += ax;

    this.vy += ay;

  };

​

  this.setPos = function (x, y) {

    this.px = x;

    this.py = y;

  };

​

  // Update the position. Another step of Euler integration.

  this.update = function () {

    if (this.bFixed == false) {

      this.vx *= this.damping;

      this.vy *= this.damping;

​

      this.limitVelocities();

      this.handleBoundaries();

      this.px += this.vx;

      this.py += this.vy;

    }

  };

​

  this.limitVelocities = function () {

    if (this.bLimitVelocities) {

      var speed = sqrt(this.vx * this.vx + this.vy * this.vy);

      var maxSpeed = 10;

      if (speed > maxSpeed) {

        this.vx *= maxSpeed / speed;

        this.vy *= maxSpeed / speed;

      }

    }

  };

​

  this.handleBoundaries = function () {

    if (this.bPeriodicBoundaries) {

      if (this.px > width) this.px -= width;

      if (this.px < 0) this.px += width;

      if (this.py > height) this.py -= height;

      if (this.py < 0) this.py += height;

    } else if (this.bHardBoundaries) {

      if (this.px >= width) {

        this.vx = abs(this.vx) * -1;

      }

      if (this.px <= 0) {

        this.vx = abs(this.vx);

      }

      if (this.py >= height) {

        this.vy = abs(this.vy) * -1;

      }

      if (this.py <= 0) {

        this.vy = abs(this.vy);

      }

    }

  };

​

  this.render = function () {

    fill(255);

    ellipse(this.px, this.py, 2, 2);

  };

​

  this.spikes = function (centroidVector) {

    let normalLinepos = createVector(this.px, this.py);

    let normalLine = p5.Vector.sub(centroidVector, normalLinepos);

    normalLine.normalize().mult(-10);

    line(this.px, this.py, this.px + normalLine.x, this.py + normalLine.y);

  };

};

​

//==========================================================

var Spring = function Spring() {

  var p;

  var q;

  var restLength;

  var springConstant;

​

  this.set = function (p1, p2, k) {

    p = p1;

    q = p2;

    var dx = p.px - q.px;

    var dy = p.py - q.py;

    restLength = sqrt(dx * dx + dy * dy);

    springConstant = k;

  };

​

  this.update = function () {

    var dx = p.px - q.px;

    var dy = p.py - q.py;

    var dh = sqrt(dx * dx + dy * dy);

​

    if (dh > 1) {

      var distention = dh - restLength;

      var restorativeForce = springConstant * distention; // F = -kx

      var fx = (dx / dh) * restorativeForce;

      var fy = (dy / dh) * restorativeForce;

      p.addForce(-fx, -fy);

      q.addForce(fx, fy);

    }

  };

​

  this.render = function () {

    stroke(255);

    line(p.px, p.py, q.px, q.py);

  };

};

​

//==========================================================

var Edge = function Edge() {

  var p;

  var q;

  var restLength;

  var springConstant;

​

  this.set = function (p1, p2, k) {

    p = p1;

    q = p2;

    var dx = p.px - q.px;

    var dy = p.py - q.py;

    restLength = sqrt(dx * dx + dy * dy);

    springConstant = k;

  };

​

  this.update = function () {

    var dx = p.px - q.px;

    var dy = p.py - q.py;

    var dh = sqrt(dx * dx + dy * dy);

​

    if (dh > 1) {

      var distention = dh - restLength;

      var restorativeForce = springConstant * distention; // F = -kx

      var fx = (dx / dh) * restorativeForce;

      var fy = (dy / dh) * restorativeForce;

      p.addForce(-fx, -fy);

      q.addForce(fx, fy);

    }

  };

​

  this.render = function () {

    stroke(255);

    strokeWeight(2);

    line(p.px, p.py, q.px, q.py);

  };

};

​