let g = 40;

let N = 20;

​

let pendulums = [];

​

​

class Pendulum {

  constructor(oX, oY, t1, t2, v1, v2, m1, m2, c, L) {

    this.oX = oX;

    this.oY = oY;

    this.t1 = t1;

    this.t2 = t2;

    this.v1 = v1;

    this.v2 = v2;

    this.a1 = 0;

    this.a2 = 0;

    this.m1 = m1;

    this.m2 = m2;

    this.c = c;

    this.L = L;

    this.path = [];

  }

  update() {

    let denom = this.L*(2*this.m1 + this.m2 - this.m2 * cos(2*(this.t1 - this.t2)));

    this.t1 += this.v1 * dt + 0.5 * this.a1 * dt * dt;

    this.t2 += this.v2 * dt + 0.5 * this.a2 * dt * dt;

​

    this.v1 += 0.5 * this.a1 * dt;

    this.v2 += 0.5 * this.a2 * dt;

​

    this.a1 = -g*(2*this.m1 + this.m2)*sin(this.t1) - this.m2*g*sin(this.t1 - 2*this.t2) - 2*this.m2*sin(this.t1 - this.t2)*(this.v2*this.v2*this.L + this.v1*this.v1*this.L*cos(this.t1 - this.t2));

    this.a1 /= denom;

​

    this.a2 = 2*sin(this.t1 - this.t2)*(this.v1*this.v1*this.L*(this.m1 + this.m2) + g*(this.m1 + this.m2)*cos(this.t1) + this.v2*this.v2*this.L*this.m2 * cos(this.t1 - this.t2));

    this.a2 /= denom;

​

    this.v1 += 0.5 * this.a1 * dt;

    this.v2 += 0.5 * this.a2 * dt;

​

    this.v1 *= 0.999

    this.v2 *= 0.999

  }

  show () {

    push()

    translate(this.oX, this.oY);

    let pos = this.theta_to_x(this.t1, this.t2);

    this.path.push(pos);

​

    stroke(0, this.c, 255)

    strokeWeight(2)

    line(0, 0, pos[0][0], pos[0][1]);

    line(pos[0][0], pos[0][1], pos[1][0], pos[1][1]);

​

    strokeWeight(5)

    stroke(this.c)

    // point(0,0);

    // point(pos[0][0], pos[0][1]);

    // point(pos[1][0], pos[1][1]);

​

    for(let i = 0; i < this.path.length; ++i) {

      let pos = this.path[i];

      strokeWeight(map(i, 0, this.path.length, 0.5, 2));

​

      // stroke(this.c + 10)

      // point(pos[0][0], pos[0][1]);

          stroke(0, this.c, 255)

​

      point(pos[1][0], pos[1][1]);  

    }

​

    if(this.path.length >= 100) {

      this.path.shift();

    }

    pop();

  }

  theta_to_x(t1, t2) {

    let x1 = sin(t1)*this.L;

    let y1 = cos(t1)*this.L;

    let x2 = x1 + sin(t2)*this.L;

    let y2 = y1 + cos(t2)*this.L;

    return [[x1, y1], [x2, y2]];

  }

}

​

function setup() {

  createCanvas(windowWidth, windowHeight);

  let oX = windowWidth/2;

  let oY = windowHeight/2;

  let L = min(width, height) / 4 - 20;

  for(let i = 0; i < N; ++i)  {

    let t1 = 0;

    let t2 = 0;

    let a1 = 0;

    let a2 = 0;

    let v1 = map(i, 0, 20, 0.9, 1);

    let v2 = map(i, 0, 20, -2, -1.9);

    let m1 = 1;

    let m2 = 1;

    let c = map(i, 0, 20,50, 150);

    pendulums.push(new Pendulum(oX, oY, t1, t2, v1, v2, m1, m2, c, L));

  }

}

​

function draw() {

  background(220,220, 220, 30);

  for(let p of pendulums) {

    p.update();

    p.show();

  }

}