{

  let k = n/d

  let r = cos(k*theta)

  let x = r*cos(theta)

  let y = r*sin(theta)

  return createVector(x, y)

}

​

// Daniel Shiffman

// http://codingtra.in

// https://youtu.be/CKeyIbT3vXI

​

class Particle {

  constructor(x, y, hu, firework, index, n, d) {

    this.pos = createVector(x, y);

    this.firework = firework;

    this.lifespan = 255;

    this.hu = hu;

    this.acc = createVector(0, 0);

    if (this.firework) {

      this.vel = createVector(0, random(-18, -8));

    } else {

      this.vel = rose(map(index, 0, 719, 0, TWO_PI*d), n, d);

      this.vel.mult(10);

    }

  }

​

  applyForce(force) {

    this.acc.add(force);

  }

​

  update() {

    if (!this.firework) {

      this.vel.mult(0.9);

      this.lifespan -= 4;

    }

    this.vel.add(this.acc);

    this.pos.add(this.vel);

    this.acc.mult(0);

  }

​

  done() {

    if (this.lifespan < 0) {

      return true;

    } else {

      return false;

    }

  }

​

  show() {

    colorMode(HSB);

​

    if (!this.firework) {

      strokeWeight(2);

      stroke(this.hu, 255, 255, this.lifespan);

    } else {

      strokeWeight(4);

      stroke(this.hu, 255, 255);

    }

​

    point(this.pos.x, this.pos.y);

  }

}