constructor(cr, f, speed) {

    this.x = [];

    this.y = [];

    this.fr = []; 

    this.f = f;

    this.cr = cr;

    this.speed = speed;

    this.angle = 0;

  }

  display() {

    push();

    blendMode(DIFFERENCE);

    noStroke();

    fill(255);

    beginShape();

    for (let i=0; i<pts; i++) {

      this.fr[i] = this.f*cos(period*360*i/pts); 

      this.x[i] = (this.cr+this.fr[i])*cos(i/pts*360 + this.angle);

      this.y[i] = (this.cr+this.fr[i])*sin(i/pts*360  + this.angle);

      vertex(this.x[i], this.y[i]);

    }

    endShape(CLOSE);

    pop();

    this.angle += this.speed;

  }

}