constructor(r, c) {

    this.x = [];

    this.y = [];

    this.radius = [];

    this.a = 0;

    this.r = r;

    this.c = c;

  }

  display(startingAngle, a) {

    push();

    blendMode(DIFFERENCE);

    noFill();

    noStroke();

    // stroke(0);

    fill(this.c);

    beginShape();

    for (let i=0; i<num; i++) {

      this.radius[i] = 15*cos(period*360*i/num); 

      this.x[i] = (this.r+this.radius[i])*cos(map(i, 0, num, 0, 360) + this.a);

      this.y[i] = (this.r+this.radius[i])*sin(map(i, 0, num, 0, 360) + this.a);

      vertex(this.x[i], this.y[i]);

    }

    endShape(CLOSE);

    pop();

    this.a += a;

  }

}