drawCircle(particle) {
    if (particle.rgb) {
      this.context.fillStyle = `rgba(${particle.rgb.r},${particle.rgb.g},${particle.rgb.b},${particle.alpha})`;
    } else {
      this.context.fillStyle = particle.color;
    }

    this.context.beginPath();
    this.context.arc(particle.p.x, particle.p.y, particle.radius, 0, Math.PI * 2, true);

    if (this.stroke) {
      this.context.strokeStyle = this.stroke.color;
      this.context.lineWidth = this.stroke.thinkness;
      this.context.stroke();
    }

    this.context.closePath();
    this.context.fill();
  }
Draws a circular particle.
@param {object} particle - The particle to draw.
@private