ctx.beginPath();
ctx.lineWidth = 1;

ctx.translate(this.cx, this.cy);               // translate to pivot

if (this.toAngle !== this.angle) {
  ctx.rotate(this.toAngle - this.angle);
}

ctx.strokeStyle = this.color;
ctx.arc(0, 0, this.radius, 0, Math.PI * 2);    // render at pivot

ctx.closePath();                               // must come before stroke() btw.
ctx.stroke();

ctx.beginPath();
ctx.fillStyle = 'black';
ctx.fillRect(-this.radius / 4, -this.radius / 4, 20, 20);  // render at pivot