private function createEllipse($color)
    {
        $alpha = imagecolorallocatealpha($this->resource, 255, 255, 255, 127);
        imagefill($this->resource, 0, 0, $alpha);

        imagefilledellipse(
            $this->resource,
            $this->width / 2,
            $this->height / 2,
            $this->width,
            $this->height,
            $color
        );
    }