ellipse(x, y, horizontal_radius, vertical_radius) {
        this.ctx.save();

        this.ctx.translate(x - horizontal_radius, y - vertical_radius);
        this.ctx.scale(horizontal_radius, vertical_radius);
        this.ctx.moveTo(2, 1);
        this.ctx.arc(1, 1, 1, 0, 2 * Math.PI, false);

        this.ctx.restore();
    }
@param {!number} x The x-coordinate of the center of the ellipse.
@param {!number} y The y-coordinate of the center of the ellipse.
@param {!number} horizontal_radius The horizontal distance from the center of the ellipse to its side.
@param {!number} vertical_radius The vertical distance from the center of the ellipse to its side.