* @param y1 a corner of the enclosing rectangle
     * @param x2 a corner of the enclosing rectangle
     * @param y2 a corner of the enclosing rectangle
     */
    public void ellipse(final float x1, final float y1, final float x2, final float y2) {
        arc(x1, y1, x2, y2, 0f, 360f);
    }