void Update()
{
    if (Input.touchCount > 0 && Input.GetTouch(0).phase == TouchPhase.Moved)
    {
        // Control sliding using touch input.
        Vector2 touchDeltaPosition = Input.GetTouch(0).deltaPosition;
        transform.Translate(touchDeltaPosition.x * slidingSpeed, 0, 0);
    }
    transform.position = new Vector3 (Mathf.Clamp(transform.position.x, - xPosLimit, xPosLimit), transform.position.y, transform.position.z);
}