public static float GetViewportSizeForScrollAxis(this ScrollRect scroll)
        {
            float result;

            if (scroll.viewport == null)
            {
                result = scroll.GetRectSizeForScrollAxis();
            }
            else
            {
                result = (scroll.horizontal)
                    ? scroll.viewport.rect.width
                    : scroll.viewport.rect.height;
            }
            return(result);
        }