private int[] GetRectangleIndices(List <UIVertex> vertices, int[] hexIndices)
        {
            if (hexIndices.Length != 6)
            {
                return(null);
            }
            var result = hexIndices.Distinct().ToArray();

            if (result.Length != System.Enum.GetValues(typeof(RectangleIndex)).Length)
            {
                return(null);
            }
            var upperLeftPosition  = new Vector2(float.MaxValue, float.MinValue);
            var lowerRightPosition = new Vector2(float.MinValue, float.MaxValue);

            foreach (var position in hexIndices.Select(x => vertices[x].position))
            {
                upperLeftPosition.x  = Mathf.Min(upperLeftPosition.x, position.x);
                upperLeftPosition.y  = Mathf.Max(upperLeftPosition.y, position.y);
                lowerRightPosition.x = Mathf.Max(lowerRightPosition.x, position.x);
                lowerRightPosition.y = Mathf.Min(lowerRightPosition.y, position.y);
            }
            foreach (var index in hexIndices)
            {
                var position       = vertices[index].position;
                var rectangleIndex = 0;
                if (position.x == upperLeftPosition.x)
                {
                    rectangleIndex = 0x0;
                }
                else if (position.x == lowerRightPosition.x)
                {
                    rectangleIndex = 0x1;
                }
                else
                {
                    return(null);
                }
                if (position.y == upperLeftPosition.y)
                {
                    rectangleIndex ^= 0x0;
                }
                else if (position.y == lowerRightPosition.y)
                {
                    rectangleIndex ^= 0x3;
                }
                else
                {
                    return(null);
                }
                result[rectangleIndex] = index;
            }
            return(result);
        }