c# 直线插值

 /// <summary>
        /// 直线插值
        /// </summary>
        /// <param name="linePoints">点击</param>
        /// <param name="x">X插值点</param>
        /// <returns>插值的Y值</returns>
        public static double? LineInterpolation(List<PointF> linePoints, double x)
        {
            int? idx1 = null;
            for (int index = 0; index < linePoints.Count; index++)
            {
                PointF linePoint = linePoints[index];
                if (linePoint.X >= x)
                {
                    idx1 = index;
                    break;
                }
            }

            int? idx2 = null;
            for (int index = linePoints.Count - 1; index >= 0; index--)
            {
                PointF linePoint = linePoints[index];
                if (linePoint.X <= x)
                {
                    idx2 = index;
                    break;
                }
            }

            if (!idx1.HasValue || !idx2.HasValue)
            {
                return null;
            }

            PointF p1 = linePoints[idx1.Value];
            PointF p2 = linePoints[idx2.Value];

            if (idx1.Value == idx2.Value || idx1 == idx2)
            {
                return p1.Y;
            }

            double xDiff = p1.X - p2.X;
            double yDiff = p1.Y - p2.Y;

            double y = p1.Y + (x - p1.X) * yDiff / xDiff;

            return y;
        }