c# 渐变算法

        /// <summary>
        /// 渐变算法
        /// </summary>
        /// <param name="sourceImg">位图源(物理路径)</param>
        /// <param name="colorHead">起点色(HTML格式)</param>
        /// <param name="colorTail">终点色(HTML格式)</param>
        /// <param name="imgPath">保存图片路径(物理路径)</param>
        public static void LinearGradient(string sourceImg, string destinationImg, string colorHead, string colorTail)
        {
            using (Image img = Image.FromFile(sourceImg))
            {
                int width = img.Width;
                RGB colorBegin = RGB.Split(colorHead);
                RGB colorEnd = RGB.Split(colorTail);
                decimal diffR = 1m;
                decimal diffG = 1m;
                decimal diffB = 1m;
                //三原色改变步长
                diffR = Math.Round(Convert.ToDecimal(Convert.ToDecimal(colorEnd.Red - colorBegin.Red) / width), 2);
                diffG = Math.Round(Convert.ToDecimal(Convert.ToDecimal(colorEnd.Green - colorBegin.Green) / width), 2);
                diffB = Math.Round(Convert.ToDecimal(Convert.ToDecimal(colorEnd.Blue - colorBegin.Blue) / width), 2);
                RGB rgb = new RGB();
                for (int i = 0; i < width; i++)
                {
                    rgb.Red = colorBegin.Red + Convert.ToInt32(diffR * i);
                    rgb.Green = colorBegin.Green + Convert.ToInt32(diffG * i);
                    rgb.Blue = colorBegin.Blue + Convert.ToInt32(diffB * i);
                    DrawItem(img, 254, rgb, i, 1, img.Height);
                }
                img.Save(destinationImg);
            }
        }

        /// <summary>
        /// 先平滑再渐变
        /// </summary>
        /// <param name="sourceImg">位图源(物理路径)</param>
        /// <param name="destinationImg">保存图片路径(物理路径)</param>
        /// <param name="flowWidth">平滑过渡宽度(以起点色为画笔颜色,在0-flowWidth的X坐标内不变色)</param>
        /// <param name="transformWidth">渐变宽度(从flowWidth向后开始渐变,宽度为transformWidth)</param>
        /// <param name="colorHead">起点色(HTML格式)</param>
        /// <param name="colorTail">终点色(HTML格式)</param>
        public static void LinearGradient(string sourceImg, string destinationImg, int flowWidth, int transformWidth, string colorHead, string colorTail)
        {
            using (Image img = Image.FromFile(sourceImg))
            {
                int width = img.Width;
                int height = img.Height;
                if (flowWidth > width)
                {
                    flowWidth = width - 1;
                }
                if (transformWidth > width - flowWidth)
                {
                    transformWidth = width - flowWidth;
                }
                RGB colorBegin = RGB.Split(colorHead);
                RGB colorEnd = RGB.Split(colorTail);
                decimal diffR = 1m;
                decimal diffG = 1m;
                decimal diffB = 1m;
                diffR = Math.Round(Convert.ToDecimal(Convert.ToDecimal(colorEnd.Red - colorBegin.Red) / transformWidth), 2);
                diffG = Math.Round(Convert.ToDecimal(Convert.ToDecimal(colorEnd.Green - colorBegin.Green) / transformWidth), 2);
                diffB = Math.Round(Convert.ToDecimal(Convert.ToDecimal(colorEnd.Blue - colorBegin.Blue) / transformWidth), 2);
                int alphaLength = 255, alpha = 254;
                //alpha值改变步长
                decimal diffA = Math.Round(Convert.ToDecimal(alphaLength / transformWidth), 2);
                //画平滑部分
                RGB rgb = colorBegin;
                DrawItem(img, alpha, rgb, 0, flowWidth, height);
                for (int i = 0; i < transformWidth; i++)
                {
                    //开始渐变
                    rgb.Red += Convert.ToInt32(diffR * i);
                    rgb.Green += Convert.ToInt32(diffG * i);
                    rgb.Blue += Convert.ToInt32(diffB * i);
                    alpha -= Convert.ToInt32(diffA);
                    alpha = Correct(alpha);
                    //alpha--;
                    DrawItem(img, alpha, rgb, i + flowWidth, 1, height);
                }
                img.Save(destinationImg);
            }
        }
        /// <summary>
        /// 单元填充操作(include alpha)
        /// </summary>
        /// <param name="img">位图源</param>
        /// <param name="alpha">alpha透明度</param>
        /// <param name="color">RGB颜色值</param>
        /// <param name="left">X坐标</param>
        /// <param name="width">画笔宽度</param>
        /// <param name="height">画笔高度</param>
        private static void DrawItem(Image img, int alpha, RGB color, int left, int width, int height)
        {
            using (Graphics g = Graphics.FromImage(img))
            {
                g.FillRectangle(new SolidBrush(Color.FromArgb(alpha, color.Red, color.Green, color.Blue)), new Rectangle(left, 0, width, height));
            }
        }

/// <summary>
    /// 颜色的10进制RGB值
    /// </summary>
    public struct RGB
    {
        /// <summary>
        /// 从HTML颜色值分离出10进制RGB值(如#000000->0,0,0)
        /// </summary>
        /// <param name="color"></param>
        /// <returns></returns>
        public static RGB Split(string color)
        {
            RGB rgb = new RGB();
            rgb.Red = Convert.ToInt32(color.Substring(1, 2), 16);
            rgb.Green = Convert.ToInt32(color.Substring(3, 2), 16);
            rgb.Blue = Convert.ToInt32(color.Substring(5, 2), 16);
            return rgb;
        }
        /// <summary>
        /// 将10进制RGB值合并为HTML颜色值(如255,255,255->#ffffff)
        /// </summary>
        /// <param name="rgb">颜色RGB</param>
        /// <returns></returns>
        public static string Join(RGB rgb)
        {
            string red = Convert.ToString(rgb.Red, 16).PadLeft(2, '0');
            string green = Convert.ToString(rgb.Green, 16).PadLeft(2, '0');
            string blue = Convert.ToString(rgb.Blue, 16).PadLeft(2, '0');
            return String.Concat("#", red, green, blue);
        }

        private int red, green, blue;

        public int Red
        {
            set { red = GDIUtility.Correct(value); }
            get { return red; }
        }
        public int Green
        {
            set { green = GDIUtility.Correct(value); }
            get { return green; }
        }
        public int Blue
        {
            set { blue = GDIUtility.Correct(value); }
            get { return blue; }
        }
    }