C# 添加文字水印类

using System;
using System.Collections.Generic;
using System.Text;
using System.Drawing;
using System.IO;
using System.Drawing.Imaging;

namespace Chen
{
    public class warterfont
    {
        public void addtexttoimg(string filename, string text)
        {
            if (!File.Exists(System.Web.HttpContext.Current.Server.MapPath(filename)))
            {
                throw new FileNotFoundException("the file don't exist!");
            }
            if (text == string.Empty)
            {
                return;
            }
            //还需要判断文件类型是否为图像类型，这里就不赘述了

            Image image = Image.FromFile(System.Web.HttpContext.Current.Server.MapPath(filename));
            Bitmap bitmap = new Bitmap(image, image.Width, image.Height);
            Graphics g = Graphics.FromImage(bitmap);
            float fontsize = 12.0f; //字体大小
            float textwidth = text.Length * fontsize; //文本的长度

            //下面定义一个矩形区域，以后在这个矩形里画上白底黑字
            float rectx = 0;
            float recty = 0;
            float rectwidth = text.Length * (fontsize + 8);
            float rectheight = fontsize + 8; //声明矩形域
            RectangleF textarea = new RectangleF(rectx, recty, rectwidth, rectheight);
            Font font = new Font("宋体", fontsize); //定义字体
            Brush whitebrush = new SolidBrush(Color.White); //白笔刷，画文字用
            Brush blackbrush = new SolidBrush(Color.Black); //黑笔刷，画背景用
            g.FillRectangle(blackbrush, rectx, recty, rectwidth, rectheight);
            g.DrawString(text, font, whitebrush, textarea);
            MemoryStream ms = new MemoryStream(); //保存为jpg类型

            bitmap.Save(ms, ImageFormat.Jpeg); //输出处理后的图像，这里为了演示方便，我将图片显示在页面中了

            bitmap.Save(System.Web.HttpContext.Current.Server.MapPath("/" + "aa.jpg"), ImageFormat.Jpeg); //保存到磁盘上

            System.Web.HttpContext.Current.Response.Clear();
            System.Web.HttpContext.Current.Response.ContentType = "image/jpeg";
            System.Web.HttpContext.Current.Response.BinaryWrite(ms.ToArray());
            g.Dispose();
            bitmap.Dispose();
            image.Dispose();
        }
    }
}