C# 添加文字水印类代码

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();
}
}
}