[C#] ASP.NET 上传图片添加半透明图片或者文字水印的方法(一)

主要用到System.Drawing 命名空间下的相关类，如Brush、Image、Bitmap、Graphics等等类

Image类可以从图片文件创建Image的实例，Bitmap可以从文件也可以从已有的Image对象创建实例，而Graphics类则是封装了对图像的相关操作，可以理解为一个绘图的面板，在这个面板里你可以添加文字，添加背景等等很多常规绘图软件具备的功能。

下面就怎样添加水印做简单的介绍：

为了方便理解我把水印分为文字型的水印以及图片型的水印，它们都派生自WatermarkPainter基类，需要实现基类中的AddWatermark的方法，这个方法是用来具体的绘图用。

WatermarkPainter类如下：

/* ***********************************************
* Author:          Raymond Tang
* Team:             Juice Sharing
* Created Time:     2009-3-11 13:33:13
* CopyRight:        Juice Sharing 团队版权所有 保留一切权利
* NameSpace:        Juice.Common.Drawing
* Class/Interface: WatermarkPainter
* ***********************************************/
using System.Drawing;
using System.IO;
using System.Text;
using System;
namespace Juice.Common.Drawing
{
     /// <summary>
     /// 图片水印绘制器
     /// </summary>
     public abstract class WatermarkPainter : IDisposable
     {
         /// <summary>
         /// 构造函数
         /// </summary>
         /// <param name="rawImagePath"></param>
         /// <param name="alpha"></param>
         /// <param name="replaceRawImage"></param>
         protected WatermarkPainter(string rawImagePath, int alpha, bool replaceRawImage)
         {
             ImageToBePainted = rawImagePath;
             WatermarkAlpha = alpha;
             ReplaceRawImage = replaceRawImage;
         }
         /// <summary>
         /// 构造函数
         /// </summary>
         /// <param name="rawImagePath"></param>
         /// <param name="alpha"></param>
         protected WatermarkPainter(string rawImagePath, int alpha)
             : this(rawImagePath, alpha, true)
         { }
         /// <summary>
         /// 为临时存储文件添加的后缀
         /// </summary>
         private string m_TempFileSuffix = ".juice.watermark.temp";
         /// <summary>
         /// 水印的透明度
         /// </summary>
         private int m_WatermarkAlpha;
         /// <summary>
         /// 水印透明度
         /// </summary>
         public int WatermarkAlpha
         {
             get
             {
                 if (m_WatermarkAlpha > 255)
                     m_WatermarkAlpha = 255;
                 else if (m_WatermarkAlpha < 0)
                     m_WatermarkAlpha = 0;
                 return m_WatermarkAlpha;
             }
             set { m_WatermarkAlpha = value; }
         }
         private string m_ImageToBePainted;
         /// <summary>
         /// 添加水印的图片的物理路径
         /// </summary>
         public string ImageToBePainted
         {
             get { return m_ImageToBePainted; }
             set { m_ImageToBePainted = value; }
         }
         private bool m_ReplaceRawImage;
         /// <summary>
         /// 是否用加了水印的图片替换原有的图片
         /// </summary>
         public bool ReplaceRawImage
         {
             get { return m_ReplaceRawImage; }
             set { m_ReplaceRawImage = value; }
         }
         private string m_TempImagePath;
         /// <summary>
         /// 加了水印后的临时储存名称
         /// </summary>
         protected string TempImagePath
         {
             get
             {
                 if (string.IsNullOrEmpty(this.m_TempImagePath))
                 {
                     StringBuilder s = new StringBuilder(ImageToBePainted);
                     s.Append(this.m_TempFileSuffix);
                     this.m_TempImagePath = s.ToString();
                 }
                 return m_TempImagePath;
             }
             set { m_TempImagePath = value; }
         }
         /// <summary>
         /// 原始图像
         /// </summary>
         private Image m_RawImage;
         /// <summary>
         /// 为图片添加水印
         /// </summary>
         public void PaintWaterMark()
         {
             if (string.IsNullOrEmpty(ImageToBePainted))
                 return;
             if (!File.Exists(ImageToBePainted))
                 throw new FileNotFoundException(string.Format("file {0} not found.", ImageToBePainted));
             bool succeed;
             if (m_RawImage == null)
                 m_RawImage = Image.FromFile(ImageToBePainted);
             ///原始的图片
             using (Bitmap newImage = new Bitmap(m_RawImage.Width, m_RawImage.Height))
             {
                 ///创建绘制图片的图面
                 using (Graphics g = Graphics.FromImage(newImage))
                 {
                     g.DrawImage(m_RawImage, 0, 0, m_RawImage.Width, m_RawImage.Height);
                     ///开始绘制水印
                     succeed = AddWatermark(g, newImage);
                 }
                 if (succeed)
                     ///将图片保存到临时的文件
                     newImage.Save(TempImagePath);
                 if (m_RawImage != null)
                     m_RawImage.Dispose();
             }
             if (succeed && ReplaceRawImage)
             {
                 //删除原来的文件
                 if (File.Exists(ImageToBePainted))
                     File.Delete(ImageToBePainted);
                 FileInfo info = new FileInfo(TempImagePath);
                 if (info.Exists)
                 {
                     info.MoveTo(ImageToBePainted);
                 }
             }
         }
         /// <summary>
         /// 添加水印，继承类可以用来添加自己的水印
         /// </summary>
         /// <param name="graphics"></param>
         /// <param name="newImage"></param>
         /// <returns></returns>
         protected abstract bool AddWatermark(Graphics graphics, Bitmap newImage);
         #region IDisposable 成员
         public virtual void Dispose()
         {
             
         }
         #endregion
     }
}

而文字型的水印的类是TextWatermarkPainter类

/* ***********************************************
* Author:          Raymond Tang
* Team:             Juice Sharing
* Created Time:     2009-3-11 15:15:16
* CopyRight:        Juice Sharing 团队版权所有 保留一切权利
* NameSpace:        Juice.Common.Drawing
* Class/Interface: TextWatermarkPainter
* ***********************************************/
using System.Drawing;
using System.IO;
using System.Text;
using System;
namespace Juice.Common.Drawing
{
     /// <summary>
     /// 添加文字水印
     /// </summary>
     public sealed class TextWatermarkPainter : WatermarkPainter
     {
         /// <summary>
         /// 构造函数
         /// </summary>
         /// <param name="rawImagePath"></param>
         /// <param name="alpha"></param>
         /// <param name="text"></param>
         public TextWatermarkPainter(string rawImagePath, int alpha, string text)
             : base(rawImagePath, alpha)
         {
             WatermarkText = text;
         }
         private Font m_Font;
         /// <summary>
         /// 水印文字的字体
         /// </summary>
         public Font Font
         {
             get
             {
                 if (null == m_Font)
                     m_Font = new Font("Arial Black", 14, FontStyle.Bold, GraphicsUnit.Pixel);
                 return m_Font;
             }
             set { m_Font = value; }
         }
         private Color m_FontColor;
         /// <summary>
         /// 字体颜色
         /// </summary>
         public Color FontColor
         {
             get
             {
                 if (m_FontColor == null)
                     m_FontColor = Color.DarkSeaGreen;
                 return m_FontColor;
             }
             set { m_FontColor = value; }
         }
         private string m_WatermarkText;
         /// <summary>
         /// 水印的文字
         /// </summary>
         public string WatermarkText
         {
             get { return m_WatermarkText; }
             set { m_WatermarkText = value; }
         }
         /// <summary>
         /// 实现添加水印的方法
         /// </summary>
         /// <param name="graphics"></param>
         /// <param name="newImage"></param>
         /// <returns></returns>
         protected override bool AddWatermark(Graphics graphics, Bitmap newImage)
         {
             if (string.IsNullOrEmpty(WatermarkText))
                 return true;
             using (SolidBrush brush = new SolidBrush(Color.FromArgb(WatermarkAlpha, FontColor.R, FontColor.G, FontColor.B)))
             {
                 Font font;
                 ///添加文字位置
                 PointF f = new PointF();
                 float totalWidth = Font.Size * WatermarkText.Length;
                 f.X = newImage.Width - totalWidth - 100;
                 f.Y = newImage.Height - Font.Height;
                 if (f.X < 0)
                 {
                     ///自动调整字体的大小
                     float width = newImage.Width / WatermarkText.Length;
                     font = new Font(Font.FontFamily, width, GraphicsUnit.Pixel);
                 }
                 else
                     font = Font;
                 graphics.DrawString(WatermarkText, font, brush, f);
             }
             return true;
         }
         #region IDisposable 成员
         public override void Dispose()
         {
             Font.Dispose();
             base.Dispose();
         }
         #endregion
     }
}

下面是对文字型水印的测试：

default.aspx内容如下：

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
     <title>无标题页</title>
</head>
<body>
     <form id="form1" runat="server">
     <div>
         水印文字:<asp:TextBox ID="watermarkTextBox" runat="server"></asp:TextBox><br />
         选择上传图片:<asp:FileUpload ID="FileUpload1" runat="server" Width="189px" />
         <br />
         <asp:Button ID="uploadFileBtn" runat="server" Text="上传图片并且加文字水印" 
             onclick="uploadFileBtn_Click" />
         <br />加了水印的图像如下：
         <asp:Image ID="image" runat="server" />
     </div>
     </form>
</body>
</html>

default.aspx.cs代码如下：

using System;
using System.Configuration;
using System.Data;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using Juice.Common.Drawing;
using System.Web.Hosting;
public partial class _Default : System.Web.UI.Page
{
     protected void Page_Load(object sender, EventArgs e)
     {
     }
     protected void uploadFileBtn_Click(object sender, EventArgs e)
     {
         if (string.IsNullOrEmpty(this.watermarkTextBox.Text))
             return;
         if (FileUpload1.HasFile)
         {
             string contentType = FileUpload1.PostedFile.ContentType;
             if (contentType.StartsWith("image/"))
             {
                 string filePath = Server.MapPath(string.Format("~/{0}", FileUpload1.FileName));
                 ///保存文件
                 FileUpload1.SaveAs(filePath);
                 ///加水印
                 this.AddWatermark(filePath, this.watermarkTextBox.Text);
                 image.ImageUrl = string.Format("~/{0}", FileUpload1.PostedFile.FileName);
             }
         }
     }
     /// <summary>
     /// 添加水印
     /// </summary>
     /// <param name="filePath"></param>
     /// <param name="watermaterText"></param>
     private void AddWatermark(string filePath, string watermaterText)
     {
         using (TextWatermarkPainter painter = new TextWatermarkPainter(filePath, 80, watermaterText))
         {
             painter.FontColor = System.Drawing.Color.DarkGreen;
             painter.PaintWaterMark();
         }
     }
}

效果如下：