Asp.net 上传图片添半透明图片或文字水印的方法（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：

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 (!System.IO.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 (System.IO.File.Exists(ImageToBePainted))
System.IO.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

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.PostedFile.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();
}

}
}