asp.net如何在图片上加水印文字具体实现

第一步，添加一个一般处理程序（Handler）,本例是ImageHandler

using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Net.Mime;
using System.IO;
using System.Drawing;
using System.Drawing.Imaging;
using System.Drawing.Drawing2D;

/// <summary>
/// Summary description for ImageHandler
/// </summary>
public class ImageHandler : IHttpHandler
{
 public ImageHandler()
 {
 }
 public string GetContentType(String path)
 {
 switch (Path.GetExtension(path))
 {
 case ".bmp": return "Image/bmp";
 case ".gif": return "Image/gif";
 case ".jpg": return "Image/jpeg";
 case ".png": return "Image/png";
 default: break;
 }
 return String.Empty;
 }
 public ImageFormat GetImageFormat(String path)
 {
 switch (Path.GetExtension(path).ToLower())
 {
 case ".bmp": return ImageFormat.Bmp;
 case ".gif": return ImageFormat.Gif;
 case ".jpg": return ImageFormat.Jpeg;
 case ".png": return ImageFormat.Png;
 default: return null;
 }
 }
 protected byte[] WatermarkImage(HttpContext context)
 {
 byte[] imageBytes = null;
 if (File.Exists(context.Request.PhysicalPath))
 {
 // Normally you'd put this in a config file somewhere.
 string watermark = "世复检测";
 Image image = Image.FromFile(context.Request.PhysicalPath);
 Graphics graphic;
 if (image.PixelFormat != PixelFormat.Indexed && image.PixelFormat != PixelFormat.Format8bppIndexed && image.PixelFormat != PixelFormat.Format4bppIndexed && image.PixelFormat != PixelFormat.Format1bppIndexed)
 {
 // Graphic is not a Indexed (GIF) image
 graphic = Graphics.FromImage(image);
 }
 else
 {
 /* Cannot create a graphics object from an indexed (GIF) image. 
 * So we're going to copy the image into a new bitmap so 
 * we can work with it. */
 Bitmap indexedImage = new Bitmap(image);
 graphic = Graphics.FromImage(indexedImage);
 // Draw the contents of the original bitmap onto the new bitmap. 
 graphic.DrawImage(image, 0, 0, image.Width, image.Height);
 image = indexedImage;
 }
 graphic.SmoothingMode = SmoothingMode.AntiAlias & SmoothingMode.HighQuality;
 Font myFont = new Font("Arial", 15);
 SolidBrush brush = new SolidBrush(Color.FromArgb(255, Color.Red));
 /* This gets the size of the graphic so we can determine 
 * the loop counts and placement of the watermarked text. */
 SizeF textSize = graphic.MeasureString(watermark, myFont);
 //// Write the text across the image. 
 //for (int y = 0; y < image.Height; y++)
 //{
 // for (int x = 0; x < image.Width; x++)
 // {
 // PointF pointF = new PointF(x, y);
 // graphic.DrawString(watermark, myFont, brush, pointF);
 // x += Convert.ToInt32(textSize.Width);
 // }
 // y += Convert.ToInt32(textSize.Height);
 //}

 // Write the text at the right bottom of the image. 
 for (int y = image.Height-25; y < image.Height; y++)
 {
 for (int x = image.Width-100; x < image.Width; x++)
 {
 PointF pointF = new PointF(x, y);
 graphic.DrawString(watermark, myFont, brush, pointF);
 x += Convert.ToInt32(textSize.Width);
 }
 y += Convert.ToInt32(textSize.Height);
 }
 using (MemoryStream memoryStream = new MemoryStream())
 {
 image.Save(memoryStream, GetImageFormat(context.Request.PhysicalPath));
 imageBytes = memoryStream.ToArray();
 }
 }
 return imageBytes;
 }
 #region IHttpHandler Members
 public bool IsReusable
 {
 get { return false; }
 }
 public void ProcessRequest(HttpContext context)
 {
 context.Response.Clear();
 context.Response.ContentType = GetContentType(context.Request.PhysicalPath);
 byte[] imageBytes = WatermarkImage(context);
 if (imageBytes != null)
 {
 context.Response.OutputStream.Write(imageBytes, 0, imageBytes.Length);
 }
 else
 {
 // No bytes = no image which equals NO FILE. 
 // Therefore send a 404 - not found response. 
 context.Response.StatusCode = 404;
 }
 context.Response.End();
 }
 #endregion
}

第二步，在web.config里添加如下代码：

 <httpHandlers>
 <!--<add verb="GET" type="ImageHandler" path="*.jpg,*.png,*.gif,*.bmp"/>-->
 <add verb="GET" type="ImageHandler" path="Uploads/*/*.jpg"/> 
 </httpHandlers>

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