客户端js不能操作文件，所以只能先上传图片再在服务器端剪切。

1、上传图片

2、js剪切图片（其实只是选取要剪切的部分）

3、服务器端剪切

     （1）在页面的cs文件中剪切。须放几个隐藏控件以便回传js选取的坐标。

其中剪切图片源码：

Code
using System;
using System.Collections.Generic;
using System.Text;
using System.Drawing;

public class Cut
{
    /// <summary>
    /// 裁剪图片
    /// </summary>
    /// <param name="sourceImg">原图片路径</param>
    /// <param name="desImg">裁剪图片路径</param>
    /// <param name="left">X</param>
    /// <param name="top">Y</param>
    /// <param name="width">宽</param>
    /// <param name="height">高</param>
    public static void CutImage(string sourceImg, string desImg, int left, int top, int width, int height)
    {
        System.Drawing.Image img = System.Drawing.Bitmap.FromFile(sourceImg);
        System.Drawing.Image imgToSave = new System.Drawing.Bitmap(width, height);
        System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(imgToSave);
        RectangleF sourceRect = new RectangleF(left, top, width, height);
        RectangleF destinationRect = new RectangleF(0, 0, width, height);

        g.DrawImage(img,
                    destinationRect,
                    sourceRect,
                    GraphicsUnit.Pixel
                    );
        g.Save();
        imgToSave.Save(desImg, System.Drawing.Imaging.ImageFormat.Jpeg);
        g.Dispose();
        imgToSave.Dispose();
        img.Dispose();
    }

}

     （2）在ashx中剪切，可回传文件流。用参数传递坐标。

Code

using System;
using System.Web;
using System.Drawing;
using System.IO;

public class ImgCropper_WebHandler : IHttpHandler
{
    public void ProcessRequest(HttpContext context)
    {
        string Pic = Convert.ToString(context.Request["p"]);
        int PointX = Convert.ToInt32(context.Request["x"]);
        int PointY = Convert.ToInt32(context.Request["y"]);
        int CutWidth = Convert.ToInt32(context.Request["w"]);
        int CutHeight = Convert.ToInt32(context.Request["h"]);
        int PicWidth = Convert.ToInt32(context.Request["pw"]);
        int PicHeight = Convert.ToInt32(context.Request["ph"]);

        context.Response.ContentType = "image/jpeg";
        ResetImg(context, System.Web.HttpContext.Current.Server.MapPath(Pic), PicWidth, PicHeight, PointX, PointY, CutWidth, CutHeight).WriteTo(context.Response.OutputStream);
    }

    public MemoryStream ResetImg(HttpContext context, string ImgFile, int PicWidth, int PicHeight, int PointX, int PointY, int CutWidth, int CutHeight)
    {
        Image imgPhoto = Image.FromFile(ImgFile);
        Bitmap bmPhoto = new Bitmap(CutWidth, CutHeight, System.Drawing.Imaging.PixelFormat.Format24bppRgb);

        Graphics gbmPhoto = Graphics.FromImage(bmPhoto);
        gbmPhoto.DrawImage(imgPhoto, new Rectangle(0, 0, CutWidth, CutHeight), PointX * imgPhoto.Width / PicWidth, PointY * imgPhoto.Height / PicHeight, CutWidth * imgPhoto.Width / PicWidth, CutHeight * imgPhoto.Height / PicHeight, GraphicsUnit.Pixel);

        //保存图片到服务器
        bmPhoto.Save(context.Server.MapPath("upload/") + Guid.NewGuid() + ".jpg", System.Drawing.Imaging.ImageFormat.Jpeg);

        //生成文件流回传
        MemoryStream ms2 = new MemoryStream();
        bmPhoto.Save(ms2, System.Drawing.Imaging.ImageFormat.Jpeg);

        imgPhoto.Dispose();
        gbmPhoto.Dispose();
        bmPhoto.Dispose();

        return ms2;
    }

    public bool IsReusable
    {
        get
        {
            return false;
        }
    }
}

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