使用JQuery插件Jcrop进行图片截取

    <div class="item">
        <h3>
            5、上传头像实例（预览\截取）
        </h3>
        <!--图片上传表单，读者也可以选择其他的上传方式-->
        <form id="form_upload" enctype="multipart/form-data" action="./UploadPhoto" method="post">
            <input id="File5" name="UserPhoto" type="file" value="" />
            <input id="btnUpload5" type="submit" value="提交上传"  />
        </form>
        
        <!--截取主要内容区-->
        <div id="photoWrap">
            
            <!--截取区-->
            <div id="crop_area">
                <img id="crop_img" alt="头像" style="display: none"/>
            </div>

            <!--预览区，我这里做了两个规格的预览 48*48 180*180 -->
            <div id="preview_area">
                <div id="preview_title">当前头像</div>
                <div id="preview_small_txt">48px × 48px</div>
                <div id="preview_small_wrap">
                    <img id="preview_small_img" alt="小预览图" src="~/Content/default_48.png"/>
                </div>
                <div id="preview_large_txt">180px × 180px</div>
                <div id="preview_large_wrap">
                    <img id="preview_large_img" alt="大预览图" src="~/Content/default_180.png"/>
                </div>
            </div>
        </div>
        
        <!--截取框坐标点数据保存区，同时也是请求后台截取接口的表单-->
        <div id="crop_operation">
            <form id="form_crop" action="./CropPhoto" method="post">
                <input id="url" type="hidden" name="url" />
                <input id="x" type="hidden" name="x" />
                <input id="y" type="hidden" name="y" />
                <input id="w" type="hidden" name="w" />
                <input id="h" type="hidden" name="h" />
                <input id="btn_crop" type="submit" value="裁剪并保存" />
            </form>
        </div>
    </div>

//jcrop 所需参数
var jcrop_api;
var boundx;
var boundy;

//上方是必选参数
//下方是用于截取预览图的参数，可选的
//我这里设置了48*48 180*180 两种规格的预览效果
var $pimg_small;
var $pimg_large; 
        
var xsize_small = 48;
var ysize_small = 48;
var xsize_large = 180;
var ysize_large = 180;

$(function() {
    $pimg_small = $(‘#preview_small_img‘);
    $pimg_large = $(‘#preview_large_img‘);
});

    //上传图片
    $(‘#form_upload‘).ajaxForm({
        dataType: "json",
        data:$(‘#form_upload‘).serialize(),
        success: function (data, textStatus, jqXHR) {
            if (data.Status == ‘success‘) {
                //上传成功后，为主截取区、截取预览区的img赋值
                $("#crop_img,#preview_small_img,#preview_large_img").attr(‘src‘, data.ImgUrl);
                //用input hidden保存返回值，以便截取时使用
                $("#url").val(data.ImgUrl);

                //if (jcrop_api != null) {
                //    jcrop_api.setImage(data.ImgUrl, function () {
                //        var bounds = jcrop_api.getBounds();
                //        boundx = bounds[0];
                //        boundy = bounds[1];
                //        var size = Math.min(boundx, boundy);
                //        jcrop_api.setSelect([0,0,size,size]);
                //    });
                //}
                return;
            }
            if (data.Status == ‘error‘) {
                showMessage(data.Msg);
            }
        },
        error: function (jqXHR, textStatus, errorThrown) {
            showMessage(‘上传失败‘);
            console.error(textStatus);
        }
    });

    //当图片加载完毕时，调用Jcrop初始化函数
    //因为存在多次上传图片的情况，所以此处用<img/>标签的load事件，每加载完毕一次就初始化一次
    $("#crop_img").load(function () {
        $("#crop_img").Jcrop({
            onChange: updatePreview,//截取框变化事件，主要用于实时更新预览图
            onSelect: updateCropData,//截取框选定事件，主要用于获得截取框的4个坐标点
            aspectRatio: 1 //截取框的比例，1则是正方形
        }, function () {
            //$().Jcrop()初始化后的回调函数；
            //这里为提高用户体验而设置了一个可选范围内最大的截取框，以告诉用户“你可以进行截取了”。
            jcrop_api = this;
            var bounds = this.getBounds();//获取图片实际尺寸，格式为：[w,h]
            boundx = bounds[0];
            boundy = bounds[1];

            var size = Math.min(boundx, boundy);
            jcrop_api.setSelect([0, 0, size, size]);//4个坐标点设定一个截取框
        });
    });

//更新预览图，这函数是官方demo给出的代码，各位可以直接copy不必深究
function updatePreview(c) {
    if (parseInt(c.w) > 0) {
        var rx_large = xsize_large / c.w;
        var ry_large = ysize_large / c.h;

        $pimg_large.css({
            width: Math.round(rx_large * boundx) + ‘px‘,
            height: Math.round(ry_large * boundy) + ‘px‘,
            marginLeft: ‘-‘ + Math.round(rx_large * c.x) + ‘px‘,
            marginTop: ‘-‘ + Math.round(ry_large * c.y) + ‘px‘
        });

        var rx_small = xsize_small / c.w;
        var ry_small = ysize_small / c.h;

        $pimg_small.css({
            width: Math.round(rx_small * boundx) + ‘px‘,
            height: Math.round(ry_small * boundy) + ‘px‘,
            marginLeft: ‘-‘ + Math.round(rx_small * c.x) + ‘px‘,
            marginTop: ‘-‘ + Math.round(ry_small * c.y) + ‘px‘
        });
    }
};

//截取框选定事件的处理函数，用于实时更新4个坐标点
function updateCropData(c) {
    jQuery("#x").val(c.x);
    jQuery("#y").val(c.y);
    jQuery("#w").val(c.w);
    jQuery("#h").val(c.h)

    console.group(‘updateCropData‘);
    console.info(c.x)
    console.info(c.y)
    console.info(c.w)
    console.info(c.h)
    console.groupEnd(‘updateCropData‘);
}


    //请求后台接口，进行真正的图片截取
    //因为4个坐标点是由updateCropData()函数实时更新至<form id="form_crop"/>的隐藏域里的，
    //所以这里只要提交表单即可，这里是使用了jquery.form.js插件，我上一篇文章中有提到jquery.form.js的使用
    $(‘#form_crop‘).ajaxForm({
        dataType: "json",
        success: function (data, textStatus, jqXHR) {
            if (data.Status == ‘success‘) {
                showMessage(‘保存成功‘);
                jcrop_api.destroy();//上传成功后释放jcrop
                return;
            }
            if (data.Status == ‘error‘) {
                showMessage(data.Msg);
            }
        },
        error: function (jqXHR, textStatus, errorThrown) {
            showMessage(‘请求错误‘);
            console.error(textStatus);
        }
    });

        [HttpPost]
        public ActionResult UploadPhoto()
        {
            HttpPostedFileBase file = Request.Files["UserPhoto"];
            string contentType = file.ContentType;
            string extension = Path.GetExtension(file.FileName);

            //检查图片格式
            if (!IsAllowImg(contentType, extension))
            {
                return Json(new { Status = "error", Msg = "上传文件格式不符合要求。" });
            }

            //保存形成保存路径
            TimeSpan ts = DateTime.UtcNow - new DateTime(1970, 1, 1, 0, 0, 0, 0);
            string newFileName = Convert.ToInt64(ts.TotalMilliseconds).ToString(CultureInfo.InvariantCulture) + new Random().Next(100, 999);
            string path = Server.MapPath("~/Upload/") + newFileName + ".jpeg";

            //压缩图片、转换格式（jpeg）
            Image ResourceImage = Image.FromStream(file.InputStream);
            if(ResourceImage.Width>300)
            {
                int dWidth = 300;
                int dHeight = 300 * ResourceImage.Height / ResourceImage.Width;
                CompressPicture(file.InputStream, path, dWidth, dHeight,100);
            }
            else
            {
                CompressPicture(file.InputStream, path, ResourceImage.Width, ResourceImage.Height, 100);
            }
            file.InputStream.Close();

            string url = Request.ApplicationPath + "Upload/" + newFileName + ".jpeg";
            return Json(new { Status = "success", Msg = "上传成功",ImgUrl= url });
        }


        #region 压缩图像
        /// <summary>
        /// 无损压缩图片
        /// </summary>
        /// <param name="inputStream">原图片</param>
        /// <param name="dFile">压缩后保存位置</param>
        /// <param name="dWidth">宽度</param>
        /// <param name="dHeight">高度</param>
        /// <param name="flag">压缩质量 1-100</param>
        /// <returns></returns>
        public bool CompressPicture(Stream inputStream, string dFile,  int dWidth, int dHeight, int flag)
        {
            System.Drawing.Image iSource = System.Drawing.Image.FromStream(inputStream);
            ImageFormat tFormat = iSource.RawFormat;
            int sW = 0, sH = 0;
            //按比例缩放
            Size tem_size = new Size(iSource.Width, iSource.Height);
            if (tem_size.Width > dWidth || tem_size.Height > dHeight)
            {
                if ((tem_size.Width * dHeight) > (tem_size.Height * dWidth))
                {
                    sW = dWidth;
                    sH = (dWidth * tem_size.Height) / tem_size.Width;
                }
                else
                {
                    sH = dHeight;
                    sW = (tem_size.Width * dHeight) / tem_size.Height;
                }
            }
            else
            {
                sW = tem_size.Width;
                sH = tem_size.Height;
            }

            Bitmap ob = new Bitmap(dWidth, dHeight);
            Graphics g = Graphics.FromImage(ob);
            g.Clear(Color.WhiteSmoke);
            g.CompositingQuality = CompositingQuality.HighQuality;
            g.SmoothingMode = SmoothingMode.HighQuality;
            g.InterpolationMode = InterpolationMode.HighQualityBicubic;
            g.DrawImage(iSource, new Rectangle((dWidth - sW) / 2, (dHeight - sH) / 2, sW, sH), 0, 0, iSource.Width, iSource.Height, GraphicsUnit.Pixel);
            g.Dispose();
            //以下代码为保存图片时，设置压缩质量
            EncoderParameters ep = new EncoderParameters();
            long[] qy = new long[1];
            qy[0] = flag;//设置压缩的比例1-100
            EncoderParameter eParam = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, qy);
            ep.Param[0] = eParam;
            try
            {
                ImageCodecInfo[] arrayICI = ImageCodecInfo.GetImageEncoders();

                ImageCodecInfo jpegICIinfo = null;

                for (int x = 0; x < arrayICI.Length; x++)
                {
                    if (arrayICI[x].FormatDescription.Equals("JPEG"))
                    {
                        jpegICIinfo = arrayICI[x];
                        break;
                    }
                }
                if (jpegICIinfo != null)
                {
                    ob.Save(dFile, jpegICIinfo, ep);//dFile是压缩后的新路径
                }
                else
                {
                    ob.Save(dFile, tFormat);
                }
                return true;
            }
            catch
            {
                return false;
            }
            finally
            {
                iSource.Dispose();
                ob.Dispose();
            }
        }

        /// <summary>
        /// 无损压缩图片
        /// </summary>
        /// <param name="sFile">原图片</param>
        /// <param name="dFile">压缩后保存位置</param>
        /// <param name="dWidth">宽度</param>
        /// <param name="dHeight">高度</param>
        /// <param name="flag">压缩质量 1-100</param>
        /// <returns></returns>
        public bool CompressPicture(string sFile, string dFile, int dWidth, int dHeight, int flag)
        {
            System.Drawing.Image iSource = System.Drawing.Image.FromFile(sFile);
            ImageFormat tFormat = iSource.RawFormat;
            int sW = 0, sH = 0;
            //按比例缩放
            Size tem_size = new Size(iSource.Width, iSource.Height);
            if (tem_size.Width > dWidth || tem_size.Height > dHeight)
            {
                if ((tem_size.Width * dHeight) > (tem_size.Height * dWidth))
                {
                    sW = dWidth;
                    sH = (dWidth * tem_size.Height) / tem_size.Width;
                }
                else
                {
                    sH = dHeight;
                    sW = (tem_size.Width * dHeight) / tem_size.Height;
                }
            }
            else
            {
                sW = tem_size.Width;
                sH = tem_size.Height;
            }

            Bitmap ob = new Bitmap(dWidth, dHeight);
            Graphics g = Graphics.FromImage(ob);
            g.Clear(Color.WhiteSmoke);
            g.CompositingQuality = CompositingQuality.HighQuality;
            g.SmoothingMode = SmoothingMode.HighQuality;
            g.InterpolationMode = InterpolationMode.HighQualityBicubic;
            g.DrawImage(iSource, new Rectangle((dWidth - sW) / 2, (dHeight - sH) / 2, sW, sH), 0, 0, iSource.Width, iSource.Height, GraphicsUnit.Pixel);
            g.Dispose();
            //以下代码为保存图片时，设置压缩质量
            EncoderParameters ep = new EncoderParameters();
            long[] qy = new long[1];
            qy[0] = flag;//设置压缩的比例1-100
            EncoderParameter eParam = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, qy);
            ep.Param[0] = eParam;
            try
            {
                ImageCodecInfo[] arrayICI = ImageCodecInfo.GetImageEncoders();

                ImageCodecInfo jpegICIinfo = null;

                for (int x = 0; x < arrayICI.Length; x++)
                {
                    if (arrayICI[x].FormatDescription.Equals("JPEG"))
                    {
                        jpegICIinfo = arrayICI[x];
                        break;
                    }
                }
                if (jpegICIinfo != null)
                {
                    ob.Save(dFile, jpegICIinfo, ep);//dFile是压缩后的新路径
                }
                else
                {
                    ob.Save(dFile, tFormat);
                }
                return true;
            }
            catch
            {
                return false;
            }
            finally
            {
                iSource.Dispose();
                ob.Dispose();
            }
        }


        /// <summary>
        /// 按指定规格裁剪图片
        /// </summary>
        /// <param name="sFile">源文件路径</param>
        /// <param name="dFile">输出文件路径</param>
        /// <param name="originPoint">裁剪区域的起点</param>
        /// <param name="sSize">裁剪区域的大小</param>
        /// <param name="dSize">生成的规格</param>
        /// <param name="flag">压缩质量 1-100</param>
        /// <returns></returns>
        public bool CropPicture(string sFile, string dFile, Point originPoint , Size sSize, Size dSize, int flag)
        {
            System.Drawing.Image iSource = System.Drawing.Image.FromFile(sFile);
            ImageFormat tFormat = iSource.RawFormat;
            Bitmap ob = new Bitmap(dSize.Width, dSize.Height);
            Graphics g = Graphics.FromImage(ob);
            g.Clear(Color.WhiteSmoke);
            g.CompositingQuality = CompositingQuality.HighQuality;
            g.SmoothingMode = SmoothingMode.HighQuality;
            g.InterpolationMode = InterpolationMode.HighQualityBicubic;
            g.DrawImage(iSource, new Rectangle(0, 0, dSize.Width, dSize.Height), originPoint.X, originPoint.Y, sSize.Width, sSize.Height, GraphicsUnit.Pixel);
            g.Dispose();
            //以下代码为保存图片时，设置压缩质量
            EncoderParameters ep = new EncoderParameters();
            long[] qy = new long[1];
            qy[0] = flag;//设置压缩的比例1-100
            EncoderParameter eParam = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, qy);
            ep.Param[0] = eParam;
            try
            {
                ImageCodecInfo[] arrayICI = ImageCodecInfo.GetImageEncoders();

                ImageCodecInfo jpegICIinfo = null;

                for (int i = 0; i < arrayICI.Length; i++)
                {
                    if (arrayICI[i].FormatDescription.Equals("JPEG"))
                    {
                        jpegICIinfo = arrayICI[i];
                        break;
                    }
                }
                if(string.IsNullOrEmpty(dFile))
                {
                    string[] temp = sFile.Split(new char[] { ‘\\‘ }, StringSplitOptions.RemoveEmptyEntries);
                    string fileName = temp[temp.Length - 1];
                    fileName = fileName.Insert(fileName.IndexOf(‘.‘), ‘_‘+ dSize.Width.ToString() + ‘_‘ + dSize.Height.ToString());
                    temp[temp.Length - 1] = fileName;
                    dFile = string.Empty;
                    foreach(string item in temp)
                    {
                        dFile += item + "\\";
                    }
                    dFile=dFile.TrimEnd(‘\\‘);
                }
                if (jpegICIinfo != null)
                {
                    ob.Save(dFile, jpegICIinfo, ep);
                }
                else
                {
                    ob.Save(dFile, tFormat);
                }
                return true;
            }
            catch
            {
                return false;
            }
            finally
            {
                iSource.Dispose();
                ob.Dispose();
            }

        }
        #endregion

        #region 判断图片格式 
        public bool IsAllowImg(string contentType, string fileExtension)
        {
            contentType = contentType.ToLower();
            if(!contentType.Contains("image"))
            {
                return false;
            }

            fileExtension = fileExtension.ToLower();
            string[] allowExtension = { ".bmp", ".gif", ".jpeg", ".jpg", ".png" };
            foreach (string item in allowExtension)
            {
                if (fileExtension == item)
                {
                    return true;
                }
            }
            return false;
        }

        public static bool IsAllowedExtension(HttpPostedFileBase file)
        {
            System.IO.Stream stream = file.InputStream;
            System.IO.BinaryReader reader = new System.IO.BinaryReader(stream);
            string fileclass = "";
            //这里的位长要具体判断. 
            byte buffer;
            try
            {
                //buffer = r.ReadByte();
                //fileclass = buffer.ToString();
                //buffer = r.ReadByte();
                //fileclass += buffer.ToString();

                for (int i = 0; i < 2; i++)
                {
                    fileclass += reader.ReadByte().ToString();
                }

            }
            catch
            {

            }
            reader.Close();
            stream.Close();
            if (fileclass == "255216" || fileclass == "7173")//说明255216是jpg;7173是gif;6677是BMP,13780是PNG;7790是exe,8297是rar 
            {
                return true;
            }
            else
            {
                return false;
            }

        }
        #endregion


        [HttpPost]
        public JsonResult CropPhoto(string url,int x,int y,int w,int h)
        {
            if (string.IsNullOrEmpty(url) || w == 0 || h == 0)
            {
                return Json(new { Status = "error", Msg = "参数错误" });
            }

            Point origin = new Point(x, y);
            Size source = new Size(w, h);
            Size destSmall = new Size(48, 48);
            Size destLarge = new Size(180, 180);

            bool result1 =CropPicture(Server.MapPath(url), null, origin, source, destSmall, 100);
            bool result2 =CropPicture(Server.MapPath(url), null, origin, source, destLarge, 100);


            var jsonResult = result1 && result2
                ? new { Status = "success", Msg = "操作成功" }
                : new { Status = "error", Msg = "裁剪图片出现错误" };

            return Json(jsonResult);
        }
    }