/// <summary>
        /// 获取小程序全局唯一后台接口调用凭据（access_token）
        /// </summary>
        /// <returns></returns>
        public string GetWechatAccessToken()
        {
            var appId = "你的小程序AppID";//小程序唯一凭证，即 AppID
            var secret = "你的小程序AppSecret"; //小程序唯一凭证密钥，即 AppSecret
            string Url = string.Format("https://api.weixin.qq.com/cgi-bin/token?grant_type=client_credential&appid={0}&secret={1}", appId, secret);

            string Result = HttpWebRequest(Url, "GET", "", Encoding.UTF8);

            var obj = JsonConvert.DeserializeObject<AccessToken>(Result);

            if (obj != null && obj.access_token != null)
            {
                return obj.access_token;
            }
            else
            {
                return "";
            }
        }


        /// <summary>
        /// WebRequest网络请求
        /// </summary>
        /// <param name="requestUrl">请求地址</param>
        /// <param name="method">请求方式（GET/POST）</param>
        /// <param name="data">请求参数(method="POST"需要携带)</param>
        /// <param name="encoding">字符编码</param>
        /// <param name="contentType">请求数据的内容类型</param>
        /// <returns></returns>
        public string HttpWebRequest(string requestUrl, string method, string data, Encoding encoding,string contentType="application/json;charset=UTF-8")
        {
            WebRequest webRequest = WebRequest.Create(requestUrl);
            webRequest.Method = method;
            if (method == "POST")
            {
                byte[] bytes = Encoding.Default.GetBytes(data);
                webRequest.ContentType = contentType;
                webRequest.ContentLength = bytes.Length;
                Stream requestStream = webRequest.GetRequestStream();
                requestStream.Write(bytes, 0, bytes.Length);
                requestStream.Close();
            }

            WebResponse response = webRequest.GetResponse();
            Stream responseStream = response.GetResponseStream();
            if (responseStream == null)
            {
                return "";
            }

            StreamReader streamReader = new StreamReader(responseStream, encoding);
            string result = streamReader.ReadToEnd();
            responseStream.Close();
            streamReader.Close();
            return result;
        }



    /// <summary>
    /// 响应模型
    /// </summary>
    public class AccessToken
    {
        /// <summary>
        /// 获取到的凭证
        /// </summary>
        public string access_token { get; set; }

        /// <summary>
        /// 凭证有效时间，单位：秒。目前是7200秒之内的值
        /// </summary>
        public int expires_in { get; set; }

        /// <summary>
        /// 错误码
        /// </summary>
        public int errcode { get; set; }

        /// <summary>
        /// 错误信息
        /// </summary>
        public string errmsg { get; set; }
    }

        /// <summary>
        /// 获取小程序码图片
        /// </summary>
        /// <param name="access_token">接口调用凭据</param>
        /// <param name="param">携带参数</param>
        private Image GetWetchatAppletQRCodeImage(string access_token, string param)
        {
            string requestData = "{\"scene\":\"" + param + "\"}";
            string requestUrl = "https://api.weixin.qq.com/wxa/getwxacodeunlimit?access_token=" + access_token;

            HttpWebRequest request = (HttpWebRequest)WebRequest.Create(requestUrl);
            request.Method = "POST";
            request.ContentType = "application/json;charset=UTF-8";
            byte[] payload = System.Text.Encoding.UTF8.GetBytes(requestData);
            request.ContentLength = payload.Length;
            Stream writer = request.GetRequestStream();
            writer.Write(payload, 0, payload.Length);
            writer.Close();
            HttpWebResponse response;
            response = (HttpWebResponse)request.GetResponse();
            Stream stream = response.GetResponseStream();//获取返回的图片 Buffer（文件流）
            byte[] imageBuffer = StreamToBytes(stream);

            return ByteArrayConvertToImage(imageBuffer);
        }

        /// <summary>
        /// 将文件数据流转为二进制byte[]字节流
        /// </summary>
        /// <param name="stream">文件流</param>
        /// <returns></returns>
        private byte[] StreamToBytes(Stream stream)
        {
            List<byte> bytes = new List<byte>();
            int temp = stream.ReadByte();
            while (temp != -1)
            {
                bytes.Add((byte)temp);
                temp = stream.ReadByte();
            }
            return bytes.ToArray();
        }


        /// <summary>
        /// byte [] 转化为Iamge
        /// </summary>
        /// <param name="buffer"></param>
        /// <returns></returns>
        public static Image ByteArrayConvertToImage(byte[] buffer)
        {
            using (MemoryStream ms = new MemoryStream(buffer))
            {
                // 直接调用Image库类中自带的方法使用MemoryStream实例对象获取Image
                return Image.FromStream(ms);
            }
        }

        /// <summary>
        /// 小程序推广二维码获取
        /// </summary>
        /// <param name="userId">小程序码携带的用户参数</param>
        /// <returns></returns>
        public JsonResult GetCompositePictureUrl(int userId)
        {
            //图片存放物理路径
            var savePhysicalPath = HttpContext.Request.MapPath("~/qrcode/");

            var imgBack = Image.FromFile(savePhysicalPath + "ewm.jpg");//合成背景图片
            var wechatQrcodeImg = GetWetchatAppletQRCodeImage(GetWechatAccessToken(),userId.ToString());//获取小程序码图片
            var compositePictureUrl = CompositePicture(imgBack, wechatQrcodeImg, savePhysicalPath, 232, 719, 290, 290);

            return Json(new { code = 0, compositePictureUrl = compositePictureUrl });
        }

        /// <summary>
        /// 合成图片
        /// </summary>
        /// <param name="backgroundImage">背景图</param>
        /// <param name="qrCodeImg">二维码图片</param>
        /// <param name="savePhysicalPath">图片存放物理路径</param>
        /// <param name="xDeviation">绘制图像X轴偏差</param>
        /// <param name="yDeviation">绘制图像Y轴偏差</param>
        /// <param name="width">绘制图像宽</param>
        /// <param name="height">绘制图像高</param>
        /// <returns></returns>
        public string CompositePicture(Image backgroundImage, Image qrCodeImg, string savePhysicalPath, int xDeviation = 0, int yDeviation = 0, int width = 0, int height = 0)
        {
            Bitmap bitmap = new Bitmap(backgroundImage.Width, backgroundImage.Height);
            Graphics graphics = Graphics.FromImage(bitmap);//绘图
            graphics.Clear(Color.White);
            SolidBrush surush = new SolidBrush(Color.White);
            graphics.DrawImage(backgroundImage, 0, 0, backgroundImage.Width, backgroundImage.Height);
            graphics.DrawImage(qrCodeImg, xDeviation, yDeviation, width, height);
            GC.Collect();//垃圾清理

            string compositePictureUrl = savePhysicalPath + Guid.NewGuid().ToString() + ".jpg";
            //合成图片保存
            bitmap.Save(compositePictureUrl, System.Drawing.Imaging.ImageFormat.Jpeg);

            return compositePictureUrl;
        }