网站截图的实现

业务很简单，就是把网页转成图片保存下来。之前也用过html2canvas来实现这一功能，测试下来除了发现截图糊了一点外倒也没什么毛病，但是这次实现完在Chrome上测试时却出现了网络错误的提示（大概是图片太大的缘故orz），于是想到走后台来实现这一功能，找了一下发现以下方案，大概就是先组装好这个页面来让WebBrowser来访问，最后把整个WebBrowser界面以字节流的方式输出给用户浏览器。具体代码如下：

        protected void btnExport_Click(object sender, EventArgs e)
        {
            try
            {
                Thread thread = new Thread(new ThreadStart(ExportImageFromHtml));
                thread.SetApartmentState(ApartmentState.STA);
                thread.Start();
                thread.Join();
                while (thread.IsAlive) System.Windows.Forms.Application.DoEvents();
            }
            catch (Exception ex)
            {
                this.HandleException(ex);
            }
        }

        public void ExportImageFromHtml()
        {
            string url = "http://ie.icoa.cn/";
            Bitmap bitmap = new Bitmap(CommonWebUtil.CaptureWebPage(url));
            Response.ContentType = "image/jpeg";
            string fileName = lbltitle.Text.Replace("\\", "").Replace("/", "").Replace(":", "").Replace("*", "").Replace("?", "").Replace("\"", "").Replace("<", "").Replace(">", "").Replace("|", "");
            fileName += "_证书.jpg";
            MemoryStream ms = new MemoryStream();
            bitmap.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);
            ms.Seek(0, SeekOrigin.Begin);
            byte[] bytes = ms.GetBuffer();
            Response.AddHeader("Content-Disposition", "attachment; filename=" + fileName);
            Response.BinaryWrite(bytes);
            Response.Flush();
            Response.End();
        }

        public static Bitmap CaptureWebPage(string URL)
        {
            //create a hidden web browser, which will navigate to the page
            System.Windows.Forms.WebBrowser web = new System.Windows.Forms.WebBrowser();
            // we don't want scrollbars on our image
            web.ScrollBarsEnabled = false;
            // don't let any errors shine through
            web.ScriptErrorsSuppressed = true;  
            // let's load up that page!
            web.Navigate(URL);
            //web.Navigate(URL, "_self", null, "User-Agent:Mozilla/5.0 (Windows NT 6.1; WOW64;Trident/7.0; rv:11.0) like Gecko");
            // wait until the page is fully loaded
            while (web.ReadyState != System.Windows.Forms.WebBrowserReadyState.Complete)
                System.Windows.Forms.Application.DoEvents();
            System.Threading.Thread.Sleep(1500); // allow time for page scripts to update
            // the appearance of the page

            // set the size of our web browser to be the same size as the page
            int width = web.Document.Body.ScrollRectangle.Width;
            int height = web.Document.Body.ScrollRectangle.Height;
            web.Width = width;
            web.Height = height;
            // a bitmap that we will draw to
            System.Drawing.Bitmap bmp = new System.Drawing.Bitmap(width, height);
            // draw the web browser to the bitmap
            web.DrawToBitmap(bmp, new System.Drawing.Rectangle(0, 0, width, height));

            return bmp; // return the bitmap for processing
        }

当然，采用webbrowser的方式存在着一定的弊端，因为其采用的是默认IE7的兼容视图，一开始我也陷入了死胡同，找了许多的解决方案：换webkit，修改注册表。但是后来突然发现我可以修改网页的meta标签，让其强制采用IE11进行渲染。

<meta http-equiv="x-ua-compatible" content="IE=11" />

山穷水尽疑无路，柳暗花明又一村。hhhh