使用Win32 API（C＃pInvoke）截屏在IIS中不起作用

Question

I want to take a screenshot of an external website. Currently my workflow is to start a Firefox instance with the specified URL and take a screenshot using PrintWindow in the Win32 API

When I run this application in IISExpress it works fine but when I run the same application in IIS on a windows VPS it is not working (screenshot is blank).

I don't know what I'm doing wrong?

My code:

using Newtonsoft.Json;
using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Drawing;
using System.Drawing.Imaging;
using System.Linq;
using System.Runtime.InteropServices;
using System.Security;
using System.Threading;
using System.Web;

namespace WebTools.Web
{
    public class RemoteScreenshot
    {
        public static Bitmap TakeScreenshot(Process process)
        {
            // may need a process Refresh before
            return TakeScreenshot(process.MainWindowHandle);
        }

        public static Bitmap TakeScreenshot(IntPtr handle)
        {
            RECT rc = new RECT();
            GetWindowRect(handle, ref rc);

            Bitmap bitmap = new Bitmap(rc.right - rc.left, rc.bottom - rc.top);

            using (Graphics graphics = Graphics.FromImage(bitmap))
            {
                PrintWindow(handle, graphics.GetHdc(), 0);
            }

            return bitmap;
        }

        [DllImport("user32.dll")]
        private static extern bool GetWindowRect(IntPtr hWnd, ref RECT rect);

        [DllImport("user32.dll")]
        private static extern bool PrintWindow(IntPtr hWnd, IntPtr hDC, int flags);

        [StructLayout(LayoutKind.Sequential)]
        private struct RECT
        {
            public int left;
            public int top;
            public int right;
            public int bottom;
        }

        public static void Save(string url, string file, int timeout = 0)
        {
            var proc = Process.Start(new ProcessStartInfo("C:\\Program Files (x86)\\Mozilla Firefox\\firefox.exe", url)
            {
                CreateNoWindow = false,
                WindowStyle = ProcessWindowStyle.Maximized
            });

            Thread.Sleep(timeout);

            var bitmap = TakeScreenshot(proc);

            bitmap.Save(file, ImageFormat.Png);
            bitmap.Dispose();

            proc.Kill();
        }
    }
}

EDIT: Running Firefox works fine because the AppPool is under another account that has the rights to execute firefox.

Answer 1

使用IIS，您无法进行屏幕截图，因为它可以在Windows服务器的NetworkService帐户下使用

Answer 2

What screen are you taking a screenshot of?

If an application is running on a laptop it will paint to a physical display adaptor. If it is running on a machine at the end of an RDP session it will paint to a virtual display adaptor, and the image will be sent over the wire.

But if an application is running in a non-interactive session then there is no display. The application won't receive WM_PAINT messages so nothing gets painted.

There is no screen bitmap to capture.

Answer 3

IIS service donot have the access to the server desktop. The code of ASP.NET in IIS is running on the server side. And it will be trying to capture the screen of the server, which is denied.

You will need to use the silverlight which runs the code on the client machine. Following link might help:

Capturing a Silverlight Screen

User using the webpage in the browser might need to provide permissions due to security reasons.