Take screenshot of multiple desktops of all visible applications and forms

Question

i tried GetDesktopWindow() function but it doesn’t work properly.

Of course not.

The GetDesktopWindow function returns a handle to the desktop window. It doesn’t have anything to do with capturing an image of that window.

Besides, the desktop window is not the same thing as “the entire screen”. It refers specifically to the desktop window. See this article for more information and what can go wrong when you abuse the handle returned by this function.

i’m working with a system that have 4 outputs (monitors) with 1280×1024(e.g) for each output. i need a screenshot from whole desktop and all open applications on it.

This is relatively simple to do in the .NET Framework using the Graphics.CopyFromScreen method. You don’t even need to do any P/Invoke!

The only trick in this case is making sure that you pass the appropriate dimensions. Since you have 4 monitors, passing only the dimensions of the primary screen won’t work. You need to pass the dimensions of the entire virtual screen, which contains all of your monitors. Retrieve this by querying the SystemInformation.VirtualScreen property, which returns the bounds of the virtual screen. As the documentation indicates, this is the bounds of the entire desktop on a multiple monitor system.

Sample code:

// Determine the size of the "virtual screen", which includes all monitors.
int screenLeft   = SystemInformation.VirtualScreen.Left;
int screenTop    = SystemInformation.VirtualScreen.Top;
int screenWidth  = SystemInformation.VirtualScreen.Width;
int screenHeight = SystemInformation.VirtualScreen.Height;

// Create a bitmap of the appropriate size to receive the screenshot.
using (Bitmap bmp = new Bitmap(screenWidth, screenHeight))
{
    // Draw the screenshot into our bitmap.
    using (Graphics g = Graphics.FromImage(bmp))
    {
        g.CopyFromScreen(screenLeft, screenTop, 0, 0, bmp.Size);
    }

    // Do something with the Bitmap here, like save it to a file:
    bmp.Save(savePath, ImageFormat.Jpeg);
}

Edit:

please check your solution with a wpf application in a thread that is not your main thread. i tried it. it doesn’t work!

Hmm, I didn’t see a WPF tag on the question or mentioned anywhere in the body.

No matter, though. The code I posted works just fine in a WPF application, as long as you add the appropriate references and using declarations. You will need System.Windows.Forms and System.Drawing. There might be a more WPF-esque way of doing this that doesn’t require a dependency on these WinForms assemblies, but I wouldn’t know what it is.

It even works on another thread. There is nothing here that would require the UI thread.

Yes, I tested it. Here is my full test code:

using System.Windows;
using System.Windows.Forms;   // also requires a reference to this assembly
using System.Drawing;         // also requires a reference to this assembly
using System.Drawing.Imaging;
using System.Threading;

public partial class MainWindow : Window
{
   public MainWindow()
   {
      InitializeComponent();
   }

   private void button1_Click(object sender, RoutedEventArgs e)
   {
      // Create a new thread for demonstration purposes.
      Thread thread = new Thread(() =>
      {
         // Determine the size of the "virtual screen", which includes all monitors.
         int screenLeft   = SystemInformation.VirtualScreen.Left;
    int screenTop    = SystemInformation.VirtualScreen.Top;
    int screenWidth  = SystemInformation.VirtualScreen.Width;
    int screenHeight = SystemInformation.VirtualScreen.Height;

         // Create a bitmap of the appropriate size to receive the screenshot.
         using (Bitmap bmp = new Bitmap(screenWidth, screenHeight))
         {
            // Draw the screenshot into our bitmap.
            using (Graphics g = Graphics.FromImage(bmp))
            {
               g.CopyFromScreen(screenLeft, screenTop, 0, 0, bmp.Size);
            }

            // Do something with the Bitmap here, like save it to a file:
            bmp.Save("G:\\TestImage.jpg", ImageFormat.Jpeg);
         }
      });
      thread.SetApartmentState(ApartmentState.STA);
      thread.Start();
   }
}

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