Take Screenshot of Fullscreen Game

Program.cs

using System;
using System.Drawing;
using System.Runtime.InteropServices;
using System.Threading;
using static System.Net.Mime.MediaTypeNames;

class Program
{
    private const int SM_XVIRTUALSCREEN = 76;
    private const int SM_YVIRTUALSCREEN = 77;
    private const int SM_CXVIRTUALSCREEN = 78;
    private const int SM_CYVIRTUALSCREEN = 79;
    private const int SRCCOPY = 0x00CC0020;
    private const int CAPTUREBLT = 0x40000000;

    [DllImport("user32.dll")]
    private static extern int GetSystemMetrics(int nIndex);

    [DllImport("user32.dll")]
    private static extern IntPtr GetDC(int hWnd);

    [DllImport("gdi32.dll")]
    private static extern IntPtr CreateCompatibleDC(IntPtr hdc);

    [DllImport("gdi32.dll")]
    private static extern IntPtr CreateCompatibleBitmap(IntPtr hdc, int nWidth, int nHeight);

    [DllImport("gdi32.dll")]
    private static extern IntPtr SelectObject(IntPtr hdc, IntPtr hgdiobj);

    [DllImport("gdi32.dll")]
    private static extern bool BitBlt(IntPtr hdcDest, int xDest, int yDest, int wDest, int hDest, IntPtr hdcSrc, int xSrc, int ySrc, int dwRop);

    [DllImport("gdi32.dll")]
    private static extern bool DeleteObject(IntPtr hObject);

    [DllImport("user32.dll")]
    private static extern int ReleaseDC(IntPtr hWnd, IntPtr hdc);

    static void Main()
    {
        Console.ReadLine();
        Thread.Sleep(5000);
        int x = GetSystemMetrics(SM_XVIRTUALSCREEN);  // left (e.g. -1024)
        int y = GetSystemMetrics(SM_YVIRTUALSCREEN);  // top (e.g. -34)
        int cx = GetSystemMetrics(SM_CXVIRTUALSCREEN); // entire width (e.g. 2704)
        int cy = GetSystemMetrics(SM_CYVIRTUALSCREEN); // entire height (e.g. 1050)

        IntPtr dcScreen = GetDC((int)IntPtr.Zero);
        IntPtr dcTarget = CreateCompatibleDC(dcScreen);
        IntPtr bmpTarget = CreateCompatibleBitmap(dcScreen, cx, cy);
        IntPtr oldBmp = SelectObject(dcTarget, bmpTarget);
        BitBlt(dcTarget, 0, 0, cx, cy, dcScreen, x, y, SRCCOPY | CAPTUREBLT);
        SelectObject(dcTarget, oldBmp);

        
        // Save the screenshot as an image file
        using (Bitmap screenshot = System.Drawing.Image.FromHbitmap(bmpTarget))
        {
            screenshot.Save("D:/screenshot.png", System.Drawing.Imaging.ImageFormat.Png);
        }

        // Cleanup
        DeleteObject(bmpTarget);
        DeleteObject(oldBmp);
        DeleteObject(dcTarget);
        ReleaseDC(IntPtr.Zero, dcScreen);
    }
}