using System;
using System.Drawing;
using System.Drawing.Imaging;
using System.Runtime.InteropServices;
using System.Windows.Forms;

public class PrintScreenHelper
{
    [DllImport("user32.dll")]
    private static extern IntPtr GetForegroundWindow();

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

    [StructLayout(LayoutKind.Sequential)]
    private struct RECT
    {
        public int Left;
        public int Top;
        public int Right;
        public int Bottom;
    }

    public static Bitmap CaptureActiveWindow()
    {
        IntPtr hWnd = GetForegroundWindow();
        RECT rect;
        GetWindowRect(hWnd, out rect);

        int width = rect.Right - rect.Left;
        int height = rect.Bottom - rect.Top;

        Bitmap bmp = new Bitmap(width, height, PixelFormat.Format32bppArgb);
        using (Graphics g = Graphics.FromImage(bmp))
        {
            g.CopyFromScreen(rect.Left, rect.Top, 0, 0, new Size(width, height), CopyPixelOperation.SourceCopy);
        }

        return bmp;
    }

    public static void SaveCapture(string filePath)
    {
        Bitmap bmp = CaptureActiveWindow();
        bmp.Save(filePath, ImageFormat.Png);
        bmp.Dispose();
    }
    public static void SaveCapture()
    {
        using (SaveFileDialog saveFileDialog = new SaveFileDialog())
        {
            saveFileDialog.Filter = "Arquivos de imagem (*.png)|*.png|Todos os arquivos (*.*)|*.*";
            saveFileDialog.Title = "Salvar Captura de Tela";
            saveFileDialog.InitialDirectory = Environment.GetFolderPath(Environment.SpecialFolder.MyPictures);

            if (saveFileDialog.ShowDialog() == DialogResult.OK)
            {
                Bitmap bmp = CaptureActiveWindow();
                bmp.Save(saveFileDialog.FileName, ImageFormat.Png);
                bmp.Dispose();
            }
        }
    }

}