c#使用API截屏类

using System;
using System.Collections.Generic;
using System.Text;
using System.Runtime.InteropServices;
using System.Drawing;
using System.Drawing.Imaging;

namespace Capture
...{
    /**////
    /// This class shall keep the GDI32 APIs used in our program.
    ///
    public sealed class GDI32
    ...{        
        public const int SRCCOPY = 13369376;

        Class Functions#region Class Functions

        [DllImport("gdi32.dll", EntryPoint = "DeleteDC")]
        public static extern IntPtr DeleteDC(IntPtr hDc);

        [DllImport("gdi32.dll", EntryPoint = "DeleteObject")]
        public static extern IntPtr DeleteObject(IntPtr hDc);

        [DllImport("gdi32.dll", EntryPoint = "BitBlt")]
        public static extern bool BitBlt(
        IntPtr hdcDest, //目的DC的句柄 
        int nXDest, //目的图形的左上角的x坐标 
        int nYDest, //目的图形的左上角的y坐标 
        int nWidth, //目的图形的矩形宽度 
        int nHeight, //目的图形的矩形高度 
        IntPtr hdcSrc, //源DC的句柄 
        int nXSrc, //源图形的左上角的x坐标 
        int nYSrc, //源图形的左上角的x坐标 
        System.Int32 dwRop //光栅操作代码 
        );

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

        [DllImport("gdi32.dll", EntryPoint = "CreateCompatibleDC")]
        public static extern IntPtr CreateCompatibleDC(IntPtr hdc);

        [DllImport("gdi32.dll", EntryPoint = "SelectObject")]
        public static extern IntPtr SelectObject(IntPtr hdc, IntPtr bmp);

        #endregion

    }

    /**////
    /// This class shall keep the User32 APIs used in our program.
    ///
    public sealed class User32
    ...{
        Class Variables#region Class Variables
        public const int SM_CXSCREEN = 0;
        public const int SM_CYSCREEN = 1;

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

        #endregion

        Class Functions#region Class Functions

        [DllImport("user32.dll", EntryPoint = "GetDesktopWindow")]
        public static extern IntPtr GetDesktopWindow();

        [DllImport("user32.dll", EntryPoint = "GetDC")]
        public static extern IntPtr GetDC(IntPtr ptr);

        [DllImport("user32.dll", EntryPoint = "GetSystemMetrics")]
        public static extern int GetSystemMetrics(int abc);

        [DllImport("user32.dll", EntryPoint = "GetWindowDC")]
        public static extern IntPtr GetWindowDC(IntPtr hWnd);

        [DllImport("user32.dll", EntryPoint = "ReleaseDC")]
        public static extern IntPtr ReleaseDC(IntPtr hWnd, IntPtr hDc);

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

        #endregion
        
    }

    /**////
    /// This class shall keep all the functionality for capturing
    /// the desktop.
    ///
    public class CaptureScreen
    ...{
        Class Variable Declaration#region Class Variable Declaration
        protected static IntPtr m_HBitmap;
        #endregion

        /**//// <summary>
        /// Creates an Image object containing a screen shot of the entire desktop
        /// </summary>
        /// <returns></returns>
        public static Image CaptureDesktop()
        ...{
            return CaptureWindow(User32.GetDesktopWindow());
        }

        /**//// <summary>
        /// Creates an Image object containing a screen shot of a specific window
        /// </summary>
        /// <param name="handle">
        /// The handle to the window. (In windows forms, this is obtained by the Handle property)
        /// </param>
        /// <returns></returns>
        public static Image CaptureWindow(IntPtr handle)
        ...{
            // get te hDC of the target window
            IntPtr hdcSrc = User32.GetWindowDC(handle);

            // get the size
            User32.RECT windowRect = new User32.RECT();
            User32.GetWindowRect(handle, ref windowRect);
            int width = windowRect.right - windowRect.left;
            int height = windowRect.bottom - windowRect.top;

            // create a device context we can copy to
            IntPtr hdcDest = GDI32.CreateCompatibleDC(hdcSrc);

            // create a bitmap we can copy it to,
            // using GetDeviceCaps to get the width/height
            IntPtr hBitmap = GDI32.CreateCompatibleBitmap(hdcSrc, width, height);

            // select the bitmap object
            IntPtr hOld = GDI32.SelectObject(hdcDest, hBitmap);

            // bitblt over
            GDI32.BitBlt(hdcDest, 0, 0, width, height, hdcSrc, 0, 0, GDI32.SRCCOPY);

            // restore selection
            GDI32.SelectObject(hdcDest, hOld);

            // clean up 
            GDI32.DeleteDC(hdcDest);
            User32.ReleaseDC(handle, hdcSrc);

            // get a .NET image object for it
            Image img = Image.FromHbitmap(hBitmap);

            // free up the Bitmap object
            GDI32.DeleteObject(hBitmap);

            return img;
        }

        /**//// <summary>
        /// Captures a screen shot of a specific window, and saves it to a file
        /// </summary>
        /// <param name="handle"></param>
        /// <param name="filename"></param>
        /// <param name="format"></param>
        public static void CaptureWindowToFile(IntPtr handle, string filename, ImageFormat format)
        ...{
            Image img = CaptureWindow(handle);
            img.Save(filename, format);
        }

        /**//// <summary>
        /// Captures a screen shot of the entire desktop, and saves it to a file
        /// </summary>
        /// <param name="filename"></param>
        /// <param name="format"></param>
        public static void CaptureScreenToFile(string filename, ImageFormat format)
        ...{
            Image img = CaptureDesktop();
            img.Save(filename, format);
        }