using System;
using System.Collections.Generic;
using System.Drawing;
using System.Linq;
using System.Runtime.InteropServices;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace LC
{
    class ScreenCapture
    {
        #region 抓取屏幕
        /// <summary>
        /// 抓取屏幕(层叠的窗口)
        /// </summary>
        /// <param name="x">左上角的横坐标</param>
        /// <param name="y">左上角的纵坐标</param>
        /// <param name="width">抓取宽度</param>
        /// <param name="height">抓取高度</param>
        /// <returns></returns>
        public static Bitmap captureScreen(int x, int y, int width, int height)
        {
            Bitmap bmp = new Bitmap(width, height);
            using (Graphics g = Graphics.FromImage(bmp))
            {
                g.CopyFromScreen(new Point(x, y), new Point(0, 0), bmp.Size);
                g.Dispose();
            }
            //bit.Save(@"capture2.png");
            return bmp;
        }

        /// <summary>
        ///  抓取整个屏幕
        /// </summary>
        /// <returns></returns>
        public static Bitmap captureScreen()
        {
            Size screenSize = Screen.PrimaryScreen.Bounds.Size;
            return captureScreen(0,0,screenSize.Width,screenSize.Height);
        }
        #endregion

        #region 使用BitBlt方法抓取控件，无论控件是否被遮挡
        /// <summary>
        /// 控件(窗口)的截图，控件被其他窗口(而非本窗口内控件)遮挡时也可以正确截图，使用BitBlt方法
        /// </summary>
        /// <param name="control">需要被截图的控件</param>
        /// <returns>该控件的截图，控件被遮挡时也可以正确截图</returns>
        public static Bitmap captureControl(Control control)
        {
            //调用API截屏
            IntPtr hSrce = GetWindowDC(control.Handle);
            IntPtr hDest = CreateCompatibleDC(hSrce);
            IntPtr hBmp = CreateCompatibleBitmap(hSrce, control.Width, control.Height);
            IntPtr hOldBmp = SelectObject(hDest, hBmp);
            if (BitBlt(hDest, 0, 0, control.Width, control.Height, hSrce, 0, 0, CopyPixelOperation.SourceCopy | CopyPixelOperation.CaptureBlt))
            {
                Bitmap bmp = Image.FromHbitmap(hBmp);
                SelectObject(hDest, hOldBmp);
                DeleteObject(hBmp);
                DeleteDC(hDest);
                ReleaseDC(control.Handle, hSrce);
                // bmp.Save(@"a.png");
                // bmp.Dispose();
                return bmp;
            }
            return null;

        }

//         /// <summary>
//         /// 有问题！！！！！用户区域坐标不对啊
//         /// 控件(窗口)的用户区域截图，控件被其他窗口(而非本窗口内控件)遮挡时也可以正确截图，使用BitBlt方法
//         /// </summary>
//         /// <param name="control">需要被截图的控件</param>
//         /// <returns>控件(窗口)的用户区域截图</returns>
//         public static Bitmap captureClientArea(Control control)
//         {
// 
//             Size sz = control.Size;
//             Rectangle rect = control.ClientRectangle;
//             
// 
//             //调用API截屏
//             IntPtr hSrce = GetWindowDC(control.Handle);
//             IntPtr hDest = CreateCompatibleDC(hSrce);
//             IntPtr hBmp = CreateCompatibleBitmap(hSrce, rect.Width, rect.Height);
//             IntPtr hOldBmp = SelectObject(hDest, hBmp);
//             if (BitBlt(hDest, 0, 0, rect.Width, rect.Height, hSrce, rect.X, rect.Y, CopyPixelOperation.SourceCopy | CopyPixelOperation.CaptureBlt))
//             {
//                 Bitmap bmp = Image.FromHbitmap(hBmp);
//                 SelectObject(hDest, hOldBmp);
//                 DeleteObject(hBmp);
//                 DeleteDC(hDest);
//                 ReleaseDC(control.Handle, hSrce);
//                 // bmp.Save(@"a.png");
//                 // bmp.Dispose();
//                 return bmp;
//             }
//             return null;
// 
//         }
        #endregion


        #region 使用PrintWindow方法抓取窗口，无论控件是否被遮挡
        /// <summary>
        /// 窗口的截图，窗口被遮挡时也可以正确截图，使用PrintWindow方法
        /// </summary>
        /// <param name="control">需要被截图的窗口</param>
        /// <returns>窗口的截图，控件被遮挡时也可以正确截图</returns>
        public static Bitmap captureWindowUsingPrintWindow(Form form)
        {
            return GetWindow(form.Handle);
        }


        private static Bitmap GetWindow(IntPtr hWnd)
        {
            IntPtr hscrdc = GetWindowDC(hWnd);
            Control control = Control.FromHandle(hWnd);
            IntPtr hbitmap = CreateCompatibleBitmap(hscrdc, control.Width, control.Height);
            IntPtr hmemdc = CreateCompatibleDC(hscrdc);
            SelectObject(hmemdc, hbitmap);
            PrintWindow(hWnd, hmemdc, 0);
            Bitmap bmp = Bitmap.FromHbitmap(hbitmap);
            DeleteDC(hscrdc);//删除用过的对象
            DeleteDC(hmemdc);//删除用过的对象
            return bmp;
        }
        #endregion

        #region  DLL calls
        [DllImport("gdi32.dll")]
        static extern bool BitBlt(IntPtr hdcDest, int xDest, int yDest, int
        wDest, int hDest, IntPtr hdcSource, int xSrc, int ySrc, CopyPixelOperation rop);
        [DllImport("gdi32.dll")]
        static extern IntPtr DeleteDC(IntPtr hDc);
        [DllImport("gdi32.dll")]
        static extern IntPtr DeleteObject(IntPtr hDc);
        [DllImport("gdi32.dll")]
        static extern IntPtr CreateCompatibleBitmap(IntPtr hdc, int nWidth, int nHeight);
        [DllImport("gdi32.dll")]
        static extern IntPtr CreateCompatibleDC(IntPtr hdc);
        [DllImport("gdi32.dll")]
        static extern IntPtr SelectObject(IntPtr hdc, IntPtr bmp);
        [DllImport("user32.dll")]
        public static extern IntPtr GetDesktopWindow();
        [DllImport("user32.dll")]
        public static extern IntPtr GetWindowDC(IntPtr ptr);
        [DllImport("user32.dll")]
        public static extern bool PrintWindow(IntPtr hwnd, IntPtr hdcBlt, UInt32 nFlags);
        [DllImport("user32.dll")]
        static extern bool ReleaseDC(IntPtr hWnd, IntPtr hDc);
        #endregion
    }
}

原文：http://cherishlc.iteye.com/blog/1687738