Capture Any Screenshot on your desktop, window or application

C#/Windows Only. Need a quick and dirty code to snap that Flash player on your screen? Need to capture the whole of the Desktop? Or just an application window? Get the code here for doing it as your please. Before we go any further, its time for the usual "Disclaimer"

First and foremost, the references

using System;

using System.Runtime.InteropServices;

using System.Drawing;

using System.Drawing.Imaging;

And then the helper classes; Not all of them are necessary. I just have the habit of keeping everything in one place.

private class GDI32

        {

            public const int SRCCOPY = 0x00CC0020; // BitBlt dwRop parameter

            [DllImport("gdi32.dll")]

            public static extern bool BitBlt(IntPtr hObject,int nXDest,int nYDest,

                int nWidth,int nHeight,IntPtr hObjectSource,

                int nXSrc,int nYSrc,int dwRop);

            [DllImport("gdi32.dll")]

            public static extern IntPtr CreateCompatibleBitmap(IntPtr hDC,int nWidth, 

                int nHeight);

            [DllImport("gdi32.dll")]

            public static extern IntPtr CreateCompatibleDC(IntPtr hDC);

            [DllImport("gdi32.dll")]

            public static extern bool DeleteDC(IntPtr hDC);

            [DllImport("gdi32.dll")]

            public static extern bool DeleteObject(IntPtr hObject);

            [DllImport("gdi32.dll")]

            public static extern IntPtr SelectObject(IntPtr hDC,IntPtr hObject);

        }

        /// 

        /// Helper class containing User32 API functions

        /// 

        private class User32

        {

            [StructLayout(LayoutKind.Sequential)]

                public struct RECT

            {

                public int left;

                public int top;

                public int right;

                public int bottom;

            }

            [DllImport("user32.dll", EntryPoint = "SendMessageA")]

            public static extern uint SendMessage(IntPtr hWnd, int  wMsg, IntPtr wParam, IntPtr lParam);

            [DllImport("user32.dll")]

            public static extern IntPtr GetDesktopWindow();

            [DllImport("user32.dll")]

            public static extern IntPtr GetWindowDC(IntPtr hWnd);

            [DllImport("user32.dll")]

            public static extern IntPtr ReleaseDC(IntPtr hWnd,IntPtr hDC);

            [DllImport("user32.dll")]

            public static extern IntPtr GetWindowRect(IntPtr hWnd,ref RECT rect);

        }

We’d also need the WM_PAINT declaration

        const int WM_PAINT = 0x000F;

Now all we need is a capture routine:

       public Bitmap getSnapShot(System.Windows.Forms.Control control)

        {

            Image image = new Bitmap(control.Width, control.Height);

            // get a graphics object we can draw into

            Graphics g = Graphics.FromImage(image);

            IntPtr hDCT = g.GetHdc();

            User32.SendMessage(control.Handle

                , WM_PAINT, hDCT, IntPtr.Zero);

            g.ReleaseHdc(hDCT);

            g.Dispose();

            return new Bitmap(image);

        }

That’s it. We’re done. Notice that we’re forcing the control or device to PAINT itself before we try to capture its drawing area. This is useful in capturing even when the control is drawing off-screen (or for example when the desktop is locked).

In case you do not have a C# Control (for example when the owner isn’t the current application), you can also use the following

        public Image CaptureWindow(IntPtr handle)

        {

            // get the 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;

        }

In case you’re wondering why not use a Control.DrawToBitmap method, it can only be used in .NET 3.0 or above and even then it cannot be used to capture screenshots from non .NET windows/devices that do not belong to your AppD hierarchy.

Oh and to get the entire desktop,

        public Image CaptureScreen() 

        {

            return CaptureWindow( User32.GetDesktopWindow() );

        }

Have fun! Let me know in comments if it helped.