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Posted By Subodh on Thursday, December 04, 2008
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Any Device Capture on Windows /C#

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 "Disclaimer1"

 

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.

1

DISCLAIMER This posting is provided "AS IS" with no warranties, and confers no rights. You assume all risk for your use.

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 Comments & Discussions

  • Gravatar
    Anand Monday, December 08, 2008 at 11:08 PM
    Re: Capture Any Screenshot on your desktop, window or application
    This is how it is done on OS X

    Cmd-Shift-3 - Save Picture of screen as a file
    Cmd-Shift-4 - Save picture of selected area as file

    Hold down Ctrl which either of them to save the picture to clipboard


  • Gravatar
    Subodh Monday, December 29, 2008 at 8:39 PM
    Re: Capture Any Screenshot on your desktop, window or application
    This is how it is done in windows happy
    Print Scr captures the entire desktop
    Alt Print Scr captures the active window.
    Window Key +S (via OneNote) allows you to capture any area.

    The point of the article above is different. To do it automatically/programmatically. Even when your desktop is locked! Try doing that on your Mac/Windows. When the terminal is locked, and you still want to capture a program's drawing area, this is the code you can use. A Prt Scr or Cmd-Shift just won't work.

  
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