Screen Capture to the Clipboard

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One of the common questions that I find on the microsoft.public forums is "How do I get a bitmap of a window on the screen?" Well, here's a little subroutine I used extensively in writing Win32 Programming, because I realized that for the number of illustrations I wanted for the book, there was no hope of doing screen captures and then hand-editing just the control I wanted to show. So all my Explorers have a little button somewhere that performs a screen capture of the example window and drops it into the clipboard. I could then paste it into the document, or paste it into an editor and save it as a TIFF or JPEG as well.

To capture a window including the cursor, a more complex approach is required. This is described in an accompanying essay.

Note that I use a base CDC object and use Attach and Detach, instead of using the classes CClientDC and CWindowDC.  I did this because each of these classes creates a specific kind of DC, but there was no one class that could create a DC that was either a client DC or a Window DC.  Rather than introduce convoluted code to handle these cases, I just bound the HDC to a generic CDC.

ToClip.h:

void toClipboard(CWnd * wnd, BOOL FullWnd);

ToClip.cpp

#include "stdafx.h"

#include "toclip.h" 

/****************************************************************

*                                 toClipboard

* Inputs:

*       CWnd * wnd: Window whose contents are to be sent 

*                   to the clipboard

*       BOOL FullWnd: TRUE for entire window, 

*                     FALSE for client area

* Result: void

*       

* Effect: 

*       Copies the contents of the client area or the window

*       to the clipboard in CF_BITMAP format.

*****************************************************************/

void toClipboard(CWnd * wnd, BOOL FullWnd)

    {

     CDC dc;

     if(FullWnd)

        { /* full window */

         HDC hdc = ::GetWindowDC(wnd->m_hWnd);

         dc.Attach(hdc);

        } /* full window */

     else

        { /* client area only */

         HDC hdc = ::GetDC(wnd->m_hWnd);

         dc.Attach(hdc);

        } /* client area only */

     CDC memDC;

     memDC.CreateCompatibleDC(&dc);

     CBitmap bm;

     CRect r;

     if(FullWnd)

        wnd->GetWindowRect(&r);

     else

         wnd->GetClientRect(&r);

     CString s;

     wnd->GetWindowText(s);

     CSize sz(r.Width(), r.Height());

     bm.CreateCompatibleBitmap(&dc, sz.cx, sz.cy);

     CBitmap * oldbm = memDC.SelectObject(&bm);

     memDC.BitBlt(0, 0, sz.cx, sz.cy, &dc, 0, 0, SRCCOPY);

     wnd->GetParent()->OpenClipboard();

     ::EmptyClipboard();

     ::SetClipboardData(CF_BITMAP, bm.m_hObject);

     CloseClipboard();

     memDC.SelectObject(oldbm);

     bm.Detach();  // make sure bitmap not deleted with CBitmap object

                   // read my essay on this technique

     ::ReleaseDC(wnd->m_hWnd, dc.Detach()); // 

    }

Acknowledgements

Special thanks to Lim Bio Liong for pointing out that the CDC destructor does not call ReleaseDC. This bug was the result of converting some pure C code to MFC without my being careful enough.

Also, thanks to Charles Tam for pointing out a typo in the previous bug fix, a missing parameter.

The views expressed in these essays are those of the author, and in no way represent, nor are they endorsed by, Microsoft.

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Last modified: May 14, 2011