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Screen Capture to the Clipboard

, 5 Apr 2001
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How do you capture the bitmap of a window? This little download shows how, and places the bitmap on the clipboard.

Introduction

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.

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
    }

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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License

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About the Author

Joseph M. Newcomer

United States United States
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Comments and Discussions

 
GeneralTake a snapshot of a hidden window PinmemberMember 368961631-Mar-08 3:39 
GeneralRe: Take a snapshot of a hidden window PinmemberJoseph M. Newcomer31-Mar-08 4:02 
GeneralRe: Take a snapshot of a hidden window PinmemberMember 368961631-Mar-08 4:58 
GeneralRe: Take a snapshot of a hidden window PinmemberJoseph M. Newcomer31-Mar-08 7:53 
GeneralRe: Take a snapshot of a hidden window PinmemberMember 368961631-Mar-08 8:20 
GeneralRe: Take a snapshot of a hidden window PinmemberJoseph M. Newcomer31-Mar-08 12:43 
GeneralCapture MineSweeper Window PinmemberSwimmerDave20-Jun-06 7:32 
GeneralRe: Capture MineSweeper Window Pinmembervikrant kpr25-Jan-08 0:25 
GeneralOther bitmap formats PinmemberNeWi13-Oct-05 7:14 
GeneralRe: Other bitmap formats PinmemberNeWi13-Oct-05 7:35 
GeneralRe: Other bitmap formats PinmemberJoseph M. Newcomer18-Oct-05 7:46 
Generalwindows on top interfere Pinmemberbbrehm0430-Aug-05 16:10 
GeneralRe: windows on top interfere PinmemberJoseph M. Newcomer5-Sep-05 16:07 
GeneralRe: windows on top interfere Pinmemberbbrehm046-Sep-05 14:13 
GeneralCapture in Win32 - code Pinmemberpowerpop30-Jun-05 16:20 
QuestionHow to send captured screen shot through a socket? Pinmemberbijut6-May-05 7:39 
AnswerRe: How to send captured screen shot through a socket? PinmemberJames R. Twine6-May-05 8:18 
AnswerRe: How to send captured screen shot through a socket? PinmemberJoseph M. Newcomer6-May-05 11:31 
AnswerRe: How to send captured screen shot through a socket? Pinmemberjags_vc8-May-05 22:52 
Questionhow to get image in memory? Pinmemberjags_vc25-Feb-05 1:00 
AnswerRe: how to get image in memory? PinmemberJoseph M. Newcomer25-Feb-05 6:18 
GeneralRe: how to get image in memory? Pinmemberjags_vc27-Feb-05 18:13 
GeneralRe: how to get image in memory? PinmemberJoseph M. Newcomer27-Feb-05 22:02 
There are several possible answers here.
 
First, if you are trying to do some sort of remote control, be aware that (a) this is very, very nontrivial and (b) it is not done by capturing screen images.
 
By "already in memory", I presume you mean that you have used the techniques I described to actually capture the screen.
 
If you have a memory DC with a bitmap, you can get the bitmap image using GetBitmapBits, GetDIBits, etc. You cannot transfer it to another PC by using a memDC; you have to extract the bits from the memory DC, then send them via a socket to another computer, which is running the other side of the communication, which transfers the bits into a memDC, and then displays it on another window.
 
Sending a bitmap for a 1024x178 display requires a minimum of 2,359,296 bytes for 24-bit color. But not all those bytes have to be transmitted. Using compression schemes such as JPEG, GIF, or even ZIP, you can sometimes compress that image down by a factor of 20:1 (on a good day, with luck). Thus, on a good day you might only need 120K bytes. Your Mileage May Vary.
 
The time taken to do the transmission is, of course, a function of the network bandwidth. But don't think 100Base-T (100Mb/s) can actually transfer 100Mb/s. Concepts such as packetization mean that you will get a certain overhead every, well, 1456 bytes. You might need 85-100 packets to transmit a compressed image; five or ten times that for one that does not compress well. Add to this the transmission overhead, packet flow control, etc. and you will be lucky to get anything vaguely useful. Figure your best will be 1Mb, your worst, 18Mb. So the worst case would take, if 100% of the bandwidth could be used, about 188ms per screen. But realistically, you might expect to get one or two screens per second under worst case, over 100Base-T. For 10Base-T, that's one screen every 5 to 10 seconds. By the time you get to 1000Base-T (gigabit copper) you would hope to see 20ms/screen, but I doubt you can get that rate (that's 50 frames/sec, and I know that doesn't happen over 1000Base-T without a LOT of effort).
 
Dialup is ruled out entirely.
GeneralRe: how to get image in memory? Pinmemberjags_vc7-Mar-05 1:13 
GeneralRe: how to get image in memory? PinmemberJoseph M. Newcomer9-Mar-05 10:40 

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