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How to Capture Screen ?

Posted on 1998-11-19
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Last Modified: 2013-11-20
Dear experts

I'm using VC++5.0 in WindowNT4.0 SP 3.
I'd like to capture the screen image programatically.
I have to save the certain area which has associated memory DC to 24 bit BMP file on any VGA color depth.
i.e. if my app run on non-true-color VGA environment, memoryDC must be changed and saved as 24 bit type.
For this, I tried as following :
 - CreateCompatibleBitmap(pMemDC,...)
 - Get 24 bit bitmap data with GetDIBits(hBitmap, ..).
But I always get empty data buffer. i.e. '0'.

Following is source code of my app.
--------
CRect rtWnd;
GetDlgItem(IDC_FRAME1)->GetClientRect(rtWnd);

CDC* pFrameWndDC;

BITMAPINFOHEADER      BmpInfoHdr;

BmpInfoHdr.biSize = sizeof(BITMAPINFOHEADER);
BmpInfoHdr.biWidth = rtWnd.Width();
BmpInfoHdr.biHeight = rtWnd.Height();
BmpInfoHdr.biPlanes = 1;
BmpInfoHdr.biBitCount = 24;
BmpInfoHdr.biCompression = BI_RGB;
BmpInfoHdr.biSizeImage = 0;
BmpInfoHdr.biXPelsPerMeter = 0;
BmpInfoHdr.biYPelsPerMeter = 0;
BmpInfoHdr.biClrUsed = 0;
BmpInfoHdr.biClrImportant = 0;

HDC hDC;
CBitmap* pBMP;
HBITMAP hBMP;

void*   pBitmapBuff = calloc((((rtWnd.Width()*3)+3)/4)*4 * rtWnd.Height() * 3, 1); // 24 Bit
      
int nTotlaFrameCount = m_lstMemDC.GetCount();

POSITION pos = m_lstMemDC.GetHeadPosition();

for(int i=0; i<nTotlaFrameCount; i++)
{
    pFrameWndDC = GetFrameDC(i);
            
    hDC = pFrameWndDC->GetSafeHdc();
    pBMP = new CBitmap;
    pBMP->CreateCompatibleBitmap(pFrameWndDC,
           (((rtWnd.Width()*3)+3)/4)*4, rtWnd.Height());
    hBMP = (HBITMAP) pBMP->GetSafeHandle();

    GetDIBits( hDC, hBMP, 0, BmpInfoHdr.biHeight,  
  pBitmapBuff, (LPBITMAPINFO) &BmpInfoHdr, DIB_RGB_COLORS);

   SaveAs24BMPFile("Test.bmp", pBitmapBuff, BmpInfoHdr);
   delete pBMP;
}
-------

Any comments will be appreciated.
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Question by:okg
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6 Comments
 

Author Comment

by:okg
ID: 1324968
Edited text of question
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Author Comment

by:okg
ID: 1324969
Edited text of question
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Author Comment

by:okg
ID: 1324970
Edited text of question
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LVL 12

Expert Comment

by:migel
ID: 1324971
HI! I can`t find BitBlt call in your code. According your code you don`t  capture screen? just create empty bitmap and get it`s buffer.
To capture screen you must select created bitmap into DC and copy screen buffer to them.
for example:
{
ClentToScreen(rtWnd);
HDC hDeskDC = ::GetDC(NULL);
HBITMAP hOldBm = ::SelectObject(hDC,  hBMP);
::BitBlt(hDC, hDeskDC, 0, 0, rtWnd.Width(), rtWnd.Height(), hDeskDC, rtWnd.Left, rtWnd. Top, SRCCOPY);
 ::SelectObject(hDC,  hOldBm );
::ReleaseDC(NULL, hDeskDC);
// now your hBMP contain copy of the screen image
}

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LVL 6

Expert Comment

by:snoegler
ID: 1324972
I've never tried this, but maybe it works ( it works at least
with CRichEditCtrl's ...)

CWnd *pDesktopWnd=GetDesktopWindow();
CDC  *pDesktopTempDC=pDesktopWnd->GetDC();
// Create compatible DC
CDC  *pMemDC=new CDC;
CBitmap *pMemBmp=new CBitmap;
pMemDC->CreateCompatibleDC(pDesktopTempDC);
pMemBmp->CreateCompatibleBitmap(pDesktopTempDC,
                                ::GetSystemMetrics(SM_CXSCREEN),
                                ::GetSystemMetrics(SM_CYSCREEN));
// Release the temporary DC
pDesktopWnd->ReleaseDC(pDesktopTempDC);

// Select the memory bitmap
int nSDC=pMemDC->SaveDC();
pMemDC->SelectObject(pMemBmp);
// Render the desktop window into the memory bitmap
GetDesktopWindow()->SendMessage(WM_PRINT,
                                (WPARAM)pMemDC->GetSafeHdc(),
                                PRF_CLIENT|
                                PRF_ERASEBKGND|
                                PRF_CHILDREN|PRF_OWNED);
pMemDC->RestoreDC(nSDC);
delete pMemDC;

// Now pMemBmp should contain the desktops' contents.
0
 
LVL 1

Accepted Solution

by:
atari earned 100 total points
ID: 1324973
Again my code snippet, it worked, I tested it yesterday 11/18/1998:

Tried to capture screen and presented in my mdi-view:

void CMyView::OnCaptureScreen()
{
  CClientDC clientDC(this); // get my dc
  CRect windowrect;
  GetClientRect(&windowrect);
 
  HDC screenDC=::GetDC(NULL); // get desktop dc
  CDC* dc = CDC::FromHandle(screenDC);
  CRect rectDesktop;
  if (!::SystemParametersInfo(SPI_GETWORKAREA,0,&rectDesktop,0))
        ::GetWindowRect(::GetDesktopWindow(),&rectDesktop);
  else
  {
      rectDesktop.right=::GetSystemMetrics(SM_CXSCREEN);
      rectDesktop.bottom=::GetSystemMetrics(SM_CYSCREEN);
      rectDesktop.right-=rectDesktop.left;
      rectDesktop.bottom-=rectDesktop.top;
      rectDesktop.left=-rectDesktop.left;
      rectDesktop.top=-rectDesktop.top;
  }
  CBitmap bitmap;
  bitmap.CreateCompatibleBitmap(dc,rectDesktop.Width(),rectDesktop.Height());
  CDC memDC;
  CBitmap *pOldBitmap;
  memDC.CreateCompatibleDC(dc);
  pOldBitmap=memDC.SelectObject(&bitmap);
  memDC.BitBlt(0,0,rectDesktop.Width(),rectDesktop.Height(),dc,0,0,SRCCOPY);
  clientDC.StretchBlt(windowrect.left,windowrect.top,windowrect.Width(),windowrect.Height(),&memDC,0,0,rectDesktop.Width(),rectDesktop.Height(),SRCCOPY);
  memDC.SelectObject(pOldBitmap);
}

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