How can I take a screenshot of a single CWnd object?

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Hi everybody!

I'm able to take a capture of entire screen by this code:

HDC hScrDC = ::GetDC(NULL);
HDC hMemDC = NULL;
BYTE *lpBitmapBits = NULL;
int xstart = 0;
int ystart = 0;
int nWidth = GetSystemMetrics(SM_CXSCREEN);
int nHeight = GetSystemMetrics(SM_CYSCREEN); 
hMemDC = CreateCompatibleDC(hScrDC); 
BITMAPINFO bi; 
ZeroMemory(&bi, sizeof(BITMAPINFO));
bi.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
bi.bmiHeader.biWidth = nWidth;
bi.bmiHeader.biHeight = nHeight;
bi.bmiHeader.biPlanes = 1;
bi.bmiHeader.biBitCount = 24;
HBITMAP bitmap = CreateDIBSection(hMemDC, &bi, DIB_RGB_COLORS, (LPVOID*)&lpBitmapBits, NULL, 0);
HGDIOBJ oldbmp = SelectObject(hMemDC, bitmap); 
::BitBlt(hMemDC, 0, 0, nWidth, nHeight, hScrDC, xstart, ystart, SRCCOPY);
BITMAPFILEHEADER bh;
ZeroMemory(&bh, sizeof(BITMAPFILEHEADER));
bh.bfType = 0x4d42; //bitmap 
bh.bfOffBits = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);
bh.bfSize = bh.bfOffBits + ((nWidth*nHeight)*3);
CFile file;
if(file.Open("sergio3.bmp", CFile::modeCreate | CFile::modeWrite))
{ 
	file.Write(&bh, sizeof(BITMAPFILEHEADER));
	file.Write(&(bi.bmiHeader), sizeof(BITMAPINFOHEADER));
	file.Write(lpBitmapBits, 3 * nWidth * nHeight);
	file.Close();
}
::SelectObject(hMemDC, oldbmp);
::DeleteObject(bitmap);
::DeleteObject(hMemDC);
::ReleaseDC(NULL, hScrDC);

That said, how can I take a screenshot of a single CWnd object?

Thank you!

Posted 9-Jun-11 11:02am

cammaratasergio

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TRK3 · Answer 1 · 2011-06-09T12:45:00

1) If you want the area the CWnd occupies exactly as it appears on the screen, use CWnd::GetWindowRect() http://msdn.microsoft.com/en-US/library/f3ef9c0s(v=VS.80).aspx[^] to get the position of the CWnd object that you are interested in and then extract just those pixels you are interested in from the code you have above.

or

2) If you want what the CWnd looks like irregardless of any other window obscuring it, use CWnd::Print() http://msdn.microsoft.com/en-US/library/90z8a14x(v=VS.80).aspx[^] and call it with a compatible DC that you created based on the size from GetClientRect.