Advanced MFC Programming

Chapter 12. Screen Capturing & Printing
DIB_RGB_COLORS
)
);
::GlobalUnlock(hDib);
dc.SelectPalette(pPalOld, FALSE);
}
return hDib;
New Command
In sample 12.1\GDI, a new command Capture | Go! is added to mainframe menu IDR_MAINFRM. This
command is handled by function CGDIDoc::OnCaptureGo(). Within the function, we first minimize the
application by calling function CMainFrame::ShowWindow(…) using SW_SHOWMINIMIZED flag. Then we call
function CGDIView::PrepareCapture() to set the timer (This function contains only one statement).
Because we will minimize our application window, the capture should be delayed for a few seconds
after the user executes Capture | Go! command. Function CGDIView::PrepareCapture() does nothing but
setting up a timer with time out period set to 2 seconds. Function CGDIView::Capture() is called when the
timer times out. Within function CGDIView::Capture(), after the capture is made, function CGDIDoc::
GetCaptureBitmap(…) will be called to convert DDB to DIB and update the client window (Within this
function, CGDIDoc::ConvertDDBtoDIB(…) will be called).
In CGDIView::OnDraw(…), we use function ::SetDIBitsToDevice(…) to display DIB data. This is the
same with sample 10.4\GDI.
Figure 12-1 shows the time sequence of function calling.
Execute Capture | Go !
command
Call CGDIView::PrepareCapture() to
set timer
Call
CGDIDoc::ConvertDDBtoDIB(…)
to convert DDB to DIB
Time out
Call CGDIView::Capture() to make
the capture and store the image as DDB
Call CDocument::UpdateAllViews(…)
to update the client window
Call
CGDIDoc::GetCaptureBitmap(…) to
convert DDB to DIB
Function
CGDIDoc::GetCaptureBitmap(…)
Figure 12-1. Time sequence of capturing window
12.2 Capturing a Specified Window
One problem of the sample implemented in the previous section is that it can capture only the whole
desktop window. To improve it, we will add some new functions so that the user can specify any window
for capturing.
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