Advanced MFC Programming

Chapter 12. Screen Capturing & Printing
For picture controls,
we can display various
types of images
Figure 12-4. Set the properties of a picture control
Variable CSelDlg::m_hWnd is used to store the handle of the selected window. Also, variable
CSelDlg::m_rectSelect is used to indicate the rectangle of the previously selected window. If this
rectangle is empty, no window is currently being reversed.
As the mouse moves, we will keep on receiving WM_MOUSEMOVE messages. In the sample, function
CSelDlg::DrawSelection(…) is implemented to handle this message. Within this function, first we create a
region that contains all of the desktop window excluding the area occupied by the application window. We
select this region into the desktop window DC before reversing any window. By doing this, if the selected
window is overlapped by the application window, the reversing effect does not apply to the application
window. The following portion of function CSelDlg::DrawSelection(…) shows how the region is created:
void CSelDlg::DrawSelection(CPoint point, BOOL bErase)
{
if(m_bCaptureOn == TRUE)
{
CWnd *pWnd;
CWindowDC dc(CWnd::GetDesktopWindow());
int nRop2Mode;
CRgn rgn;
CRgn rgnDesk;
CRect rect;
……
GetWindowRect(rect);
rgn.CreateRectRgnIndirect(rect);
AfxGetApp()->m_pMainWnd->GetWindowRect(rect);
rgnDesk.CreateRectRgnIndirect(rect);
rgn.CombineRgn(&rgnDesk, &rgn, RGN_OR);
rgnDesk.DeleteObject();
CWnd::GetDesktopWindow()->GetWindowRect(rect);
rgnDesk.CreateRectRgnIndirect(rect);
rgn.CombineRgn(&rgnDesk, &rgn, RGN_DIFF);
dc.SelectClipRgn(&rgn);
In order to resume the reversed window, the drawing mode should be set to R2_NOT, which will reverse
all the pixels contained in the rectangle when function CDC::Rectangle(…) is called. The drawing mode
can be set by calling function CDC::SetROP2(…):
……
……
nRop2Mode=dc.SetROP2(R2_NOT);
Then we call function CWnd::WindowFromPoint(…) to see if the current mouse cursor is over any
window. We use the returned pointer to retrieve the handle of that window, and compare it with the handles
of our application windows (both mainframe window and dialog box window). If there is a match, we
should not draw the rectangle because the cursor is over the application window (In this case, if there exists
a window that has been reversed, we should resume it). Otherwise, we further compare it with the handle
stored in CSelDlg::m_hWnd, if they are the same, we don’t do anything because the window under the
cursor has been reversed. If not, this means a new window is being selected and we should resume the old
reversed window (If there exists such a window) then reverse the newly selected one:
……
if
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