Advanced MFC Programming

Chapter 13. Adding Special Features to Application
{
}
return TRUE;
Disabling Non-client Area Painting
We also need to pay attention to non-client area. Although the window does not have a caption bar, it
has resizable border, which also belongs to non-client area. By default, the border will be painted as a 3D
frame, which can be used for resizing the window. To make it transparent, we need to handle message
WM_NCPAINT. We don’t need to provide any implementation here because there is nothing to be painted. In
the sample, this message is handled in CBalloonDlg::OnNcPaint(), which is an empty function:
void CBalloonDlg::OnNcPaint()
{
}
We do need to override CBalloonDlg::OnPaint() to paint the elliptical area. Within this function, an
ellipse is drawn in the client area, also a pointer is drawn at the left bottom corner. Both ellipse and its
pointer are painted using yellow color.
Moving the Window with Mouse
Because the application does not have caption bar, we must provide a method to let the window be
moved through using mouse. This should be implemented by handling three messages: WM_LBUTTONDOWN,
WM_LBUTTONUP and WM_MOUSEMOVE. When the left button is pressed down, we need to set the window
capture. As the mouse moves (with left button held down), we need to move the window according to the
new mouse position by calling function CWnd::MoveWindow(…). When the left button is released, we need to
release the window capture.
Two variables are declared in class CBalloonDlg for this purpose: Boolean type variable
CBalloonDlg::m_bCapture and CPoint type variable CBalloonDlg::m_ptMouse. Here, CBalloonDlg::
m_ptMouse is used to record the previous mouse position. Whenever the window needs to be moved, we
call function CWnd::GetWindowRect(…) to obtain its current position and size, then offset the rectangle (The
size and position of the window is stored in a CRect type variable) according to both current and previous
mouse positions, and update variable CBalloonDlg::m_ptMosue. Since all the calculation is carried out in
the desktop coordinate system, we need to call function CWnd::ClientToScreen(…) to convert the mouse
position before using it (Mouse position is passed to the message handlers in the coordinate system of the
application window). The following is the WM_MOUSEMOVE message handler implemented in the sample:
void CBalloonDlg::OnMouseMove(UINT nFlags, CPoint point)
{
CRect rect;
POINT pt;
}
CDialog::OnMouseMove(nFlags, point);
if((nFlags & MK_LBUTTON) && m_bCapture)
{
pt=point;
ClientToScreen(&pt);
GetWindowRect(rect);
rect.OffsetRect(CPoint(pt)-m_ptMouse);
m_ptMouse=pt;
MoveWindow(rect);
}
This implementation is slow, because when mouse moves a small distance, the whole window need to
be redrawn at the new position. An alternative solution is to draw only the rectangular outline when mouse
is moving (with the left button held down), and update the window only when the left button is released. To
implement this, instead of calling function CWnd::MoveWindow(…) in WM_MOUSEMOVE message handler, we
need to call function CDC::DrawDragRect(…) to erase the previous rectangle outline and draw a new one.
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