void CCanvasStatic::OnLButtonDown(UINT nFlags, CPoint point)
{
    SetCapture ();
    if (this == GetCapture ())
        (*m_pBGDlg->m_Shape).m_ptStart = point;

    CStatic::OnLButtonDown(nFlags, point);
}

void CCanvasStatic::OnLButtonUp(UINT nFlags, CPoint point)
{
    if (some expression)
    {
        (*m_pBGDlg->m_Shape).m_ptEnd = point;
        Invalidate ();
        UpdateWindow ();
    }
    ReleaseCapture ();

    CStatic::OnLButtonUp(nFlags, point);
}