MFC对话框中绘制橡皮筋矩形

POINT ptDown;
POINT ptUp;

//Windows事件属于同步操作，必须在事件回调完成，才能进行下一步的操作
void CWinDlgDlg::OnMouseMove(UINT nFlags, CPoint point)
{
    if (nFlags == MK_LBUTTON)
    {

        CClientDC   dc(this);
        CRect   rc;
        rc.SetRect(ptDown.x, ptDown.y, ptUp.x, ptUp.y);
        rc.NormalizeRect();
        dc.DrawFocusRect(&rc);
        rc.SetRect(CPoint(ptDown.x, ptDown.y), point);
        rc.NormalizeRect();
        dc.DrawFocusRect(&rc);
        ptUp.x = point.x;
        ptUp.y = point.y;

    }

}

void CWinDlgDlg::OnLButtonDown(UINT nFlags, CPoint point)
{
    SetCapture();
    ptDown.x = point.x;
    ptDown.y = point.y;

    ptUp.x = point.x;
    ptUp.y = point.y;

}

void CWinDlgDlg::OnLButtonUp(UINT nFlags, CPoint point)
{
    ReleaseCapture();
    CClientDC   dc(this);
    CRect   rc;
    rc.SetRect(ptDown, point);
    rc.NormalizeRect();
    dc.DrawFocusRect(&rc);
    //dc.BitBlt(0,0,rc.Width(),rc.Height(),&dc ,rc.left,rc-,MERGECOPY);

}

LRESULT CTSCPlayer::OnMouseMove(UINT uMsg, WPARAM wParam, LPARAM lParam, BOOL& bHandled)
{
    //WPARAM wParam=MAKEWPARAM(IDOK,0);

    //if(uMsg == WM_KEYDOWN)消息类型
    if(wParam == MK_LBUTTON) //wParam == (MK_LBUTTON | MK_CONTROL) (wParam &MK_CONTROL) != NULL
    {

    }
    m_startPoint.x = LOWORD(lParam);
    m_startPoint.y = HIWORD(lParam);

    return 0;
}
    POINT pt;
    pt.x = GET_X_LPARAM(lParam);
    pt.y = GET_Y_LPARAM(lParam);