void CDocViewView::OnMouseMove(UINT nFlags, CPoint point) 
{
	// TODO: Add your message handler code here and/or call default
	if( m_bMouseDown )
	{
		CClientDC dc(this);
		dc.SetROP2( R2_NOT );
		dc.MoveTo( m_ptStart );	//д(갴µ)
		dc.LineTo( m_ptOld );	//ϴƶλ֮ʱ
		dc.MoveTo( m_ptStart );	//д㵽굱ǰλû
		dc.LineTo( point );		// 
		m_ptOld = point;	//굱ǰλһƶ¼"λ"
	}
	CView::OnMouseMove(nFlags, point);
}
