急急急！

但是还是要擦除上一次画的线 最好能给段代码

谢谢了 我弄出来了 在OnMouseMove中加入
if(m_flag==1)
            {
                CPen     newPen1(PS_SOLID,   0,RGB(255,0,0));
                CPen   *   pOldPen1   =   m_Pdc->SelectObject(&newPen1);
                int   nOldMode1;
                nOldMode1   =   m_Pdc->SetROP2(R2_NOTXORPEN);
                m_Pdc->MoveTo(0,oldbegin);
                m_Pdc->LineTo(rc.Width() ,oldbegin);
               
                m_Pdc->SetROP2(nOldMode1);
                m_Pdc->SelectObject(pOldPen1);
                oldbegin=point.y;
                m_flag=0;
            }
            
            if(m_flag==0)
            {
                CPen     newPen(PS_SOLID,   0,RGB(255,0,0));
                CPen   *   pOldPen   =   m_Pdc->SelectObject(&newPen);
                int   nOldMode;
                nOldMode   =   m_Pdc->SetROP2(R2_NOTXORPEN);
                m_Pdc->MoveTo(0,oldbegin);
                m_Pdc->LineTo(rc.Width() ,oldbegin);
                m_Pdc->SetROP2(nOldMode);
                m_Pdc->SelectObject(pOldPen);
                m_flag=1;
            }