请问这里的SetROP2函数是什么意思?
void CDrawLineView::OnLButtonDown(UINT nFlags, CPoint point)
{
CDC* pDC = GetDC();
pDC->SelectStockObject(NULL_BRUSH);
switch(m_Step)
{
case 0:
m_Startp = point;
m_Endp = point;
m_Step++;
break;
case 1:
m_Endp = point;
m_Step = 0 ;
pDC->MoveTo(m_Startp);
pDC->LineTo(m_Endp);
break;
default: ;
}
ReleaseDC(pDC);
CView::OnLButtonDown(nFlags, point);
}
void CDrawLineView::OnMouseMove(UINT nFlags, CPoint point)
{
CDC* pDC = GetDC();
int nDrawmode = pDC->SetROP2(R2_NOT);
pDC->SelectStockObject(NULL_BRUSH);
if(m_Step==1)
{
pDC->MoveTo(m_Startp);
pDC->LineTo(m_Endp);
pDC->MoveTo(m_Startp);
pDC->LineTo(point);
m_Endp = point;
}
pDC->SetROP2(nDrawmode);
ReleaseDC(pDC);
CView::OnMouseMove(nFlags, point);
}
请问这两句 int nDrawmode = pDC->SetROP2(R2_NOT);
pDC->SetROP2(nDrawmode); 在这里是什么意思 ?没有为什么就不行?