如何画矩形和椭圆？在线等！

[wolf2004]

当按住鼠标左键画图的时候，能实时显示图形，但如何擦除先前的图形痕迹

[Loveedom]

用橡皮筋线的方法啊

[wolf2004]

to Loveedom(华莱士)
不会啊，请说的具体些

[thisisyjs]

异或方式画（画与檫除交替）

[Loveedom]

void CVistaView::OnLButtonDown(UINT nFlags, CPoint point)
{
m_ptFrom = point;
m_ptTo = point;
m_bTracking = TRUE;
}

void CVistaView::OnMouseMove(UINT nFlags, CPoint point)
{
CClientDC dc (this);
InvertLine (&dc, m_ptFrom, m_ptTo);
InvertLine (&dc, m_ptFrom, point);
m_ptTo = point;
}

void CVistaView::OnLButtonUp(UINT nFlags, CPoint point)
{
if (GetCapture () == this)
::ReleaseCapture ();
CClientDC dc (this);
CPen pen (PS_SOLID, 2, RGB (255, 0, 0));
dc.SelectObject (&pen);
dc.SelectStockObject(NULL_BRUSH);
dc.Rectangle(m_ptFrom.x, m_poFrom.y, point.x, point.y);
}

void CVistaView::InvertLine (CDC* pDC, CPoint ptFrom, CPoint ptTo)
{
//
// Invert a line of pixels by drawing a line in the R2_NOT drawing mode.
//
int nOldMode = pDC->SetROP2 (R2_NOT);
pDC->SelectStockObject(NULL_BRUSH);

pDC->Rectangle(ptFrom.x, ptFrom.y, ptTo.x, ptTo.y);

pDC->SetROP2 (nOldMode);
}

[byry]

在OnMouseMove事件中：
void CView::OnMouseMove(UINT nFlags, CPoint point)
{
CDC* pDC = GetDC();
//以下设置DC
CPen pen(PS_SOLID, 2, RGB(255,0,0)), *oldpen;
oldpen = pDC->SelectObject(&pen);

int oldmode = pDC->GetROP2();
pDC->SetROP2(R2_XORPEN);

//以下移动直线
pDC->MoveTo(m_firstPoint);
pDC->LineTo(m_lastPoint);//删除原图形

m_lastPoint = point;
//以下移动直线
pDC->MoveTo(m_firstPoint);
pDC->LineTo(m_lastPoint);

//以下恢复DC
pDC->SetROP2(oldmode);
pDC->SelectObject(oldpen);
pen.DeleteObject();//释放笔资源
ReleaseDC(pDC);
}
关键是一定要设置绘图模式pDC->SetROP2(R2_XORPEN);

[wolf2004]

to Loveedom(华莱士)
感谢！

[wolf2004]

to byry(pepsi)
感谢！