怎样在不同位置重画其中一条线使原来位置上的线消失,并保持背景?

Question

各位高手:
  模态对话框中的CListCtrl控件中设置了背景位图,并画了很多条直线,怎样在不同位置重画其中一条线使原来位置上的线消失,并保持背景? 最好给出例子代码.
  高分求教!

Answer 1

创建画笔的时候用xor，擦的时候再画一遍就行了

Answer 2

BOOL CMyView::ReDrawRect(CRect Oldrect)
{
CDC *pdc = GetDC();
CPen pen, *oldPen = NULL;

pen.CreatePen(PS_SOLID, 2, RGB(255, 255, 255));
oldPen = pdc->SelectObject(&pen);
INT OldMode = pdc->SetROP2(R2_XORPEN);

pdc->MoveTo(Oldrect.TopLeft());
pdc->LineTo(Oldrect.right, Oldrect.top);
pdc->MoveTo(Oldrect.right, Oldrect.top);
pdc->LineTo(Oldrect.BottomRight());
pdc->MoveTo(Oldrect.BottomRight());
pdc->LineTo(Oldrect.left, Oldrect.bottom);
pdc->MoveTo(Oldrect.left, Oldrect.bottom);
pdc->LineTo(Oldrect.TopLeft());

pdc->SetROP2(OldMode);
pdc->SelectObject(oldPen);
ReleaseDC(pdc);

return TRUE;
}
同样的位置画两遍就好了

Answer 3

CPen pen(PS_SOLID, 0, RGB(0,255,0));
CPen* pOldPen=pDC->SelectObject(&pen);
CBrush* pOldBrush=(CBrush*)pDC->SelectStockObject(NULL_BRUSH);
int nOldDrawMode=pDC->SetROP2(R2_XORPEN);
...//绘制代码
pDC->SelectObject(pOldPen);
pDC->SelectObject(pOldBrush);
pDC->SetROP2(nOldDrawMode);

Answer 4

按各位指导的方法直接在显示CDC上画2次实现了使直线消失,但是直接在显示CDC上画线界面切换后就使需要的线段也消失了;
所以我在内存CDC上画线后拷贝到显示CDC.结果使直线消失出现了问题.
在自定义函数OnDrawLine()中内存CDC上创建画笔的时候用xor,结果什么线都画不出,
在系统函数OnDraw(CDC* pDC)中显示CDC上加上一句int nOldDrawMode=pDC->SetROP2(R2_XORPEN),函数OnDrawLine()中屏蔽掉相关语句, 结果重画第2次不能使直线消失,
请高手们指导.
代码如下:m_pMemDC和m_pBitmap 是全局变量:int CMyView::OnCreate(LPCREATESTRUCT lpCreateStruct) {
.....
  m_nMaxX = GetSystemMetrics(SM_CXSCREEN);
  m_nMaxY = GetSystemMetrics(SM_CYSCREEN);
  CDC* pDC = GetDC();
  m_pMemDC->CreateCompatibleDC(pDC);
  m_pBitmap->CreateCompatibleBitmap(pDC,m_nMaxX,m_nMaxY);
....
}
void CLineTstView::OnDraw(CDC* pDC)
{
....
CBitmap* pOldBitmap = m_pMemDC->SelectObject(m_pBitmap); pDC->BitBlt(0,0,m_nMaxX,
m_nMaxY,m_pMemDC,0,0,SRCCOPY);
m_pMemDC->SelectObject(pOldBitmap);
}void CMyView::OnDrawLine() 
{
CBitmap* pOldBitmap = m_pMemDC->SelectObject(m_pBitmap);
CPen pen;
pen.CreatePen(PS_SOLID,m_nLineWidth,m_cLineColor);
CPen* pOldPen = m_pMemDC->SelectObject(&pen);
CBrush* pOldBrush = (CBrush*)m_pMemDC->SelectStockObject(NULL_BRUSH); int nOldDrawMode=m_pMemDC->SetROP2(R2_XORPEN); m_pMemDC->MoveTo(m_ptStart);
m_pMemDC->LineTo(point); Invalidate(FALSE); m_pMemDC->SelectObject(pOldBitmap);
m_pMemDC->SelectObject(pOldPen);
m_pMemDC->SelectObject(pOldBrush);
m_pMemDC->SetROP2(nOldDrawMode);
}

Answer 5

你应该将内存的 绘图上下文传递给函数，而不能直接用OnDraw(CDC *pDC);

Answer 6

zhaogaojian(米柑年成):
   能否具体点,将内存的绘图上下文传递给什么函数? 给几句代码.