橡皮条如何不擦除背景?

Question

做了一个橡皮条的直线,不过在移动时背景内容也被擦除了~~~
请问怎么做到不擦除背景部分?
谢谢!

Answer 1

设置绘图模式，SetROP2(R2_NOT)
http://msdn2.microsoft.com/en-us/library/99ax95h9(VS.71).aspx

Answer 2

试下来使用NOT NOTXORPEN的效果是一样的,都是将背景擦掉了,XORPEN则是都是黑线.我还是把代码贴出来吧:(写在MouseMove函数里的)
if(m_CurrentOperation == Query_Distance && m_Dist_Click != 0)
{
m_Curr_Move = m_map.ToMapPoint(float(X),float(Y));

CDC* pDC = GetDC();
int DrawMode = pDC->SetROP2(R2_NOTXORPEN);
pDC->SelectStockObject(NULL_BRUSH); DrawLine(pDC,m_Dist_Start,m_Dist_End); pDC->SetROP2(DrawMode);
DrawLine(pDC,m_Dist_Start,m_Curr_Move);
m_Dist_End = m_Curr_Move; ReleaseDC(pDC);
}

Answer 3

problems solved.
the order ofpDC->SetROP2(DrawMode);
DrawLine(pDC,m_Dist_Start,m_Curr_Move);should be changed