绘图 在客户区 在窗口全区 在屏幕全区 透明画刷

void CMy0617AView::OnLButtonUp(UINT nFlags, CPoint point)

{

//CWindowDC dc(this);//客户区

//CWindowDC dc(this->GetParent());//窗口区
CWindowDC dc(this->GetDesktopWindow());//全屏

dc.MoveTo(this->m_origin_point);

dc.LineTo(point);

//透明画刷

CClientDC dc(this);

CBrush *pBrush=CBrush::Fromhandle((HBRUSH)GetStockObject(NULL_BRUSH) );

CBrush *pOldBrush=dc.SelectObject(pBrush);

dc.Rectangle(...);

dc.SelectObject(pOldBrush);//恢复先前的画刷