MFC实现透明画刷

CPoint ptOrigin; //定义一个点，用于存储画线的起点
void CMapBigView::OnLButtonDown(UINT nFlags, CPoint point)
{
// TODO: Add your message handler code here and/or call default

ptOrigin = point; //保存

CView::OnLButtonDown(nFlags, point);
}

void CMapBigView::OnLButtonUp(UINT nFlags, CPoint point)
{
// TODO: Add your message handler code here and/or call default

CClientDC dc(this);//获取设备描述表
CBrush *pBrush=CBrush::FromHandle((HBRUSH)GetStockObject(NULL_BRUSH));
//FromHandle一个画刷句柄转化为一个画刷对象
//GetStockObject(NULL) 获取一个透明画刷句柄
CBrush *pOldBrush=dc.SelectObject(pBrush);// 把画刷加载到设备表述表
dc.Rectangle(CRect(ptOrigin, point));
dc.SelectObject(pOldBrush);

CView::OnLButtonUp(nFlags, point);
}