创建圆角矩形窗口的问题

 

void CMainFrame::OnSize(UINT nType, int cx, int cy)
{
 CFrameWnd::OnSize(nType, cx, cy);

 // TODO: 在此处添加消息处理程序代码
 CRgn m_rgn;
 CRect m_rect;
 GetWindowRect(&m_rect);
 m_rect-=m_rect.TopLeft();//请问这个什么意思
 m_rgn.CreateRoundRectRgn(m_rect.left,m_rect.top,m_rect.right,m_rect.bottom,50,50);
 SetWindowRgn(m_rgn,true);

}

 

 

谢谢