MFC picture control控件不失真自适应图片显示

void CPrintScreen::OnPaint()
{
    CPaintDC dc(this);
    CImage  image;  
    CRect   rect;  
    //根据路径载入图片  
    image.Load(m_filepath);  

    CWnd *pWnd = NULL;  
    pWnd = GetDlgItem(IDC_PIC_STATIC);//获取控件句柄  
    pWnd->GetClientRect(&rect);//获取句柄指向控件区域的大小  
    CDC *pDc = NULL;  
    pDc = pWnd->GetDC();//获取picture的DC  
    SetStretchBltMode(pDc->m_hDC,STRETCH_HALFTONE);
    image.StretchBlt(pDc->m_hDC,rect,SRCCOPY);   
    ReleaseDC(pDc);  
}