HPS APIENTRY WinGetPS( hwnd )
    HWND        hwnd;
{
    GrafPtr     pgraf;
    RgnHandle   hrgn;
    Rect        rect;

    ASSERT( ! ( _ps1.flags & PSF_INUSE ),
            "WinGetPS: PS already in use" );

    if( ! hwnd  ||  hwnd == HWND_DESKTOP )
      hwnd = _hwndDesktop;

    if( ! MpmValidateWindow(hwnd) )
      return NULL;

    /* Clear the cache PS and mark it as in use */

    memzero( &_ps1 );
    _ps1.hwnd = hwnd;
    _ps1.flags |= PSF_INUSE;

    /* Copy the Mac window's GrafPort */

    if( hwnd == _hwndDesktop )
      GetWMgrPort( &pgraf );
    else
      pgraf = &PWINOFHWND(hwnd)->port;

    _ps1.port = *pgraf;

    _ps1.port.visRgn = NewRgn();
    CopyRgn( pgraf->visRgn, _ps1.port.visRgn );

    _ps1.port.clipRgn = NewRgn();
    CopyRgn( pgraf->clipRgn, _ps1.port.clipRgn );

    /* Clip the visRgn down to this window's rectangle in case it's
       a child window */

    if( ! ( MYWNDOF(hwnd).flStyle & WS_PARENTCLIP ) )
    {
      hrgn = NewRgn();
      MpmQueryMacRect( hwnd, &rect );
      RectRgn( hrgn, &rect );
      SectRgn( _ps1.port.visRgn, hrgn, _ps1.port.visRgn );
      DisposeRgn( hrgn );
    }

    /* Handle WS_CLIPCHILDREN and WS_CLIPSIBLINGS here? */

    return _hps1;
}