procedure TWinControl.WMNCPaint(var Message: TMessage);

const

  InnerStyles: array[TBevelCut] of Integer = (, BDR_SUNKENINNER, BDR_RAISEDINNER, );

  OuterStyles: array[TBevelCut] of Integer = (, BDR_SUNKENOUTER, BDR_RAISEDOUTER, );

  EdgeStyles: array[TBevelKind] of Integer = (, , BF_SOFT, BF_FLAT);

  Ctl3DStyles: array[Boolean] of Integer = (BF_MONO, );

var

  DC: HDC;

  RC, RW, SaveRW: TRect;

  EdgeSize: Integer;

  WinStyle: Longint;

begin

  { Get window DC that is clipped to the non-client area }

  if (BevelKind <> bkNone) or (BorderWidth > ) then

  begin

    DC := GetWindowDC(Handle);

    try

      Windows.GetClientRect(Handle, RC);

      GetWindowRect(Handle, RW);

      MapWindowPoints(, Handle, RW, );

      OffsetRect(RC, -RW.Left, -RW.Top);

      ExcludeClipRect(DC, RC.Left, RC.Top, RC.Right, RC.Bottom);

      { Draw borders in non-client area }

      SaveRW := RW;

      InflateRect(RC, BorderWidth, BorderWidth);

      RW := RC;

      if BevelKind <> bkNone then

      begin

        EdgeSize := ;

        if BevelInner <> bvNone then Inc(EdgeSize, BevelWidth);

        if BevelOuter <> bvNone then Inc(EdgeSize, BevelWidth);

        with RW do

        begin

          WinStyle := GetWindowLong(Handle, GWL_STYLE);

          if beLeft in BevelEdges then Dec(Left, EdgeSize);

          if beTop in BevelEdges then Dec(Top, EdgeSize);

          if beRight in BevelEdges then Inc(Right, EdgeSize);

          if (WinStyle and WS_VSCROLL) <>  then Inc(Right, GetSystemMetrics(SM_CYVSCROLL));

          if beBottom in BevelEdges then Inc(Bottom, EdgeSize);

          if (WinStyle and WS_HSCROLL) <>  then Inc(Bottom, GetSystemMetrics(SM_CXHSCROLL));

        end;

        DrawEdge(DC, RW, InnerStyles[BevelInner] or OuterStyles[BevelOuter],

          Byte(BevelEdges) or EdgeStyles[BevelKind] or Ctl3DStyles[Ctl3D] or BF_ADJUST);

      end;

      IntersectClipRect(DC, RW.Left, RW.Top, RW.Right, RW.Bottom);

      RW := SaveRW;

      { Erase parts not drawn }

      OffsetRect(RW, -RW.Left, -RW.Top);

      Windows.FillRect(DC, RW, Brush.Handle);

    finally

      ReleaseDC(Handle, DC);

    end;

  end;

  inherited; // 又发现这句对TWinControl.DefaultHandler的调用

  if ThemeServices.ThemesEnabled and (csNeedsBorderPaint in ControlStyle) then

    ThemeServices.PaintBorder(Self, False);

end;