unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;

type
  TForm1 = class(TForm)
    Edit1: TEdit;
    Label1: TLabel;
    Button1: TButton;
  protected
    procedure RebuildWindowRgn;
    procedure Resize; override;
  public
    constructor Create(AOwner:TComponent);override;
  end;

var
  Form1: TForm1;

implementation
{$R *.DFM}

constructor TForm1.Create(AOwner:TComponent);
begin
  inherited;
  HorzScrollbar.Visible := false;
  VertScrollbar.Visible := false;
  RebuildWindowRgn;
end;

procedure TForm1.Resize;
begin
  inherited;
  RebuildWindowRgn;
end;

procedure TForm1.RebuildWindowRgn;
var
  FullRgn, Rgn: THandle;
  ClientX, ClientY, i: integer;
begin
  ClientX:=(Width-ClientWidth) div 2;
  ClientY:=Height-ClientHeight-ClientX;

  FullRgn:=CreateRectRgn(0,0,Width,Height);
  Rgn:=CreateRectRgn(ClientX,ClientY,ClientX+ClientWidth,
  ClientY+ClientHeight);

  CombineRgn(FullRgn,FullRgn,Rgn,RGN_DIFF);

  for i:=0 to ControlCount-1 do
    with Controls[i] do
    begin
      Rgn:=CreateRectRgn(ClientX+Left,ClientY+Top,
      ClientX+Left+Width,ClientY+Top+Height);
      CombineRgn(FullRgn,FullRgn,Rgn,RGN_OR);
    end;

  SetWindowRgn(Handle,FullRgn,true);
end;

end.