interface

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

type
 TForm1 = class(TForm)
   Button1: TButton;
   Button2: TButton;
   procedure Button1Click(Sender: TObject);
   procedure Button2Click(Sender: TObject);
 private
   { Private declarations }
procedure WMGetMinMaxInfo(var msg: TWMGetMinMaxInfo);
message WM_GETMINMAXINFO;

 public
   { Public declarations }
 end;

var
 Form1: TForm1;

implementation

{$R *.DFM}
procedure TForm1.WMGetMinMaxInfo(var msg:
TWMGetMinMaxInfo);
begin
 inherited;
 with msg.MinMaxInfo^.ptMaxTrackSize do begin
   X := GetDeviceCaps( Canvas.handle, HORZRES ) +
(Width - ClientWidth);
   Y := GetDeviceCaps( Canvas.handle, VERTRES ) +
(Height - ClientHeight );
 end;

end;

procedure TForm1.Button1Click(Sender: TObject);
const
Rect: TRect = (Left: 0; Top: 0; Right: 0; Bottom: 0);
FullScreen: Boolean = False;
// Разворачиваем на весь экран
begin
FullScreen := not FullScreen;
if FullScreen then begin
Rect := BoundsRect;
SetBounds( Left - ClientOrigin.X,
Top - ClientOrigin.Y, GetDeviceCaps( Canvas.handle,
HORZRES )
+ (Width - ClientWidth), GetDeviceCaps( Canvas.handle,
VERTRES )
+ (Height - ClientHeight ));
                  end
else BoundsRect := Rect;
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
Close;
end;

end.