How to tell if a TPanel is moved outside the visible part of a TForm

Problem/Question/Abstract:

I use SC_DRAGMOVE so I can drag a TPanel around a form. Now, how do I tell the form when the panel is outside the form and the form should add some scrollbars?

Answer:

unit Unit1;

interface

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

type
  TPanel = class(ExtCtrls.TPanel)
  private
    procedure WMExitSizeMove(var message: TMessage); message WM_EXITSIZEMOVE;
  end;

  TForm1 = class(TForm)
    StatusBar: TStatusBar;
    Button1: TButton;
    OpenDialog1: TOpenDialog;
    Label1: TLabel;
    ComboBox1: TComboBox;
    CheckBox1: TCheckBox;
    Panel1: TPanel;
    procedure Panel1MouseDown(Sender: TObject; Button: TMouseButton;
      Shift: TShiftState; X, Y: Integer);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.DFM}

procedure TForm1.Panel1MouseDown(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
const
  SC_DRAGMOVE = $F012;
begin
  Mouse.Capture := 0;
  sendmessage(panel1.handle, WM_SYSCOMMAND, SC_DRAGMOVE, 0);
end;

{ TPanel }

procedure TPanel.WMExitSizeMove(var message: TMessage);
begin
  Left := Left + 1;
  Left := Left - 1;
end;

end.