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DoubleBuffered := True;					

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procedure TForm1.Button1Click(Sender: TObject);
var
  n: Integer;
begin
  for n := 1 to 1000 do
    begin
      application.ProcessMessages;
      panel1.left := n;
      if application.Terminated  then break;
    end;
end;					

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unit Unit1;

interface

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

type
  TForm1 = class(TForm)
    Panel1: TPanel;
    Panel2: TPanel;
    procedure Image1MouseEnter(Sender: TObject);
    procedure Image1MouseLeave(Sender: TObject);
    procedure FormCreate(Sender: TObject);
  private
    { Private-Deklarationen }
  public
    { Public-Deklarationen }
    procedure OnIdle(Sender: TObject; var Done: Boolean);
  end;

var
  Form1: TForm1;
  over: boolean = false;
implementation

{$R *.dfm}


procedure TForm1.OnIdle(Sender: TObject; var Done: Boolean);
begin
  if not over then exit;

  if (panel1.Left < 500) then
    begin
      panel1.Left := panel1.Left + 1;
      done := false;
    end;
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  application.OnIdle := onIdle;
end;

procedure TForm1.Image1MouseEnter(Sender: TObject);
begin
  over := true;
  panel1.Left := -300;
end;

procedure TForm1.Image1MouseLeave(Sender: TObject);
begin
  over := false;
end;

end.