Right Scrolling text - delphi

Question

I am having one Delphi XE2 Project to display scrolling text (better "Marquee Text").
In my project I am having Timer1, Timer2, Button1, Button2, Label1 and Label2.
My object is to display some left scrolling text on Label1 after Button1.Click using Timer1 and some right scrolling text on Label2 after Button1.Click using Timer2.
I have defined the following codes:
unit Unit1;
interface
uses
Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.ExtCtrls, Vcl.StdCtrls;
type
TForm1 = class(TForm)
Label1: TLabel;
Label2: TLabel;
Button1: TButton;
Button2: TButton;
Timer1: TTimer;
Timer2: TTimer;
procedure FormCreate(Sender: TObject);
procedure Button1Click(Sender: TObject);
procedure Button2Click(Sender: TObject);
procedure Timer1Timer(Sender: TObject);
procedure Timer2Timer(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;
var
Form1: TForm1;
implementation
{$R *.dfm}
procedure TForm1.Button1Click(Sender: TObject);
begin
Timer1.Enabled := true;
Timer2.Enabled := true;
end;
procedure TForm1.Button2Click(Sender: TObject);
begin
Timer1.Enabled := false;
Timer2.Enabled := false;
end;
procedure TForm1.FormCreate(Sender: TObject);
begin
Timer1.Interval := 100;
Timer2.Interval := 100;
end;
procedure TForm1.Timer1Timer(Sender: TObject);
const
{$WRITEABLECONST ON}
ScrollingText : string = 'This is left scrolling text ';
{$WRITEABLECONST OFF}
var
ScrollPosition: Integer;
begin
Label1.Caption := ScrollingText;
for ScrollPosition := 1 to (Length(ScrollingText) - 1) do
begin
ScrollingText[ScrollPosition] := Label1.Caption[ScrollPosition + 1];
ScrollingText[Length(ScrollingText)] := Label1.Caption[1];
end;
end;
procedure TForm1.Timer2Timer(Sender: TObject);
const
{$WRITEABLECONST ON}
ScrollingText : string = 'This is right scrolling text ';
{$WRITEABLECONST OFF}
var
ScrollPosition: Integer;
begin
Label2.Caption := ScrollingText;
for ScrollPosition := (Length(ScrollingText) - 1) to 1 do
begin
ScrollingText[ScrollPosition] := Label2.Caption[ScrollPosition - 1];
ScrollingText[Length(ScrollingText)] := Label2.Caption[1];
end;
end;
end.
My problem is that Left Scrolling is happening using Timer1 but Right Scrolling is not happening using Timer2.

Answer 1

The for loop in Timer2Timer should run down instead of up:
procedure TForm1.Timer2Timer(Sender: TObject);
const
{$WRITEABLECONST ON}
ScrollingText : string = 'This is right scrolling text ';
{$WRITEABLECONST OFF}
var
ScrollPosition: Integer;
begin
Label2.Caption := ScrollingText;
for ScrollPosition := (Length(ScrollingText) - 1) downto 2 do
begin
ScrollingText[ScrollPosition] := Label2.Caption[ScrollPosition - 1];
ScrollingText[1] := Label2.Caption[Length(ScrollingText) - 1];
end;
end;
But I suggest not using writeable const nor using the for loop at all:
procedure TForm1.FormCreate(Sender: TObject);
begin
...
Label2.Caption := 'This is right scrolling text ';
end;
procedure TForm1.Timer2Timer(Sender: TObject);
var
S: String;
begin
S := Label2.Caption;
S := S[Length(S)] + Copy(S, 1, Length(S) - 1);
Label2.Caption := S;
end;