Как реализовать выделение резиновым прямоугольником

uses stdctrls;

var
  Selecting: boolean = false;
  FirstPoint: TPoint;
  sel: TRect;

procedure DrawRect;
begin
  with Form1.Canvas do begin
    Pen.Style := psDot;
    Pen.Color := clGray;
    Pen.Mode := pmXor;
    Brush.Style := bsClear;
    Rectangle(sel.Left, sel.Top, sel.Right, sel.Bottom);
  end;
end;

procedure NormalRect(p1, p2: TPoint);
begin
  if p1.x <  p2.x then begin
    sel.Left := p1.x;
    sel.Right := p2.x;
  end else begin
    sel.Left := p2.x;
    sel.Right := p1.x;
  end;
  if p1.y <  p2.y then begin
    sel.Top := p1.y;
    sel.Bottom := p2.y;
  end else begin
    sel.Top := p2.y;
    sel.Bottom := p1.y;
  end;
end;

procedure TForm1.FormCreate(Sender: TObject);
var i: integer;
begin
  randomize;
  for i := 1 to random(5) + 5 do begin
    with TLabel.Create(Form1) do begin
      Caption := 'Label' + IntToStr(i);
      Left := random(Form1.ClientWidth - Width);
      Top := random(Form1.ClientHeight - Height);
      Visible := true;
      Parent := Form1;
    end;
  end;
end;

procedure TForm1.FormMouseDown(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
  if selecting or (Button < >  mbLeft) then Exit;
  SetCapture(Form1.Handle);
  Selecting := true;
  FirstPoint := Point(X, Y);
  sel := Bounds(X, Y, 0, 0);
end;

procedure TForm1.FormMouseMove(Sender: TObject; Shift: TShiftState; X,
  Y: Integer);
  procedure SelectLebel(lb: TLabel; r: TRect);
  var
    select: boolean;
    res: TRect;
  begin
    select := IntersectRect(res, lb.BoundsRect, r);
    if select and (lb.Color = clNavy) then Exit;
    if select then begin
      lb.Color := clNavy;
      lb.Font.Color := clWhite;
    end else begin
      lb.Color := clBtnFace;
      lb.Font.Color := clBlack;
    end;
  end;
var
  i: integer;
begin
  if not Selecting then Exit;
  DrawRect;
  NormalRect(FirstPoint, Point(X, Y));
  for i := 0 to Form1.ComponentCount - 1 do
    if (Form1.Components[i] is TLabel) then
      SelectLebel(Form1.Components[i] as TLabel, sel);
  Application.ProcessMessages;
  DrawRect;
end;

procedure TForm1.FormMouseUp(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
  if (not Selecting) or (Button < >  mbLeft) then Exit;
  NormalRect(FirstPoint, Point(X, Y));
  DrawRect;
  ReleaseCapture;
  Selecting := false;
end;

{
Программа была протестирована:
Дмитрий Бажин mailto:bsdriver@mail.ru
Юрий Кравченко mailto:ykravchenko@ukr.net

Все советы и замечания, пожалуйста,
присылайте на subscribe@program.dax.ru

Всего доброго,
Даниил Карапетян.
}