Пример отрисовки TOutline

procedure TForm1.FormCreate(Sender: TObject);
begin
  BitmapPlus := TBitmap.Create;
  BitmapPlus.LoadFromFile('c:\delphi\images\default\outplus.bmp');
  BitmapMinus := TBitmap.Create;
  BitmapMinus.LoadFromFile('c:\delphi\images\default\outminus.bmp');
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  BitMapPlus.Destroy;
  BitMapMinus.Destroy;
end;

procedure TForm1.Outline1DrawItem(Control: TWinControl;
  Index: Integer; Rect: TRect; State: TOwnerDrawState);
var
  iLeft, iht: integer;
  s: string;
  NodeInView: TOutlineNode;
  col: TColor;
  {Примечание: BitMapvariables BitMapPlus и ..
  Минус объявлены глобально и грузятся при создании формы}
begin
  with (Control as TOutline).Canvas do
  begin
    {рисуем на холсте элемента управления, не на форме}
    IndexInFull := outline1.getitem(rect.left + 1, rect.top + 1);
    NodeInView := Outline1.Items[IndexInFull];
    Font := Outline1.Font;
    iLeft := Rect.Left;
    iht := Outline1.ItemHeight;
    inc(iLeft, iht * (NodeInView.level - 1));
    s := NodeInView.Text;
    Col := clWindow;
    Font.Color := clWindowText;
    Brush.Color := col;
    FillRect(Rect); { очищаем прямоугольник }
    if NodeInView.HasItems and not NodeInView.Expanded then
      {Draw(iLeft,Rect.Top, BitmapPlus)}
      BrushCopy(Bounds(iLeft + 1, Rect.Top + 1, iht - 2, iht - 2), BitMapPlus,
        Bounds(0, 0, BitMapPlus.Width, BitMapPlus.Height),
        BitMapPlus.TransparentColor);
    if NodeInView.Expanded and NodeInView.HasItems then
      BrushCopy(Bounds(iLeft + 1, Rect.Top + 1, iht - 2, iht - 2), BitMapMinus,
        Bounds(0, 0, BitMapMinus.Width, BitMapMinus.Height),
        BitMapMinus.TransparentColor);
    if Copy(NodeInView.Text, Length(NodeinView.Text), 1) = 'y' then
      Col := clAqua;
    if Outline1.SelectedItem = IndexInFull then
    begin
      Col := clHighlight;
      Font.Color := clHighlightText
    end;
    Brush.Color := col;
    inc(ILeft, iht);
    TextOut(iLeft, Rect.Top, s);
  end;
end;