Effacer la dernière image dessinée

{-----------------------------------------
procedure TTreeShape.DrawShadowEtiqCircle;
 var rl,rt,rw,rh: Integer;
begin
  if Shadow then
  begin
    { Calcul dimensions width et height de l'ombre}
    ...
    Canvas.Ellipse(rl,rt,rl+rw,rt+rh);
  end;
end;
procedure TTreeShape.DrawEtiqCircle;
 var rl,rt,rw,rh: Integer;
begin
  { Calcul dimensions width et height de l'étiquette}
  ...
  Canvas.Ellipse(rl,rt,rl+rw,rt+rh);
end;

procedure TTreeShape.PaintTree;
begin
 With Canvas do
 begin
   Canvas.Brush.Color := FBrush.Color;
   Canvas.Pen.Color   := FPen.Color;
   Case FEtiquette of
     teCircle     : DrawEtiqCircle;
     teEllipse    : DrawEtiqEllipse;
     …
   end;
 end;
end;

procedure TTreeShape.ChangeRedraw(Sender: TObject);
begin
  Invalidate;
end;

procedure TTreeShape.SetEtiquette(value: TTypeEtiquet);
begin
  if value <> FEtiquette then
  begin
    FEtiquette := value;
    Paint;
  end;
end;

  protected
    procedure Paint; override;
    procedure PaintShadow; virtual;
    procedure PaintTree; virtual;

procedure TTreeShape.Paint;
var
  rc: bool;
  oldBmp: HBitmap;
  oldThumb: TRect;
begin
  inherited Paint;
  with Canvas do
  begin
    Brush.Color := FBrush.Color;
  //    FillRect(Canvas.ClipRect);
//    Pen.Mode := pmblack;//pmxor;
    {Création mémoire pour lasauvegarde du bitmap}
    if MemDC = 0 then MemDC := CreateCompatibleDC(Canvas.Handle);
    {Create image arbre}
    if Bitmap = 0 then
       Bitmap := CreateCompatibleBitmap(Canvas.Handle, Width, Height);
    Rect.top    := 0;
    Rect.bottom := Height;
    Rect.left   := (Width - 10) div 2;
    Rect.Right  := Rect.Left + 10;

  SelectObject(MemDC, OldBmp);
  end;
  if Shadow then PaintShadow;
  PaintTree;
end;