TGraphicObject = class
 public
   X1: integer;
   Y1: integer;
   X2: integer;
   Y2: integer;
   procedure Draw(ACanvas: TCanvas); virtual; abstract;
   constructor Create(AX1, AY1, AX2, AY2: integer);
 end;

 TLine = class(TGraphicObject)
 public
   procedure Draw(ACanvas: TCanvas); override;
 end;

 TEllipse = class(TGraphicObject)
 public
   procedure Draw(ACanvas: TCanvas); override;
 end;

constructor TGraphicObject.Create(AX1, AY1, AX2, AY2: integer);
begin
 X1 := AX1;
 Y1 := AY1;
 X2 := AX2;
 Y2 := AY2;
end;

procedure TLine.Draw(ACanvas: TCanvas);
begin
 ACanvas.MoveTo(X1, Y1);
 ACanvas.LineTo(X2, Y2);
end;

procedure TEllipse.Draw(ACanvas: TCanvas);
begin
 ACanvas.Ellipse(X1, Y1, X2, Y2);
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
 FGraphObjs := TList.Create;
 FGraphObjs.Add(TLine.Create(10, 10, 50, 50));
 FGraphObjs.Add(TEllipse.Create(10, 60, 100, 120));
end;

procedure TForm1.MagicButtonClick(Sender: TObject);
var i: integer;
begin
 for i := 0 to FGraphObjs.Count-1 do begin
    TGraphicObject(FGraphObjs[i]).Draw(Image2.Canvas);
 end;
end;