public void OnSaveConvexShape()
 {
     _fd      = new FileDialog();
     _fd.Mode = FileDialog.ModeEnum.SaveFile;
     _fd.AddFilter("*.tres, *.res ; Resource files");
     _fd.Connect("file_selected", this, "OnConvexShapeSaveOK");
     _fd.DialogHideOnOk = true;
     AddChild(_fd);
     _fd.PopupCentered(new Vector2(800, 600));
 }