path = gc->CreatePath ();
path.MoveToPoint (time_x (i), y_pos (_track.get()) + 4);
path.AddLineToPoint (time_x (i), y_pos (_track.get() + 1) - 4);
path = gc->CreatePath ();
path.MoveToPoint (time_x (i), y_pos (_track.get()) + 4);
path.AddLineToPoint (time_x (i), y_pos (_track.get() + 1) - 4);