if (new_pos != points.front().get_x()) {
points.front().set_x (new_pos);
points.back().set_x (new_pos);
canvas_item.property_points() = points;
if (new_pos != points.front().get_x()) {
points.front().set_x (new_pos);
points.back().set_x (new_pos);
canvas_item.property_points() = points;