layout.signal_object_added.connect(sigc::mem_fun(this, &Layout3D::object_added));
layout.signal_object_removed.connect(sigc::mem_fun(this, &Layout3D::object_removed));
layout.signal_object_added.connect(sigc::mem_fun(this, &Layout3D::object_added));
layout.signal_object_removed.connect(sigc::mem_fun(this, &Layout3D::object_removed));