grab_button->show();
add_action_widget(*grab_button,2);
grab_button->signal_clicked().connect(sigc::mem_fun(*this, &Dialog_Gradient::on_grab_pressed));
grab_button->show();
add_action_widget(*grab_button,2);
grab_button->signal_clicked().connect(sigc::mem_fun(*this, &Dialog_Gradient::on_grab_pressed));