Disable gravity for links

[chapulina]

Gazebo Classic supports the <link><gravity> SDF element, which makes links float.

That hasn't been ported to Ignition yet, we aren't even parsing the flag into sdf::Link.

[rachase]

Ive been working on a plugin to disable grav, but not sure the right way to do it (ignition documentation is really rough...). I have the plugin loading, and the gravity is being printed out as 0 0 0 , but not sure if its being applied to the model at all. Any suggestions?

void AntiGrav::Configure(const ignition::gazebo::Entity &_entity,
    const std::shared_ptr<const sdf::Element> &_sdf,
    ignition::gazebo::EntityComponentManager &_ecm,
    ignition::gazebo::EventManager &/*_eventMgr*/)
{
    std::string link_name_;
    //ignition::gazebo::Model model{ ignition::gazebo::kNullEntity};
    ignition::gazebo::Model model{_entity};

    // Get sdf parameters
    if (_sdf->HasElement("linkName"))
    {
      link_name_ = _sdf->Get<std::string>("linkName");
    }
    else
    {
      ignerr << "The AntiGrav plugin for " << "[MODEL  NAME] " << "requires a `linkName` parameter tag" <<std::endl;
      return;
    }

    if(!model.Valid(_ecm))
    {
      ignerr << "AntiGrav plugin should be attached to a model entity. " << std::endl;
    return;
    }
    
    ignition::gazebo::Entity E = model.LinkByName(_ecm,link_name_);
    
    _ecm.CreateComponent<ignition::gazebo::components::Gravity>(_entity,ignition::gazebo::components::Gravity());

    //const components::Gravity *gravity = _ecm.Component<components::Gravity>(this->dataPtr->world);
    const ignition::gazebo::components::Gravity *gravity = _ecm.Component<ignition::gazebo::components::Gravity>(_entity);

    if(nullptr == gravity)
    {
      ignmsg << "gravity is a null pointer" << std::endl;
    }
    else
    {
      ignmsg << gravity->Data().X() << gravity->Data().Y() << gravity->Data().Z() << std::endl;
    }
}