Is it possible if two object are on the same place to choose which object hides behind the other ?
Yes -- and no. The setPaintOrder method can be used to have ALL of one type object showing over ALL of another type. Otherwise, there is no documented way of doing it. Currently, however, objects more recently added into the world will show over those objects already in the world. This means you can take an actor and remove and re-add it into the world to have it show above another actor.