About Mass Traits

See UMassEntityTraitBase. In BuildTemplate you can add fragments and cache values. This is run when you press the “Validate Entity Config” button.

To use AddSharedFragment you must first create a shared fragment. Here is a code snippet for that.

FMassEntityManager& EntityManager = UE::Mass::Utils::GetEntityManagerChecked(World);
FSharedStruct SharedFragment = EntityManager.GetOrCreateSharedFragment<FMassSimulationLODSharedFragment>(FConstStructView::Make(Params), Params);

If you want to pass constructor params see other usages in engine.