SimulationLOD in Mass Framework

Author: Vlad Nepor
Updated on

How does SimulationLOD work in Mass Framework? Mass Framework is a ECS for managing crowds and traffic in Unreal 5.0 and above.

SimulationLOD with MassGameplay built-in resources

  • SimulationLOD Trait

    • Built-in MassGameplay.
    • Trait located At UE5/Engine/Plugins/Runtime/MassGameplay/Source/MassLOD.
    • SimulationLOD trait shares the same Trait file with LODCollector.
    UCLASS(meta = (DisplayName = "SimulationLOD"))
class MASSLOD_API UMassSimulationLODTrait : public UMassEntityTraitBase
{
	GENERATED_BODY()

	UPROPERTY(Category = "Config", EditAnywhere)
	FMassSimulationLODParameters Params;

	UPROPERTY(Category = "Config", EditAnywhere)
	bool bEnableVariableTicking = false;

	UPROPERTY(Category = "Config", EditAnywhere, meta = (EditCondition = "bEnableVariableTicking", EditConditionHides))
	FMassSimulationVariableTickParameters VariableTickParams;

protected:
	virtual void BuildTemplate(FMassEntityTemplateBuildContext& BuildContext, const UWorld& World) const override;
};
    void UMassSimulationLODTrait::BuildTemplate(FMassEntityTemplateBuildContext& BuildContext, const UWorld& World) const
{
	BuildContext.RequireFragment<FMassViewerInfoFragment>();
	BuildContext.RequireFragment<FTransformFragment>();

	FMassSimulationLODFragment& LODFragment = BuildContext.AddFragment_GetRef<FMassSimulationLODFragment>();

	// Start all simulation LOD in the Off 
	if(Params.bSetLODTags || bEnableVariableTicking)
	{
		LODFragment.LOD = EMassLOD::Off;
		BuildContext.AddTag<FMassOffLODTag>();
	}

	FMassEntityManager& EntityManager = UE::Mass::Utils::GetEntityManagerChecked(World);

	FConstSharedStruct ParamsFragment = EntityManager.GetOrCreateConstSharedFragment(Params);
	BuildContext.AddConstSharedFragment(ParamsFragment);

	uint32 ParamsHash = UE::StructUtils::GetStructCrc32(FConstStructView::Make(Params));
	FSharedStruct SharedFragment = EntityManager.GetOrCreateSharedFragmentByHash<FMassSimulationLODSharedFragment>(ParamsHash, Params);
	BuildContext.AddSharedFragment(SharedFragment);

	// Variable ticking from simulation LOD
	if(bEnableVariableTicking)
	{
		BuildContext.AddFragment<FMassSimulationVariableTickFragment>();
		BuildContext.AddChunkFragment<FMassSimulationVariableTickChunkFragment>();

		FConstSharedStruct VariableTickParamsFragment = EntityManager.GetOrCreateConstSharedFragment(VariableTickParams);
		BuildContext.AddConstSharedFragment(VariableTickParamsFragment);

		uint32 VariableTickParamsHash = UE::StructUtils::GetStructCrc32(FConstStructView::Make(VariableTickParams));
		FSharedStruct VariableTickSharedFragment = EntityManager.GetOrCreateSharedFragmentByHash<FMassSimulationVariableTickSharedFragment>(VariableTickParamsHash, VariableTickParams);
		BuildContext.AddSharedFragment(VariableTickSharedFragment);
	}
}