// Copyright Epic Games, Inc. All Rights Reserved.

/*=============================================================================
	GeometryCollection.cpp: UGeometryCollection methods.
=============================================================================*/
#include "GeometryCollection/GeometryCollectionObject.h"
#include "GeometryCollection/GeometryCollection.h"
#include "GeometryCollection/GeometryCollectionCache.h"
#include "UObject/DestructionObjectVersion.h"
#include "UObject/UE5MainStreamObjectVersion.h"
#include "Serialization/ArchiveCountMem.h"
#include "HAL/IConsoleManager.h"
#include "Interfaces/ITargetPlatform.h"
#include "UObject/Package.h"
#include "Materials/MaterialInstance.h"
#include "ProfilingDebugging/CookStats.h"
#include "EngineUtils.h"
#include "Engine/StaticMesh.h"
#include "PhysicsEngine/PhysicsSettings.h"


#if WITH_EDITOR
#include "GeometryCollection/DerivedDataGeometryCollectionCooker.h"
#include "GeometryCollection/GeometryCollectionConvexUtility.h"
#include "GeometryCollection/GeometryCollectionEngineSizeSpecificUtility.h"
#include "GeometryCollection/GeometryCollectionComponent.h"
#include "DerivedDataCacheInterface.h"
#include "Serialization/MemoryReader.h"
#include "NaniteBuilder.h"
#include "Rendering/NaniteResources.h"
// TODO: Temp until new asset-agnostic builder API
#include "StaticMeshResources.h"
#endif

#include "GeometryCollection/GeometryCollectionSimulationCoreTypes.h"
#include "Chaos/ChaosArchive.h"
#include "GeometryCollectionProxyData.h"

DEFINE_LOG_CATEGORY_STATIC(LogGeometryCollectionInternal, Log, All);

bool GeometryCollectionAssetForceStripOnCook = false;
FAutoConsoleVariableRef CVarGeometryCollectionBypassPhysicsAttributes(
	TEXT("p.GeometryCollectionAssetForceStripOnCook"),
	GeometryCollectionAssetForceStripOnCook,
	TEXT("Bypass the construction of simulation properties when all bodies are simply cached. for playback."));

bool bGeometryCollectionEnableForcedConvexGenerationInSerialize = true;
FAutoConsoleVariableRef CVarGeometryCollectionEnableForcedConvexGenerationInSerialize(
	TEXT("p.GeometryCollectionEnableForcedConvexGenerationInSerialize"),
	bGeometryCollectionEnableForcedConvexGenerationInSerialize,
	TEXT("Enable generation of convex geometry on older destruction files.[def:true]"));


#if ENABLE_COOK_STATS
namespace GeometryCollectionCookStats
{
	static FCookStats::FDDCResourceUsageStats UsageStats;
	static FCookStatsManager::FAutoRegisterCallback RegisterCookStats([](FCookStatsManager::AddStatFuncRef AddStat)
	{
		UsageStats.LogStats(AddStat, TEXT("GeometryCollection.Usage"), TEXT(""));
	});
}
#endif

static constexpr float DefaultMaxSizeValue = 99999.9;

UGeometryCollection::UGeometryCollection(const FObjectInitializer& ObjectInitializer)
	: Super(ObjectInitializer)
	#if WITH_EDITOR
	, bManualDataCreate(false)
	#endif
	, EnableClustering(true)
	, ClusterGroupIndex(0)
	, MaxClusterLevel(100)
	, DamageThreshold({ 500000.f, 50000.f, 5000.f })
	, PerClusterOnlyDamageThreshold(false)
	, ClusterConnectionType(EClusterConnectionTypeEnum::Chaos_MinimalSpanningSubsetDelaunayTriangulation)
	, ConnectionGraphBoundsFilteringMargin(0)
	, bUseFullPrecisionUVs(false)
	, bStripOnCook(false)
	, EnableNanite(false)
#if WITH_EDITORONLY_DATA
	, CollisionType_DEPRECATED(ECollisionTypeEnum::Chaos_Volumetric)
	, ImplicitType_DEPRECATED(EImplicitTypeEnum::Chaos_Implicit_Convex)
	, MinLevelSetResolution_DEPRECATED(10)
	, MaxLevelSetResolution_DEPRECATED(10)
	, MinClusterLevelSetResolution_DEPRECATED(50)
	, MaxClusterLevelSetResolution_DEPRECATED(50)
	, CollisionObjectReductionPercentage_DEPRECATED(0.0f)
#endif
	, bMassAsDensity(true)
	, Mass(2500.0f)
	, MinimumMassClamp(0.1f)
	, bRemoveOnMaxSleep(false)
	, MaximumSleepTime(5.0, 10.0)
	, RemovalDuration(2.5, 5.0)
	, EnableRemovePiecesOnFracture(false)
	, GeometryCollection(new FGeometryCollection())
{
	PersistentGuid = FGuid::NewGuid();
	InvalidateCollection();
#if WITH_EDITOR
	SimulationDataGuid = StateGuid;
	bStripOnCook = GeometryCollectionAssetForceStripOnCook;
#endif
}

FGeometryCollectionLevelSetData::FGeometryCollectionLevelSetData()
	: MinLevelSetResolution(5)
	, MaxLevelSetResolution(10)
	, MinClusterLevelSetResolution(25)
	, MaxClusterLevelSetResolution(50)
{
}

FGeometryCollectionCollisionParticleData::FGeometryCollectionCollisionParticleData()
	: CollisionParticlesFraction(1.0f)
	, MaximumCollisionParticles(60)
{
}



FGeometryCollectionCollisionTypeData::FGeometryCollectionCollisionTypeData()
	: CollisionType(ECollisionTypeEnum::Chaos_Volumetric)
	, ImplicitType(EImplicitTypeEnum::Chaos_Implicit_Convex)
	, LevelSet()
	, CollisionParticles()
	, CollisionObjectReductionPercentage(0.0f)
	, CollisionMarginFraction(0.f)
{
}

FGeometryCollectionSizeSpecificData::FGeometryCollectionSizeSpecificData()
	: MaxSize(DefaultMaxSizeValue)
	, CollisionShapes({ FGeometryCollectionCollisionTypeData()})
#if WITH_EDITORONLY_DATA
	, CollisionType_DEPRECATED(ECollisionTypeEnum::Chaos_Volumetric)
	, ImplicitType_DEPRECATED(EImplicitTypeEnum::Chaos_Implicit_Convex)
	, MinLevelSetResolution_DEPRECATED(5)
	, MaxLevelSetResolution_DEPRECATED(10)
	, MinClusterLevelSetResolution_DEPRECATED(25)
	, MaxClusterLevelSetResolution_DEPRECATED(50)
	, CollisionObjectReductionPercentage_DEPRECATED(0)
	, CollisionParticlesFraction_DEPRECATED(1.f)
	, MaximumCollisionParticles_DEPRECATED(60)
#endif
	, DamageThreshold(5000.0)
{
}


bool FGeometryCollectionSizeSpecificData::Serialize(FArchive& Ar)
{
	Ar.UsingCustomVersion(FUE5MainStreamObjectVersion::GUID);
	Ar.UsingCustomVersion(FPhysicsObjectVersion::GUID);
	return false;	//We only have this function to mark custom GUID. Still want serialize tagged properties
}

#if WITH_EDITORONLY_DATA
void FGeometryCollectionSizeSpecificData::PostSerialize(const FArchive& Ar)
{
	const int32 PhysicsObjectVersion = Ar.CustomVer(FPhysicsObjectVersion::GUID);
	const int32 StreamObjectVersion = Ar.CustomVer(FUE5MainStreamObjectVersion::GUID);
	// make sure to load back the deprecated values in the new structure if necessary
	// IMPORTANT : this was merge backed in UE4 and PhysicsObjectVersion had to be used,
	//		that's why we need to test both version to make sure backward asset compatibility is maintained
	if (Ar.IsLoading() && (
		StreamObjectVersion < FUE5MainStreamObjectVersion::GeometryCollectionUserDefinedCollisionShapes &&
		PhysicsObjectVersion < FPhysicsObjectVersion::GeometryCollectionUserDefinedCollisionShapes
		)) 
	{
		if (CollisionShapes.Num())
		{
			// @todo(chaos destruction collisions) : Add support for many
			CollisionShapes[0].CollisionType = CollisionType_DEPRECATED;
			CollisionShapes[0].ImplicitType = ImplicitType_DEPRECATED;
			CollisionShapes[0].CollisionObjectReductionPercentage = CollisionObjectReductionPercentage_DEPRECATED;
			CollisionShapes[0].CollisionMarginFraction = UPhysicsSettings::Get()->SolverOptions.CollisionMarginFraction;
			CollisionShapes[0].CollisionParticles.CollisionParticlesFraction = CollisionParticlesFraction_DEPRECATED;
			CollisionShapes[0].CollisionParticles.MaximumCollisionParticles = MaximumCollisionParticles_DEPRECATED;
			CollisionShapes[0].LevelSet.MinLevelSetResolution = MinLevelSetResolution_DEPRECATED;
			CollisionShapes[0].LevelSet.MaxLevelSetResolution = MaxLevelSetResolution_DEPRECATED;
			CollisionShapes[0].LevelSet.MinClusterLevelSetResolution = MinClusterLevelSetResolution_DEPRECATED;
			CollisionShapes[0].LevelSet.MaxClusterLevelSetResolution = MaxClusterLevelSetResolution_DEPRECATED;
		}
	}
}
#endif



void FillSharedSimulationSizeSpecificData(FSharedSimulationSizeSpecificData& ToData, const FGeometryCollectionSizeSpecificData& FromData)
{
	ToData.MaxSize = FromData.MaxSize;

	ToData.CollisionShapesData.SetNumUninitialized(FromData.CollisionShapes.Num());

	if (FromData.CollisionShapes.Num())
	{
		for (int i = 0; i < FromData.CollisionShapes.Num(); i++)
		{
			ToData.CollisionShapesData[i].CollisionType = FromData.CollisionShapes[i].CollisionType;
			ToData.CollisionShapesData[i].ImplicitType = FromData.CollisionShapes[i].ImplicitType;
			ToData.CollisionShapesData[i].LevelSetData.MinLevelSetResolution = FromData.CollisionShapes[i].LevelSet.MinLevelSetResolution;
			ToData.CollisionShapesData[i].LevelSetData.MaxLevelSetResolution = FromData.CollisionShapes[i].LevelSet.MaxLevelSetResolution;
			ToData.CollisionShapesData[i].LevelSetData.MinClusterLevelSetResolution = FromData.CollisionShapes[i].LevelSet.MinClusterLevelSetResolution;
			ToData.CollisionShapesData[i].LevelSetData.MaxClusterLevelSetResolution = FromData.CollisionShapes[i].LevelSet.MaxClusterLevelSetResolution;
			ToData.CollisionShapesData[i].CollisionObjectReductionPercentage = FromData.CollisionShapes[i].CollisionObjectReductionPercentage;
			ToData.CollisionShapesData[i].CollisionMarginFraction = FromData.CollisionShapes[i].CollisionMarginFraction;
			ToData.CollisionShapesData[i].CollisionParticleData.CollisionParticlesFraction = FromData.CollisionShapes[i].CollisionParticles.CollisionParticlesFraction;
			ToData.CollisionShapesData[i].CollisionParticleData.MaximumCollisionParticles = FromData.CollisionShapes[i].CollisionParticles.MaximumCollisionParticles;
		}
	}
	ToData.DamageThreshold = FromData.DamageThreshold;
}

FGeometryCollectionSizeSpecificData UGeometryCollection::GeometryCollectionSizeSpecificDataDefaults() 
{
	FGeometryCollectionSizeSpecificData Data;

	Data.MaxSize = DefaultMaxSizeValue;
	if (Data.CollisionShapes.Num())
	{
		Data.CollisionShapes[0].CollisionType = ECollisionTypeEnum::Chaos_Volumetric;
		Data.CollisionShapes[0].ImplicitType = EImplicitTypeEnum::Chaos_Implicit_Capsule;
		Data.CollisionShapes[0].LevelSet.MinLevelSetResolution = 5;
		Data.CollisionShapes[0].LevelSet.MaxLevelSetResolution = 10;
		Data.CollisionShapes[0].LevelSet.MinClusterLevelSetResolution = 25;
		Data.CollisionShapes[0].LevelSet.MaxClusterLevelSetResolution = 50;
		Data.CollisionShapes[0].CollisionObjectReductionPercentage = 1.0;
		Data.CollisionShapes[0].CollisionMarginFraction = UPhysicsSettings::Get()->SolverOptions.CollisionMarginFraction;
		Data.CollisionShapes[0].CollisionParticles.CollisionParticlesFraction = 1.0;
		Data.CollisionShapes[0].CollisionParticles.MaximumCollisionParticles = 60;
	}
	Data.DamageThreshold = 5000.0f;
	return Data;
}


void UGeometryCollection::ValidateSizeSpecificDataDefaults()
{
	auto HasDefault = [](const TArray<FGeometryCollectionSizeSpecificData>& DatasIn)
	{
		for (const FGeometryCollectionSizeSpecificData& Data : DatasIn)
		{
			if (Data.MaxSize >= DefaultMaxSizeValue)
			{
				return true;
			}
		}
		return false;
	};

	if (!SizeSpecificData.Num() || !HasDefault(SizeSpecificData))
	{
		FGeometryCollectionSizeSpecificData Data = GeometryCollectionSizeSpecificDataDefaults();
		if (Data.CollisionShapes.Num())
		{
#if WITH_EDITORONLY_DATA
			Data.CollisionShapes[0].CollisionType = CollisionType_DEPRECATED;
			Data.CollisionShapes[0].ImplicitType = ImplicitType_DEPRECATED;
			Data.CollisionShapes[0].LevelSet.MinLevelSetResolution = MinLevelSetResolution_DEPRECATED;
			Data.CollisionShapes[0].LevelSet.MaxLevelSetResolution = MaxLevelSetResolution_DEPRECATED;
			Data.CollisionShapes[0].LevelSet.MinClusterLevelSetResolution = MinClusterLevelSetResolution_DEPRECATED;
			Data.CollisionShapes[0].LevelSet.MaxClusterLevelSetResolution = MaxClusterLevelSetResolution_DEPRECATED;
			Data.CollisionShapes[0].CollisionObjectReductionPercentage = CollisionObjectReductionPercentage_DEPRECATED;
			Data.CollisionShapes[0].CollisionMarginFraction = UPhysicsSettings::Get()->SolverOptions.CollisionMarginFraction;
#endif
			if (Data.CollisionShapes[0].ImplicitType == EImplicitTypeEnum::Chaos_Implicit_LevelSet)
			{
				Data.CollisionShapes[0].CollisionType = ECollisionTypeEnum::Chaos_Surface_Volumetric;
			}
		}
		SizeSpecificData.Add(Data);
	}
	check(SizeSpecificData.Num());
}

void UGeometryCollection::UpdateConvexGeometry()
{
#if WITH_EDITOR
	if (GeometryCollection)
	{
		FGeometryCollectionConvexPropertiesInterface::FConvexCreationProperties ConvexProperties = GeometryCollection->GetConvexProperties();
		FGeometryCollectionConvexUtility::CreateNonOverlappingConvexHullData(GeometryCollection.Get(), ConvexProperties.FractionRemove, ConvexProperties.SimplificationThreshold, ConvexProperties.CanExceedFraction);
		InvalidateCollection();
	}
#endif
}


float KgCm3ToKgM3(float Density)
{
	return Density * 1000000;
}

float KgM3ToKgCm3(float Density)
{
	return Density / 1000000;
}

void UGeometryCollection::GetSharedSimulationParams(FSharedSimulationParameters& OutParams) const
{
	const FGeometryCollectionSizeSpecificData& SizeSpecificDefault = GetDefaultSizeSpecificData();

	OutParams.bMassAsDensity = bMassAsDensity;
	OutParams.Mass = bMassAsDensity ? KgM3ToKgCm3(Mass) : Mass;	//todo(ocohen): we still have the solver working in old units. This is mainly to fix ui issues. Long term need to normalize units for best precision
	OutParams.MinimumMassClamp = MinimumMassClamp;

	FGeometryCollectionSizeSpecificData InfSize;
	if (SizeSpecificDefault.CollisionShapes.Num())
	{
		InfSize.CollisionShapes.SetNum(1); // @todo(chaos destruction collisions) : Add support for multiple shapes. 
		OutParams.MaximumCollisionParticleCount = SizeSpecificDefault.CollisionShapes[0].CollisionParticles.MaximumCollisionParticles;

		ECollisionTypeEnum SelectedCollisionType = SizeSpecificDefault.CollisionShapes[0].CollisionType;

		if (SelectedCollisionType == ECollisionTypeEnum::Chaos_Volumetric && SizeSpecificDefault.CollisionShapes[0].ImplicitType == EImplicitTypeEnum::Chaos_Implicit_LevelSet)
		{
			UE_LOG(LogGeometryCollectionInternal, Verbose, TEXT("LevelSet geometry selected but non-particle collisions selected. Forcing particle-implicit collisions for %s"), *GetPathName());
			SelectedCollisionType = ECollisionTypeEnum::Chaos_Surface_Volumetric;
		}

		InfSize.CollisionShapes[0].CollisionType = SelectedCollisionType;
		InfSize.CollisionShapes[0].ImplicitType = SizeSpecificDefault.CollisionShapes[0].ImplicitType;
		InfSize.CollisionShapes[0].LevelSet.MinLevelSetResolution = SizeSpecificDefault.CollisionShapes[0].LevelSet.MinLevelSetResolution;
		InfSize.CollisionShapes[0].LevelSet.MaxLevelSetResolution = SizeSpecificDefault.CollisionShapes[0].LevelSet.MaxLevelSetResolution;
		InfSize.CollisionShapes[0].LevelSet.MinClusterLevelSetResolution = SizeSpecificDefault.CollisionShapes[0].LevelSet.MinClusterLevelSetResolution;
		InfSize.CollisionShapes[0].LevelSet.MaxClusterLevelSetResolution = SizeSpecificDefault.CollisionShapes[0].LevelSet.MaxClusterLevelSetResolution;
		InfSize.CollisionShapes[0].CollisionObjectReductionPercentage = SizeSpecificDefault.CollisionShapes[0].CollisionObjectReductionPercentage;
		InfSize.CollisionShapes[0].CollisionMarginFraction = SizeSpecificDefault.CollisionShapes[0].CollisionMarginFraction;
		InfSize.CollisionShapes[0].CollisionParticles.CollisionParticlesFraction = SizeSpecificDefault.CollisionShapes[0].CollisionParticles.CollisionParticlesFraction;
		InfSize.CollisionShapes[0].CollisionParticles.MaximumCollisionParticles = SizeSpecificDefault.CollisionShapes[0].CollisionParticles.MaximumCollisionParticles;
	}
	InfSize.MaxSize = TNumericLimits<float>::Max();
	OutParams.SizeSpecificData.SetNum(SizeSpecificData.Num() + 1);
	FillSharedSimulationSizeSpecificData(OutParams.SizeSpecificData[0], InfSize);

	for (int32 Idx = 0; Idx < SizeSpecificData.Num(); ++Idx)
	{
		FillSharedSimulationSizeSpecificData(OutParams.SizeSpecificData[Idx+1], SizeSpecificData[Idx]);
	}

	if (EnableRemovePiecesOnFracture)
	{
		FixupRemoveOnFractureMaterials(OutParams);
	}

	OutParams.SizeSpecificData.Sort();	//can we do this at editor time on post edit change?
}

void UGeometryCollection::FixupRemoveOnFractureMaterials(FSharedSimulationParameters& SharedParms) const
{
	// Match RemoveOnFracture materials with materials in model and record the material indices

	int32 NumMaterials = Materials.Num();
	for (int32 MaterialIndex = 0; MaterialIndex < NumMaterials; MaterialIndex++)
	{
		UMaterialInterface* MaterialInfo = Materials[MaterialIndex];

		for (int32 ROFMaterialIndex = 0; ROFMaterialIndex < RemoveOnFractureMaterials.Num(); ROFMaterialIndex++)
		{
			if (MaterialInfo == RemoveOnFractureMaterials[ROFMaterialIndex])
			{
				SharedParms.RemoveOnFractureIndices.Add(MaterialIndex);
				break;
			}
		}

	}
}

void UGeometryCollection::Reset()
{
	if (GeometryCollection.IsValid())
	{
		Modify();
		GeometryCollection->Empty();
		Materials.Empty();
		EmbeddedGeometryExemplar.Empty();
		InvalidateCollection();
	}
}

/** AppendGeometry */
int32 UGeometryCollection::AppendGeometry(const UGeometryCollection & Element, bool ReindexAllMaterials, const FTransform& TransformRoot)
{
	Modify();
	InvalidateCollection();

	// add all materials
	// if there are none, we assume all material assignments in Element are shared by this GeometryCollection
	// otherwise, we assume all assignments come from the contained materials
	int32 MaterialIDOffset = 0;
	if (Element.Materials.Num() > 0)
	{
		MaterialIDOffset = Materials.Num();
		Materials.Append(Element.Materials);
	}	

	return GeometryCollection->AppendGeometry(*Element.GetGeometryCollection(), MaterialIDOffset, ReindexAllMaterials, TransformRoot);
}

/** NumElements */
int32 UGeometryCollection::NumElements(const FName & Group) const
{
	return GeometryCollection->NumElements(Group);
}

/** RemoveElements */
void UGeometryCollection::RemoveElements(const FName & Group, const TArray<int32>& SortedDeletionList)
{
	Modify();
	GeometryCollection->RemoveElements(Group, SortedDeletionList);
	InvalidateCollection();
}

int UGeometryCollection::GetDefaultSizeSpecificDataIndex() const
{
	int LargestIndex = INDEX_NONE;
	float MaxSize = TNumericLimits<float>::Lowest();
	for (int i = 0; i < SizeSpecificData.Num(); i++)
	{
		const float SizeSpecificDataMaxSize = SizeSpecificData[i].MaxSize;
		if (MaxSize < SizeSpecificDataMaxSize)
		{
			MaxSize = SizeSpecificDataMaxSize;
			LargestIndex = i;
		}
	}
	check(LargestIndex != INDEX_NONE && LargestIndex < SizeSpecificData.Num());
	return LargestIndex;
}

/** Size Specific Data Access */
FGeometryCollectionSizeSpecificData& UGeometryCollection::GetDefaultSizeSpecificData()
{
	if (!SizeSpecificData.Num())
	{
		SizeSpecificData.Add(GeometryCollectionSizeSpecificDataDefaults());
	}
	const int DefaultSizeIndex = GetDefaultSizeSpecificDataIndex();
	return SizeSpecificData[DefaultSizeIndex];
}

const FGeometryCollectionSizeSpecificData& UGeometryCollection::GetDefaultSizeSpecificData() const
{
	ensure(SizeSpecificData.Num());
	const int DefaultSizeIndex = GetDefaultSizeSpecificDataIndex();
	return SizeSpecificData[DefaultSizeIndex];
}

/** ReindexMaterialSections */
void UGeometryCollection::ReindexMaterialSections()
{
	Modify();
	GeometryCollection->ReindexMaterials();
	InvalidateCollection();
}

void UGeometryCollection::InitializeMaterials()
{
	Modify();

	// Last Material is the selection one
	UMaterialInterface* BoneSelectedMaterial = LoadObject<UMaterialInterface>(nullptr, GetSelectedMaterialPath(), nullptr, LOAD_None, nullptr);

	TManagedArray<int32>& MaterialID = GeometryCollection->MaterialID;

	// normally we filter out instances of the selection material ID, but if it's actually used on any face we have to keep it
	bool bBoneSelectedMaterialIsUsed = false;
	for (int32 FaceIdx = 0; FaceIdx < MaterialID.Num(); ++FaceIdx)
	{
		int32 FaceMaterialID = MaterialID[FaceIdx];
		if (FaceMaterialID < Materials.Num() && Materials[FaceMaterialID] == BoneSelectedMaterial)
		{
			bBoneSelectedMaterialIsUsed = true;
			break;
		}
	}
	
	// We're assuming that all materials are arranged in pairs, so first we collect these.
	using FMaterialPair = TPair<UMaterialInterface*, UMaterialInterface*>;
	TSet<FMaterialPair> MaterialSet;
	for (int32 MaterialIndex = 0; MaterialIndex < Materials.Num(); ++MaterialIndex)
	{
		UMaterialInterface* ExteriorMaterial = Materials[MaterialIndex];
		if (ExteriorMaterial == BoneSelectedMaterial && !bBoneSelectedMaterialIsUsed) // skip unused bone selected material
		{
			continue;
		}
		
		// If we have an odd number of materials, the last material duplicates itself.
		UMaterialInterface* InteriorMaterial = Materials[MaterialIndex];
		while (++MaterialIndex < Materials.Num())
		{
			if (Materials[MaterialIndex] == BoneSelectedMaterial && !bBoneSelectedMaterialIsUsed) // skip bone selected material
			{
				continue;
			}
			InteriorMaterial = Materials[MaterialIndex];
			break;
		}

		MaterialSet.Add(FMaterialPair(ExteriorMaterial, InteriorMaterial));
	}
	
	// create the final material array only containing unique materials
	// alternating exterior and interior materials
	TMap<UMaterialInterface*, int32> ExteriorMaterialPtrToArrayIndex;
	TMap<UMaterialInterface*, int32> InteriorMaterialPtrToArrayIndex;
	TArray<UMaterialInterface*> FinalMaterials;
	for (const FMaterialPair& Curr : MaterialSet)
	{
		// Add base material
		TTuple< UMaterialInterface*, int32> BaseTuple(Curr.Key, FinalMaterials.Add(Curr.Key));
		ExteriorMaterialPtrToArrayIndex.Add(BaseTuple);

		// Add interior material
		TTuple< UMaterialInterface*, int32> InteriorTuple(Curr.Value, FinalMaterials.Add(Curr.Value));
		InteriorMaterialPtrToArrayIndex.Add(InteriorTuple);
	}

	// Reassign material ID for each face given the new consolidated array of materials
	for (int32 Material = 0; Material < MaterialID.Num(); ++Material)
	{
		if (MaterialID[Material] < Materials.Num())
		{
			UMaterialInterface* OldMaterialPtr = Materials[MaterialID[Material]];
			if (MaterialID[Material] % 2 == 0)
			{
				MaterialID[Material] = *ExteriorMaterialPtrToArrayIndex.Find(OldMaterialPtr);
			}
			else
			{
				MaterialID[Material] = *InteriorMaterialPtrToArrayIndex.Find(OldMaterialPtr);
			}
		}
	}

	// Set new material array on the collection
	Materials = FinalMaterials;

	// Last Material is the selection one
	BoneSelectedMaterialIndex = Materials.Add(BoneSelectedMaterial);

	GeometryCollection->ReindexMaterials();
	InvalidateCollection();
}



/** Returns true if there is anything to render */
bool UGeometryCollection::HasVisibleGeometry() const
{
	if(ensureMsgf(GeometryCollection.IsValid(), TEXT("Geometry Collection %s has an invalid internal collection")))
	{
		return ( (EnableNanite && NaniteData) || GeometryCollection->HasVisibleGeometry());
	}

	return false;
}

struct FPackedHierarchyNode_Old
{
	FSphere		LODBounds[64];
	FSphere		Bounds[64];
	struct
	{
		uint32	MinLODError_MaxParentLODError;
		uint32	ChildStartReference;
		uint32	ResourcePageIndex_NumPages_GroupPartSize;
	} Misc[64];
};

FArchive& operator<<(FArchive& Ar, FPackedHierarchyNode_Old& Node)
{
	for (uint32 i = 0; i < 64; i++)
	{
		Ar << Node.LODBounds[i];
		Ar << Node.Bounds[i];
		Ar << Node.Misc[i].MinLODError_MaxParentLODError;
		Ar << Node.Misc[i].ChildStartReference;
		Ar << Node.Misc[i].ResourcePageIndex_NumPages_GroupPartSize;
	}

	return Ar;
}


struct FPageStreamingState_Old
{
	uint32			BulkOffset;
	uint32			BulkSize;
	uint32			PageUncompressedSize;
	uint32			DependenciesStart;
	uint32			DependenciesNum;
};

FArchive& operator<<(FArchive& Ar, FPageStreamingState_Old& PageStreamingState)
{
	Ar << PageStreamingState.BulkOffset;
	Ar << PageStreamingState.BulkSize;
	Ar << PageStreamingState.PageUncompressedSize;
	Ar << PageStreamingState.DependenciesStart;
	Ar << PageStreamingState.DependenciesNum;
	return Ar;
}

// Parse old Nanite data and throw it away. We need this to not crash when parsing old files.
static void SerializeOldNaniteData(FArchive& Ar, UGeometryCollection* Owner)
{
	check(Ar.IsLoading());

	int32 NumNaniteResources = 0;
	Ar << NumNaniteResources;

	for (int32 i = 0; i < NumNaniteResources; ++i)
	{
		FStripDataFlags StripFlags(Ar, 0);
		if (!StripFlags.IsDataStrippedForServer())
		{
			bool bLZCompressed;
			TArray< uint8 >						RootClusterPage;
			FByteBulkData						StreamableClusterPages;
			TArray< uint16 >					ImposterAtlas;
			TArray< FPackedHierarchyNode_Old >	HierarchyNodes;
			TArray< FPageStreamingState_Old >	PageStreamingStates;
			TArray< uint32 >					PageDependencies;

			Ar << bLZCompressed;
			Ar << RootClusterPage;
			StreamableClusterPages.Serialize(Ar, Owner, 0);
			Ar << PageStreamingStates;

			Ar << HierarchyNodes;
			Ar << PageDependencies;
			Ar << ImposterAtlas;
		}
	}
}


/** Serialize */
void UGeometryCollection::Serialize(FArchive& Ar)
{
	bool bCreateSimulationData = false;
	Ar.UsingCustomVersion(FDestructionObjectVersion::GUID);
	Ar.UsingCustomVersion(FUE5MainStreamObjectVersion::GUID);
	Ar.UsingCustomVersion(FUE5ReleaseStreamObjectVersion::GUID);
	Ar.UsingCustomVersion(FPhysicsObjectVersion::GUID);
	
	Chaos::FChaosArchive ChaosAr(Ar);

	// The Geometry Collection we will be archiving. This may be replaced with a transient, stripped back Geometry Collection if we are cooking.
	TSharedPtr<FGeometryCollection, ESPMode::ThreadSafe> ArchiveGeometryCollection = GeometryCollection;

	bool bIsCookedOrCooking = Ar.IsCooking();
	if (bIsCookedOrCooking && Ar.IsSaving())
	{
#if WITH_EDITOR
		if (bStripOnCook && EnableNanite && NaniteData)
		{
			// If this is a cooked archive, we strip unnecessary data from the Geometry Collection to keep the memory footprint as small as possible.
			ArchiveGeometryCollection = GenerateMinimalGeometryCollection();
		}
#endif
	}

#if WITH_EDITOR
	//Early versions did not have tagged properties serialize first
	if (Ar.CustomVer(FDestructionObjectVersion::GUID) < FDestructionObjectVersion::GeometryCollectionInDDC)
	{
		if (Ar.IsLoading())
		{
			GeometryCollection->Serialize(ChaosAr);
		}
		else
		{
			ArchiveGeometryCollection->Serialize(ChaosAr);
		}
	}

	if (Ar.CustomVer(FDestructionObjectVersion::GUID) < FDestructionObjectVersion::AddedTimestampedGeometryComponentCache)
	{
		if (Ar.IsLoading())
		{
			// Strip old recorded cache data
			int32 DummyNumFrames;
			TArray<TArray<FTransform>> DummyTransforms;

			Ar << DummyNumFrames;
			DummyTransforms.SetNum(DummyNumFrames);
			for (int32 Index = 0; Index < DummyNumFrames; ++Index)
			{
				Ar << DummyTransforms[Index];
			}
		}
	}
	else
#endif
	{
		// Push up the chain to hit tagged properties too
		// This should have always been in here but because we have saved assets
		// from before this line was here it has to be gated
		Super::Serialize(Ar);
	}


	if (!SizeSpecificData.Num())
	{
		ValidateSizeSpecificDataDefaults();
	}

	if (Ar.CustomVer(FDestructionObjectVersion::GUID) < FDestructionObjectVersion::DensityUnitsChanged)
	{
		if (bMassAsDensity)
		{
			Mass = KgCm3ToKgM3(Mass);
		}
	}

	if (Ar.CustomVer(FDestructionObjectVersion::GUID) >= FDestructionObjectVersion::GeometryCollectionInDDC)
	{
		Ar << bIsCookedOrCooking;
	}

	//new versions serialize geometry collection after tagged properties
	if (Ar.CustomVer(FDestructionObjectVersion::GUID) >= FDestructionObjectVersion::GeometryCollectionInDDCAndAsset)
	{
#if WITH_EDITOR
		if (Ar.IsSaving() && !Ar.IsTransacting())
		{
			CreateSimulationDataImp(/*bCopyFromDDC=*/false);	//make sure content is built before saving
		}
#endif
		if (Ar.IsLoading())
		{
			GeometryCollection->Serialize(ChaosAr);
		}
		else
		{
			ArchiveGeometryCollection->Serialize(ChaosAr);
		}

		// Fix up the type change for implicits here, previously they were unique ptrs, now they're shared
		TManagedArray<TUniquePtr<Chaos::FImplicitObject>>* OldAttr = ArchiveGeometryCollection->FindAttributeTyped<TUniquePtr<Chaos::FImplicitObject>>(FGeometryDynamicCollection::ImplicitsAttribute, FTransformCollection::TransformGroup);
		TManagedArray<TSharedPtr<Chaos::FImplicitObject, ESPMode::ThreadSafe>>* NewAttr = ArchiveGeometryCollection->FindAttributeTyped<TSharedPtr<Chaos::FImplicitObject, ESPMode::ThreadSafe>>(FGeometryDynamicCollection::SharedImplicitsAttribute, FTransformCollection::TransformGroup);
		if (OldAttr)
		{
			if (!NewAttr)
			{
				NewAttr = &ArchiveGeometryCollection->AddAttribute<TSharedPtr<Chaos::FImplicitObject, ESPMode::ThreadSafe>>(FGeometryDynamicCollection::SharedImplicitsAttribute, FTransformCollection::TransformGroup);

				const int32 NumElems = GeometryCollection->NumElements(FTransformCollection::TransformGroup);
				for (int32 Index = 0; Index < NumElems; ++Index)
				{
					(*NewAttr)[Index] = TSharedPtr<Chaos::FImplicitObject, ESPMode::ThreadSafe>((*OldAttr)[Index].Release());
				}
			}

			ArchiveGeometryCollection->RemoveAttribute(FGeometryDynamicCollection::ImplicitsAttribute, FTransformCollection::TransformGroup);
		}
	}

	if (Ar.CustomVer(FDestructionObjectVersion::GUID) < FDestructionObjectVersion::GroupAndAttributeNameRemapping)
	{
		ArchiveGeometryCollection->UpdateOldAttributeNames();
		InvalidateCollection();
		bCreateSimulationData = true;
	}

	if (Ar.CustomVer(FUE5MainStreamObjectVersion::GUID) == FUE5MainStreamObjectVersion::GeometryCollectionNaniteData || 
		(Ar.CustomVer(FUE5MainStreamObjectVersion::GUID) >= FUE5MainStreamObjectVersion::GeometryCollectionNaniteCooked &&
		Ar.CustomVer(FUE5MainStreamObjectVersion::GUID) < FUE5MainStreamObjectVersion::GeometryCollectionNaniteTransient))
	{
		// This legacy version serialized structure information into archive, but the data is transient.
		// Just load it and throw away here, it will be rebuilt later and resaved past this point.
		SerializeOldNaniteData(ChaosAr, this);
	}

	if (Ar.CustomVer(FUE5MainStreamObjectVersion::GUID) >= FUE5MainStreamObjectVersion::GeometryCollectionNaniteTransient)
	{
		bool bCooked = Ar.IsCooking();
		Ar << bCooked;
		if (bCooked)
		{
			if (NaniteData == nullptr)
			{
				NaniteData = MakeUnique<FGeometryCollectionNaniteData>();
			}

			NaniteData->Serialize(ChaosAr, this);
		}
	}


	// will generate convex bodies when they dont exist. 
	if (Ar.CustomVer(FUE5ReleaseStreamObjectVersion::GUID) < FUE5ReleaseStreamObjectVersion::GeometryCollectionConvexDefaults
		&& Ar.CustomVer(FPhysicsObjectVersion::GUID) < FPhysicsObjectVersion::GeometryCollectionConvexDefaults)
	{
#if WITH_EDITOR
		if (bGeometryCollectionEnableForcedConvexGenerationInSerialize)
		{
			if (!FGeometryCollectionConvexUtility::HasConvexHullData(GeometryCollection.Get()) &&
				GeometryCollection::SizeSpecific::UsesImplicitCollisionType(SizeSpecificData, EImplicitTypeEnum::Chaos_Implicit_Convex))
			{
				GeometryCollection::SizeSpecific::SetImplicitCollisionType(SizeSpecificData, EImplicitTypeEnum::Chaos_Implicit_Box, EImplicitTypeEnum::Chaos_Implicit_Convex);
				bCreateSimulationData = true;
				InvalidateCollection();
			}
		}
#endif
	}

	if (Ar.CustomVer(FUE5MainStreamObjectVersion::GUID) < FUE5MainStreamObjectVersion::GeometryCollectionPerChildDamageThreshold)
	{
		// prior this version, damage threshold were computed per cluster and propagated to children
		PerClusterOnlyDamageThreshold = true; 
	}

#if WITH_EDITORONLY_DATA
	if (bCreateSimulationData)
	{
		CreateSimulationData();
	}

	//for all versions loaded, make sure sim data is up to date
 	if (Ar.IsLoading())
	{
		EnsureDataIsCooked();	//make sure loaded content is built
	}
#endif
}

const TCHAR* UGeometryCollection::GetSelectedMaterialPath()
{
	return TEXT("/Engine/EditorMaterials/GeometryCollection/SelectedGeometryMaterial.SelectedGeometryMaterial");
}

#if WITH_EDITOR

void UGeometryCollection::CreateSimulationDataImp(bool bCopyFromDDC)
{
	COOK_STAT(auto Timer = GeometryCollectionCookStats::UsageStats.TimeSyncWork());

	// Skips the DDC fetch entirely for testing the builder without adding to the DDC
	const static bool bSkipDDC = false;

	//Use the DDC to build simulation data. If we are loading in the editor we then serialize this data into the geometry collection
	TArray<uint8> DDCData;
	FDerivedDataGeometryCollectionCooker* GeometryCollectionCooker = new FDerivedDataGeometryCollectionCooker(*this);

	if (GeometryCollectionCooker->CanBuild())
	{
		if (bSkipDDC)
		{
			GeometryCollectionCooker->Build(DDCData);
			COOK_STAT(Timer.AddMiss(DDCData.Num()));
		}
		else
		{
			bool bBuilt = false;
			const bool bSuccess = GetDerivedDataCacheRef().GetSynchronous(GeometryCollectionCooker, DDCData, &bBuilt);
			COOK_STAT(Timer.AddHitOrMiss(!bSuccess || bBuilt ? FCookStats::CallStats::EHitOrMiss::Miss : FCookStats::CallStats::EHitOrMiss::Hit, DDCData.Num()));
		}

		if (bCopyFromDDC)
		{
			FMemoryReader Ar(DDCData, true);	// Must be persistent for BulkData to serialize
			Chaos::FChaosArchive ChaosAr(Ar);
			GeometryCollection->Serialize(ChaosAr);

			NaniteData = MakeUnique<FGeometryCollectionNaniteData>();
			NaniteData->Serialize(ChaosAr, this);
		}
	}
}

void UGeometryCollection::CreateSimulationData()
{
	CreateSimulationDataImp(/*bCopyFromDDC=*/false);
	SimulationDataGuid = StateGuid;
}

TUniquePtr<FGeometryCollectionNaniteData> UGeometryCollection::CreateNaniteData(FGeometryCollection* Collection)
{
	TUniquePtr<FGeometryCollectionNaniteData> NaniteData;

	TRACE_CPUPROFILER_EVENT_SCOPE(UGeometryCollection::CreateNaniteData);

	Nanite::IBuilderModule& NaniteBuilderModule = Nanite::IBuilderModule::Get();

	NaniteData = MakeUnique<FGeometryCollectionNaniteData>();

	// Transform Group
	const TManagedArray<int32>& TransformToGeometryIndexArray = Collection->TransformToGeometryIndex;
	const TManagedArray<int32>& SimulationTypeArray = Collection->SimulationType;
	const TManagedArray<int32>& StatusFlagsArray = Collection->StatusFlags;

	// Vertices Group
	const TManagedArray<FVector3f>& VertexArray = Collection->Vertex;
	const TManagedArray<TArray<FVector2f>>& UVsArray = Collection->UVs;
	const TManagedArray<FLinearColor>& ColorArray = Collection->Color;
	const TManagedArray<FVector3f>& TangentUArray = Collection->TangentU;
	const TManagedArray<FVector3f>& TangentVArray = Collection->TangentV;
	const TManagedArray<FVector3f>& NormalArray = Collection->Normal;
	const TManagedArray<int32>& BoneMapArray = Collection->BoneMap;

	// Faces Group
	const TManagedArray<FIntVector>& IndicesArray = Collection->Indices;
	const TManagedArray<bool>& VisibleArray = Collection->Visible;
	const TManagedArray<int32>& MaterialIndexArray = Collection->MaterialIndex;
	const TManagedArray<int32>& MaterialIDArray = Collection->MaterialID;

	// Geometry Group
	const TManagedArray<int32>& TransformIndexArray = Collection->TransformIndex;
	const TManagedArray<FBox>& BoundingBoxArray = Collection->BoundingBox;
	const TManagedArray<float>& InnerRadiusArray = Collection->InnerRadius;
	const TManagedArray<float>& OuterRadiusArray = Collection->OuterRadius;
	const TManagedArray<int32>& VertexStartArray = Collection->VertexStart;
	const TManagedArray<int32>& VertexCountArray = Collection->VertexCount;
	const TManagedArray<int32>& FaceStartArray = Collection->FaceStart;
	const TManagedArray<int32>& FaceCountArray = Collection->FaceCount;

	// Material Group
	const int32 NumGeometry = Collection->NumElements(FGeometryCollection::GeometryGroup);

	const uint32 NumTexCoords = Collection->NumUVLayers();
	const bool bHasColors = ColorArray.Num() > 0;

	TArray<FStaticMeshBuildVertex> BuildVertices;
	TArray<uint32> BuildIndices;
	TArray<int32> MaterialIndices;

	TArray<uint32> MeshTriangleCounts;
	MeshTriangleCounts.SetNum(NumGeometry);

	for (int32 GeometryGroupIndex = 0; GeometryGroupIndex < NumGeometry; GeometryGroupIndex++)
	{
		const int32 VertexStart = VertexStartArray[GeometryGroupIndex];
		const int32 VertexCount = VertexCountArray[GeometryGroupIndex];

		uint32 DestVertexStart = BuildVertices.Num();
		BuildVertices.Reserve(DestVertexStart + VertexCount);
		for (int32 VertexIndex = 0; VertexIndex < VertexCount; ++VertexIndex)
		{
			FStaticMeshBuildVertex& Vertex = BuildVertices.Emplace_GetRef();
			Vertex.Position = VertexArray[VertexStart + VertexIndex];
			Vertex.Color = bHasColors ? ColorArray[VertexStart + VertexIndex].ToFColor(false /* sRGB */) : FColor::White;
			Vertex.TangentX = FVector3f::ZeroVector;
			Vertex.TangentY = FVector3f::ZeroVector;
			Vertex.TangentZ = NormalArray[VertexStart + VertexIndex];
			for (int32 UVIdx = 0; UVIdx < UVsArray[VertexStart + VertexIndex].Num(); ++UVIdx)
			{
				Vertex.UVs[UVIdx] = UVsArray[VertexStart + VertexIndex][UVIdx];
				if (Vertex.UVs[UVIdx].ContainsNaN())
				{
					Vertex.UVs[UVIdx] = FVector2f::ZeroVector;
				}
			}
		}

		const int32 FaceStart = FaceStartArray[GeometryGroupIndex];
		const int32 FaceCount = FaceCountArray[GeometryGroupIndex];

		// TODO: Respect multiple materials like in FGeometryCollectionConversion::AppendStaticMesh

		int32 DestFaceStart = MaterialIndices.Num();
		MaterialIndices.Reserve(DestFaceStart + FaceCount);
		BuildIndices.Reserve((DestFaceStart + FaceCount) * 3);
		for (int32 FaceIndex = 0; FaceIndex < FaceCount; ++FaceIndex)
		{
			if (!VisibleArray[FaceStart + FaceIndex]) // TODO: Always in range?
			{
				continue;
			}

			FIntVector FaceIndices = IndicesArray[FaceStart + FaceIndex];
			FaceIndices = FaceIndices + FIntVector( DestVertexStart - VertexStart );

			// Remove degenerates
			if( BuildVertices[ FaceIndices[0] ].Position == BuildVertices[ FaceIndices[1] ].Position ||
				BuildVertices[ FaceIndices[1] ].Position == BuildVertices[ FaceIndices[2] ].Position ||
				BuildVertices[ FaceIndices[2] ].Position == BuildVertices[ FaceIndices[0] ].Position )
			{
				continue;
			}

			BuildIndices.Add(FaceIndices.X);
			BuildIndices.Add(FaceIndices.Y);
			BuildIndices.Add(FaceIndices.Z);

			const int32 MaterialIndex = MaterialIDArray[FaceStart + FaceIndex];
			MaterialIndices.Add(MaterialIndex);
		}

		MeshTriangleCounts[GeometryGroupIndex] = MaterialIndices.Num() - DestFaceStart;
	}

	FMeshNaniteSettings NaniteSettings = {};
	NaniteSettings.bEnabled = true;
	NaniteSettings.TargetMinimumResidencyInKB = 0;	// Default to smallest possible, which is a single page
	NaniteSettings.KeepPercentTriangles = 1.0f;
	NaniteSettings.TrimRelativeError = 0.0f;
	NaniteSettings.FallbackPercentTriangles = 1.0f; // 100% - no reduction
	NaniteSettings.FallbackRelativeError = 0.0f;

	NaniteData->NaniteResource = {};
	if (!NaniteBuilderModule.Build(NaniteData->NaniteResource, BuildVertices, BuildIndices, MaterialIndices, MeshTriangleCounts, NumTexCoords, NaniteSettings))
	{
		UE_LOG(LogStaticMesh, Error, TEXT("Failed to build Nanite for geometry collection. See previous line(s) for details."));
	}

	return NaniteData;
}

TSharedPtr<FGeometryCollection, ESPMode::ThreadSafe> UGeometryCollection::GenerateMinimalGeometryCollection() const
{
	TMap<FName, TSet<FName>> SkipList;
	static TSet<FName> GeometryGroups{ FGeometryCollection::GeometryGroup, FGeometryCollection::VerticesGroup, FGeometryCollection::FacesGroup };
	if (bStripOnCook)
	{
		// Remove all geometry
		//static TSet<FName> GeometryGroups{ FGeometryCollection::GeometryGroup, FGeometryCollection::VerticesGroup, FGeometryCollection::FacesGroup, FGeometryCollection::MaterialGroup };
		for (const FName& GeometryGroup : GeometryGroups)
		{
			TSet<FName>& SkipAttributes = SkipList.Add(GeometryGroup);
			SkipAttributes.Append(GeometryCollection->AttributeNames(GeometryGroup));
		}
	}

	TSharedPtr<FGeometryCollection, ESPMode::ThreadSafe> DuplicateGeometryCollection(new FGeometryCollection());
	DuplicateGeometryCollection->AddAttribute<bool>(FGeometryCollection::SimulatableParticlesAttribute, FTransformCollection::TransformGroup);
	DuplicateGeometryCollection->AddAttribute<FVector3f>("InertiaTensor", FGeometryCollection::TransformGroup);
	DuplicateGeometryCollection->AddAttribute<float>("Mass", FGeometryCollection::TransformGroup);
	DuplicateGeometryCollection->AddAttribute<FTransform>("MassToLocal", FGeometryCollection::TransformGroup);
	DuplicateGeometryCollection->AddAttribute<FGeometryDynamicCollection::FSharedImplicit>(
		FGeometryDynamicCollection::ImplicitsAttribute, FTransformCollection::TransformGroup);
	DuplicateGeometryCollection->CopyMatchingAttributesFrom(*GeometryCollection, &SkipList);
	// If we've removed all geometry, we need to make sure any references to that geometry are removed.
	// We also need to resize geometry groups to ensure that they are empty.
	if (bStripOnCook)
	{
		const TManagedArray<int32>& TransformToGeometryIndex = DuplicateGeometryCollection->GetAttribute<int32>("TransformToGeometryIndex", FTransformCollection::TransformGroup);

		//
		// Copy the bounds to the TransformGroup.
		//  @todo(nanite.bounds) : Rely on Nanite bounds in the component instead and dont copy here
		//
		if (!DuplicateGeometryCollection->HasAttribute("BoundingBox", "Transform"))
		{
			DuplicateGeometryCollection->AddAttribute<FBox>("BoundingBox", "Transform");
		}

		if (!DuplicateGeometryCollection->HasAttribute("NaniteIndex", "Transform"))
		{
			DuplicateGeometryCollection->AddAttribute<FBox>("NaniteIndex", "Transform");
		}

		const int32 NumTransforms = GeometryCollection->NumElements(FGeometryCollection::TransformGroup);
		TManagedArray<int32>& NaniteIndex = DuplicateGeometryCollection->ModifyAttribute<int32>("NaniteIndex", "Transform");
		TManagedArray<FBox>& TransformBounds = DuplicateGeometryCollection->ModifyAttribute<FBox>("BoundingBox", "Transform");
		const TManagedArray<FBox>& GeometryBounds = GeometryCollection->GetAttribute<FBox>("BoundingBox", "Geometry");

		NaniteIndex.Fill(INDEX_NONE);
		for (int TransformIndex = 0; TransformIndex < NumTransforms; TransformIndex++)
		{
			NaniteIndex[TransformIndex] = TransformToGeometryIndex[TransformIndex];
			const int32 GeometryIndex = TransformToGeometryIndex[TransformIndex];
			if (GeometryIndex != INDEX_NONE)
			{
				TransformBounds[TransformIndex] = GeometryBounds[GeometryIndex];
			}
			else
			{
				TransformBounds[TransformIndex].Init();
			}
		}

		//
		//  Clear the geometry and the transforms connection to it. 
		//
		//TransformToGeometryIndex.Fill(INDEX_NONE);
		for (const FName& GeometryGroup : GeometryGroups)
		{
			DuplicateGeometryCollection->EmptyGroup(GeometryGroup);
		}
	}
	return DuplicateGeometryCollection;
}

#endif

void UGeometryCollection::InitResources()
{
	if (NaniteData)
	{
		NaniteData->InitResources(this);
	}
}

void UGeometryCollection::ReleaseResources()
{
	if (NaniteData)
	{
		NaniteData->ReleaseResources();
	}
}

void UGeometryCollection::InvalidateCollection()
{
	StateGuid = FGuid::NewGuid();
}

#if WITH_EDITOR
bool UGeometryCollection::IsSimulationDataDirty() const
{
	return StateGuid != SimulationDataGuid;
}
#endif

int32 UGeometryCollection::AttachEmbeddedGeometryExemplar(const UStaticMesh* Exemplar)
{
	FSoftObjectPath NewExemplarPath(Exemplar);
	
	// Check first if the exemplar is already attached
	for (int32 ExemplarIndex = 0; ExemplarIndex < EmbeddedGeometryExemplar.Num(); ++ExemplarIndex)
	{
		if (NewExemplarPath == EmbeddedGeometryExemplar[ExemplarIndex].StaticMeshExemplar)
		{
			return ExemplarIndex;
		}
	}

	return EmbeddedGeometryExemplar.Emplace( NewExemplarPath );
}

void UGeometryCollection::RemoveExemplars(const TArray<int32>& SortedRemovalIndices)
{
	if (SortedRemovalIndices.Num() > 0)
	{
		for (int32 Index = SortedRemovalIndices.Num() - 1; Index >= 0; --Index)
		{
			EmbeddedGeometryExemplar.RemoveAt(Index);
		}
	}
}

FGuid UGeometryCollection::GetIdGuid() const
{
	return PersistentGuid;
}

FGuid UGeometryCollection::GetStateGuid() const
{
	return StateGuid;
}

#if WITH_EDITOR

void UGeometryCollection::PostEditChangeProperty(struct FPropertyChangedEvent& PropertyChangedEvent)
{
	if (PropertyChangedEvent.Property)
	{
		FName PropertyName = PropertyChangedEvent.Property->GetFName();

		bool bDoInvalidateCollection = false;
		bool bDoEnsureDataIsCooked = false;
		bool bValidateSizeSpecificDataDefaults = false;
		bool bDoUpdateConvexGeometry = false;
		bool bRebuildSimulationData = false;

		if (PropertyChangedEvent.Property->GetFName() == GET_MEMBER_NAME_CHECKED(UGeometryCollection, EnableNanite))
		{
			bDoInvalidateCollection = true;
			bDoEnsureDataIsCooked = true;
		}
		else if (PropertyChangedEvent.Property->GetFName() == GET_MEMBER_NAME_CHECKED(UGeometryCollection, bUseFullPrecisionUVs))
		{
			bDoInvalidateCollection = true;
		}
		else if (PropertyChangedEvent.Property->GetFName() == GET_MEMBER_NAME_CHECKED(UGeometryCollection, SizeSpecificData))
		{
			bDoInvalidateCollection = true;
			bDoUpdateConvexGeometry = true;
			bValidateSizeSpecificDataDefaults = true;
			bRebuildSimulationData = true;
		}		
		else if (PropertyName.ToString().Contains(FString("ImplicitType")))
			//SizeSpecificData.Num() && SizeSpecificData[0].CollisionShapes.Num() &&
			//	PropertyChangedEvent.Property->GetFName() == GET_MEMBER_NAME_CHECKED(UGeometryCollection, SizeSpecificData[0].CollisionShapes[0].ImplicitType))
		{
				bDoInvalidateCollection = true;
				bDoUpdateConvexGeometry = true;
				bRebuildSimulationData = true;
		}
		else if (PropertyChangedEvent.Property->GetFName() != GET_MEMBER_NAME_CHECKED(UGeometryCollection, Materials))
		{
			bDoInvalidateCollection = true;
			bRebuildSimulationData = true;
		}


		if (bDoInvalidateCollection)
		{
			InvalidateCollection();
		}

		if (bValidateSizeSpecificDataDefaults)
		{
			ValidateSizeSpecificDataDefaults();
		}

		if (bDoUpdateConvexGeometry)
		{
			UpdateConvexGeometry();
		}

		if (bDoEnsureDataIsCooked)
		{
			EnsureDataIsCooked();
		}

		if (bRebuildSimulationData)
		{
			if (!bManualDataCreate)
			{
				CreateSimulationData();
			}
		}
	}
}

bool UGeometryCollection::Modify(bool bAlwaysMarkDirty /*= true*/)
{
	bool bSuperResult = Super::Modify(bAlwaysMarkDirty);

	UPackage* Package = GetOutermost();
	if (Package->IsDirty())
	{
		InvalidateCollection();
	}

	return bSuperResult;
}

void UGeometryCollection::EnsureDataIsCooked(bool bInitResources)
{
	if (StateGuid != LastBuiltGuid)
	{
		CreateSimulationDataImp(/*bCopyFromDDC=*/ true);

		if (FApp::CanEverRender() && bInitResources)
		{
			// If there is no geometry in the collection, we leave Nanite data alone.
			if (GeometryCollection->NumElements(FGeometryCollection::GeometryGroup) > 0)
			{
				NaniteData->InitResources(this);
			}
		}
		LastBuiltGuid = StateGuid;
	}
}
#endif

void UGeometryCollection::PostLoad()
{
	Super::PostLoad();

	// Initialize rendering resources.
	if (FApp::CanEverRender())
	{
		InitResources();
	}
}

void UGeometryCollection::BeginDestroy()
{
	Super::BeginDestroy();
	ReleaseResources();
}

FGeometryCollectionNaniteData::FGeometryCollectionNaniteData()
{
}

FGeometryCollectionNaniteData::~FGeometryCollectionNaniteData()
{
	ReleaseResources();
}

void FGeometryCollectionNaniteData::Serialize(FArchive& Ar, UGeometryCollection* Owner)
{
	if (Ar.IsSaving())
	{
		if (Owner->EnableNanite)
		{
			// Nanite data is currently 1:1 with each geometry group in the collection.
			const int32 NumGeometryGroups = Owner->NumElements(FGeometryCollection::GeometryGroup);
			if (NumGeometryGroups != NaniteResource.HierarchyRootOffsets.Num())
			{
				Ar.SetError();
			}
		}

		NaniteResource.Serialize(Ar, Owner, true);
	}
	else if (Ar.IsLoading())
	{
		NaniteResource.Serialize(Ar, Owner, true);
	
		if (!Owner->EnableNanite)
		{
			NaniteResource = {};
		}
	}
}

void FGeometryCollectionNaniteData::InitResources(UGeometryCollection* Owner)
{
	if (bIsInitialized)
	{
		ReleaseResources();
	}

	NaniteResource.InitResources(Owner);

	bIsInitialized = true;
}

void FGeometryCollectionNaniteData::ReleaseResources()
{
	if (!bIsInitialized)
	{
		return;
	}

	if (NaniteResource.ReleaseResources())
	{
		// HACK: Make sure the renderer is done processing the command, and done using NaniteResource, before we continue.
		// This code could really use a refactor.
		FRenderCommandFence Fence;
		Fence.BeginFence();
		Fence.Wait();
	}

	bIsInitialized = false;
}