UnrealEngineUWP/Engine/Source/Editor/SparseVolumeTexture/Private/SparseVolumeTextureFactory.cpp

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

#include "SparseVolumeTextureFactory.h"

#include "SparseVolumeTexture/SparseVolumeTexture.h"

#if WITH_EDITOR

#include "SparseVolumeTextureOpenVDB.h"
#include "SparseVolumeTextureOpenVDBUtility.h"
#include "OpenVDBImportOptions.h"

#include "Serialization/EditorBulkDataWriter.h"
#include "Misc/Paths.h"
#include "Misc/ScopedSlowTask.h"
#include "Misc/FileHelper.h"
#include "Async/Async.h"
#include "Async/ParallelFor.h"

#include "Editor.h"

#include "OpenVDBImportWindow.h"
#include "HAL/PlatformApplicationMisc.h"
#include "HAL/Event.h"
#include "HAL/PlatformProcess.h"
#include "Interfaces/IMainFrameModule.h"

#include <atomic>
#include <mutex>

#define LOCTEXT_NAMESPACE "USparseVolumeTextureFactory"

DEFINE_LOG_CATEGORY_STATIC(LogSparseVolumeTextureFactory, Log, All);

static void ComputeDefaultOpenVDBGridAssignment(const TArray<TSharedPtr<FOpenVDBGridComponentInfo>>& GridComponentInfo, int32 NumFiles, FOpenVDBImportOptions* ImportOptions)
{
	for (FOpenVDBSparseVolumeAttributesDesc& AttributesDesc : ImportOptions->Attributes)
	{
		for (FOpenVDBSparseVolumeComponentMapping& Mapping : AttributesDesc.Mappings)
		{
			Mapping.SourceGridIndex = INDEX_NONE;
			Mapping.SourceComponentIndex = INDEX_NONE;
		}
		AttributesDesc.Format = ESparseVolumeAttributesFormat::Float32;
		AttributesDesc.bRemapInputForUnorm = false;
	}

	// Assign the components of the input grids to the components of the output SVT.
	uint32 DstAttributesIdx = 0;
	uint32 DstComponentIdx = 0;
	for (const TSharedPtr<FOpenVDBGridComponentInfo>& GridComponent : GridComponentInfo)
	{
		if (GridComponent->Index == INDEX_NONE)
		{
			continue;
		}
		ImportOptions->Attributes[DstAttributesIdx].Mappings[DstComponentIdx].SourceGridIndex = GridComponent->Index;
		ImportOptions->Attributes[DstAttributesIdx].Mappings[DstComponentIdx].SourceComponentIndex = GridComponent->ComponentIndex;
		++DstComponentIdx;
		if (DstComponentIdx == 4)
		{
			DstComponentIdx = 0;
			++DstAttributesIdx;
			if (DstAttributesIdx == 2)
			{
				break;
			}
		}
	}
	ImportOptions->bIsSequence = NumFiles > 1;
}

static TArray<FString> FindOpenVDBSequenceFileNames(const FString& Filename)
{
	TArray<FString> SequenceFilenames;

	// The file is potentially a sequence if the character before the `.vdb` is a number.
	const bool bIsFilePotentiallyPartOfASequence = FChar::IsDigit(Filename[Filename.Len() - 5]);

	if (!bIsFilePotentiallyPartOfASequence)
	{
		SequenceFilenames.Add(Filename);
	}
	else
	{
		const FString Path = FPaths::GetPath(Filename);
		const FString CleanFilename = FPaths::GetCleanFilename(Filename);
		FString CleanFilenameWithoutSuffix;
		{
			const FString CleanFilenameWithoutExt = CleanFilename.LeftChop(4);
			const int32 LastNonDigitIndex = CleanFilenameWithoutExt.FindLastCharByPredicate([](TCHAR Letter) { return !FChar::IsDigit(Letter); }) + 1;
			const int32 DigitCount = CleanFilenameWithoutExt.Len() - LastNonDigitIndex;
			CleanFilenameWithoutSuffix = CleanFilenameWithoutExt.LeftChop(CleanFilenameWithoutExt.Len() - LastNonDigitIndex);
		}

		// Find all files potentially part of the sequence
		TArray<FString> PotentialSequenceFilenames;
		IFileManager::Get().FindFiles(PotentialSequenceFilenames, *Path, TEXT("*.vdb"));
		PotentialSequenceFilenames = PotentialSequenceFilenames.FilterByPredicate([CleanFilenameWithoutSuffix](const FString& Str) { return Str.StartsWith(CleanFilenameWithoutSuffix); });

		auto GetFilenameNumberSuffix = [](const FString& Filename) -> int32
		{
			const FString FilenameWithoutExt = Filename.LeftChop(4);
			const int32 LastNonDigitIndex = FilenameWithoutExt.FindLastCharByPredicate([](TCHAR Letter) { return !FChar::IsDigit(Letter); }) + 1;
			const FString NumberSuffixStr = FilenameWithoutExt.RightChop(LastNonDigitIndex);

			int32 Number = INDEX_NONE;
			if (NumberSuffixStr.IsNumeric())
			{
				TTypeFromString<int32>::FromString(Number, *NumberSuffixStr);
			}
			return Number;
		};

		// Find range of number suffixes
		int32 LowestIndex = INT32_MAX;
		int32 HighestIndex = INT32_MIN;
		for (FString& ItemFilename : PotentialSequenceFilenames)
		{
			const int32 Index = GetFilenameNumberSuffix(ItemFilename);
			if (Index == INDEX_NONE)
			{
				ItemFilename.Empty();
				continue;
			}
			LowestIndex = FMath::Min(LowestIndex, Index);
			HighestIndex = FMath::Max(HighestIndex, Index);
		}

		check(HighestIndex >= LowestIndex);

		// Sort the filenames into the result array
		SequenceFilenames.SetNum(HighestIndex - LowestIndex + 1);
		for (const FString& ItemFilename : PotentialSequenceFilenames)
		{
			const int32 Index = ItemFilename.IsEmpty() ? INDEX_NONE : GetFilenameNumberSuffix(ItemFilename);
			if (Index == INDEX_NONE)
			{
				continue;
			}
			SequenceFilenames[Index - LowestIndex] = Path / ItemFilename;
		}

		// Chop off any items after finding the first gap
		for (int32 i = 0; i < SequenceFilenames.Num(); ++i)
		{
			if (SequenceFilenames[i].IsEmpty())
			{
				SequenceFilenames.SetNum(i);
				break;
			}
		}
	}

	check(!SequenceFilenames.IsEmpty());

	return SequenceFilenames;
}

struct FOpenVDBPreviewData
{
	TArray64<uint8> LoadedFile;
	TArray<FOpenVDBGridInfo> GridInfo;
	TArray<TSharedPtr<FOpenVDBGridInfo>> GridInfoPtrs;
	TArray<TSharedPtr<FOpenVDBGridComponentInfo>> GridComponentInfoPtrs;
	TArray<FString> SequenceFilenames;
	FOpenVDBImportOptions DefaultImportOptions;
};

static bool LoadOpenVDBPreviewData(const FString& Filename, FOpenVDBPreviewData* OutPreviewData)
{
	FOpenVDBPreviewData& Result = *OutPreviewData;
	check(Result.LoadedFile.IsEmpty());
	check(Result.GridInfo.IsEmpty());
	check(Result.GridInfoPtrs.IsEmpty());
	check(Result.GridComponentInfoPtrs.IsEmpty());
	check(Result.SequenceFilenames.IsEmpty());

	if (!FFileHelper::LoadFileToArray(Result.LoadedFile, *Filename))
	{
		UE_LOG(LogSparseVolumeTextureFactory, Error, TEXT("OpenVDB file could not be loaded: %s"), *Filename);
		return false;
	}
	if (!GetOpenVDBGridInfo(Result.LoadedFile, true /*bCreateStrings*/, &Result.GridInfo))
	{
		UE_LOG(LogSparseVolumeTextureFactory, Error, TEXT("Failed to read OpenVDB file: %s"), *Filename);
		return false;
	}
	if (Result.GridInfo.IsEmpty())
	{
		UE_LOG(LogSparseVolumeTextureFactory, Error, TEXT("OpenVDB file contains no grids: %s"), *Filename);
		return false;
	}

	// We need a <None> option to leave channels empty
	FOpenVDBGridComponentInfo NoneGridComponentInfo;
	NoneGridComponentInfo.Index = INDEX_NONE;
	NoneGridComponentInfo.ComponentIndex = INDEX_NONE;
	NoneGridComponentInfo.Name = TEXT("<None>");
	NoneGridComponentInfo.DisplayString = TEXT("<None>");

	Result.GridComponentInfoPtrs.Add(MakeShared<FOpenVDBGridComponentInfo>(NoneGridComponentInfo));

	// Create individual entries for each component of all valid source grids.
	// This is an array of TSharedPtr because SComboBox requires its input to be wrapped in TSharedPtr.
	bool bFoundSupportedGridType = false;
	for (const FOpenVDBGridInfo& Grid : Result.GridInfo)
	{
		// Append all grids, even if we don't actually support them
		Result.GridInfoPtrs.Add(MakeShared<FOpenVDBGridInfo>(Grid));

		if (Grid.Type == EOpenVDBGridType::Unknown || !IsOpenVDBGridValid(Grid, Filename))
		{
			continue;
		}

		bFoundSupportedGridType = true;

		// Create one entry per component
		for (uint32 ComponentIdx = 0; ComponentIdx < Grid.NumComponents; ++ComponentIdx)
		{
			FOpenVDBGridComponentInfo ComponentInfo;
			ComponentInfo.Index = Grid.Index;
			ComponentInfo.ComponentIndex = ComponentIdx;
			ComponentInfo.Name = Grid.Name;

			const TCHAR* ComponentNames[] = { TEXT(".X"), TEXT(".Y"),TEXT(".Z"),TEXT(".W") };
			FStringFormatOrderedArguments FormatArgs;
			FormatArgs.Add(ComponentInfo.Index);
			FormatArgs.Add(ComponentInfo.Name);
			FormatArgs.Add(Grid.NumComponents == 1 ? TEXT("") : ComponentNames[ComponentIdx]);

			ComponentInfo.DisplayString = FString::Format(TEXT("{0}. {1}{2}"), FormatArgs);

			Result.GridComponentInfoPtrs.Add(MakeShared<FOpenVDBGridComponentInfo>(MoveTemp(ComponentInfo)));
		}
	}

	if (!bFoundSupportedGridType)
	{
		UE_LOG(LogSparseVolumeTextureFactory, Error, TEXT("OpenVDB file contains no grids of supported type: %s"), *Filename);
		return false;
	}

	Result.SequenceFilenames = FindOpenVDBSequenceFileNames(Filename);

	ComputeDefaultOpenVDBGridAssignment(Result.GridComponentInfoPtrs, Result.SequenceFilenames.Num(), &Result.DefaultImportOptions);

	return true;
}

static bool ShowOpenVDBImportWindow(const FString& Filename, const FOpenVDBPreviewData& PreviewData, FOpenVDBImportOptions* OutImportOptions)
{
	TSharedPtr<SWindow> ParentWindow;

	if (FModuleManager::Get().IsModuleLoaded("MainFrame"))
	{
		IMainFrameModule& MainFrame = FModuleManager::LoadModuleChecked<IMainFrameModule>("MainFrame");
		ParentWindow = MainFrame.GetParentWindow();
	}

	// Compute centered window position based on max window size, which include when all categories are expanded
	const float ImportWindowWidth = 450.0f;
	const float ImportWindowHeight = 750.0f;
	FVector2D ImportWindowSize = FVector2D(ImportWindowWidth, ImportWindowHeight); // Max window size it can get based on current slate


	FSlateRect WorkAreaRect = FSlateApplicationBase::Get().GetPreferredWorkArea();
	FVector2D DisplayTopLeft(WorkAreaRect.Left, WorkAreaRect.Top);
	FVector2D DisplaySize(WorkAreaRect.Right - WorkAreaRect.Left, WorkAreaRect.Bottom - WorkAreaRect.Top);

	float ScaleFactor = FPlatformApplicationMisc::GetDPIScaleFactorAtPoint(DisplayTopLeft.X, DisplayTopLeft.Y);
	ImportWindowSize *= ScaleFactor;

	FVector2D WindowPosition = (DisplayTopLeft + (DisplaySize - ImportWindowSize) / 2.0f) / ScaleFactor;

	TSharedRef<SWindow> Window = SNew(SWindow)
		.Title(NSLOCTEXT("UnrealEd", "OpenVDBImportOptionsTitle", "OpenVDB Import Options"))
		.SizingRule(ESizingRule::Autosized)
		.AutoCenter(EAutoCenter::None)
		.ClientSize(ImportWindowSize)
		.ScreenPosition(WindowPosition);

	TArray<TSharedPtr<ESparseVolumeAttributesFormat>> SupportedFormats =
	{
		MakeShared<ESparseVolumeAttributesFormat>(ESparseVolumeAttributesFormat::Float32),
		MakeShared<ESparseVolumeAttributesFormat>(ESparseVolumeAttributesFormat::Float16),
		MakeShared<ESparseVolumeAttributesFormat>(ESparseVolumeAttributesFormat::Unorm8)
	};

	TSharedPtr<SOpenVDBImportWindow> OpenVDBOptionWindow;
	Window->SetContent
	(
		SAssignNew(OpenVDBOptionWindow, SOpenVDBImportWindow)
		.ImportOptions(OutImportOptions)
		.DefaultImportOptions(&PreviewData.DefaultImportOptions)
		.NumFoundFiles(PreviewData.SequenceFilenames.Num())
		.OpenVDBGridInfo(&PreviewData.GridInfoPtrs)
		.OpenVDBGridComponentInfo(&PreviewData.GridComponentInfoPtrs)
		.OpenVDBSupportedTargetFormats(&SupportedFormats)
		.WidgetWindow(Window)
		.FullPath(FText::FromString(Filename))
		.MaxWindowHeight(ImportWindowHeight)
		.MaxWindowWidth(ImportWindowWidth)
	);

	FSlateApplication::Get().AddModalWindow(Window, ParentWindow, false);

	OutImportOptions->bIsSequence = OpenVDBOptionWindow->ShouldImportAsSequence();

	return OpenVDBOptionWindow->ShouldImport();
}

static bool ValidateImportOptions(const FOpenVDBImportOptions& ImportOptions, const TArray<FOpenVDBGridInfo>& GridInfo)
{
	const int32 NumGrids = GridInfo.Num();

	for (const FOpenVDBSparseVolumeAttributesDesc& AttributesDesc : ImportOptions.Attributes)
	{
		for (const FOpenVDBSparseVolumeComponentMapping& Mapping : AttributesDesc.Mappings)
		{
			const int32 SourceGridIndex = Mapping.SourceGridIndex;
			const int32 SourceComponentIndex = Mapping.SourceComponentIndex;
			if (Mapping.SourceGridIndex != INDEX_NONE)
			{
				if (SourceGridIndex >= NumGrids)
				{
					return false; // Invalid grid index
				}
				if (SourceComponentIndex == INDEX_NONE || SourceComponentIndex >= (int32)GridInfo[SourceGridIndex].NumComponents)
				{
					return false; // Invalid component index
				}
			}
		}
	}
	return true;
}

USparseVolumeTextureFactory::USparseVolumeTextureFactory(const FObjectInitializer& ObjectInitializer)
	: Super(ObjectInitializer)
{
	bCreateNew = true;
	bEditAfterNew = true;
	bEditorImport = true;
	SupportedClass = USparseVolumeTexture::StaticClass();

	Formats.Add(TEXT("vdb;OpenVDB Format"));
}

FText USparseVolumeTextureFactory::GetDisplayName() const
{
	return LOCTEXT("SparseVolumeTextureFactoryDescription", "Sparse Volume Texture");
}

bool USparseVolumeTextureFactory::ConfigureProperties()
{
	return true;
}

bool USparseVolumeTextureFactory::ShouldShowInNewMenu() const
{
	return false;
}


///////////////////////////////////////////////////////////////////////////////
// Create asset


bool USparseVolumeTextureFactory::CanCreateNew() const
{
	return false;	// To be able to import files and call 
}

UObject* USparseVolumeTextureFactory::FactoryCreateNew(UClass* InClass, UObject* InParent, FName InName, EObjectFlags Flags, UObject* Context, FFeedbackContext* Warn)
{
	USparseVolumeTexture* Object = NewObject<USparseVolumeTexture>(InParent, InClass, InName, Flags);

	// SVT_TODO initialize similarly to UTexture2DFactoryNew

	return Object;
}


///////////////////////////////////////////////////////////////////////////////
// Import asset


bool USparseVolumeTextureFactory::DoesSupportClass(UClass* Class)
{
	return Class == USparseVolumeTexture::StaticClass();
}

UClass* USparseVolumeTextureFactory::ResolveSupportedClass()
{
	return USparseVolumeTexture::StaticClass();
}

bool USparseVolumeTextureFactory::FactoryCanImport(const FString& Filename)
{
	const FString Extension = FPaths::GetExtension(Filename);
	if (Extension == TEXT("vdb"))
	{
		return true;
	}
	return false;
}

void USparseVolumeTextureFactory::CleanUp()
{
	Super::CleanUp();
}

UObject* USparseVolumeTextureFactory::FactoryCreateFile(UClass* InClass, UObject* InParent, FName InName, EObjectFlags Flags, const FString& Filename,
	const TCHAR* Parms, FFeedbackContext* Warn, bool& bOutOperationCanceled)
{
#if OPENVDB_AVAILABLE

	GEditor->GetEditorSubsystem<UImportSubsystem>()->BroadcastAssetPreImport(this, InClass, InParent, InName, Parms);
	TArray<UObject*> ResultAssets;

	bOutOperationCanceled = false;

	const bool bIsUnattended = (IsAutomatedImport()
		|| FApp::IsUnattended()
		|| IsRunningCommandlet()
		|| GIsRunningUnattendedScript);

	// Load file and get info about each contained grid
	FOpenVDBPreviewData PreviewData;
	if (!LoadOpenVDBPreviewData(Filename, &PreviewData))
	{
		return nullptr;
	}

	FOpenVDBImportOptions ImportOptions = PreviewData.DefaultImportOptions;
	
	if (!bIsUnattended)
	{
		// Show dialog for import options
		if (!ShowOpenVDBImportWindow(Filename, PreviewData, &ImportOptions))
		{
			bOutOperationCanceled = true;
			return nullptr;
		}
	}

	if (!ValidateImportOptions(ImportOptions, PreviewData.GridInfo))
	{
		UE_LOG(LogSparseVolumeTextureFactory, Error, TEXT("Import options are invalid! This is likely due to invalid/out-of-bounds grid or component indices."));
		return nullptr;
	}

	// Utility function for computing the bounding box encompassing the bounds of all frames in the SVT.
	auto ExpandVolumeBounds = [](const FOpenVDBImportOptions& ImportOptions, const TArray<FOpenVDBGridInfo>& GridInfoArray, FIntVector3& VolumeBoundsMin, FIntVector3& VolumeBoundsMax)
	{
		for (const FOpenVDBSparseVolumeAttributesDesc& Attributes : ImportOptions.Attributes)
		{
			for (const FOpenVDBSparseVolumeComponentMapping& Mapping : Attributes.Mappings)
			{
				if (Mapping.SourceGridIndex != INDEX_NONE)
				{
					const FOpenVDBGridInfo& GridInfo = GridInfoArray[Mapping.SourceGridIndex];
					VolumeBoundsMin.X = FMath::Min(VolumeBoundsMin.X, GridInfo.VolumeActiveAABBMin.X);
					VolumeBoundsMin.Y = FMath::Min(VolumeBoundsMin.Y, GridInfo.VolumeActiveAABBMin.Y);
					VolumeBoundsMin.Z = FMath::Min(VolumeBoundsMin.Z, GridInfo.VolumeActiveAABBMin.Z);

					VolumeBoundsMax.X = FMath::Max(VolumeBoundsMax.X, GridInfo.VolumeActiveAABBMax.X);
					VolumeBoundsMax.Y = FMath::Max(VolumeBoundsMax.Y, GridInfo.VolumeActiveAABBMax.Y);
					VolumeBoundsMax.Z = FMath::Max(VolumeBoundsMax.Z, GridInfo.VolumeActiveAABBMax.Z);
				}
			}
		}
	};

	auto ComputeNumMipLevels = [](const FIntVector3& VolumeBoundsMin, const FIntVector3& VolumeBoundsMax)
	{
		int32 Levels = 1;
		FIntVector3 Resolution = VolumeBoundsMax - VolumeBoundsMin;
		while (Resolution.X > 1 || Resolution.Y > 1 || Resolution.Z > 1)
		{
			Resolution /= 2;
			++Levels;
		}
		return Levels;
	};

	FIntVector3 VolumeBoundsMin = FIntVector3(INT32_MAX, INT32_MAX, INT32_MAX);
	FIntVector3 VolumeBoundsMax = FIntVector3(INT32_MIN, INT32_MIN, INT32_MIN);

	// Import as either single static SVT or a sequence of frames, making up an animated SVT
	if (!ImportOptions.bIsSequence)
	{
		// Import as a static sparse volume texture asset.

		FScopedSlowTask ImportTask(1.0f, LOCTEXT("ImportingVDBStatic", "Importing static OpenVDB"));
		ImportTask.MakeDialog(true);

		FName NewName(InName.ToString() + TEXT("VDB"));
		UStaticSparseVolumeTexture* StaticSVTexture = NewObject<UStaticSparseVolumeTexture>(InParent, UStaticSparseVolumeTexture::StaticClass(), NewName, Flags);

		ExpandVolumeBounds(ImportOptions, PreviewData.GridInfo, VolumeBoundsMin, VolumeBoundsMax);
		StaticSVTexture->VolumeResolution = VolumeBoundsMax - VolumeBoundsMin;
		StaticSVTexture->Frames.SetNum(1);

		const int32 NumMipLevels = ComputeNumMipLevels(VolumeBoundsMin, VolumeBoundsMax);

		FSparseVolumeRawSource SparseVolumeRawSource{};
		const bool bConversionSuccess = ConvertOpenVDBToSparseVolumeTexture(PreviewData.LoadedFile, ImportOptions, VolumeBoundsMin, SparseVolumeRawSource);

		if (!bConversionSuccess)
		{
			UE_LOG(LogSparseVolumeTextureFactory, Error, TEXT("Failed to convert OpenVDB file to SparseVolumeTexture: %s"), *Filename);
			return nullptr;
		}

		// Serialize the raw source data into the asset object.
		// After serializing the data, we generate the next mip level by downsampling the current one (with a call to GenerateMipMap())
		// and then repeating the loop until we processed all levels.
		StaticSVTexture->Frames[0].SetNum(NumMipLevels);
		for (int32 MipLevel = 0; MipLevel < NumMipLevels; ++MipLevel)
		{
			UE::Serialization::FEditorBulkDataWriter RawDataArchiveWriter(StaticSVTexture->Frames[0][MipLevel].RawData);
			SparseVolumeRawSource.Serialize(RawDataArchiveWriter);
			if ((MipLevel + 1) < NumMipLevels)
			{
				SparseVolumeRawSource = SparseVolumeRawSource.GenerateMipMap();
			}
		}

		if (ImportTask.ShouldCancel())
		{
			bOutOperationCanceled = true;
			return nullptr;
		}
		ImportTask.EnterProgressFrame(1.0f, LOCTEXT("ConvertingVDBStatic", "Converting static OpenVDB"));

		ResultAssets.Add(StaticSVTexture);
	}
	else
	{
		// Import as an animated sparse volume texture asset.
		
		// Data from original file is no longer needed; we iterate over all frames later
		PreviewData.LoadedFile.Empty();

		FName NewName(InName.ToString() + TEXT("VDBAnim"));
		UAnimatedSparseVolumeTexture* AnimatedSVTexture = NewObject<UAnimatedSparseVolumeTexture>(InParent, UAnimatedSparseVolumeTexture::StaticClass(), NewName, Flags);
		
		const int32 NumFrames = PreviewData.SequenceFilenames.Num();

		FScopedSlowTask ImportTask(NumFrames + 1, LOCTEXT("ImportingVDBAnim", "Importing OpenVDB animation"));
		ImportTask.MakeDialog(true);

		// Allocate space for each frame
		AnimatedSVTexture->Frames.SetNum(NumFrames);

		std::atomic_bool bErrored = false;
		std::atomic_bool bCanceled = false;

		// Compute volume bounds and check sequence files for compatiblity
		std::mutex VolumeBoundsMutex;
		ParallelFor(NumFrames, [&bErrored, &VolumeBoundsMutex, &VolumeBoundsMin, &VolumeBoundsMax, &ExpandVolumeBounds, &PreviewData, &ImportOptions](int32 FrameIdx)
			{
				if (bErrored.load())
				{
					return;
				}

				// Load file and get info about each contained grid
				const FString& FrameFilename = PreviewData.SequenceFilenames[FrameIdx];
				TArray64<uint8> LoadedFrameFile;
				if (!FFileHelper::LoadFileToArray(LoadedFrameFile, *FrameFilename))
				{
					UE_LOG(LogSparseVolumeTextureFactory, Error, TEXT("OpenVDB file could not be loaded: %s"), *FrameFilename);
					bErrored.store(true);
					return;
				}

				TArray<FOpenVDBGridInfo> FrameGridInfo;
				if (!GetOpenVDBGridInfo(LoadedFrameFile, true, &FrameGridInfo))
				{
					UE_LOG(LogSparseVolumeTextureFactory, Error, TEXT("Failed to read OpenVDB file: %s"), *FrameFilename);
					bErrored.store(true);
					return;
				}

				// Sanity check for compatibility
				for (const FOpenVDBSparseVolumeAttributesDesc& AttributesDesc : ImportOptions.Attributes)
				{
					for (const FOpenVDBSparseVolumeComponentMapping& Mapping : AttributesDesc.Mappings)
					{
						const uint32 SourceGridIndex = Mapping.SourceGridIndex;
						if (SourceGridIndex != INDEX_NONE)
						{
							if ((int32)SourceGridIndex >= FrameGridInfo.Num())
							{
								UE_LOG(LogSparseVolumeTextureFactory, Error, TEXT("OpenVDB file is incompatible with other frames in the sequence: %s"), *FrameFilename);
								bErrored.store(true);
								return;
							}
							const FOpenVDBGridInfo& OrigSourceGrid = PreviewData.GridInfo[SourceGridIndex];
							const FOpenVDBGridInfo& FrameSourceGrid = FrameGridInfo[SourceGridIndex];
							if (OrigSourceGrid.Type != FrameSourceGrid.Type || OrigSourceGrid.Name != FrameSourceGrid.Name)
							{
								UE_LOG(LogSparseVolumeTextureFactory, Error, TEXT("OpenVDB file is incompatible with other frames in the sequence: %s"), *FrameFilename);
								bErrored.store(true);
								return;
							}
						}
					}
				}

				// Update sequence volume bounds and increment ProcessedFramesCounter
				{
					std::lock_guard<std::mutex> Lock(VolumeBoundsMutex);
					ExpandVolumeBounds(ImportOptions, FrameGridInfo, VolumeBoundsMin, VolumeBoundsMax);
				}
			});

		if (bErrored.load())
		{
			return nullptr;
		}

		ImportTask.EnterProgressFrame(1.0f, LOCTEXT("ConvertingVDBAnim", "Converting OpenVDB animation"));

		const int32 NumMipLevels = ComputeNumMipLevels(VolumeBoundsMin, VolumeBoundsMax);

		FEvent* AllTasksFinishedEvent = FPlatformProcess::GetSynchEventFromPool();
		std::atomic_int FinishedTasksCounter = 0; // Will be incremented even if frame processing failed
		std::atomic_int ProcessedFramesCounter = 0;

		// Load individual frames, process/convert them and append them to the resulting asset
		for (int32 FrameIdx = 0; FrameIdx < NumFrames; ++FrameIdx)
		{
			// Increments the atomic counter when going out of scope. Triggers an event once the counter reaches a given value.
			struct FScopedIncrementer
			{
				std::atomic_int& Counter;
				int32 MaxValue;
				FEvent* Event;
				explicit FScopedIncrementer(std::atomic_int& InCounter, int32 InMaxValue, FEvent* InEvent) 
					: Counter(InCounter), MaxValue(InMaxValue), Event(InEvent) {}
				~FScopedIncrementer() 
				{ 
					if ((Counter.fetch_add(1) + 1) == MaxValue)
					{
						Event->Trigger();
					}
				}
			};

			AsyncTask(ENamedThreads::AnyNormalThreadNormalTask, 
				[FrameIdx, NumFrames, &PreviewData, &ImportOptions, &AnimatedSVTexture,
				AllTasksFinishedEvent, &bErrored, &bCanceled, &FinishedTasksCounter, &ProcessedFramesCounter, &VolumeBoundsMin, &NumMipLevels]()
				{
					// Ensure the FinishedTasksCounter will be incremented in all cases
					FScopedIncrementer Incremeter(FinishedTasksCounter, NumFrames, AllTasksFinishedEvent);

					if (bErrored.load() || bCanceled.load())
					{
						return;
					}

					const FString& FrameFilename = PreviewData.SequenceFilenames[FrameIdx];

					UE_LOG(LogSparseVolumeTextureFactory, Display, TEXT("Loading OpenVDB sequence frame #%i %s."), FrameIdx, *FrameFilename);

					// Load file
					TArray64<uint8> LoadedFrameFile;
					if (!FFileHelper::LoadFileToArray(LoadedFrameFile, *FrameFilename))
					{
						UE_LOG(LogSparseVolumeTextureFactory, Error, TEXT("OpenVDB file could not be loaded: %s"), *FrameFilename);
						bErrored.store(true);
						return;
					}

					FSparseVolumeRawSource SparseVolumeRawSource{};
					const bool bConversionSuccess = ConvertOpenVDBToSparseVolumeTexture(LoadedFrameFile, ImportOptions, VolumeBoundsMin, SparseVolumeRawSource);

					if (!bConversionSuccess)
					{
						UE_LOG(LogSparseVolumeTextureFactory, Error, TEXT("Failed to convert OpenVDB file to SparseVolumeTexture: %s"), *FrameFilename);
						bErrored.store(true);
						return;
					}

					// Serialize the raw source data from this frame into the asset object.
					// After serializing the data, we generate the next mip level by downsampling the current one (with a call to GenerateMipMap())
					// and then repeating the loop until we processed all levels.
					AnimatedSVTexture->Frames[FrameIdx].SetNum(NumMipLevels);
					for (int32 MipLevel = 0; MipLevel < NumMipLevels; ++MipLevel)
					{
						UE::Serialization::FEditorBulkDataWriter RawDataArchiveWriter(AnimatedSVTexture->Frames[FrameIdx][MipLevel].RawData);
						SparseVolumeRawSource.Serialize(RawDataArchiveWriter);
						if ((MipLevel + 1) < NumMipLevels)
						{
							SparseVolumeRawSource = SparseVolumeRawSource.GenerateMipMap();
						}
					}

					// Increment ProcessedFramesCounter
					ProcessedFramesCounter.fetch_add(1);
				});
		}

		// Wait for frames to be processed
		{
			int NumFinishedTasks = 0;
			int NumProcessedFrames = 0;
			
			while (NumFinishedTasks < NumFrames)
			{
				// We can't block here because we want to regularly update the progress bar and check for user input.
				const uint32 WaitTimeMS = 2;
				AllTasksFinishedEvent->Wait(WaitTimeMS);

				if (!bCanceled.load() && !bErrored.load() && ImportTask.ShouldCancel())
				{
					bCanceled.store(true);
				}

				const int NewNumFinishedTasks = FinishedTasksCounter.load();
				if (NewNumFinishedTasks > NumFinishedTasks)
				{
					const int NewNumProcessedFrames = ProcessedFramesCounter.load();
					if (NewNumProcessedFrames > NumProcessedFrames && !bErrored.load())
					{
						const float Progress = float(NewNumProcessedFrames - NumProcessedFrames);
						ImportTask.EnterProgressFrame(Progress, LOCTEXT("ConvertingVDBAnim", "Converting OpenVDB animation"));
					}

					NumFinishedTasks = NewNumFinishedTasks;
					NumProcessedFrames = NewNumProcessedFrames;
				}
			}
		}
		FPlatformProcess::ReturnSynchEventToPool(AllTasksFinishedEvent);

		if (bCanceled.load())
		{
			bOutOperationCanceled = true;
			return nullptr;
		}
		if (bErrored.load())
		{
			return nullptr;
		}

		AnimatedSVTexture->VolumeResolution = VolumeBoundsMax - VolumeBoundsMin;

		ResultAssets.Add(AnimatedSVTexture);
	}

	// Now notify the system about the imported/updated/created assets
	check(ResultAssets.Num() == 1);
	GEditor->GetEditorSubsystem<UImportSubsystem>()->BroadcastAssetPostImport(this, ResultAssets[0]);

	return ResultAssets[0];

#else // OPENVDB_AVAILABLE

	// SVT_TODO Make sure we can also import on more platforms such as Linux. See SparseVolumeTextureOpenVDB.h
	UE_LOG(LogSparseVolumeTextureFactory, Error, TEXT("Cannot import OpenVDB asset any platform other than Windows."));
	return nullptr;

#endif // OPENVDB_AVAILABLE

}

#endif // WITH_EDITORONLY_DATA

#undef LOCTEXT_NAMESPACE

#include "Serialization/EditorBulkDataWriter.h"