はじめに
LZ4に正式対応し, Pak File Compression Format(s)で指定できるように思えますが, そんなことはないです.
原因
FCompression::IsFormatValidが原因と思われます. コメントからすると, 不具合のように見えます.
bool FCompression::IsFormatValid(FName FormatName){// build in formats are always validif (FormatName == NAME_Zlib || FormatName == NAME_Gzip){return true;}// otherwise, if we can get the format class, we are good!return GetCompressionFormat(FormatName, false) != nullptr;}
圧縮形式
zlibのチェックサム計算も軽くはないことに注意です.
- zlib
- 圧縮率と速度のバランスが良いが, 今では旧い, zstandardを代わりに使うべき
- checksumは必ず計算する
- ZStandard
- 圧縮率と速度のバランスが良い
- checksumはオプション
- LZ4
- 圧縮・伸張速度に重点を置いたもの
- LZSSだけなので上記2つより圧縮率は低い
- 圧縮に時間をかけても, 伸張速度はほとんど変わらない
- checksumはオプション
- 圧縮・伸張速度に重点を置いたもの
- Lizard
- LZ5を名乗る, LZ4を改良したと主張している
PakのLZ4圧縮
FCompressionを書き換えることは影響範囲を考えてやりたくないです. エンジンのプラグインを書きます.
UnrealPakは独立したプログラムのため, 単純なエディタ拡張ではUnrealPakから見えません.
LZ4CompressionFormat.cpp
#include "LZ4Compression.h"#include "CoreMinimal.h"#include "Misc/Compression.h"#include "Misc/ICompressionFormat.h"#define LOCTEXT_NAMESPACE "FLZ4CompressionModule"namespace{DEFINE_LOG_CATEGORY_STATIC(LogLZ4CompressionFormat, Log, All);struct LZ4CompressionFormat : public ICompressionFormat{FName GetCompressionFormatName() override;bool Compress(void* CompressedBuffer, int32& CompressedSize, const void* UncompressedBuffer, int32 UncompressedSize, int32 CompressionData) override;bool Uncompress(void* UncompressedBuffer, int32& UncompressedSize, const void* CompressedBuffer, int32 CompressedSize, int32 CompressionData) override;int32 GetCompressedBufferSize(int32 UncompressedSize, int32 CompressionData) override;uint32 GetVersion() override;FString GetDDCKeySuffix() override;};FName LZ4CompressionFormat::GetCompressionFormatName(){return "lz4";}bool LZ4CompressionFormat::Compress(void* CompressedBuffer, int32& CompressedSize, const void* UncompressedBuffer, int32 UncompressedSize, int32 CompressionData){UE_LOG(LogLZ4CompressionFormat, Warning, TEXT("Compress"));if(!FCompression::CompressMemory(NAME_LZ4, CompressedBuffer, CompressedSize, UncompressedBuffer, UncompressedSize, COMPRESS_NoFlags, CompressionData)) {UE_LOG(LogLZ4CompressionFormat, Warning, TEXT("Faile to compress"));return false;}return true;}bool LZ4CompressionFormat::Uncompress(void* UncompressedBuffer, int32& UncompressedSize, const void* CompressedBuffer, int32 CompressedSize, int32 CompressionData){UE_LOG(LogLZ4CompressionFormat, Warning, TEXT("Uncompress"));if(!FCompression::UncompressMemory(NAME_LZ4, UncompressedBuffer, UncompressedSize, CompressedBuffer, CompressedSize, COMPRESS_NoFlags, CompressionData)) {UE_LOG(LogLZ4CompressionFormat, Warning, TEXT("Faile to uncompress"));return false;}return true;}int32 LZ4CompressionFormat::GetCompressedBufferSize(int32 UncompressedSize, int32 CompressionData){return FCompression::CompressMemoryBound(NAME_LZ4, UncompressedSize, COMPRESS_NoFlags, CompressionData);}uint32 LZ4CompressionFormat::GetVersion(){return FCompression::GetCompressorVersion(NAME_LZ4);}FString LZ4CompressionFormat::GetDDCKeySuffix(){static const FString suffix = "2AEE7CBB0BD24E71B0D516ECE2AB68C1";return suffix;}} // namespaceFLZ4CompressionModule::FLZ4CompressionModule(): compressionFormat_(nullptr){}FLZ4CompressionModule::~FLZ4CompressionModule(){delete compressionFormat_;}void FLZ4CompressionModule::StartupModule(){compressionFormat_ = new LZ4CompressionFormat();IModularFeatures::Get().RegisterModularFeature(COMPRESSION_FORMAT_FEATURE_NAME, compressionFormat_);}void FLZ4CompressionModule::ShutdownModule(){IModularFeatures::Get().UnregisterModularFeature(COMPRESSION_FORMAT_FEATURE_NAME, compressionFormat_);delete compressionFormat_;compressionFormat_ = nullptr;}#undef LOCTEXT_NAMESPACEIMPLEMENT_MODULE(FLZ4CompressionModule, LZ4Compression)
まとめ
今回は, Pak File Compression Format(s)にlz4を書けばLZ4圧縮になるはずです. これを応用すれば好きなフォーマットにできるはずです.