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Oodle Library

Darktide bundles use Oodle (Kraken) compression. The Oodle shared library is a proprietary Epic Games component required at runtime; it is not open source. dtex loads it dynamically via libloading (dlopen on Linux, LoadLibrary on Windows).

Neither library is redistributed in this repository (both are listed in .gitignore). CI workflows download them automatically before running tests; developers obtain them locally as described below.

Auto-discovery

dtex searches for the Oodle library in the following order:

  1. --oodle-lib <path> command-line flag
  2. DTEX_OODLE_LIB environment variable
  3. Windows only: <game-dir>/binaries/oo2core_9_win64.dll (if --game-dir is provided or auto-discovered)
  4. Next to the dtex binary (exe-dir)
  5. Current working directory
  6. System library search path (bare library name)

If the library cannot be found, dtex prints an error with platform-specific hints:

  • On Linux, the error message references this document.
  • On Windows, the error message mentions that the DLL ships with the game in <game-dir>/binaries/ and suggests using --game-dir if Steam auto-discovery fails.

Supported platforms

Platform Library file Oodle version Size
Linux liboo2corelinux64.so.9 2.9.14 688,096 bytes
Windows oo2core_9_win64.dll 2.9.10 637,952 bytes

The Oodle FFI signature (OodleLZ_Decompress) is identical across platforms. The Linux build uses a 14-argument calling convention where the scratch argument is a size, not a pointer. The signature is reverse-engineered and verified empirically against 9,648 Darktide bundles (see crates/darktide-bundle/src/oodle.rs).

Obtaining the library

The library is distributed as an Unreal Engine build dependency on Epic's CDN. The process requires a Commit.gitdeps.xml file from the EpicGames/UnrealEngine repo (requires GitHub org membership; free signup at https://github.com/EpicGames/Signup).

The XML links four elements to locate a file:

  1. <DependencyManifest> has BaseUrl (e.g. https://cdn.unrealengine.com/dependencies)
  2. <File> has Name and Hash — find the file by name
  3. <Blob> matches Hash to a File; provides Size, PackOffset, and PackHash
  4. <Pack> matches Hash to a Blob's PackHash; provides RemotePath

Download URL: {BaseUrl}/{Pack.RemotePath}/{Pack.Hash} — the response is gzip-compressed. Seek to Blob.PackOffset, then read Blob.Size bytes.

Linux (v2.9.14)

XML trace:

<File Name="Engine/Source/Runtime/OodleDataCompression/Sdks/2.9.14/lib/Linux/liboo2corelinux64.so.9"
      Hash="ff1f6d0faa4fceaeec9d4c1a0a391160dfe78b54" />

<Blob Hash="ff1f6d0faa4fceaeec9d4c1a0a391160dfe78b54"
      Size="688096"
      PackHash="4f6c5fd233cb85f91497bd8c722fd7a89f1c657a"
      PackOffset="1399275" />

<Pack Hash="4f6c5fd233cb85f91497bd8c722fd7a89f1c657a"
      RemotePath="UnrealEngine-42566482" />

Download (Linux/macOS):

curl -sL "https://cdn.unrealengine.com/dependencies/UnrealEngine-42566482/4f6c5fd233cb85f91497bd8c722fd7a89f1c657a" \
  | gunzip \
  | dd bs=1 skip=1399275 count=688096 of=liboo2corelinux64.so.9

Result: 672 KB ELF shared object, MD5 18aa46f51f41f8c81cde1636ad486c81.

Windows (v2.9.10)

XML trace:

  • Pack RemotePath: UnrealEngine-27563807
  • Pack Hash: 51bf6515dd35ac8361c9a324b6deb1736a61240c
  • PackOffset: 1240856
  • Size: 637952

Download (Linux/macOS):

curl -sL "https://cdn.unrealengine.com/dependencies/UnrealEngine-27563807/51bf6515dd35ac8361c9a324b6deb1736a61240c" \
  | gunzip \
  | dd bs=1 skip=1240856 count=637952 of=oo2core_9_win64.dll

Download (Windows PowerShell):

$url = "https://cdn.unrealengine.com/dependencies/UnrealEngine-27563807/51bf6515dd35ac8361c9a324b6deb1736a61240c"
$response = Invoke-WebRequest -Uri $url -UseBasicParsing
$gzip = [System.IO.Compression.GzipStream]::new(
    [System.IO.MemoryStream]::new($response.Content),
    [System.IO.Compression.CompressionMode]::Decompress
)
$bytes = [System.IO.MemoryStream]::new()
$gzip.CopyTo($bytes)
$gzip.Dispose()
$data = $bytes.ToArray()
$offset = 1240856
$count = 637952
$dll = $data[$offset..($offset + $count - 1)]
[System.IO.File]::WriteAllBytes("oo2core_9_win64.dll", $dll)

Result: 623 KB PE DLL, Oodle 2.9.10.