IW4L

IW4L is a standalone, experimental Call of Duty runtime written in Rust on top of bevy and wgpu. It reads the game data of an installation you already own and runs it in its own engine.

Development uses reverse engineering of the original binaries and public technical references to understand game data and behaviour. IW4L implements its own runtime architecture; it does not aim to reconstruct the original source code or to reproduce every behaviour exactly. Compatibility is incomplete, and behaviour may differ from the original games.

IW4L is not affiliated with, endorsed by or supported by the rights holders of the original games. No game assets are contained in this repository or in any IW4L release. You supply your own legally obtained installation.

This whole project is written by an LLM.

Scope

area	what IW4L promises
IW4 / Modern Warfare 2	the primary target of the runtime
IW5 (MW3) / T5 (Black Ops)	experimental: selected maps and weapons
IW4L multiplayer	experimental matches between IW4L clients
a drop-in replacement for the original games	not claimed
a general engine for every older CoD title	not claimed
the original network protocols, ABI or modified executables	not a goal, and no compatibility is promised

Where reproducing a detail exactly would cost disproportionate complexity and the demo scenarios do not need it, IW4L implements it differently or leaves it out. That is a scope decision, not a blanket excuse: a desync in IW4L's own multiplayer is a bug in IW4L, while a difference from the original animation timing may be an accepted limitation.

What runs today

• loading IW4 maps, weapons, models, materials, effects and world geometry
• rendering the world, models, materials and effects
• player and entity simulation, animation, sound and effects
• p2p matches between IW4L clients, introduced through a master server
• selected IW5 and T5 data (see docs/MAP-LOAD.md for what each lane actually accepts; MW3 x64 Steam zones are detected and refused)

Verified scenario for this cut: mp_boneyard from a retail MW2 multiplayer install on Linux — map load, movement, weapons, bots and effects, driven by make scenario and make chaos. Anything past that list is untested rather than promised. Expect missing gameplay systems, incomplete compatibility, bugs and desyncs.

Game data

IW4L needs a copy of the games whose content you want to load — MW2 for the IW4 path, MW3 or Black Ops for the experimental lanes. Point IW4L_GAMES at the folder holding those game trees.

The original installation is used read only. IW4L does not patch it, replace files in it, or write into it; its own caches, settings, demos and logs go to iw4l-artifacts/ next to the IW4L binary.

Build and run

cp .env.example .env          # IW4L_GAMES — folder containing the game trees
make map mp_boneyard          # run a map
make map mp_boneyard CMDS='spawn assault; wait 2s; quit'
make help                     # every recipe

Live runs use the [profile.play] profile, optimized for development builds. PROFILE=release builds the full release binary. Windows setup is documented in docs/WINDOWS.md.

Releases, network and updates

Builds are published as pre-releases (v0.1.0-demo.N, "IW4L Technical Demo N"). Each one names the commit it was built from, the platforms it was actually run on, the demo scenario and its known limitations, and carries LICENSE, NOTICE and the bundled font licences. A platform appears in that list only when a build for it was run, not when it merely compiled.

• Nothing is stable yet. The Rust API, the config format, caches, replay files and the network protocol may change between any two builds. Play a session on one release.
• The network is experimental, meant for arranged playtests between people who agreed to play. It is not a vetted environment for connecting to strangers.
• Updating is an explicit action. A release archive runs on its own; no build replaces its own binary without you asking it to.
• No telemetry. IW4L sends nothing home. Diagnostic files are yours to attach to a report. The demo master keeps operational logs for its own running; what it records is in docs/MASTER.md.
• The demo master is experimental infrastructure with no uptime promise. Running IW4L locally never depends on it, and you can run your own.

Security reports: SECURITY.md.

Documentation

Detailed implementation notes live under docs/ — start at docs/INDEX.md.

file	about
docs/RUN.md	running the game, console scripts, commands and traps
docs/PERF.md	Perfetto tracing and performance analysis
docs/RENDER.md	rendering pipeline
docs/MAP-LOAD.md	map loading and asset installation
docs/ENTITIES.md	simulation data flow and entity taxonomy
docs/SIM-STEP.md	simulation step architecture
docs/ANIM.md	animation system
docs/WINDOWS.md	portable Windows build
docs/DEPLOY.md	release, publishing and deployment
docs/MASTER.md	running your own master server

Contributing and support

IW4L is a personal experimental project; see CONTRIBUTING.md for what a useful bug report contains and how changes are reviewed. Reports are welcome, with no promised fix date, and "add everything the original had" is not a roadmap.

Acknowledgements

IW4L is written from scratch, but it was not worked out in a vacuum.

• OpenAssetTools and its iw4x-x64 fork — open-source modding tools whose asset-structure headers document the on-disk layouts IW4L reads.
• IW4x — a custom client for MW2 (2009); read as a cross-reference for asset and protocol behaviour.
• KisakCOD — an open-source CoD4 reimplementation; read as a cross-reference for engine structure in a neighbouring generation of the same engine family.
• Ghidra — the reverse engineering framework the original binaries were read with.

Nothing from these projects is vendored, linked or distributed with IW4L. NOTICE carries the full attribution, their licences, and the bundled fonts.

License

IW4L is licensed under the Apache License 2.0. Copyright and attribution notices are in NOTICE.

This applies to the IW4L source code only. Call of Duty, Modern Warfare, Black Ops and related game assets, trademarks and other intellectual property belong to their respective owners and are not distributed with this project.