JohnM
c94e2197d1
IW4L_PIPELINED_RENDERING=1 panicked on the first frame on macOS ("can only
access NSView on the main thread" in raw-window-metal), which is why the
default is off there. Bevy's create_surfaces takes a NonSendMarker so that
the multi-threaded executor hands it back to the main thread, but the render
app's Render schedule runs on a single-threaded executor. With pipelining on
that schedule runs on the render thread, so create_surfaces built the
CAMetalLayer there and touched the NSView off the main thread.
With pipelining on, macOS now also runs create_surfaces in the render app's
ExtractSchedule, after extract_cameras and so after the windows are
extracted. Extraction runs on the main thread, so the surface is created and
configured there. The Render schedule's instance then finds it configured
and skips, or after a resize reconfigures it, which only sets CAMetalLayer
properties and is allowed off the main thread.
The macOS default stays off, so nothing changes unless
IW4L_PIPELINED_RENDERING=1 is set. docs/BUILD.md now says how to turn it on
instead of pointing at the plugins.rs explanation this removes.
Measured on an Apple M3 (mp_terminal, 9 bots, uncapped present, bench
recorder), pipelining off -> on: 87 -> 105 fps average, frame p50 10.8 ->
8.3 ms, p99 19.4 -> 18.4 ms, worst frames about the same (36 -> 34 ms),
main/render overlap 5.4 ms per frame, presented state one frame older.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
IW4L
IW4L is an open-source runtime for Call of Duty: Modern Warfare 2 (2009), written in Rust with Bevy. Point it at a copy of MW2 you already own and it loads that installation's maps, models, textures and weapons into its own engine. You can try implemented movement and combat on multiplayer maps, then inspect or change how those systems work.
What you can try
Explore maps, fight bots, and record and replay demos. Gameplay remains incomplete; expect missing behavior, bugs and desyncs. The asset readers also cover MW3 and Black Ops.
APIs, configuration, caches and the wire protocol change between commits; multiplayer peers must run the same build.
Windows: prebuilt release
- Download
iw4l-windows.zipfrom Releases and extract it into an empty writable folder. The archive password ist.me/contextrot. - Launch
iw4l.exe. It finds MW2 in your Steam libraries and creates aModern Warfare 2.lnkshortcut next to itself. For an install outside Steam, create that shortcut to your MW2 folder yourself.
For online play, put the .iw4l-server file you received from a server operator next
to iw4l.exe. With it the game finds that master and updates itself on launch. Details:
Windows guide.
Build and run
Install Rust through rustup and GNU Make. Build dependencies cover Linux's C/C++ toolchain and system libraries, and macOS's Xcode command line tools. Windows instructions cover building and arranging a portable folder.
You need your own installed MW2 Multiplayer data. IW4L
distributes no game assets and reads installations without patching or replacing their
files. Caches, demos and logs go under iw4l-artifacts/; Linux settings use a separate
configuration directory described in the run guide.
From the repository root:
cp .env.example .env
# Edit .env: set IW4L_GAMES to the folder containing your game installations.
make map mp_boneyard CMDS='wait world; spawn 0; force_match_start; bot add 3'
This builds the optimized play profile and starts a local match with three bots.
force_match_start skips the warmup that otherwise freezes movement.
Inside the engine
| Area | Implementation |
|---|---|
| Assets | Native FastFile readers convert game data into a shared intermediate representation. |
| Shaders | Retail Direct3D 9 Shader Model 3 bytecode is translated to WGSL. |
| Rendering | World geometry, models and effects feed one sorted draw-surface list. |
| Simulation | Server authority, client prediction and replay share one simulation step over explicit Bevy ECS state. |
| Networking | Custom UDP traffic; a QUIC master provides browsing and relaying. The host simulates the match. |
Where to go next
- Run guide: console commands, classes and demo playback; master setup for playtests.
- Rendering and simulation: inspect the engine's implementation.
- Map loading, GSC runtime and bot AI: starting points for experiments and modifications.
- Documentation index, contributing and security reports.
This whole project is written by an LLM.
Acknowledgements and license
Thank you to all contributors for code, bug reports, testing and feedback. Special thanks to ju1cedr1nker and silvernote03 for QA testing weapons, maps, attachments and other gameplay features.
OpenAssetTools and its iw4x-x64 fork informed asset layouts; IW4x informed asset and protocol behavior; KisakCOD informed engine structure. Ghidra was used to inspect the original binaries.
Movement implementation history and source boundaries are recorded in its provenance note.
IW4L's source is licensed under Apache 2.0. Preserve required attribution and bundled font license texts when redistributing; see NOTICE. Original game assets and trademarks belong to their owners. IW4L is unaffiliated with them.