vcod

A from-scratch reimplementation of bits of Call of Duty (2003), patch 1.1, in Rust. A map viewer, a client that spectates and plays on real 1.1 servers, and a dedicated server a retail 1.1 client can join. It reads the game's own pk3s and speaks the original 1.1 wire protocol, which nobody ever wrote down, so I dug it out of the binaries.

Read this first: it's a toy

vcod is a hobby project. I work on it while poking at a 2003 engine is fun, and I stop when it isn't.

• It is not a playable game. You can run around, shoot people and plant a bomb, and some evenings it almost feels like Call of Duty. It is still a research rig with a renderer bolted on. Expect missing pieces and the occasional soldier living inside a wall.
• Retail parity is not a goal. No roadmap, no "1.0". If it ever becomes fully playable, that's an accident and I'll take the credit anyway.
• It doesn't replace your copy of the game. It needs that copy to run.
• Don't host real players on it. No anti-cheat, an rcon that knows a couple of dozen commands, and strong opinions about tick order. Your regulars deserve a server that was tested on someone other than bots.

If you want to play Call of Duty, play Call of Duty. If you want to watch a 2003 game boot in a window someone rebuilt from the bytes up, stick around.

What it does

Map viewer

• Draws any stock or custom map with textures, lightmaps and props. Skies, water, fences, foliage and terrain blends run through the maps' own Q3-style shader scripts, sun disc and fog included.
• Culls with retail's cells, portals and occluders. F4 freezes or disables culling so you can fly out and see what the camera was drawing.
• Plays the map's ambient loop.

Walk mode (--walk), offline

• Spawns a soldier on a spawn point with retail movement: gravity, crouch, prone, stepping, leaning, wall sliding.
• Seven weapons with their own viewmodels, animations, sounds and reserve ammo. Hitscan shots with per-surface impacts and tracers.
• Footsteps on retail's cadence per surface; the landing sound scales with fall speed.

Client

• Opens on the stock main menu and server browser, drawn from the game's own ui_mp/*.menu files. The browser's three sources are retail's: Local (a getinfo broadcast to ports 28960-28963), Internet (what codmaster.activision.com knows) and Favorites (kept in servercache.dat beside CoDMP.exe, the file retail uses). It pings, filters, sorts by column, joins on double-click, and runs the stock password, server info, filter and favourite popups. Losing the server drops you back on the menu with the localized reason in the stock error popup. In a game, Esc opens the script menu and its Main Menu tab the stock in-game main menu (Back to Game, Disconnect). The stock Mods menu lists the mod directories beside main/ and switches to one, in a game too, and the menus load from the mod's own ui_mp/menus.txt.
• The stock Options and Multiplayer Options screens: rebind keys, mouse sensitivity and invert, player name, rate, master volume, video mode and full screen. Choices land in the console's binds and cvars and persist in vcod_mp.cfg; settings vcod has no use for are kept but do nothing.
• Joins a 1.1 server (--connect or the browser): handshake, Huffman, netchan, delta snapshots, and pak downloads for whatever the server has and you don't, matched by checksum as retail does. Pure servers take its pak checksums. Modded servers work too: a server's fs_game layers its mod directory over main/ and swaps in the mod's menus, its cl_allowDownload decides whether to download, and a mod's script menus and hud.menu text show up.
• Answers the stock team and weapon menus as a keyboard list built from their .menu files, or straight from --team and --weapon.
• Spectates. Every player is an assembled, animated soldier. Kill feed, chat, scoreboard, sounds, tracers, impacts and muzzle flashes come off the same events retail reads.
• Plays. Move, jump, crouch, prone, lean, fire, aim down the sight, reload, melee, use, switch weapons, on retail's default binds. A usercmd is built every 8 ms, like a 125 fps retail client, and they go out at retail's cl_maxpackets 30 with cl_packetdup 1 off the LAN.
• Predicts your movement by replaying unacknowledged cmds through the same step the server runs. A correction eases out over 100 ms.
• Draws and stamps cmds on retail's client clock, which slews a millisecond or two per snapshot instead of stepping on jitter; cl_timeNudge works.
• First-person weapon with your team's hands, sight zoom at the weapon's FOV, sniper scope overlay that follows the sway and the hit kick, and your own fire, reload and footstep sounds played off the prediction.
• Fire recoil off the weapon file's view and gun kick keys: the view kick rides your cmd angles, as retail's does, rolls the view with it, springs back to centre and clears on a respawn.
• Mounted MG42s with their fire anim and flash; on the gun the view rides tag_player and the crosshair turns into the gun's reticle.
• The HUD the stock hud.menu lays out: crosshair that opens with spread, health, ammo, stance, compass with objectives and teammates, use hints, hit direction, chat and announcements. Also the gametype script's own HUD elements (S&D clock, bomb icons, progress bar) in retail's fonts, and head icons over players. A spectator following someone sees their HUD, weapon and scope.
• Follows the server through a map change: loading screen, downloads, new map.
• Retail's drop-down console on `. It takes the commands under Console; binds and archived cvars persist in main/vcod_mp.cfg.

I have played it against my own server and the retail Linux 1.1d server, and spectated public servers with it. I haven't joined a public server as a player, and neither should you. Those people signed up for Call of Duty, not for my test suite.

Dedicated server (vcod-server)

• Answers server browsers, accepts retail 1.1 clients, sends the gamestate and delta snapshots.
• Runs Activision's own gametype and map scripts on vcod-gsc, a VM for CoD's .gsc language that lives in this repo. Menus, spawns, scoring, rounds and limits all come from the stock scripts, not from Rust. All five stock gametypes are checked against retail: dm, tdm and sd end to end, re and bel through their key events (cod11-gametypes-re-bel.md).
• Shared pmove with capsule players that block and push each other. Falls stun and hurt.
• Bullets trace the world, players and static props, through the stock damage callback with per-bone hit locations. Rifle rounds go through players, every round goes through glass. Melee works. Grenades are real missiles that bounce, rest and explode with retail's falloff, and a blast walks its victims in retail's area-tree order, so the guy in front still eats it for the guy behind.
• Corpses in the eight-slot body queue, dropped weapons, pickups by touch or use key, items that fly retail's arc and respawn on its timer.
• Search & Destroy end to end: plant, defuse, progress bar, compass objectives.
• Mounted MG42s: mount, aim inside the arc, fire, dismount.
• Map triggers, script movers that carry and shove players and items, and linkTo on script models, brush models, items, turrets and player tags.
• Intermission, map_restart and sv_mapRotation the way retail runs them.
• Spectator follow and the killcam, replayed from a ring of archived frames.
• rcon with retail's commands and replies, bans, the master heartbeat, zombie slots and retail-measured pings.
• Publishes retail's pak lists and checksums in the systeminfo, serves the paks it lists to clients that lack them at retail's pace, and with --set sv_pure=1 checks each client's pak checksums the way a pure retail server does. sv_minPing/sv_maxPing refuse off-LAN clients by challenge ping, and an off-LAN client's messages wait out its rate and snaps. Big messages, the gamestate included, go one fragment per frame.
• --bots adds bots that join through the stock menus and roam a nav graph built from pmove runs, ladders and jumps. They play the objectives: S&D plants and defuses, Retrieval carries and escorts, Behind Enemy Lines hunts. With --bots-shoot they fight back, with a reaction delay, a turn cap and aim that settles on target. They are still bad at it. So am I.

How I know it's right (when it is)

The retail 1.1d Linux server is the oracle. When vcod and retail disagree, retail wins and the disagreement goes into a research doc.

• A headless probe client (vcod --net-probe) joins a server and records what it sees, with a few dozen scripted modes: shoot someone, throw a grenade, plant the bomb, crawl prone up a hill, get stuck inside another player.
• The retail recordings are committed as fixtures. A/B tests replay the same inputs on vcod's server and diff the result snapshot by snapshot.
• Small .gsc probes run on retail and on vcod-gsc, and the suite compares their output.

This catches a lot. Anything about how it looks or sounds still needs a human squinting at a screen.

What it doesn't do

Retail does a lot more than this list. These are the gaps you'll hit first.

Front end. Main menu, browser and its popups, options, quit and error popups work. On the options screens only binds, sensitivity, invert mouse, name, rate, volume, video mode, full screen, brightness and the crosshair and HUD toggles take effect; texture, lighting, sound quality and language settings are stored but ignored. Show Compass and Team Overlay do nothing, as in retail 1.1. Start New Server and CD key print "not in vcod yet". The browser's game type filter, map preview and refresh date are missing.

Client

• Protocol 1 (patch 1.1) only. 1.5 and United Offensive servers won't talk to it.
• Prediction carries you on a moving brush model but not its rotation. Neither does retail's.
• A mod's UI DLL is ignored; only its menu files count (cod11-front-end.md sections 16-17). Switching mods in a game keeps the loaded map's geometry.

Server

• An entity linked to a player tag sits within a few units of retail's spot and doesn't follow the body after setPlayerAngles. A tag on an attached model can't take a link.
• A brush model that turned and turned back keeps a sliver of yaw on retail and drifts its riders about 0.02 units a frame. vcod's comes back to zero. Yes, I'm calling that a bug in retail.
• sv_pure defaults to 0 where retail's default is 1, and a client may download only the paks the server lists. Retail serves any file under its directories, .. included, so I'm keeping that one on purpose.
• rcon runs map, devmap, map_restart, map_rotate, status, clientkick, kick, banUser, banClient, dumpuser, serverinfo, systeminfo, say, set, seta, cvarlist, cvar queries, heartbeat, killserver and quit. Not gameCompleteStatus, scriptUsage or stringUsage. Bans live in vcod (--ban-file keeps them across runs) where retail hands them to Activision's authorize server. Like retail's, a ban refuses an address off the LAN and leaves the banned player connected until they leave on their own. After killserver the process sits there deaf, since there is no stdin console.
• A heartbeat reaches the master, which probes back. I haven't seen vcod listed yet.

Rendering and sound

• Props are lit per vertex from the map's lights and its light-visibility grid at load, as retail does. Dynamic lights add on top with retail's falloff instead of competing for a prop's eight light slots. Players, other entity models and the viewmodel pick their eight lights from the grid every frame, fx lights among them (cod11-light-grid-and-leaf-lights.md).
• The frame holds retail's framebuffer bytes and the gamma ramp doubles it once at the end, as retail's hardware ramp did; windowed it draws as retail's windowed mode does, with no doubling and lightmaps shifted at load (cod11-gamma.md). Entity models draw only their first stage, lit, whatever their material says.
• Only the ocean's deformVertexes wave moves; the other forms parse and do nothing. NV/ATI hardware-path stages are dropped, as retail did on cards without them. $dlight and the ship's deckflag have no file behind them, so stand-ins draw (cod11-shader-scripts.md).
• Visibility draws a bit more than retail on purpose. Retail assumes nobody looks over a cell's walls, and the mp_ship decks disagree.
• Audio follows the engine on paper (falloff, panning, voice pools, stealing, ducking) but hasn't been checked by ear against the real game. Wall occlusion is a vcod addition.

Things that look like gaps and aren't

• No mantling, no swimming. Retail 1.1 MP has neither (cod11-mantle.md).
• No grenade cooking. The fuse runs in full from the release, however long you clutched it.
• No doppler. The 1.1 engine never gives a sound a velocity.
• Quick chat (vsay) does nothing on a stock install, same as retail: its .voice tables only ship in mods.
• Asphalt footsteps are silent in retail because the engine asks for asphalt and the sound table spells it asphault. vcod uses the table's spelling, so you can hear asphalt. Twenty-three years late, Infinity Ward, you're welcome.

Requirements

• A purchased copy of Call of Duty (2003) with patch 1.1. This repo has no game data. Patch 1.5 ships the same pak1-4.pk3 and a different pak0.pk3; a 1.5 install works as the asset source, but its pak0 is not on a pure 1.1 server's list. The netcode is 1.1 only.
• Rust 1.90 or newer.
• For the client, a GPU with BC (DXT) texture compression. wgpu picks a backend; WGPU_BACKEND=vulkan|gl|dx12|metal narrows it. The server needs no GPU.
• Linux is the only platform I run. Windows and macOS builds exist and are untested, so godspeed.
• An audio device if you want sound. Without one the client warns and runs silent.

Building

Prebuilt Linux amd64, Windows amd64 and macOS arm64 binaries are on the nightly release, rebuilt from master on every push that touches code. It's a rolling tag: the assets are replaced in place and the previous build is gone.

cargo build --release

gives target/release/vcod and target/release/vcod-server. Both expect to sit next to CoDMP.exe and read the paks from main/. Copy them there, set COD_DIR=/path/to/CallOfDuty, or pass --game-dir. --game-dir beats COD_DIR, which beats the executable's directory.

COD_DIR=/path/to/CallOfDuty cargo test

Without COD_DIR the tests that need game data return early and pass, so a green run without the game proves nothing about the parsers. CI runs that way, because it can't ship the game either.

Usage

The closest thing to a game

vcod-server mp_carentan --bots 4 --bots-shoot
vcod --connect 127.0.0.1:28960

Pick a team, pick a weapon, go get shot by a bot.

Client

vcod                                   # main menu and server browser
vcod mp_pavlov                         # fly
vcod mp_pavlov --walk                  # walk, offline
vcod --list                            # every .bsp in the search path
vcod --connect <ip:port> --team axis --weapon kar98k_mp

• The map name is case-insensitive.
• --team <allies|axis|autoassign|spectator> and --weapon <file> answer the menus without showing them, for --connect and every console connect. If the menu refuses the weapon, you pick by hand.
• --mod-dir uo indexes United Offensive's pk3s instead of main/. One directory mounts at a time, so a UO map whose art lives in main/ shows missing textures. I've flown noville this way. Anything else in UO is untested.
• --debug-overlay (or F3) shows frame, draw, vis, net and audio counters.
• --no-audio runs silent; --volume <0..1> sets the master volume (mss_volume, default 0.8, also on the Sound screen).
• --net-probe <ip:port> is the headless probe client; vcod --help documents its modes.

Server

vcod-server mp_carentan --port 28960 --hostname "my server" --gametype tdm

• Binds 0.0.0.0 and answers getstatus from anyone, like retail. Keep it on a LAN or behind a firewall you control.
• --gametype picks the script under maps/mp/gametypes/ (default dm); --max-clients sets sv_maxclients (default 8).
• --set NAME=VALUE is retail's +set, repeatable: --set scr_friendlyfire=1, --set sv_mapRotation="...".
• --set rconPassword=<pw> turns rcon on.
• --set g_password=<pw> makes the server private, checked as retail does at connect, map_restart and map change.
• --set sv_privateClients=N --set sv_privatePassword=<pw> reserves the first N slots for clients that send that password, as retail does.
• dedicated defaults to 1, not retail's 2, so dev runs stay off the master list. --set dedicated=2 heartbeats codmaster.activision.com every three minutes and sends a flatline on Ctrl-C or quit.
• --bots <n> adds n bots in real client slots. The nav graph builds on its own thread on the first tick (a second or two on big maps); bots wander until it's ready. --bots-shoot lets them fight.
• --gametype-script <file> runs a gametype from disk instead of the paks.
• --test-entities <n> adds invisible entities that move on the wire, to exercise the entity encoding.
• --trace logs every snapshot per client, and once a second the slowest tick and how far the loop fell behind its 20 Hz schedule.

Controls

Click to capture the mouse, Esc to release it.

Fly mode

Input	Action
W / A / S / D	Move
Space / Ctrl	Up / down
Shift	Speed boost
Scroll	Fly speed

Playing

The stock config_mp.cfg binds, with the sight on the right mouse button as +speed. bind MOUSE2 "toggle cl_run" makes the sight a toggle.

Input	Action
W / A / S / D	Move
Space	Stand up; jump when standing
C / Ctrl	Crouch / prone
Q / E	Lean (held)
LMB	Fire (semi-autos fire once per click)
RMB	Aim down the sight (held)
R	Reload
Shift	Melee
F	Use: pick up, mount an MG, plant, defuse, respawn
1 / 2 / 3 / 4	Primary, second primary, pistol, grenade
Scroll	Next / previous weapon
Tab	Scoreboard (held)
T / Y	Chat to everyone / your team
M	Script menu: team, or weapon once you have a team
Esc	Script menu, as retail; its Main Menu row opens the main menu (Back to Game, Disconnect, Quit)

With a script menu open, digits pick a row, Up / Down and Enter navigate, and Esc closes it. The main menu takes the mouse; Esc or Back to Game returns to the game. As a spectator, Space rises and C sinks.

Walk mode

Input	Action
W / A / S / D	Move
Space	Jump (no autohop)
Ctrl	Crouch (held)
Z	Toggle prone
Q / E	Lean
Shift	Slow walk
LMB / RMB	Fire / aim down sights
R	Reload
1-7	colt, thompson, mp40, mp44, enfield, kar98k, scoped kar98k

Console

` or ~ toggles it; while it's down the game gets no keys. Up / Down walk history, Tab completes, Page Up / Page Down scroll. In game, a line without a leading / or \ is chat, as in retail. ; separates commands.

Command	Does
connect <ip:port>, disconnect, reconnect, quit	What they say
say, say_team	Chat
cmd <text>	Send a raw client command
bind, unbind, unbindall, bindlist	Binds
set, seta, toggle, <cvar> [value]	Cvars; seta also saves
cvarlist, cmdlist, echo, clear	The usual

Anything else goes to the server while connected (callvote, kill, follownext). Bindable commands and key names are retail's (+attack, +speed, weaponslot pistol, MOUSE1, MWHEELUP). The client cvars are name, cl_run, sensitivity, m_yaw, m_pitch, cg_fov (cheat-protected, so 80 unless the server runs sv_cheats 1), rate (25000; retail's first-run 5000 starves snapshots), snaps, scr_conspeed, mss_volume, r_mode / r_fullscreen (applied at start and by vid_restart), password and the browser's ui_netSource and ui_browserShow*. exec <file> runs a config from the paks or main/, and ui_load reloads the menus off the list ui_menuFiles names. Binds only act while connected.

Main menu and browser

Mouse to pick, double-click or Enter to join, wheel or Page Up / Down to scroll, Esc to go back. Click Source to cycle Local, Internet and Favorites. On a bind, click or Enter, then press the new key (Esc cancels, Backspace clears); a third key replaces both of the old ones. Click a text field to type into it; Enter, Tab or Esc finishes.

Everywhere

Input	Action
` / ~	Console
F3	Debug overlay
F4	Culling: on, locked, off

Documentation

• docs/protocol-1.1.md: the 1.1 wire protocol, both directions, with every divergence from RTCW/Q3 at the end.
• docs/research/: about thirty documents on file formats, movement, combat, items, turrets, movers, HUD, sound, script semantics, the console, the front end, bots and more. Every claim names the module and address it rests on and says whether it was verified against a binary or capture, or inferred. I'd call this the most useful part of the repo.
• tools/re/: the scripts that pull tables out of the binaries, and the Linux server disassembly notes.
• AGENTS.md: the contributor guide. Layout, measuring against retail, and the traps I already paid for.

The code is four crates: vcod-common (formats, collision, movement, protocol; no GPU or audio), vcod (client), vcod-server and vcod-gsc (the script VM, which depends on nothing else here).

Some numbers, for fun

As of October 2026:

• about 173,000 lines of Rust,
• about 2,200 tests,
• about 270,000 words of protocol and research notes, longer than most novels and with a worse plot, except the twist where grenade cooking turned out not to exist,
• one asphalt footstep restored.

Why

Mostly to see whether it could be done. CoD 1 descends from id Tech 3, and the Quake III and RTCW sources are public, but the 1.1 wire protocol was never documented. Every field width, enum order and place Infinity Ward wandered off from RTCW had to come out of the binaries and be confirmed against the retail server. Also, watching a 2003 game come back to life in a window you built yourself is a lot of fun.

This is an AI-driven project

An AI coding agent wrote most of the code and docs here, under my direction. I decide what to build, review what comes back, run it against the real game and the retail server, and do the pixel and by-ear checks the agent can't. The research docs label each fact verified or inferred so you can tell them apart. Treat the code as a working prototype, not a reference implementation.

Lineage and inspiration

• Quake III Arena and Return to Castle Wolfenstein by id Software, GPL. CoD1 descends from RTCW-MP, and its netcode, movement and animation code follow those sources closely. Where vcod ports a routine, the comment names the file it came from.
• ioquake3, for a cleaner reading of the same netcode.
• CoDExtended, a GPL server extension for CoD1 1.1 whose struct layouts were the starting point for the netfield tables.
• cod-asset-importer, a GPL Blender add-on. The xmodel triangle-strip decoder is ported from it.
• wgpu, winit and kira for graphics, windowing and audio.

Legal

vcod is not affiliated with or endorsed by Activision or Infinity Ward. Call of Duty is a trademark of Activision Publishing, Inc. This repository contains no game assets, game code or binaries; it reads the files of a copy you own. The reverse engineering was done to interoperate with the game's own files and servers. The research notes document file formats and the network protocol for that purpose: layouts and addresses recovered from the binaries, no copied code. The screenshots show art owned by Activision.

Quake III Arena and Return to Castle Wolfenstein are trademarks of id Software. Their GPL sources, and the other ported code, are credited in NOTICE.

License

GPL-3.0-or-later; see LICENSE. The network code was written with the RTCW (GPLv3) and Quake 3 (GPLv2-or-later) sources as reference, so the project is GPL to stay compatible with them.