This applies to forks, ports, mod packs, videos, tutorials and any code, offset or idea reused in another project.

Drive together in Forza Horizon 2 on the Azimuth emulator, without Xbox Live.

Version 1.0.5 — by MrReLaX

The online servers of Forza Horizon 2 have been closed since 22 August 2023. Horizon Online brings its own small network: each machine sends its car to the others, and in your game each friend's car is played by one of the game's AI cars, which takes their model, livery, pseudo and level and replays their exact moves.

Everything happens in memory: the game, Azimuth and your saves are never modified on disk.

Horizon Online was vibe-coded. I had the idea, directed the work and tested every version in game with a friend.

The code itself, including the reverse engineering of the game, was written by an AI coding assistant (Claude, by Anthropic) through conversation. No professional programmer wrote or reviewed it line by line.

It works on our machines, but expect bugs, crashes and rough edges. Read the source code if you want to know exactly what it does, and keep backups of your saves.

Windows Defender will probably flag Horizon Online.exe or fh2multi.dll, or delete them when you extract the zip. This is a false positive.

Why it happens: the launcher starts the game, then loads fh2multi.dll into the azimuth.exe process with CreateRemoteThread + LoadLibraryW. Cheats, trainers and some malware use the same technique, and the files are new, unsigned and downloaded by few people, so antivirus heuristics distrust them.

What you can do:

1. Only download Horizon Online from the Releases of this repository. Any other copy may really be malicious.
2. Read the source code in this repository, or build the files yourself (see Building).
3. If you want a second opinion, upload the files to VirusTotal.
4. If Defender quarantined a file you downloaded from the Releases: Windows Security → Virus & threat protection → Protection history, select the Horizon Online detection, then Actions → Allow on device (or Restore).

Do not turn Windows Defender off. Allowing these two files is enough.

• Automatic discovery of the other players on the same local network (UDP), or a list of IPs for a VPN.
• Your friend's car in your game, played by a drivatar:
  • their real model, parts, tuning and full livery (paint and vinyls, even redone in game);
  • their pseudo and level above the car;
  • their moves to the centimetre, with collisions;
  • their engine (revs, gear, clutch) and so its sound, their steering and wheel rotation.
• Real car from the reserve: when the game keeps a friend's real car in its reserve, Horizon Online puts it on the road itself, the way the game does for its drivatars.
• Pause: when a friend pauses their game, their car stays in yours, parked where they left it.
• Shared time and weather: the host gives its time of day and weather to the others. Time keeps going while a player is paused, and their game catches up when they resume.
• Host's drivatars and traffic: within 400 m of the host, the host's AI cars replace yours (same cars, colours, pseudos and levels, at the same places).
• Map: each friend has a yellow "online player" marker on the minimap and on the pause map, at their real position, even far away, updated during the pause too.
• Notifications "pseudo joined / left" (HUD minor notifications).
• "Online" behaviour while a friend is connected: the world keeps going in the pause menu and the map, rewind is off. Without friends, everything is solo again.
• Free race: pick a destination on the map, hold Y for one second, and everyone starts 5 s later towards the same point on the group GPS; the first one there wins and their time shows for everyone.
• Duel: press B behind a friend's car, as you would to challenge a drivatar: the game's 1 vs 1 starts in your game against their car and in theirs against yours, towards the same destination; the first one there wins, and the duel ends in the other game too.
• Launcher checks: at each start, Horizon Online.exe tells you when a newer release is on GitHub, and warns you when your pseudo is not set in fh2multi.ini.
• Measured link: the log gives the round trip time to each friend; game mode messages use a reliable channel (acknowledgements, resends).

• Outside free races and duels, a friend's car only appears when they are within about 200 m of you (beyond that, the game puts its drivatars away).
• For a few seconds after connecting, after a car change or when they come back near you, a friend can be played by a "borrowed" drivatar that keeps its own car and name. It can last longer after a duel where you drove apart; a teleport usually fixes it.
• No other multiplayer events yet: Festival races, Infected, King and Road Trip are still to do.
• Playing over the Internet (Hamachi, Radmin VPN, Tailscale…) should work with the Amis= line, but it has not been tested much.
• The log and the in-game notifications are in French.

• Windows 10 or 11, 64-bit.
• Azimuth 0.9.9.
• Your own copy of Forza Horizon 2 for Xbox One, version 1.0.0.64 (FH2_Anthem_1.0.0.64_x64__8wekyb3d8bbwe). Horizon Online recognises this version by its code before hooking into it: on another version it does not hook, and the log says so.
• A controller: the game is played with a controller. Everything uses the game's own input, except holding Y to start a free race: with Azimuth 0.9.9, Horizon Online no longer finds Azimuth's controller table, so it only sees Xbox controllers there (not the DualSense and keyboard mods). Press F9 on the keyboard instead.
• Optional: "FH2 DLC Launcher.exe" (Storm Island, ExtraOptions). If it is there, it is kept; Horizon Online's hooks chain in front of ExtraOptions' ones.

This repository contains no game files and never will. Everyone uses their own copy of the game.

All machines must run the same version of Horizon Online.

1. Download Horizon-Online-1.0.5.zip from the Releases.
2. Copy these 3 files into the Azimuth folder, next to azimuth.exe:
   • Horizon Online.exe
   • fh2multi.dll
   • fh2multi.ini
3. Open fh2multi.ini and put your pseudo on the Pseudo= line (15 characters max). Give each machine a different pseudo. While it is empty, the launcher warns you and you appear with the name of the Azimuth launcher.
4. Start the game with "Horizon Online.exe". It starts "FH2 DLC Launcher.exe" if it is there, otherwise azimuth.exe, then attaches the module. The usual Azimuth menu opens: press Start.
5. If the Windows firewall asks to allow azimuth.exe, allow it for private networks only.

To go back to normal: start the game with "FH2 DLC Launcher.exe" (or azimuth.exe). To uninstall: delete the 3 files.

At each start, Horizon Online.exe asks GitHub for the latest release of this repository. When it is newer than yours, it offers to open the download page. Nothing shows when you are offline.

To update, replace fh2multi.dll and Horizon Online.exe, and keep your fh2multi.ini (it holds your pseudo). The game must be closed: the DLL is locked while it runs.

The host is the machine whose IPHote= line is empty. If several machines leave it empty, one is picked automatically. To choose yourself, put the host's IP on IPHote= on the other machines, for example:

IPHote=192.168.1.42

Guests take the host's time of day and follow its weather. The sky changes with the game's normal fade, so going from sun to storm can take a while. While they follow a host, guests do not change weather on their own.

Near the host (less than 400 m), the host's drivatars and traffic replace the guest's: each car arrives once it is loaded (a few seconds, one at a time) and the guest's own traffic fades out along the road.

1. Pick a destination on the map.
2. Hold Y for one second (controller; F9 on the keyboard). Everyone gets the destination, drawn on the group GPS, and a notification that the free race starts in 5 s.
3. "GO !": everyone starts from where they are. The first one within 20 m of the destination wins; their time shows for everyone.

Holding Y for one second again (or F10) cancels the race you started. If the map still offers "group destination" (Y), it is shared with your friends without starting a race.

Drive behind a friend's car and press B, as you would to challenge a drivatar. The game's duel starts in your game against their car; in theirs, the same duel starts against yours, towards the destination your game picked (it replaces the one their game would have picked). Each player runs the game's own duel with its countdown and finish; both cars stay played at any distance until the end.

The key names are in French: do not rename them.

Test and development settings, to leave as they are:

On the same network they find each other automatically. Otherwise (Wi-Fi that isolates devices, Hamachi, Radmin VPN…), put the other machine's IP on the Amis= line, for example Amis=192.168.1.42.

Horizon Online is a hobby project made for playing with friends you trust.

• No password, no encryption. Anyone who can send UDP packets to your ports 5300–5303 can join as a player. That is fine on your home network or in a private VPN network with your friends. Do not open or forward these ports on your router, and do not use Horizon Online in public Hamachi / Radmin VPN networks full of strangers.
• The game's own code reads what your friends send (car setups, liveries). Horizon Online checks the sizes and ranges of everything it receives, but the game was never written for hostile input: a malicious player could probably crash your game.
• The game stays offline: with Internet=0, it cannot resolve any domain name, so it cannot contact the old Microsoft / Turn 10 servers.
• The update check: Horizon Online.exe sends one HTTPS request to api.github.com at each start and only reads the version number of the latest release. Like any web request, GitHub sees your public IP. When you click Yes, it opens the fixed address of this repository's Releases page, never an address taken from the response.
• The log (data\logs\fh2multi.log) contains your local IP addresses, your network card names and your pseudo, and fh2multi-trajet.csv contains your driving route. Hide your IPs before posting the log online.

Since version 1.0.0, Horizon Online checks what arrives from the network before it reaches the game: livery chunks (earlier, unreleased versions had an out-of-bounds write there), friends' positions and received destinations. Since 1.0.5, each rejected packet is written in the log.

Azimuth\data\logs\fh2multi.log, reset at each start (in French). Useful lines:

• multi : ami « … » connecté depuis …: a friend was found; liaison avec « … » : N ms aller-retour: link quality;
• modèle : … préparée avec la configuration de l'ami: their car is arriving;
• marionnettes : ami « … » à …, 0.0 m de sa cible: their car follows them;
• monde : …: who gives time and weather; PNJ : …, trafic : …: the host's drivatars and traffic;
• GPS : …: destinations picked and drawn; course : …: free race; duel : …: shared duel;
• crochet : 0x… déjà détourné vers … : on passe avant lui: another mod (ExtraOptions) hooks the same code, Horizon Online chains in front of it.

• Launcher: checks GitHub and your pseudo, starts the game, waits for azimuth.exe, then loads fh2multi.dll into its process.

• Reading your car: position, axes, speed, controls, engine and wheels, read from the game's physics about 10 times per second.

• Network: "FH2M" UDP packets (protocol 8), sent locally and broadcast on each network:

  Type	Content	Rate
  1	Position, axes, speed, model, controls, engine and wheels	~10 / s
  2	Car setup (parts, tuning, colours), livery fingerprint, experience	on change and every 2 s
  3	Livery in 1 KB chunks (512 KB max)	when it changes
  4	Time of day and weather	every second, pause included
  5	The host's AI cars (nearby drivatars and traffic: position, axes, speed)	~5 / s
  6	Card of one of the host's AI cars (model, setup, pseudo, level)	on demand
  7	Reliable channel for game modes (ping/pong, free race, shared destination, duel and its win), with acknowledgements and resends	on event

• Puppets: a drivatar is picked for each friend. After each step of its physics, its state is replaced with the friend's: position and speed interpolated 150 ms in the past, then engine, gearbox, steering and wheel rotation. Before each step, its controls become the friend's. The host's AI cars are played the same way by cars of the same model, the local traffic being cut near the host.

• Your friend's real car: when the game asks for a new drivatar, its car is swapped on the fly for the friend's model, dressed with their setup and livery. If needed, a drivatar out of sight is handed back to the game to free a slot. When the real car stays in the game's reserve, it is put on the road with the game's own spawn function.

• Name tag: pseudo and experience (shown as a level) are written into the drivatar's driver.

• Time and weather: the host sends its time, its time speed, its sky target, the 4 presets of its weather cycle and its rain. Guests apply them the way the game's online mode did.

• Map: one "online player" map item (the game's yellow marker) per friend, moved every frame, pause included. Notifications: the game's HUD minor notification, with its icon.

• Session: while a friend is connected, the game gets the same settings as online (simulation during the pause, rewind blocked).

• Game modes: the destination you pick on the map is caught when the GPS draws it; the free race and the shared destination go through the reliable channel, and the shared route is put on the game's group GPS. The duel reuses the game's "Race Encounter": on the challenger's side, the duel start is recognised when the opponent is a friend's car; on the challenged side, the same "B accepted" is replayed against the challenger's car, which is found in memory and becomes the target, and the destination picked by the challenger's game replaces the local one. When a game declares the win, it sends it; in the other game, the loss is declared by the game's own function.

You need Visual Studio Build Tools (version 18, x64 C++ tools).

build.bat

The script makes build\fh2multi.dll and build\Horizon Online.exe (icon and version information included). The version number is in src\version.h, the only place to change.

Releases: publish them with a tag such as v1.0.1. Horizon Online.exe compares the tag of the latest GitHub release with its own version (src\version.h); a release without a newer tag shows nothing.

test\harness.cpp loads the game executable (your own copy) at its original address, attaches the DLL and simulates a player car, a car list, a puppet, the time and the weather. Two instances started in two folders (each with the DLL and an fh2multi.ini with PortMulti=5600, so they do not join a real game) talk to each other. The path of the game executable is at the top of harness.cpp (kExe). The bench has no HUD, map, GPS or entities: it checks that the hooks install, not the in-game behaviour.

cl /nologo /O1 /MT /EHsc /std:c++17 /utf-8 test\harness.cpp /Feharness.exe /link /BASE:0x200000000 /DYNAMICBASE:NO kernel32.lib ws2_32.lib ole32.lib
harness.exe <folder containing fh2multi.dll> [seconds to wait at the end]

src/fh2multi.cpp        the module: hooks into the game, network, puppets, models, liveries, name tags, time,
                        weather, host's AI cars, map, notifications, session, reliable channel, free race, duel
src/gamedata.h          addresses and offsets in the game (FH2 1.0.0.64)
src/version.h           version number (DLL, log, launcher, update check)
src/launcher.cpp        the launcher (update check, pseudo check, start, attach); launcher.rc, launcher.ico,
                        launcher-logo.png: icon and version information
src/thunk.asm           call relays
test/harness.cpp        offline test bench
build.bat               build script
dist/                   released files (DLL, launcher, .ini, README.txt, LICENSE.txt)
LICENSE                 MIT license

The source comments are in French.

Horizon Online is released under the MIT License. You can use, modify and share it, even in other projects, as long as you keep the copyright notice and the license text: that is how MrReLaX stays credited.