OpenGG

An open-source engine for Gearhead Garage: The Virtual Mechanic (1999), in the spirit of OpenTTD, OpenRCT2 and OpenMW. It plays the original game with your own copy of it: cars, jobs, decals, screens, sounds and 3D scenes are read from your game folder at every start, and nothing is copied out of it.

Beta, Windows and Linux (changes). Rules, prices, screens, sounds and views follow the original as measured in the running game (docs/FIDELITY.md). Expect rough edges.

Playing

1. Download OpenGG-…-windows-x64.zip from Releases, unpack it anywhere and start OpenGG.exe. The program is not signed, so Windows may warn about an unknown publisher: More info → Run anyway (or build it yourself). Windows 11 with Smart App Control turned on blocks unsigned programs outright, your own build too: there OpenGG will not run until it is signed. On Linux (x86-64): unpack OpenGG-…-linux-x64.tar.gz and start OpenGG.x86_64.
2. On the sign-in sheet press GAME FOLDER… and pick your Gearhead Garage folder, the one with Data\Cars.
3. Create a mechanic with NEW, or bring your .mek saves over with IMPORT MECHANICS (cash, skill, cars, Parts Bin, decals).

Without the original, OpenGG plays a beta of its own: one generated placeholder car and jobs of its own, in a look of its own.

The game folder

• Usually C:\Program Files (x86)\HeadGames\Gearhead Garage (only the CD? install the game first). Its Data folder, or the folder above the game (HeadGames), works too; on Linux, a copy of the installed folder (from Windows or a Wine prefix); a folder without the game is refused with a message.
• It is remembered and only read: nothing is written there.
• A line on the sign-in sheet says what is missing: blue while no folder is picked; red when the folder has gone (the placeholders play until you pick it again) or has no archives (Data\*.dat: its cars and jobs then play in OpenGG's own look).
• CONTENT and LOOK switch between the original's and OpenGG's own.
• For one run: OpenGG.exe -- --original "D:\Games\Gearhead Garage".

Controls

The original's help (the Help folder of the installed game) is the manual; FIDELITY lists what OpenGG does differently. Those marked * are OpenGG's own.

Turn the view	hold the arrow keys (or the number pad's 2, 4, 6, 8), or drag with the right button
Zoom the WorkShop's view*	mouse wheel
Show Condition	hold its button (or C*)
Take a part off, bolts and all*	Shift+click the part
Impact Wrench, Body Paint, Camera, Start Engine*	1, 2, 3, hold 4
Bolt mode's CANCEL, stop aiming a decal*	Esc
Answer a box*	Enter (OK), Esc (cancel)
Full screen or a window*	F11, Alt+Enter, or SCREEN on the sign-in sheet

The original's 640 × 480 screens are scaled at 4:3; SCALE on the sign-in sheet keeps them at whole multiples. Saves and settings live in %APPDATA%\Godot\app_userdata\OpenGG (on Linux ~/.local/share/godot/app_userdata/OpenGG).

Assets

Without the original, OpenGG uses placeholders: the ai_ files in data/ai (one car with its parts, textures, sounds, icons, customer portraits and job data). They are generated by code in tools/gen written with an AI assistant, not drawn, modelled or recorded by hand (docs/ASSETS.md). They are stand-ins: hand-made assets are planned for 1.0, so that OpenGG can be played on its own too; until then it is for playing the original's content. The photographic surfaces in data/hd (asphalt, grass, planks, metal) are CC0 pictures from ambientCG (data/hd/LICENSES.md); the fonts in game/Fonts are under the SIL Open Font License (game/Fonts/LICENSES.md).

Legal

• OpenGG is not affiliated with or endorsed by Ratloop, Inc., Mekada, Head Games, Activision or Snap-on. Gearhead Garage and the other names are their owners' trademarks.
• This repository contains no code, assets or text from the original game, and OpenGG ships none. The engine was written from scratch without decompiling or disassembling the original's programs; the file formats were worked out from the data files alone (docs/formats).
• To play with the original's content you need your own copy. Its files are read at runtime from the folder you pick; its encrypted archives are decrypted in memory, and nothing from them is written to disk.

Building from source

Needs Godot 4.7.1 .NET (the "mono" build) with its export templates, the .NET SDK 8 and Node.js 22.18 or newer.

npm ci
npm run gen:assets        # the placeholder pack: data/ai
dotnet test core/OpenGG.Core.Tests
godot --path game         # run from source (or open game/project.godot in the editor)
godot --headless --path game --export-release "Windows Desktop" ../build/OpenGG/OpenGG.exe
godot --headless --path game --export-release "Linux" ../build/OpenGG-linux/OpenGG.x86_64

An exported build looks for data/ai and data/hd next to the program. The version is config/version in game/project.godot; pushing the tag v + that version (such as v0.1.0) makes .github/workflows/release.yml build the Windows and Linux packages and attach them to a release.

More: ARCHITECTURE (how it fits together), ORIGINAL_IMPORT (what is read from the original, and how), ASSETS (the placeholders), formats (the original's files).

Contributing

Bug reports, differences from the original and pull requests are welcome: see CONTRIBUTING.md. Questions and ideas go to Discussions.

Licence

OpenGG is free software under the GNU General Public License, version 3, the generated placeholder pack included. The pictures in data/hd are CC0; the fonts in game/Fonts are under the SIL Open Font License 1.1.