Thandor: The Invasion (Open Thandor)

You need the original game. Open Thandor contains no game data: it runs on the data of an installed full version of Thandor (the folder with DATEN.PCK). Community: thandor.cc and its Discord.

Deutsch: Open Thandor ist ein vollständiger Nachbau von "Thandor: Die Invasion" in C++. Der Patch-Installer Thandor-Patch-7.exe macht eine vorhandene Thandor-Installation zu Open Thandor 1.0.7 - 64 Bit, Vulkan/DirectX 12, Auflösungen bis 4K, UI-Skalierung und viele Absturzkorrekturen. Spielstände und Karten des Originals funktionieren weiter. Details: Patch notes.

Install and play

You need an installed full version of Thandor and 64-bit Windows 10 or 11.

1. Download Thandor-Patch-7.exe from the latest release.
2. Run it. It finds your Thandor folder (the one with DATEN.PCK); Patch 5 is not required.
3. Start the game as before with thandor.exe in the game folder.

• The installer keeps your old thandor.exe as thandor-1.05.exe. Uninstalling ("Apps" in Windows, entry "Thandor Patch 7") puts it back.
• Your saves, your settings and the game data (*.PCK, movies) are never changed. Saves of the original game load, and the game still writes saves in the original format.
• The installer is not signed, so Windows SmartScreen may warn ("More info" -> "Run anyway").
• The settings are in thandor.ini next to the game; your old thandor.dat settings are taken over once.

What's new compared with Thandor 1.05

	Thandor 1.05 (original)	Open Thandor 1.0.7
Program	32-bit, 1999 Windows APIs	native 64-bit, C++20 on SDL3
Graphics	DirectDraw, Glide (3dfx), Direct3D	Vulkan, DirectX 12 or the software renderer, switched in the menu
Resolution	only the ten smallest display modes listed	every mode of your display up to 4K, window / borderless / fullscreen
UI on large screens	tiny	UI scaling Auto, 1x, 2x, 3x (crisp, 3D view at full resolution)
Frame pacing	-	VSync and an optional frame limit (60, 120, 144)
Sound, music, movies	DirectSound, WinMM	SDL3, works on current Windows
Settings	binary thandor.dat	readable thandor.ini (old settings taken over)
Damaged files, odd maps	crashes	rejected with a message; safe saving
Rules, AI, saves, maps, LAN	-	unchanged: saves, levels and multiplayer stay compatible with the original

Full list: Patch notes.

What works

Area	Status
Single player: menus, campaigns, skirmish, AI, save/load, movies, sound	playable. An automated run starts all 56 missions: 50 play without problems, 1 level file is missing from the original data, and the 5 levels that need the units carried over from the previous level play when reached through that level. A campaign run wins every level in turn and reaches the end of all four campaigns (tutorial, Luke, Nimm2, Hansolo)
Graphics	Vulkan (default), DirectX 12 or software; window, borderless or exclusive fullscreen (details). The original's Glide (3dfx) and Direct3D renderers were removed
Multiplayer (LAN, UDP)	works in a local two-instance test: lobby, map and faction choice, briefing, in-game commands; protocol-compatible with the original game
Map editor	hidden in the original; opened by a hotkey on the experimental/map-editor branch

For developers

Current state

All of thandor.exe is reimplemented in readable C++ (C++20), as a 64-bit program on SDL3. No original machine code is executed and the original executable is not needed. Its data (tables, UI templates, strings) is compiled in as ordinary variables of the modules; only the game's data files (*.PCK, movies) come from an installation.

• 1,919 original functions in about 160,000 lines (198 source files, 52 modules).
• Every function has a header comment (what it does, who calls it); names, constants and structure types are readable throughout, control flow is structured.
• The code no longer refers to the original binary: the original addresses of all functions and data are kept in one list, docs/original_addresses.txt, for comparisons with the original.
• Bugs and quirks of the original game are kept on purpose and marked "Original quirk" in the code; only the ones that corrupt memory or crash are bounded.

Roadmap

1. Step 8 (done): a full code review and idiomatic C++, following the C++ Core Guidelines (plan).
2. Step 9 (done): the UI and the 2D overlays drawn on the GPU, UI scaling at 1440p and 4K (plan).
3. Step 10 (done): the patch installer "Thandor Patch 6" (Inno Setup 7) for version 1.0.6, built by GitHub Actions on a release tag (plan).
4. Step 11 (done): security and crash fixes for local input - level, savegame and asset files, local crashes, thread races, undefined behaviour (plan).
5. Step 12 (next): the multiplayer security fixes - data received from peers, lobby and session transfer, the UDP backend; tested against the original game (plan).
6. Step 13 (done): modern C++ - typed UI objects instead of template offsets, named casts, constexpr and enum class, RAII, bool, named key actions and plain loops (plan).

How correctness is kept

The project gave up byte-identical machine code in favour of readable code; behaviour is checked instead (tools/test/run_checks.py, run after every change):

• Determinism: scripted battles with a fixed random seed write a hash of the game state every simulation step; every build must produce the same hash sequence as the reference.
• AI hash, pixels, save/load, text editing: AI decisions per step, screenshots of fixed scenes, a saved and reloaded game, the in-game text editor.
• Multiplayer: two instances play a game against each other over UDP.
• Campaign and all missions: the campaign chain with carried-over units and a start of every mission (run_all_maps.py, run_campaign_chain.py).
• GPU renderers: Vulkan and DirectX 12 compared with the software renderer (gpu_compare.py).
• Self-tests for the number formatting, fixed-point math, key mapping, triangle setup, the archive codec, the movie encoder and more compare their output between builds.

Building

The main compiler is MinGW-w64 GCC (x86_64, SEH; tested with GCC 15.2): CMake 3.25+, Ninja, g++ on the PATH or MINGW_ROOT set (cmake/mingw-x64.cmake), SDL3 with Vulkan from vcpkg install sdl3[vulkan]:x64-mingw-dynamic, and dxc for the Vulkan shaders, vcpkg install directx-dxc:x64-windows. CMake finds them through the environment variable VCPKG_ROOT (the vcpkg directory).

set PATH=C:\mingw64\bin;%PATH%
set VCPKG_ROOT=C:\path\to\vcpkg
cmake --preset mingw-release
cmake --build --preset mingw-release

The result is build-mingw-release\thandor.exe (x64) with SDL3.dll next to it; copy both into a copy of an installed Thandor folder and start it there (e.g. thandor.exe -NOINTRO). --target installer builds Thandor-Patch-7.exe (needs Inno Setup 7, see docs/BUILDING.md). mingw-test (build-mingw-test) adds the developer tools: self-tests, windowed mode, several instances, scripted input, starting any campaign level, the determinism state hash; the automated checks use this build.

MSVC (Visual Studio 2022 or newer, SDL3 from vcpkg install sdl3[vulkan]:x64-windows) is the second compiler, kept building for the Visual Studio debugger (presets release, debug, test, gpu-test in CMakePresets.json). Details in docs/BUILDING.md.

Source tree

Public headers under include/thandor, implementations under src, grouped by area (assets, audio, core, gameplay, graphics, movie, network, platform, ui, world).

• Module tree - every module with its .cpp and .h files.
• Source file guide - what each source/header pair owns, its callers and dependencies.
• Types: each module's structures are in include/thandor/<area>/<module>/types.h, the common ones in core/types.h.
• File formats: levels, field grids.

About

Got this game back then and can't forget it, so this project rebuilds it in C++ to fix things, replace the AI, change the graphics API, fix sound and so on. I hope some of you want to join this effort too - come by on thandor.cc / Discord.

Contributors

• idkFoxes - reverse engineering of the game and the original decompilation this project grew from.
• Crankerer - compilable build, the C/C++ reimplementation and its verification, and the patches 1.0.6 and 1.0.7 (Open Thandor) including the patch installer.

Contributions are welcome.

License

The source code and documentation are under the MIT License: free to use, change and share, as long as the copyright notice is kept. The original game and its data (artwork, texts, sounds, movies) belong to their rights holders and are not part of this project; you need an original copy to play. This project is not affiliated with the original developers or publishers. This is an unofficial reverse-engineering and preservation project. It is not affiliated with or endorsed by the original copyright holders. Original game assets and software remain the property of their respective owners.