Dragoman

Translate maps between Open Doctrines (.odmap) and Greater Diplomacy 5 (map directories), in both directions, losing as little as the two formats allow — and nothing at all on a round trip.

A dragoman was the interpreter attached to an embassy: the person through whom two powers who shared no language could nonetheless sign something. This is that, for map files.

pip install open-dragoman

dragoman convert 1914.odmap base_maps/1914 --to gd5
dragoman convert base_maps/GD4 gd4.odmap   --to odmap
dragoman roundtrip 1914.odmap              # prove nothing was lost

import dragoman

dragoman.convert("1914.odmap", "base_maps/1914", to="gd5")

world = dragoman.load("1914.odmap")
print(world.name, len(world.provinces), "provinces")

Read the wiki → — what it is, how to use it, what every message means, and what it cannot do.

Status

Every map both games ship round-trips without losing a single modelled field:

Verified against Open Doctrines and against GitGetGot415/Greater-Diplomacy-5. Reproduce with python3 tools/conformance.py <directory of maps>.

Converted maps have also been played in both games, not merely loaded by this library. Open Doctrines' world map converted to GD5 boots through GD5's own Controller and Map state with all 23 screens, its flags drawn, its oceans navigable and every province centre inside its own province; a GD5 map converted to Open Doctrines plays five AI turns under OpenDoctrines --simulate. Nearly everything this library gets right, it gets right because somebody opened the result in the game and looked at it — the flag encoding, the ocean, the political layer's colour key and the province-border fill were all found that way.

One thing crossing to Open Doctrines still needs a human: GD5 starts its nations with an empty stockpile and Open Doctrines expects a starting endowment, so a converted map bankrupts its world on the first turn unless treasuries are set. Reported as od.treasury rather than guessed at.

What "lossless" means here

The two games are not the same game, so a straight translation always loses something: Open Doctrines models a province's population, its port and its ethnic minorities, and GD5 has no field for any of them; GD5 models terrain, province adjacency, unit rosters and research, and Open Doctrines has no field for those.

Dragoman writes the difference down. Everything the destination cannot hold goes into a sidecar beside the map — dragoman_sidecar/ in a GD5 directory, dragoman/ inside a .odmap archive. Both games read a fixed list of filenames and ignore everything else, so the sidecar is invisible to them and costs the converted map nothing.

The result:

• Converting one way is as faithful as the target format permits, and every approximation is reported by a stable code you can act on.
• Converting back restores what the target could not hold. A → B → A keeps every province, nation, relation, claim, core, script and carried file, and the province raster hashes identical.

dragoman roundtrip <map> asserts exactly that. Pass --no-sidecar for a smaller, genuinely lossy conversion — the round trip then fails, on purpose.

Not promised: byte-identical container files. Two zip archives holding identical members are different files, because deflate is not reproducible across implementations, and Open Doctrines packs with Python's zlib while this packs with miniz. Every file inside is preserved exactly.

What crosses

Adjacency and centroids are computed from the province raster when converting to GD5, since Open Doctrines derives both at load and never stores them. The centroid finder deliberately handles crescent-shaped provinces, whose mean pixel falls outside themselves.

Full field-by-field detail: docs/mapping.md.

Scripts

Open Doctrines' scripting is imperative and line-based, with loops and waitUntil suspension points. GD5's is a list of declarative events, each a set of conditions and a set of actions. The overlap is the shape both express: a gate, and things that happen when it opens.

An Open Doctrines script written as top-level waitUntil stages becomes GD5 events, one stage at a time. A GD5 event becomes an entry script with a waitUntil and some set lines. Anything outside that overlap — a foreach over a country's provinces, conditions chained with XOR — is reported by name and carried unchanged rather than half-translated. GD5 event types this library has never heard of pass through untouched, so a GD5 → OD → GD5 trip is lossless even for conditions added to the game after this was written.

Details and the full vocabulary: docs/scripting.md.

Installing

pip install open-dragoman

The wheel carries the compiled library inside the package, so there is no compiler needed at install time and nothing to locate afterwards. You get both the Python API and a dragoman command.

Prebuilt binaries for people who want nothing to do with Python are attached to each release. The full set of options — release archives, source builds, CMake FetchContent — is on the Installing page.

Building from source

Needs CMake 3.16 and a C++17 compiler. There are no external dependencies — miniz, stb and nlohmann/json are vendored, all MIT or public domain.

cmake -S . -B build -DCMAKE_BUILD_TYPE=Release
cmake --build build
ctest --test-dir build --output-on-failure

This produces libdragoman.a, a shared libdragoman.{so,dylib,dll}, and the dragoman command line tool.

Using it from your language

The core is C++17 behind a flat C99 ABI, so anything with an FFI can call it. The whole interchange model is available as JSON through dg_world_to_json, which is how a binding reads or edits a map without needing an accessor per field.

• C — #include <dragoman/dragoman.h>, link dragoman. See bindings/c/example.c.
• C++ — #include <dragoman/dragoman.hpp> for an RAII wrapper over the same ABI. See bindings/cpp/example.cpp.
• Python — pip install open-dragoman. Pure ctypes, and the wheel carries the library, so no compiler is needed at install time.
• Anything else — Rust, Go, C#, Java, Lua and WebAssembly all bind the same header. docs/abi.md documents the contract.

Versioning

Two numbers that move for different reasons:

• Library version (VERSION, semver) — the release. Currently 0.2.0.
• ABI version (DRAGOMAN_ABI_VERSION) — bumped only when an existing symbol changes meaning, so a binding can refuse to load a library it cannot speak to without parsing semver.

The version lives in VERSION and is mirrored into the C header, the Python package and the CMake project. tools/check_version.py and tests/test_version.cpp both fail if any copy drifts, and CI runs them on every push. Details: docs/versioning.md.

Licence

Dragoman is MIT. It is an independent implementation written from observing both file formats; no code from either game is copied into it. Open Doctrines and Greater Diplomacy 5 remain under their own licences (Open Doctrines Non-Commercial, and GPL-3.0 respectively), and neither project's maps are redistributed here.