Round Trips

Round Trips

dragoman roundtrip <map> converts a map to the other format and back, and fails if anything was lost. This page says exactly what that covers, because a guarantee nobody can check is not one.

dragoman roundtrip 1914.odmap                 # to GD5 and back
dragoman roundtrip "base_maps/GD4"            # to .odmap and back
dragoman roundtrip 1914.odmap --no-sidecar    # fails, on purpose

The sidecar

The two formats are not equally expressive, so a straight translation always loses something. Everything the destination cannot hold is written beside the map instead:

• dragoman_sidecar/ in a GD5 map directory
• dragoman/ inside a .odmap archive

This is safe because of how both games load. Open Doctrines reads a fixed needed[] list plus a scan for the scripts/, licenses/ and symbols/ prefixes; GD5 reads a handful of specific filenames. Neither looks at anything else, so the sidecar is invisible to both and costs the converted map nothing but disk.

--no-sidecar writes only what the destination can express. The result is smaller and entirely playable — it simply stops being reversible. The test suite asserts that this mode does fail the round trip, so the two modes cannot quietly become the same thing.

What is preserved

• every province: id, name, owner, population, industry, fortification, port, resources, cores, garrison, and anything carried in extra
• every nation: key, display name, colour, treasury, leader, flag, relations (including the non-aggression pacts and guarantees GD5 cannot store), claims
• every script, every scripted event, and their order
• the map's name, description, author, licence and date
• every file carried opaquely — policies.json, flag images, the symbol set, the thumbnail, GD5's terrain layer and history log
• the province raster, compared by digest

What is not promised

Byte-identical container files. Two zip archives holding identical members are different files: deflate is not reproducible across implementations, and Open Doctrines packs with Python's zlib while Dragoman packs with miniz. Every file inside is preserved exactly; the envelope around them is not.

Two deliberate asymmetries

Derived geometry is excluded from the comparison. Adjacency, centres and coastal flags are not facts a map states — they are functions of the raster, recomputed identically by whichever side needs them, and the raster itself is compared. Including them would fail a round trip for having worked out, on the way home, a neighbour list the Open Doctrines map never had to store.

A round trip may come home richer. The check is containment, not equality: every fact in the original must be present and equal in the result, and the result may hold more. Crossing to GD5 and back picks up that game's hand-painted terrain layer, which the returning .odmap then carries so the next crossing keeps it. That is a gain. Losing anything still fails.

From code

dg_report* report = NULL;
int same = dg_roundtrip_check("1914.odmap", DG_FORMAT_GD5, &opts, &report);
/* 1 identical, 0 something changed, -1 could not be checked */

identical, report = dragoman.roundtrip_check("1914.odmap", to="gd5")

A failure names the field:

error roundtrip.differs: the round trip did not preserve
      provinces -> [1030] -> owner -> value changed

Coverage

Every map both games ship: 28 GD5 maps and 6 Open Doctrines maps. Each of those found bugs a hand-built fixture could not — a nation named "Unclaimed" that really is a country, two nations sharing a display name, claims that are not cores, GD5 event types this library has never heard of.

python3 tools/conformance.py ~/games