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BRE save-file format notes (data/game.dat)

Partial map of BRE v0.988's binary save, from differential diffing (make one known in-game change, diff the file). Reference for understanding BRE, not for IB's own save format (IB uses JSON). Key finding: BRE validates record integrity, so naive byte-edits are rejected — see the warning below.

Files

  • data/game.dat (~29 KB) — the empire records. Fixed-size records (~1069 bytes apart: two empires' name fields sat at file offsets 2521 and 3590). Each record's name is a Turbo Pascal ShortString (1 length byte + chars), e.g. 04 "Rome".
  • data/planet.bre (~360 KB) — planet/region map data; holds no empire name strings.
  • data/ids.dat — empty in this game.

Region counts (mapped)

The eight region-type counts are int32 little-endian, stored contiguously in Buy-Regions display order:

Coastal, River, Agricultural, Desert, Industrial, Urban, Mountain, Technology

For the "Rome" record (name at file offset 3590) the block began at offset 3708 (0xE7C) — i.e. name + 118 bytes. Confirmed: buying exactly 10 Coastal changed the first int32 there from 16 00 00 00 (22) to 20 00 00 00 (32), and nothing else in the block moved. Two int32 = 100 fields sat just before the block (0xE74/0xE78) — likely Popular Support / Morale, unconfirmed.

offset 0xE7C  Coastal   int32 LE
offset 0xE80  River      "
offset 0xE84  Agricultural
offset 0xE88  Desert
offset 0xE8C  Industrial
offset 0xE90  Urban
offset 0xE94  Mountain
offset 0xE98  Technology

⚠ Integrity check — direct edits are rejected

Patching Coastal from 32 to 200 directly in game.dat (with BRE closed) and relaunching made BRE fail to find the empire and prompt the caller to name a new realm — the edited record was discarded, no explicit "tampered" message. Restoring the pre-edit backup brought the empire back intact. So BRE stores a per-record (or per-file) integrity value that a raw field edit invalidates.

Consequence for test setup: you cannot just poke region counts to stage a scenario — the empire gets reset. To edit safely you would first have to locate the checksum field and its algorithm (another differential-diff pass: change one field in-game and find which other bytes move — those are the checksum), then recompute it after each edit. Until that is done, prefer in-game changes (e.g. buying regions over a few turns) for staging tests.

Always back up data/game.dat (and planet.bre) before any experiment.