dat Files and Formats

dat Files and Formats

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_{.dat file sizes and roles}

MM2-local inventory and current format status for data files in this workspace.

MM2-Local Inventory

Canonical set in project root (same bytes are mirrored under EXTRACTED/ and MM2BOOT/):

• attrib.dat - 3840 bytes
• event.dat - 95687 bytes
• items.dat - 5120 bytes
• map.dat - 30720 bytes
• monsters.dat - 6656 bytes
• roster.dat - 8320 bytes
• spells.dat - 256 bytes
• str.dat - 7808 bytes

Confirmed Formats

items.dat (confirmed)

Cross-validated with:

• MM2 asset filename references in binary (items.dat appears with spells.dat near code offset 0x29868)
• Legacy reverse code: C:\_20260421_\D-REC\development\Amiga\Smite-and-Magic\Blitz3d\b3dmm2\Item_ED.bb

Layout:

• 256 records
• 20 bytes per record (0x14)
• Record fields:
  • 0x00..0x0B - item name (12-byte ASCII, space-padded)
  • 0x0C - separator/pad (editor writes 0)
  • 0x0D - usable-by bitmask
  • 0x0E - bonus packed nibble (hi=bonus_type, lo=bonus_amount)
  • 0x0F - effect packed nibble (hi=effect_type, lo=effect_amount)
  • 0x10 - damage byte
  • 0x11 - pad/unused byte (editor writes 0)
  • 0x12..0x13 - gold (uint16 little-endian on disk; shop price in gp; game byte-swaps each record word on load, asm 0x26030)

Notes:

• 5120 = 256 * 20, which matches the editor loader/saver loops.
• Item names align 1:1 with b3dmm2/items.txt.

roster.dat (confirmed layout + C loader/saver)

Cross-validated with:

• MM2 executable ASM (EXTRACTED/mm2.asm, EXTRACTED/mm2.capstone.asm)
• New C codec in EXTRACTED/decomp/mm2_roster_codec.h + .c

Layout:

• 64 records
• 130 bytes per record (0x82)
• Key fields:
  • 0x00..0x0A - character name (11-byte ASCII)
  • 0x0B - town/inn byte (low7=town, bit7=party flag inferred)
  • 0x0C - sex
  • 0x0D - alignment (current)
  • 0x0E - race
  • 0x0F - class
  • 0x10..0x15 - current core stats
  • 0x27 - current endurance
  • 0x28..0x39 - equipped items (6 slots x 3 bytes)
  • 0x3A..0x4B - backpack items (6 slots x 3 bytes)
  • 0x4C..0x57 - spellbook bytes
  • 0x58..0x61 - SP/HP/Gems words (little-endian)
  • 0x62..0x65 - XP (little-endian dword)
  • 0x66..0x69 - Gold (little-endian dword)
  • 0x6A..0x73 - base alignment/stats/level/spell-level/endurance
  • 0x74..0x75 - HP current (word)
  • 0x76..0x81 - unresolved tail bytes

Notes:

• Loader/saver round-trips unknown spans byte-for-byte.
• The codec treats numeric multibyte fields in roster.dat as little-endian on disk.

monsters.dat (confirmed record geometry + C loader/saver)

Cross-validated with:

• MM2 executable ASM loader path (allocates/reads 0x1A00 bytes for monsters.dat)
• MM2 accessor routine around 0x99C8 (mulu #$1a, then copies exactly 26 bytes)
• C codec in EXTRACTED/decomp/mm2_monsters_codec.h + .c

Layout:

• 256 records
• 26 bytes per record (0x1A)
• Record shape currently modeled as:
  • 0x00..0x0D - monster name (14-byte fixed field)
  • 0x0E..0x19 - 12-byte stat/behavior payload (still being field-lifted)

Notes:

• This is sufficient for byte-perfect load/edit/save and safe round-tripping.
• Field-level semantics for the 12-byte payload remain TODO pending deeper combat call-site traces.

str.dat (confirmed encoding, partial semantics)

Encoding:

• Byte transform: decoded char = (encoded + 0x1C) & 0xFF
• 0x01 acts as newline/line break

Observed content:

• Contains many in-game text strings (jokes, prompts, shop/guild text, menu/help text).

map.dat (confirmed)

Cross-validated with:

• MM2 executable ASM (flat load into A4-$EEF4, 3D hood reads page 0 @ 0x2900)
• editor/src/core/MapFile.{h,cpp} — 60 screens × 512 bytes
• Collision 0x80 event alignment vs event.dat triplets

Layout:

• 60 map screens
• 512 bytes per screen (0x200)
• Per screen:
  • 0x000..0x0FF — page 0 (visual): 16×16 grid; four 2-bit wall fields per cell (N/E/S/W)
  • 0x100..0x1FF — page 1 (collision): same geometry; (dark<<1)|wall per direction; bit 0x80 = event flag

Notes:

• 30720 = 60 × 512, which matches the editor loader/saver loops.
• Row 0 on disk = south; MM2ED and wiki grids draw north-up.
• Full field decode: map.dat format.

Partially Characterized / TODO

These files are inventoried and size-confirmed, but structure still needs field-level confirmation against ASM call sites:

• event.dat (95687 bytes)
• spells.dat (256 bytes)
• attrib.dat (3840 bytes)

Working rule:

• Use ASM first (EXTRACTED/mm2.capstone.asm, EXTRACTED/mm2.asm) to identify true runtime reads/writes.
• Use legacy Blitz3d reverse code as a cross-check.
• Resolve conflicts in favor of observed assembly behavior.

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See also

Page	Why
items dat Format	256 items
map dat Format	Visual + collision pages
event dat Format	71 script locations
MM2ED Editor	Edit in GUI