IGI Reverse Engineering

Reverse engineering documentation for Project IGI (1999) by Innerloop Studios.

Updated revision. A substantially deeper pass over the original write-up: every format claim is now anchored to the loader code in IGI.exe (see the loader map), reproduced by parsers that print the pass counts quoted in the docs (reverse/tools/verify_all.py), and stress-tested against rival interpretations (reverse/tools/adversarial_checks.py). The weapon damage formula and the world scale (4096 units = 1 m) are recovered. STATUS.md tracks what is proven, partial, and still open.

Platform. Developed and verified on Linux (x86-64), which is the best-suited platform for this kind of work (radare2, binutils and the usual RE tooling are happiest there). The tooling is pure Python 3 (standard library only, no POSIX-specific calls), so it is expected to run on Windows and macOS as-is - but only Linux has been tested, so some scripts may need porting; reports are welcome. reverse/tools/exe_dis.py additionally needs radare2 on PATH. The shell examples below use bash and 7z.

What's Here

Documentation (16 sections)

• File format specifications with byte-level details
• Game structure analysis
• Executable reverse engineering
• AI, weapons, terrain, and rendering docs

Tooling

• reverse/tools/igi_formats.py - parsers for ILFF, .bit, .hmp, .ctr, .cmd, .lmp and MEF models
• reverse/tools/cmd_deep.py - deep .ctr + .cmd decoder (tile tree with commands)
• reverse/tools/loop.py - LOOP texture decoder (writes PNG, stdlib only)
• reverse/tools/loop_headers.py - LOOP container header dumper (versions, scale levels)
• reverse/tools/mef_deep.py - MEF vertex-layout probe (the 40/32-byte stride split)
• reverse/tools/nav_mtp.py - navigation graph and .mtp manifest decoders
• reverse/tools/misc.py - ILSF-to-WAV, .iff, .fnt and menu .res decoders
• reverse/tools/qvm.py - QVM bytecode disassembler
• reverse/tools/qvmdec.py - readable decompiler for QVM data scripts
• reverse/tools/langdump.py - dumps the localisation resources (mission names, menus)
• reverse/tools/exe_dis.py - IGI.exe static-disassembly harness (radare2 wrapper: disassemble, xrefs, byte search)
• reverse/tools/verify_formats.py - runs every parser over an extracted game tree and prints the pass counts quoted in the docs
• reverse/tools/adversarial_checks.py - runs the strongest rival interpretation against each format claim
• reverse/tools/verify_all.py - the single end-to-end gate: every decoder over the whole tree
• reverse/tools/mdf2iso.py - converts the retail .mdf CD image to a plain ISO so the game tree can be extracted

Decoded data

• reverse/data/lod_table.tsv - 462 models with their LOD distances and cutoff
• reverse/data/config_options.tsv - the shipped config.qvm defaults
• reverse/data/weapon_table.tsv - all 24 weapons with their 50 parameters
• reverse/data/weapon_parameters.tsv - the weapon parameter declaration

The tools take the extracted game tree as an argument; the default is reverse/extracted/pc (gitignored), so pass your own path if the tree lives elsewhere.

python3 reverse/tools/mdf2iso.py "Project IGI.mdf" project_igi.iso
7z x project_igi.iso -oextracted 'pc/*'
python3 reverse/tools/verify_all.py /path/to/extracted/pc
python3 reverse/tools/verify_formats.py /path/to/extracted/pc
python3 reverse/tools/adversarial_checks.py /path/to/extracted/pc
python3 reverse/tools/loop.py /path/to/terrain.tex out/
python3 reverse/tools/qvm.py /path/to/mission.qvm
python3 reverse/tools/langdump.py /path/to/extracted/pc/language/english
python3 reverse/tools/exe_dis.py func 0x4bce60   # QVM interpreter loop

Documentation

Section	Topic	Confidence	Key Unknowns
01-overview	Game info, structure	MEDIUM	Difficulty ratings inferred
02-executable	PE analysis, memory	HIGH	Loader map verified; runtime memory layout inferred
03-scripting	QVM bytecode	HIGH	Reversed numbering, PUSHA intent
04-rendering	Graphics pipeline	HIGH	Model vertex + texture formats verified; pipeline order open
05-ai-system	NPC behavior	MEDIUM	Behaviour architecture inferred; navigation verified
06-weapons	Weapon data	HIGH	Internal damage-path details
07-terrain	Heightmap, tiles	HIGH	All terrain formats verified
08-resources	ILFF format	HIGH	Container fully verified
09-audio	Sound system	HIGH	Container + encodings verified
10-menus	Menu system	MEDIUM	Hierarchy reconstructed
11-task-system	Task types	MEDIUM	Descriptions inferred
12-level-system	Mission structure	MEDIUM	Loading sequence inferred
13-implementation	Implementation notes	-	See STATUS.md
14-lod-system	LOD distances	MEDIUM	LOD 4 semantics (billboard vs low-poly)
15-configuration	Config options	HIGH	Runtime values unverified
16-verified-formats	Byte-level verified specs	HIGH	Evidence for every claim

See INDEX.md for complete reference.

Status

Component	Status
File formats	✅ Container, terrain, model, texture, bytecode, audio, font, navigation, manifest and animation formats verified
Game structure	⚠️ Partially mapped
Executable analysis	✅ Verified (PE header + loader map)
AI system	⚠️ Partially documented
Weapons	✅ Parameters + damage model verified
Terrain	✅ Formats verified
Resources	✅ Container verified
Scripting	✅ Bytecode verified
Audio	✅ Container + encodings verified
Menus	⚠️ Partially documented
Tasks	⚠️ Partially documented
Levels	⚠️ Partially documented
LOD	⚠️ Partially documented
Configuration	⚠️ Partially documented

Quick Start

View Documentation

ls reverse/docs/

Verify the format claims

python3 reverse/tools/verify_formats.py /path/to/extracted/pc

File Formats

Format	Status	Notes
ILFF	✅ Verified	Container; 92/92 archives parse cleanly
LOOP	✅ Verified	Texture archive; 8,232 textures decoded, 0 exceptions
MEF	✅ Vertex layout verified	40-byte vertex (6,178 models) / 32-byte (617), proven by unit-length normals
BIT	✅ Verified	256-slot descriptor table + bit-packed arrays
CTR	✅ Verified	32-byte tile-tree records
CMD	✅ Verified	Byte stream addressed by .ctr offsets; indices + packed vertices proven
LMP	✅ Verified	Size-prefixed 8-bit greyscale images
HMP	✅ Verified	256-slot descriptor table + (size+1)^2 byte grids
DAT	✅ Verified	Navigation routing table [destination][source] = {next_hop, distance}
MTP	✅ Verified	Level manifest; INST = model_index + texture_count + gtt_index[]
ILSF	✅ Verified	Audio container; 759/759 payloads
IFF	✅ Verified	Skeletal animation; SLERP playback chain
FNT	✅ Verified	154/154 glyphs; TRAN map verified
QVM	✅ Verified	Bytecode; 997/997 files disassemble clean

Structure

igi/
└── reverse/
    ├── docs/              # Documentation (16 sections)
    │   ├── INDEX.md       # Complete reference
    │   ├── STATUS.md      # What we know vs don't know
    │   ├── 16-verified-formats/   # Byte-level verified specs + evidence
    │   └── ...
    ├── tools/             # 15 tools; see Tooling above
    │   ├── igi_formats.py
    │   ├── loop.py
    │   ├── qvm.py
    │   ├── mdf2iso.py
    │   ├── verify_formats.py
    │   ├── adversarial_checks.py
    │   └── verify_all.py
    └── extracted/         # (gitignored) game files

Related research

• heaven-hm/project-igi-research-data - please check it out. Runtime analysis (a Cheat Engine table with live pointer chains, a Ghidra database, the natives list), format documentation for IGI1 and IGI2, 010 Editor templates and a tool index, plus a web portal at project-igi-research.vercel.app. The cross-check against it added the player difficulty scaling (0.75 / 1.0 / 1.25) and the second gravity handler to this repo.

Legal

• No game assets included
• Format analysis performed against a legally owned retail copy
• For educational purposes
• Users must own original game
• See LICENSE for details

Credits

Original game: Project IGI (1999) by Innerloop Studios

Independent research project for game preservation.