RE: Chaos Overlords (1996)

This repository documents the reverse engineering progress of the classic turn-based strategy game Chaos Overlords.

All information here is based on the last available release for Windows 95:

$ sha256sum "Chaos Overlords.exe"
0791e6209d573a79882675d1236737f5c9b369ea4af541a7dbd03cbadf4493d5

About this project

Disclaimer

I began deconstructing and decompiling Chaos Overlords as a low-priority side project in 2020, initially only to practice reverse engineering with a fun target. It then lay dormant for a few years due to a lack of interest and time. Now I have even less time to dedicate to it. Progress will continue at a glacial pace. Do not expect to see a working re-implementation anytime soon; it may never even be finished. Nevertheless it would be a waste to let the information gathered thus far rot on my SSD, so here it is.

Goals

The hypothetical long-term goal is a modern, open-source re-implementation — a perfectly deterministic copy of the original. That is, if one were to extract the RNG seed from the original and start the clone with it, everything, including the AI, should behave exactly the same.

Additionally, the clone should feature optional improvements:

• Display scaling (2x, 3x, 4x, etc. to keep the pixel art pristine).
• Widescreen support (more game state displayed on one screen).
• Improved keyboard controls

Compatibility may be broken for networking. The original networking code is not robust or secure. I strongly recommend against exposing the original game to the internet.

Data file formats

• Most strings are ASCII, not null-terminated.
• Some strings are stored Pascal-style, i.e. not terminated but prefixed with their length (uint8_t).
• All integers are stored in Little Endian byte order.

SITES

sizeof(Site): 62
len(sites): 22
Total: 1364 bytes

Offset	Length	Type	Description
0	20	string	Name
14	2	int16	ID
16	2	int16	Resistance
18	2	int16	Support
1A	2	int16	Frequency
1C	2	int16	Tolerance
1E	2	int16	Cash
20	2	int16	Combat
22	2	int16	Defense
24	2	int16	Stealth
26	2	int16	Detect
28	2	int16	Chaos
2A	2	int16	Control
2C	2	int16	Heal
2E	2	int16	Influence
30	2	int16	Research
32	2	int16	Strength
34	2	int16	Blade
36	2	int16	Range
38	2	int16	Fighting
3A	2	int16	Martial arts
3C	2	int16	Special flags*

Special flags

Value	Meaning
0	Nothing
1	SCIENCE CENTER (Tech 8)
2	RESEARCH LAB (Tech 10)
3	FACTORY

GANGS

sizeof(Gang): 156 bytes
len(gangs): 90
Total: 14040 bytes

Offset	Length	Type	Description
0	30	string	Name
1E	2	int16	ID
20	90	string	Description
7A	2	int16	Force
7C	2	int16	Upkeep
7E	2	int16	Combat
80	2	int16	Defense
82	2	int16	Tech Level
84	2	int16	Stealth
86	2	int16	Detect
88	2	int16	Chaos
8A	2	int16	Control
8C	2	int16	Heal
8E	2	int16	Influence
90	2	int16	Research
92	2	int16	Strength
94	2	int16	Blade
96	2	int16	Range
98	2	int16	Fighting
9A	2	int16	Martial Arts

ITEMS

sizeof(Item): 166 bytes
len(items): 160
Total: 10624 bytes

Offset	Length	Type	Description
0	30	string	Name
1E	2	int16	ID
20	90	string	Description
7A	2	int16	Type*
7C	2	int16	Research difficulty
7E	2	int16	Cost
80	2	int16	Tech level
82	2	int16	Combat
84	2	int16	Defense
86	2	int16	Stealth
88	2	int16	Detect
8A	2	int16	Chaos
8C	2	int16	Control
8E	2	int16	Heal
90	2	int16	Influence
92	2	int16	Research
94	2	int16	Strength
96	2	int16	Blade
98	2	int16	Range
9A	2	int16	Fighting
9C	2	int16	Martial arts
9E	2	int16	Weapon attack animation
A0	2	int16	Weapon hit animation
A2	2	int16	Weapon sound
A4	2	int16	Unknown

SND00xxx

Sounds are stored as regular WAV files.

RIFF (little-endian) data, WAVE audio, Microsoft PCM, 8 bit, mono 22050 Hz.

PX16/PXxxxxx

These are uncompressed BMP images with parts of the header zeroed out. The headers are hardcoded in the executable.

It is sufficient to fix up the following bytes to make the images readable:

Offset	Length	Type	Description
12	4	int32	Width
16	4	int32	Height
1A	2	int16	Color planes (1)
1C	2	int16	Bits per pixel (16)

Save game format

There are two slightly different save game formats, determined by the magic marker at the start.

• If the save game starts with 0x57303453, the size is 45305 bytes.
• If the save game starts with 0x5730344E, the size is 45329 bytes.

Offset	Length	Type	Description
0	4	int32	Magic (0x57303453 or 0x5730344E)
4	15552	GangInstance[6][81]	Gang instances
3CC4	2304	SectorData36[64]	Sectors
45C4	24	int32[6]	Player cursor positions (sector ID)
45DC	6	int8[6]	Player portraits
45E2	24	int32[6]	Player status (Human, AI, ...)
45FA	4	int32	Turn number
45FE	4	int32	Objective
4602	4	int32	Max turns
4606	24	int32[6]	Cash [player_id]
461E	18	int8[6][3]	hire_pool[player_id][] = gang_id
4630	18	int8[6][3]	hire_pool_target[player_id][] = sector_id
4642	384	int8[64][6]	research_progress[item_id][player_id]
47C2	6	int8[6]	player_alive[player_id] = bool
47C8	7776	GangData16[6][81]	...[player_id][gang_nr]
6628	6	int8[6]	UNKNOWN [player_id]
662E	24	int32[6]	UNKNOWN [player_id]
6646	1944	int32[6][81]	UNKNOWN [player_id][gang_nr]
6DDE	6	int8[6]	UNKNOWN [player_id]
6DE4	24	int32[6]	Initial HQ position + 64
6DFC	24	int32[6]	UNKNOWN [player_id]
6E14	24	int32[6]	UNKNOWN [player_id]
6E2C	24	int32[6]	Score
6E44	256	int16[64][2]	Sector crackdown history
6F44	1920	Notification[6][32]	Notification queues
76C4	9600	SectorData150[64]	TBD
9C44	4860	GangData10[6][81]	TBD
AF40	2	int16	Current player id
AF42	72	char[6][12]	Player names (Pascal style strings)
AF8A	24	int32[6]	Total sectors overtaken
AFA2	24	int32[6]	Total damage inflicted
AFBA	24	int32[6]	Total times hidden
AFD2	24	int32[6]	Total cash spent
AFEA	24	int32[6]	Total casualties
B002	24	int32[6]	Total cash earned
B01A	144	int32[6][6]	UNKNOWN
B0AA	24	int32[6]	UNKNOWN
B0C2	6	int8[6]	UNKNOWN
B0C8	24	int32[6]	Luck boost
B0E0	6	int8[6]	Is player human?
B0E6	1	int8	Preference: Difficulty
B0E7	1	int8	Preference: Time Limit
B0E8	1	int8	Preference: Objective
B0E9	6	int8[6]	Cheat Hubble Yes/No
B0EF	6	int8[6]	Cheat Milk Yes/No
B0F5	24	int32[6]	UNKNOWN, only present if magic == 0x5730344E
B10D	4	int32	Magic (0x57303453 or 0x5730344E)

References

• Wikipedia: Chaos Overlords
• GOG: Chaos Overlords