FISSION Combat AI Mini‑Guide

Define Custom AI Packets (Dispositions, Combat Behaviour, Taunts)

This guide assumes you have a working mod folder (e.g., mods/mod_mytown.dat/ from the Quick Start Guide). You’ll add new AI packets that control how critters behave in combat – their aggression, weapon preferences, movement, and taunts.

1. What You Need

Your existing mod folder: mods/mod_mytown.dat/. (a folder for development, compress into actual .dat for release)

You will create two new files:

• data/ai_mytown.txt – defines the AI packet(s) and their numeric parameters
• text/english/game/combatai_mytown.msg – provides the taunt messages (optional)

No .lst file is required – the engine automatically picks up any ai_*.txt file.

2. Create the AI Packet Definition File

File: mods/mod_mytown/data/ai_mytown.txt

Each section (inside [ ]) defines one AI packet. The section name is the packet’s display name.

[MyGuard custom]
packet_num = -1
max_dist = 12
min_to_hit = 20
min_hp = 12
aggression = 80
hurt_too_much = blind,crippled_arms
secondary_freq = 4
called_freq = 5
font = 1
color = 992
outline_color = 0
chance = 50
run_start = 100
run_end = 109
move_start = 110
move_end = 119
attack_start = 120
attack_end = 129
miss_start = 130
miss_end = 139
hit_head_start = 140
hit_head_end = 149
hit_left_arm_start = 150
hit_left_arm_end = 159
hit_right_arm_start = 160
hit_right_arm_end = 169
hit_torso_start = 170
hit_torso_end = 179
hit_right_leg_start = 180
hit_right_leg_end = 189
hit_left_leg_start = 190
hit_left_leg_end = 199
hit_eyes_start = 200
hit_eyes_end = 209
hit_groin_start = 210
hit_groin_end = 219
area_attack_mode = be_sure
run_away_mode = bleeding
best_weapon = melee
distance = charge
attack_who = strongest
chem_use = stims_when_hurt_little
chem_primary_desire = 10, 11, 12
disposition = custom
body_type = human
general_type = guard

Key fields explained:

The run_start … hit_groin_end fields define the message ID ranges for taunts (see next section).

3. Create the Taunt Message File (Optional)

File: mods/mod_mytown/text/english/game/combatai_mytown.msg

Each AI packet gets its own block of messages. The IDs are relative to the ranges in ai_mytown.txt.

{100}{}{"Get out of my sight!"}
{101}{}{"You'll pay for that!"}
...
{140}{}{"Nice try shithead!"}
...

• The numbers (100, 101, etc.) are offsets. The game adds a base ID (generated from your mod name + combatai) to these offsets.
• You do not need to calculate the final IDs – the engine does it for you.

If you omit the .msg file, the AI will still work, but no taunts will be displayed.

4. Disposition Variants (Important!)

The system can automatically generate disposition variants of your custom packet. Name your packet as:

[MyGuard custom]
...
disposition = custom

Then create additional sections with the same base name followed by the disposition keyword:

[MyGuard coward]
disposition = coward
...
[MyGuard defensive]
disposition = defensive
...
[MyGuard aggressive]
disposition = aggressive
...
[MyGuard berserk]
disposition = berserk
...

The engine will map these variants to the base custom packet ([MyGuard custom] in this case). When you change a critter’s disposition in‑game (via aiSetDisposition), the AI switches to the appropriate variant without needing to change the proto.

If you don’t create variants, the system falls back to simple sequential numbering (original Fallout 2 behaviour).

5. How to Use Your AI Packet

In a Critter Prototype (.pro file) via .lst Override

Add an ai= override in your critters_mytown.lst file:

myguard.pro ai=4096

Where 4096 is the packet number from data/lists/ai_list.txt. This will set the AI packet for all instances of that critter.

In a Script

set_critter_ai_packet(critter_obj, 4096);

Changing Disposition (in Script)

// disposition: -1=none, 0=custom, 1=coward, 2=defensive, 3=aggressive, 4=berserk

ai_set_disposition(critter_obj, 3);

This will switch the critter to the aggressive variant of its base packet (if you created one with the same base name).

6. Find Your Packet Number

Run the game once (or reload if already running).

Open data/lists/ai_list.txt.

Look for your packet under “AI Packets Report”. The PacketNum column shows the final index.

Example:

Index  PacketNum  Name
0      4096       MyGuard custom
1      4097       MyGuard coward
...

Use that PacketNum in your prototypes or scripts.

7. Important Notes

Stable indices – The same mod name + section name always produce the same packet number. You can safely hardcode the number from the report.

Collisions – If two mods produce the same packet number, a warning appears and the second packet is skipped. Rename your section or mod to resolve.

Message IDs – The base ID for taunts is generated from your mod name + combatai. You never need to assign numbers manually.

Disposition mapping – The system looks for sections where the name ends with a disposition keyword (space + keyword). The keyword must match exactly the values in gDispositionKeys (lowercase).

Vanilla packets – You can also override existing vanilla packets by using the same packet_num (not recommended – better to create new ones).

8. Quick Troubleshooting