Fallout FISSION Modding: Quick Start Guide

Get Your First Mod Running in About 10 Minutes

1. What is FISSION?

FISSION is a new engine for Fallout 2 that lets you add new content without editing original game files. You simply add your files inside a mod folder (or .dat archive) inside the mods/ directory.

Key Benefits:

• No original file editing – just add new files
• Automatic, stable ID assignment – no manual number wrangling
• Built‑in testing reports – see exactly what the game loaded
• Works with vanilla saves – your mods are optional

2. Your First ‘Location’ Mod in 4 Steps

Before You Start: Pick a Mod Name

Choose a short, unique name. Example: mytown
This name goes in all your filenames. It will be used to generate unique, stable IDs for your mod’s assets.

Step 1: Create Your Map

1. Put FISSION in your game directory and run it once – this creates the mods/ folder.
2. Open Mapper.exe (original Fallout 2 location).
3. Create a new map or use a simple test map.
4. Save it with a name 8 characters or less (e.g., mytown1.map).
   Critical: Map names longer than 8 characters will fail to load.
5. Create a mod folder inside mods/ called mod_mytown (or mod_mytown.dat if you prefer a single archive).
6. Export the .map file to:
   mods/mod_mytown/data/MAPS/mytown1.map
   (The MAPS folder must be uppercase.)

Note: If your map uses map‑level global variables (e.g., for quest flags), the Mapper will create a .GAM file with the same base name as your .map file. Place it alongside the .map file in data/MAPS/. This is not required for the basic example.

Step 2: Create These 4 Essential Files

File 1: mods/mod_mytown/data/city_mytown.txt

(Defines your new location on the world map)

[Area 0]
area_name = MYTOWN ; UPPERCASE, globally unique name
world_pos = 400,300 ; Where it appears on world map (x,y)
start_state = on ; on, off
size = medium ; small, medium, large (lowercase)
entrance_0 = on,100,200,MYMAP,-1,-1,0

entrance_0 field format (comma‑separated, in order):

1. state – on or off (whether this entrance is available). Example: on
2. x – X coordinate of the entrance button on the town map (in pixels). Example: 100
3. y – Y coordinate of the entrance button on the town map (in pixels). Example: 200
4. lookup_name – Must match a lookup_name in your maps_<modname>.txt file. Example: MYMAP
5. elevation – Which map elevation to use (-1 = any, or 0, 1, 2). Example: -1
6. tile – Starting tile on the map (-1 = random valid start point). Example: -1
7. rotation – Facing direction when entering (0 = north, 2 = east, 4 = south, 6 = west). Example: 0

File 2: mods/mod_mytown/data/maps_mytown.txt

(Defines your actual game map)

[Map 0]
lookup_name = MYMAP ; Matches entrance_0 above
map_name = mytown1 ; Must match .map filename *and* interal .map name
saved = yes ; yes or no (lowercase)
automap = yes ; yes or no (lowercase)
music = fs_grand ; Optional: music track name

Connection: entrance_0 in city_mytown.txt references lookup_name in maps_mytown.txt.

File 3: mods/mod_mytown/text/english/game/map_mytown.msg

(Map elevation names + area name)

# Map elevation names (3 per map, sequential)
{0}{}{Town Gate}
{1}{}{Town Interior}
{2}{}{Town Basement}

# Area name (starts at 1500)
{1500}{}{My Town}

Important: Each map uses three consecutive IDs (elevations 0,1,2).
If you add a second map, its elevations start at {3}{}{...}, {4}{}{...}, {5}{}{...}.

File 4: mods/mod_mytown/text/english/game/worldmap_mytown.msg

(Town map entrance labels – one per entrance)

{0}{}{My Town - Main Gate}

Each entrance_X gets one label, in the same order as defined in city_mytown.txt.

3. Where to Put All Files

Your mod folder (or .dat archive) must mirror the game’s original structure:

Fallout 2/
└─ mods/
    └─ mod_mytown.dat/ <- can be a folder or actual .dat file
        ├─ data/
        │   ├─ city_mytown.txt
        │   ├─ maps_mytown.txt
        │   └─ MAPS/
        │       └─ mytown1.map
        └─ text/
            └─ english/
                └─ game/
                    ├─ map_mytown.msg
                    └─ worldmap_mytown.msg

Notes:

• The mods/ folder is created automatically the first time you run FISSION.
• Your mod folder must start with mod_ (e.g., mod_mytown).
• It can be a normal folder (for easy editing) or a .dat archive (for distribution).

3.5 (Optional) Add Mod Metadata & an Icon

FISSION can display your mod in an in‑game Loaded Mods mod list (accessible from the main menu FISSION icon). To give your mod a name, description, author credit, and an icon, create a simple configuration file.

Step A: Create mods/mod_mytown/data/mod_mytown.cfg

[mod_info]
display_name = The Quick Start Town
name = mytown
description = Adds a new settlement called My Town with custom quests.
author = YourName
dependencies = anothermod, thirdmod

• display_name - User friendly name of your mod. Used only in the Loaded Mods window.
• name – Internal name of your mod. Must be the same as your mod folder name without the mod_ prefix (e.g., mytown). No spaces or special characters. This is used to generate a stable ID for the mod icon.
• description – Short description (shown when the mod is selected in the list).
• author – Your name or alias.
• dependencies – (Optional) Comma‑separated list of other mod internal names that your mod works with or requires. This is informational only – it tells players which other mods they should install. The engine does not enforce this list.

How to actually check for another mod in your scripts:
Every mod that provides an icon also gets a stable art index (the same index used for the icon). This index is written to data/lists/mod_ids_list.txt when the game runs.
To check if another mod (e.g., anothermod) is installed, use its icon’s art index in your script:

#define OBJ_TYPE_INVEN 7

procedure start begin
   if (sfall_func2("art_exists_by_index", OBJ_TYPE_INVEN, 5628)) then
       display_msg("Art found!");
   else
       display_msg("Art not found.");
   end
end

Replace 5628 with the actual ID from mod_ids_list.txt. This allows you to conditionally enable cross‑mod features.

Step B: Add the Icon to the Interface Art List

Create an art list file for the interface category:

File: mods/mod_mytown/art/intrface/intrface_mytown.lst

mytown.frm

Each line is the filename of an interface .frm file (one per line). The name must match the name field from your .cfg file.

Step C: Place the Icon File

Put your custom icon .frm file in the same folder as the .lst file:

mods/mod_mytown/art/intrface/mytown.frm

• Recommended size: 140×116 pixels (same size as perk/trait/karma fallout boy images).
• The icon appears next to your mod in the mod list.
• This icon’s art index is what other mods will use to detect your mod’s presence.

If you omit the icon, the mod list will show a blank space, and other mods cannot reliably detect your mod via art_exists_by_index.

That’s it! Your mod will now appear with proper metadata and an icon in the mod list, making it easier for players to identify and manage – and for other mods to conditionally integrate with yours.

4. Test Your Mod

Test 1: Check the Reports

Run the game once, then look in data/lists/ (inside the game’s root folder – not inside your mod):

• area_list.txt – Your area “MYTOWN” should be listed.
• maps_list.txt – Your map “MYMAP” should be listed.

If both appear, your mod loaded successfully!

Test 2: Play Your Mod

1. Start a new game or load a save.
2. Enter the world map.
3. Travel to coordinates 400,300.
4. You should see a circle labelled “My Town”.
5. Click the circle to enter – you’ll load into mytown1.map.
6. The location name should show “Town Gate” (elevation 0).

If you can walk around your map, your mod is working!

4.5 Example Mod (Download)

If you want to skip manual file creation and see a working example, download the pre‑built template:

Download mod_mytown.dat.zip

Inside the zip you’ll find a folder mod_mytown.dat/ containing the complete file structure from this guide:

• data/city_mytown.txt
• data/maps_mytown.txt
• data/MAPS/mytown1.map
• text/english/game/map_mytown.msg
• text/english/game/worldmap_mytown.msg

How to use it:

1. Extract the zip file into your mods/ folder (so you have mods/mod_mytown.dat/).
2. Run the game – the new location “My Town” will appear on the world map at coordinates 400,300.

You can edit the files inside to learn how each part works or use them as a starting point for your own mod.

5. Common Mistakes & Troubleshooting

Remember: All text values are case‑insensitive, but it’s safest to use lowercase for on/off, yes/no, small/medium/large.

6. What’s Next?

Add a Second Map to the Same Area

Add another entrance in city_mytown.txt:

entrance_1 = on,200,200,MYMAP2,-1,-1,0

Add a new map definition in maps_mytown.txt:

[Map 1]
lookup_name = MYMAP2
map_name = mytown2
saved = yes
automap = yes

Extend map_mytown.msg with the three elevation names for the second map (offsets 3,4,5):

{3}{}{Underground Entrance}
{4}{}{Underground Tunnels}
{5}{}{Hidden Vault}

7. Final Notes

• Mod name stability: If you change your mod’s name after starting a game, saved games will no longer recognise your mod’s content. Choose a name once and keep it. Hashed IDs will also be changed, breaking some of your content.
• lookup_name uniqueness: Avoid using common names like “VAULT13”. Use a prefix like MYTOWN_MAP1 to prevent accidental overrides with other mods.
• No manual ID assignment: FISSION calculates and assigns stable IDs automatically from your mod’s name and the order of items in your files.

8. What’s Next?

Once your basic location mod is working, expand it with these additional features: