FISSION Script Mini-Guide

Add Custom Behavior with .int Scripts

This guide assumes you have a working mod folder (e.g., mods/mod_mytown.dat/ from the Quick Start Guide). You’ll add a script that can be attached to a critter, item, or map.

1. What You Need

Your existing mod folder: mods/mod_mytown.dat/.

You will create one new file (plus the compiled script):

  • scripts/scripts_mytown.lst – lists your script name(s) and optional local variable count
  • Your compiled .int script file (e.g., myscript.int) – created with the ScriptEditor.exe (SSC)

No .msg file is required – scripts use dialog messages separately (see Dialog guide).

2. Create the Script List File

File: mods/mod_mytown/scripts/scripts_mytown.lst

myscript.int local_vars=5
another.int
  • Each line is a script filename (with .int extension).
  • Optionally add local_vars=N to reserve local variables for the script (default 0).
  • The script name (without .int) is used to generate a stable script index (slot).

Important: The list file must be named scripts_<modname>.lst (e.g., scripts_mytown.lst).
The base scripts.lst is for vanilla scripts and is not modified.

3. Place Your Compiled Script

Put your .int file in the same folder as the .lst file:

mods/mod_mytown/
        └─ scripts/
            ├─ scripts_mytown.lst
            └─ myscript.int

How to compile a script:

  • Write your script in Fallout 2 script syntax (.ssl).
  • Compile with ScriptEditor.exe to produce .int file.
  • Name the .int file exactly as listed (e.g., myscript.int).

4. Using Your Script in the Game

The script index is automatically assigned by hashing the script name.
To find the index, run the game once and check data/lists/scripts_list.txt.

Example output:

MOD SCRIPTS:
    207: myscript (local_vars=5)

Use this index (207 in the example) when:

  • Assigning a script to a critter (in .pro file or via override script=207)
  • Assigning to an item or scenery in the mapper

In a prototype .lst override:

myguard.pro script=207

In a map object property: set Script field to 207.

5. Test Your Script

  1. Run the game once – this generates data/lists/scripts_list.txt.
  2. Find your script index in the report.
  3. Attach the script to an object (e.g., a critter in the mapper).
  4. Trigger the script (e.g., talk to the critter, enter a map, etc.).

If the script doesn’t run, check:

  • The .int file is compiled correctly and placed in the right folder.
  • The script index matches the one in the report.
  • Your script has the required procedure (e.g., talk_p_proc for dialogue).

6. Important Notes

  • Stable indices – The same mod name + script name always produce the same index. You can safely hardcode the index from scripts_list.txt.
  • Hash collisions – If two different mods produce the same index, a warning appears and the script is not loaded. Rename your script file to resolve.
  • Local variables – Use local_vars=N to allocate N local variables. They persist across saves.
  • No message file – Script messages are loaded from dialog/ files using message_str() calls. See the Dialog guide for that.

7. Quick Troubleshooting

Problem Likely Fix
Script not in scripts_list.txt Check .lst filename matches scripts_<modname>.lst and is in the correct folder.
Script index shows “Error” The .int file is missing or misnamed. Must match exactly the name in .lst.
“Hash collision” popup Another mod uses the same hash. Rename your script file (change the name).
Script doesn’t execute Verify the script has the correct procedure (e.g., start, talk_p_proc).
Local variables not working Add local_vars=N to the .lst line.

Now you can add custom scripts to your mod – for quests, NPC behaviors, items, and more!