FISSION GVAR Mini-Guide

Add Persistent Global Variables for Quest States, Flags & More

This guide assumes you have a working mod folder (e.g., mods/mod_mytown.dat/ from the Quick Start Guide). You’ll define custom global variables (GVARs) that are saved with the game and can be used in scripts.

1. What Are GVARs?

Global variables are integer values stored in the save file. They are used for:

  • Quest progress (active, completed, failed)
  • Town reputation
  • Permanent flags (e.g., “already talked to NPC”)
  • Any other persistent data

Vanilla GVARs are defined in data/vault13.gam (indices 0…N‑1).
Mod GVARs are defined in data/gvar_<modname>.txt and receive stable indices in the range 4096 … 8191.

2. Create Your Mod GVAR File

File: mods/mod_mytown/data/gvar_mytown.txt

Format: SYMBOL = value (or SYMBOL := value)

MY_QUEST_STATE = 0
TOWN_REP_MYTOWN = 0
HAS_MET_BOSS = 0
  • Each line defines one GVAR.
  • Symbols can contain letters, digits, underscores (case‑sensitive).
  • Values are integers (default when the game starts).
  • Comments start with # or //.

3. Where to Put the File

mods/mod_mytown.dat/
        └─ data/
            └─ gvar_mytown.txt

No other files are required. The game will read all gvar_*.txt files from the data folder (including inside your mod folder/dat).

4. How It Works (Behind the Scenes)

  • The mod name is extracted from the filename (mytown from gvar_mytown.txt).
  • For each GVAR, the engine computes a stable hash of modname:symbol.
  • The hash is mapped to an index in the mod range (4096 … 8191).
  • If two different mods produce the same index, a popup appears and the second GVAR is skipped.
  • The game generates a report: data/lists/gvars_list.txt showing every GVAR and its final index.

5. Find Your GVAR Index

  1. Run the game once (or reload if already running).
  2. Open data/lists/gvars_list.txt.
  3. Look under “MOD GLOBAL VARIABLES”:
Index Mod Symbol Default
4096 mytown MY_QUEST_STATE 0
57345 mytown TOWN_REP_MYTOWN 0
57346 mytown HAS_MET_BOSS 0

Use these numbers in your scripts.

6. Use GVARs in Scripts

In your .int script (standard Fallout 2 script syntax):

// Set a GVAR
set_global_var(4096, 1);

// Check a GVAR
if (get_global_var(4096) == 2) then
    // Quest completed
endif

7. Important Notes

Stable indices – The same mod name + symbol always produce the same index. You can hardcode the index from the report.

Collisions – If a collision occurs, a warning popup appears and the conflicting GVAR is not loaded. Rename your symbol or mod to resolve.

Default values – When a new game starts, mod GVARs are initialised to the values in your gvar_*.txt.

Save compatibility – Mod GVARs are saved separately; removing a mod later does not corrupt the save (the values are ignored).

Vanilla GVARs – You cannot override vanilla GVAR indices; they remain in the lower range.

8. Quick Troubleshooting

Problem Likely Fix
GVAR not in gvars_list.txt Filename must be gvar_<modname>.txt. Check the data/ folder.
Wrong index used Always use the index from the report – it is not the same as the symbol order.
“Hash collision” popup Another mod already uses that index. Change your symbol or mod name.
GVAR value resets every load Make sure you set the GVAR with set_global_var() and save the game.
Script uses wrong value Verify the index matches the report. Use debug_msg to print the value.

Now you can add persistent data to your mod – perfect for quests, reputation, and any other flags!