Tutorial:Modding tutorial/Gangsir

This is a modding tutorial for Factorio version 0.15. In this tutorial, the author will explain how Factorio works behind the scenes, how to modify Factorio, where to find documentation, and explain concepts.

Overview

Before we start the tutorial, a few things to note:

Code tinted green like this should be included into the mod this tutorial is going to create; If the reader follows along with it. The best way to do this is to copy and paste, to ensure faithful reproduction.
Whenever code is added to the mod, a Lua comment with the file name will be at the beginning of the green box. Place the code in the box into that file. Eg:
--control.lua

Code tinted purple like this should not be included into the mod, it's just for educational/example purposes, and to boost understanding.

This tutorial was created for version 0.15, so any viewers in the future should take note that some minor changes may have been made, and should look at the changelogs up to the current version.

Terminology used in modding

Before we start the tutorial, a few terms and definitions should be laid out, to ensure the reader understands.

Mod

A script or series of scripts that allow modifications to the game through the API.

Entity

An entity in Factorio is anything in the game that is not a concept, event, or tile. Examples of entities include the character, an assembling machine, a biter, etc. This can be 'machines' or free-moving objects like the character.

Character

The actual entity that the player manipulates the world through.

Player

All the data that defines a player, such as username, position in the player table, etc. All players have characters, but no characters have players within them.

Prototype

A prototype is an internal handling of entities, a bit like a template. It defines stats, what the entity actually is, etc. A prototype is used to create an entity.

Surface

A surface is a bit like a dimention. It is composed of terrain, such as grass, sand, and water, and all the entities on the surface. By defualt, there is only one surface in Factorio, referred to internally as "nauvis", or game.surfaces[1], but mods may create additional surfaces through the API.

Event

An event is a recurring...event, that is triggered internally by the game. There are several events that mods may connect functions to, such as on_entity_died, etc. More on this in the control scripting section.

Recipe

This is a data structure a bit like a prototype that defines a recipe for the internal crafting engine. A technology follows a similar setup.

More terminology may be declared and defined later in this tutorial.

Before beginning to mod

Before we can start modding Factorio, we must understand what Factorio is. You may be tempted to answer in lieu of the about page, but that is what a player would say. Since we are trying to become a modder, we need a more detailed explanation. Factorio is a game that is coded in the language C++, with an API provided by Wube (the developers of Factorio) to mod Factorio in the programming language Lua. This API allows adding scripts to the Factorio init process, to modify it without the source code of the base game being exposed, or modifying memory. This may be different than other games that offer modding, but this is a more professional and proper way of supporting modding.

To aid in the use of this API, the devs have kindly provided fairly comprehensive documentation at their API site. Get used to using this site, as it will become a frequent visit you will make while you develop mods. It contains information on factorio's classes, information on concepts, and information on events that you can hook into. You will need to check this site often, so the author reccomends bookmarking it. In addition to this site, there is also many resources to be found created by the community, such as this tutorial.

Setup

The best way to develop a mod is to develop it in a place where it can be easily tested. When the tutorial gets to making the mod, this will be explained further. Additionally, using an editor that allows ease of typing and Lua language support is reccomended. Emacs, Vim, Sublime Text, and Notepad++ are all viable candidates. This author prefers Emacs, but it does not make a difference in the mod itself.

How Factorio loads mods

The data stage

When Factorio first initializes, it initializes part of itself, then starts looking for mods. Mods are loaded by dependency, then by alphabetical order. This is very important to understand, as it can cause you problems if you neglect it and try to add inter-mod support to your mod.

Factorio has two kinds of dependencies. There are required dependencies, and optional dependencies. Required dependencies are loaded first, always. The game will fail to initialize if one of these is not present. Optional dependencies are loaded first if present, but do not have to be present. This is useful for enabling bonus features if mods are used together. Required dependencies should be used for mod libraries, and similar infrastructure.

This is the most restricted part of the Factorio init, there's not much you can do here other than declare prototypes for technologies and entities. Stuff like manipulating files, affecting the world, etc, are blocked/unavailable. In fact, any functions or changes made will be discarded, as the lua session is terminated. You also cannot mess with the data table, it will error or be ignored. When using data:extend({}), it expects a specific format, more on this later.

When running through this stage, the game looks through all mods for a file called data.lua. This file is executed, then each mod's data-updates.lua, and finally each mod's data-final-fixes.lua. All other files to be loaded will need to be required. All the files run here should contain nothing but prototype definitions. More on requiring files later.

Migrations

Migrations are scripts that are used to "fix" a save after a mod updates. Whenever prototypes change within a mod, migrations must be setup to correct all the old instances of the prototyped entity in the world. This must be done for all updated entities, or the old entities will be removed from the world, which is an unprofessional fallback that makes users dislike you. While this tutorial will not discuss migrations, there are many resources on migrations to be found around the community, and the API site.

To avoid having to write migrations, avoid making changes to prototypes that effect prototype name, type, recipe, or technology. These things cannot be dynamically changed, and resetting techs or recipes may be necessary. Try to avoid these changes after shipping the mod out to the public. Try to come up with a finalized version of the prototype that you can base the mod around. Of course, migrations are unnecessary if the user simply starts a new world with each mod update, but do not expect the community to do this.

Control

Within most mods is a file called control.lua. This file contains scripting that makes the mod actually do things, beyond simply adding entities to the game. During this stage, each mod's control.lua is run, in it's own lua instance (this means no inter-communication without special setup) which it will own for the rest of the play session. Because this is run every time a save file is created or loaded you don't need to restart the game to see changes made to the control.lua file. Simply restarting or reloading a save will re-run this stage. There are a few other caveats to this stage, reading the data life cycle page on the API site provides the best overview.

Runtime

At this stage, the mod is setup, and the save is running. Access to all tables provided by the game can be done inside of event handlers. (More on those below.)

The major components to any Factorio mod

Whithin the average mod, there are several components that make the mod function. Every mod needs some form of "data" file, this may be called data.lua, data-updates.lua, or data-final-fixes.lua. In addition to that, mods that define new entities will need to declare these entities somewhere, the standard is in a file required by data.lua.

Some mods that need to do more than just add entities/tweak stats will also need a control.lua file, to add scripting. The mod that we'll make in this tutorial will include both prototypes, and control scripting, to give you a feel for both.

Over time, the community has settled on a specific arrangement for how a mod's directory structure should look. Following this to a T is not necessary, but can simplify things. More on directory structure below.

The tutorial mod

And now for the moment you've been waiting for. Let's start making your first mod. You'll need:

• A recent install of Factorio
• A text editor, such as Emacs, Vim, Sublime text, etc
• An understanding of the tutorial above

Once you have all of these things, we can begin.

For this mod, we're going to make a set of armor that leaves behind damaging fire behind you as you walk. It will be fully resistant to fire, but weaker towards physical damage than heavy armor, making it an armor for hit and run attacks.

Creation of the directory structure

Like this tutorial mentioned earlier, there is a somewhat community standard around for how a mod is laid out. This, combined with how the game expects mods to be laid out, limits us slightly. To start out, create a folder in your user data directory/mods folder. This folder must have a specific name, FireArmor_0.1.0. When you're finished, the mod directory should look like this:

• (user data directory, sometimes called .factorio)
  • mods
    • FireArmor_0.1.0

Then, inside FireArmor_0.1.0, create two files, info.json and data.lua. The directory should now look like:

• (user data directory, sometimes called .factorio)
  • mods
    • FireArmor_0.1.0
      • data.lua
      • info.json

The info.json file

Then, inside info.json, copy and paste the following into it:

{
    "name": "FireArmor",
    "version": "0.1.0",
    "title": "Fire Armor",
    "author": "You",
    "contact": "",
    "homepage": "",
    "factorio_version": "0.15",
    "dependencies": ["base >= 0.15"],
    "description": "This mod adds in fire armor that leaves behind damaging fire as you walk around."
}

To explain each field:

name

This is the internal name of your mod, it is used to identify your mod in code.

version

This is the version of your mod. This can be anything you want, provided it's a number. Most people start at some form of 0.1.0.

title

The pretty title of your mod, this will be displayed on the mods screen and when you submit it to the mod portal.

author

Your name! You can change this in the example above.

contact

Put contact info here, so someone can find you in the event of a problem.

homepage

The homepage of your mod, put a website here if you have one for the mod. Not required.

factorio_version

This tells the game what version the mod is for, this must match the version you're developing the mod for, 0.15 in this case.

dependencies

Any dependencies of your mod. Some form of "base" should always be here, so base gets loaded first.

description

A short description of your mod.

And that's all for info.json! Next, in the data.lua file:

--data.lua

require("prototypes.item")

It's a pretty simple file, all we're doing here is just telling the game to execute the file called item.lua in prototypes, which we're about to create. Create a folder in FireArmor_0.1.0 called prototypes, then inside prototypes, create a file called item.lua. The directory structure should now look like:

• (user data directory, sometimes called .factorio)
  • mods
    • FireArmor_0.1.0
      • prototypes
        • item.lua
      • data.lua
      • info.json

Notice how our earlier require used the folder and file name in it?

Prototype creation

Now, there are two ways to create prototypes in Factorio. There's the short way, and the long way. The long way requires copying an existing definition from one of the default lua files provided with an install of Factorio, and the short way just uses a lua function to copy and modify a definition. For the sake of this tutorial, we'll do it the short way.

In item.lua, copy and paste the following:

--item.lua

require("data")

local fireArmor = table.deepcopy(data.raw["armor"]["heavy-armor"])

fireArmor.name = "fire-armor"
fireArmor.icons= {
   {
      icon=item.icon,
      tint={r=1,g=0,b=0,a=0.3}
   },
}
fireArmor.resistances = {
   {
      type = "physical",
      decrease = 6,
      percent = 10
   },
   {
      type = "explosion",
      decrease = 10,
      percent = 30
   },
   {
      type = "acid",
      decrease = 5,
      percent = 30
   },
   {
      type = "fire",
      decrease = 0,
      percent = 100
   }
}
data:extend(fireArmor)

What we've just done here is we've copied the definition of heavy armor, then changed it's properties, and injected it into the Factorio init with data:extend. The second line of code is probably the most interesting. table.deepcopy copies a table fully into another table. We do this from data.raw. The data part is a table, which will be used by game to setup the Factorio universe. In fact, it contains the function extend(self,prototypes) and a table called raw. The former is customary way to add new stuff to the latter. It is actually data.raw that holds the prototypes for the game. (You can view the implementation in the file /factorio/data/core/lualib/dataloader.lua)