dfhack/docs/guides/modding-guide.rst

.. _modding-guide:

DFHack modding guide
====================

What is a mod/script?
---------------------

A script is a single file that can be run as a command in DFHack, like something that modifies or displays game data on request. A mod is something you install to get persistent behavioural changes in the game and/or add new content. DFHack mods contain and use scripts as well as often having a raw mod component.

DFHack scripts are written in Lua. If you don't already know Lua, there's a great primer at https://www.lua.org/pil/1.html.

Why not just use raw modding?
-----------------------------

For many things it's either completely and only (sensibly) doable in raws or completely and only doable with DFHack. For mods where DFHack is an alternative and not the only option, it's much less hacky, easier to maintain, and easier to extend, and is not prone to side-effects. A great example is adding a syndrome when a reaction is performed requiring an exploding boulder in raws but having dedicated tools for it if you use DFHack. Many things will require a mix of raw modding and DFHack.

A mod-maker's development environment
-------------------------------------

Scripts can be run from a world's ``raw/scripts/`` directory, and (configurably) are run by default from ``hack/scripts/``. Scripts in ``raw/init.d/`` are automatically run on world load. Scripts within the raws are a component for more advanced mods.

A script is run by writing its path and name from a script path folder without the file extension into a DFHack command prompt (in-game or the external one). E.g. ``gui/gm-editor`` for ``hack/scripts/gui/gm-editor.lua``.

You can make all your scripts in ``hack/scripts/``, but this is not recommended as it makes things much harder to maintain each update. It's recommended to make a folder with a name like "own-scripts" and add it to ``dfhack-config/script-paths.txt``. You should also make a folder for external installed scripts from the internet that are not in ``hack/scripts/``. You can prepend your script paths entries with a ``+`` so that they take precedence over other folders.

If your mod is installed into ``raw/scripts/`` be aware that the copies of the scripts in ``data/save/*/raw/`` are checked first and will run instead of any changes you make to an in-development copy outside of a raw folder.

The structure of the game
-------------------------

"The game" is in the global variable `df <lua-df>`. The game's memory can be found in ``df.global``, containing things like the list of all items, whether to reindex pathfinding, et cetera. Also relevant to us in ``df`` are the various types found in the game, e.g. ``df.pronoun_type`` which we will be using.

Your first script
-----------------

So! It's time to write your first script. We are going to make a script that will get the pronoun type of the currently selected unit (there are many contexts where the function that gets the currently selected unit works).

First line, we get the unit. ::

    local unit = dfhack.gui.getSelectedUnit()

If no unit is selected, an error message will be printed (which can be silenced by passing ``true`` to ``getSelectedUnit``) and ``unit`` will be ``nil``.

If ``unit`` is ``nil``, we don't want the script to run anymore. ::

    if not unit then
        return
    end

Now, the field ``sex`` in a unit is an integer, but each integer corresponds to a string value (it, she, or he). We get this value by indexing the bidirectional map ``df.pronoun_type`` with an integer from the unit. Indexing the other way, with one of the strings, will yield its corresponding number. So: ::

    local pronounTypeString = df.pronoun_type[unit.sex]
    print(pronounTypeString)

Simple. Save this as a Lua file in your own scripts directory and run it as shown before when focused on a unit one way or another.

Getting used to gm-editor and DFStructs exploration
---------------------------------------------------

So how could you have known about the field and type we just used? Well, there are two main tools for discovering the various fields in the game's data structures. The first is the ``df-structures`` repository (at https://github.com/DFHack/df-structures) that contains XML files denoting the contents of the game's structures. The second is the script ``gui/gm-editor`` which is an interactive data explorer. You can run the script while objects like units are selected to view the data within them. You can also pass ``scr`` as an argument to the script to view the data for the current screen. Press ? while the script is active to view help.

Familiarising yourself with the many structs of the game will help with ideas immensely, and you can always ask for help in the right places (e.g. DFHack's Discord).

Detecting triggers
------------------

One main method for getting new behaviour into the game is callback functions. There are two main libraries for this, ``repeat-util`` and ``eventful``. ``repeat-util`` is used to run a function once per configurable number of frames (paused or unpaused), ticks (unpaused), in-game days, months, or years. For adding behaviour you will most often want something to run once a tick. ``eventful`` is used to get code to run (with special parameters!) when something happens in the game, like a reaction or job being completed or a projectile moving.

To get something to run once per tick, we would want to call ``repeat-util``'s ``scheduleEvery`` function.

First, we load the module: ::

    local repeatUtil = require("repeat-util")

Both ``repeat-util`` and ``eventful`` require keys for registered callbacks. It's recommended to use something like a mod id. ::

    local modId = "my-test-mod"

Then, we pass the key, amount of time units between function calls, what the time units are, and finally the callback function itself: ::

    repeatUtil.scheduleEvery(modId, 1, "ticks", function()
        -- Do something like iterating over all units
        for _, unit in ipairs(df.global.world.units.all) do
            print(unit.id)
        end
    end)

``eventful`` is slightly more involved. First get the module: ::

    local eventful = require("plugins.eventful")

``eventful`` contains a table for each event which you populate with functions. Each function in the table is then called with the appropriate arguments when the event occurs. So, for example, to print the position of a moving (item) projectile: ::

    eventful.onProjItemCheckMovement[modId] = function(projectile)
        print(projectile.cur_pos.x, projectile.cur_pos.y, projectile.cur_pos.z)
    end

Check the full list of events at https://docs.dfhack.org/en/stable/docs/Lua%20API.html#list-of-events.

Custom raw tokens
-----------------

In this section, we are going to use `custom raw tokens <_custom-raw-tokens>` applied to a reaction to transfer the material of a reagent to a product as a handle improvement (like on artifact buckets), and then we are going to see how you could make boots that make units go faster when worn. Both of these involve custom raw tokens.

First, let's define a custom crossbow with its own custom reaction. The crossbow: ::

    [ITEM_WEAPON:ITEM_WEAPON_CROSSBOW_SIEGE]
        [NAME:crossbow:crossbows]
        [SIZE:600]
        [SKILL:HAMMER]
        [RANGED:CROSSBOW:BOLT]
        [SHOOT_FORCE:4000]
        [SHOOT_MAXVEL:800]
        [TWO_HANDED:0]
        [MINIMUM_SIZE:17500]
        [MATERIAL_SIZE:4]
        [ATTACK:BLUNT:10000:4000:bash:bashes:NO_SUB:1250]
            [ATTACK_PREPARE_AND_RECOVER:3:3]
        [TUTORIAL_MOD_FIRE_RATE_MULTIPLIER:2] custom token (you'll see)

The reaction to make it (you would add the reaction and not the weapon to an entity raw): ::

    [REACTION:MAKE_SIEGE_CROSSBOW]
        [NAME:make siege crossbow]
        [BUILDING:BOWYER:NONE]
        [SKILL:BOWYER]
        [REAGENT:mechanism 1:2:TRAPPARTS:NONE:NONE:NONE]
        [REAGENT:bar:150:BAR:NONE:NONE:NONE]
            [METAL_ITEM_MATERIAL]
        [REAGENT:handle 1:1:BLOCKS:NONE:NONE:NONE] wooden handles
            [ANY_PLANT_MATERIAL]
        [REAGENT:handle 2:1:BLOCKS:NONE:NONE:NONE]
            [ANY_PLANT_MATERIAL]
        [TUTORIAL_MOD_TRANSFER_HANDLE_MATERIAL_TO_PRODUCT_IMPROVEMENT:1] another custom token
        [PRODUCT:100:1:WEAPON:ITEM_WEAPON_CROSSBOW_SIEGE:GET_MATERIAL_FROM_REAGENT:bar:NONE]

So, we are going to use the ``eventful`` module to make it so that (after the script is run) when this crossbow is crafted, it will have two handles, each with the material given by the block reagents.

First, require the modules we are going to use. ::

    local eventful = require("plugins.eventful")
    local customRawTokens = require("custom-raw-tokens")

Now, let's make a callback: ::

    local modId = "siege-crossbow"
    eventful.onReactionComplete[modId] = function(reaction, reactionProduct, unit, inputItems, inputReagents, outputItems)

First, we check to see if it the reaction that just happened is relevant to this callback: ::

    if not customRawTokens.getToken(reaction, "TUTORIAL_MOD_TRANSFER_HANDLE_MATERIAL_TO_PRODUCT_IMPROVEMENT") then
        return
    end

Then, we get the product number listed. Next, for every reagent, if the reagent name starts with "handle" then we get the corresponding item, and... ::

    for i, reagent in ipairs(inputReagents) do
        if reagent.code:sub(1, #"handle") == "handle" then
            -- Found handle reagent
            local item = inputItems[i] -- hopefully found handle item

...We then add a handle improvement to the listed product within our loop. ::

    local new = df.itemimprovement_itemspecificst:new()
    new.mat_type, new.mat_index = item.mat_type, item.mat_index
    -- new.maker = outputItems[0].maker -- not a typical improvement
    new.type = df.itemimprovement_specific_type.HANDLE
    outputItems[productNumber - 1].improvements:insert("#", new)
    -- break -- multiple handles, multiple "the handle is made from"s, so no break

It's all a bit loose and hacky but it works, at least if you don't have multiple stacks filling up one reagent.

Let's also make some code to modify the fire rate of the siege crossbow. ::

    eventful.onProjItemCheckMovement[modId] = function(projectile)
        if projectile.distance_flown > 0 then -- don't repeat this
            return
        end

        local firer = projectile.firer
        if not firer then
            return
        end

        local weapon = df.item.find(projectile.bow_id)
        if not weapon then
            return
        end

        local multiplier = tonumber(customRawTokens.getToken(weapon.subtype, "TUTORIAL_MOD_FIRE_RATE_MULTIPLIER")) or 1
        firer.counters.think_counter = math.floor(firer.counters.think_counter * multiplier)
    end

Now, let's see how we could make some "pegasus boots". First, let's define the item in the raws: ::

[ITEM_SHOES:ITEM_SHOES_BOOTS_PEGASUS]
    [NAME:pegasus boot:pegasus boots]
    [ARMORLEVEL:1]
    [UPSTEP:1]
    [METAL_ARMOR_LEVELS]
    [LAYER:OVER]
    [COVERAGE:100]
    [LAYER_SIZE:25]
    [LAYER_PERMIT:15]
    [MATERIAL_SIZE:2]
    [METAL]
    [LEATHER]
    [HARD]
    [EXAMPLE_MOD_MOVEMENT_TIMER_REDUCTION_PER_TICK:5] custom raw token (you don't have to say this every time)

Then, let's make a ``repeat-util`` callback for once a tick: ::

    repeatUtil.scheduleEvery(modId, 1, "ticks", function()

Let's iterate over every active unit, and for every unit, initialise a variable for how much we are going to take from their movement timer and iterate over all their worn items: ::

    for _, unit in ipairs(df.global.world.units.active) do
        local amount = 0
        for _, entry in ipairs(unit.inventory) do

Now, we will add up the effect of all speed-increasing gear and apply it: ::

        if entry.mode == df.unit_inventory_item.T_mode.Worn then
            amount = amount + tonumber((customRawTokens.getToken(entry.item, "EXAMPLE_MOD_MOVEMENT_TIMER_REDUCTION_PER_TICK")) or 0)
        end
    end
    dfhack.units.addMoveTimer(-amount) -- Subtract amount from movement timer if currently moving

Your first whole mod
--------------------

Now, you may have noticed that you won't be able to run multiple functions on tick/as event callbacks with that ``modId`` idea alone. To solve that we can just define all the functions we want and call them from a single function.

TODO