LuaAPI/wesnoth

The wesnoth module contains most of the core Wesnoth API. It is always loaded and available.

Functions

wesnoth.dofile

• wesnoth.dofile(file_path [, ...]) → ...

Loads and executes a file. The rules for locating the files are the same as for WML files, except that they require a .lua extension instead of .cfg. Any extra parameters to dofile are forwarded to the script (which can access them via the special ... variable), and dofile returns all the values returned by the script.

wesnoth.require

• wesnoth.require(module) → module_contents

Returns the contents of the specified module, loading it if necessary. The module can either be a simple name or a file path similar to that used by wesnoth.dofile. In addition, the .lua extension will automatically be appended if necessary. The module script is invoked with no arguments, and wesnoth.require then passes back its first return value, discarding any additional ones. If the module is a directory, then all lua files are loaded, and a table containing the resulting modules is returned, with the keys being the filenames minus the .lua extension.

wesnoth.require returns nil on failure, for example if it could not locate the module. If it did locate the module, but the module did not return anything (or returned nil), then wesnoth.require returns an empty table with a metatable that raises an error on any attempt to access it.

wesnoth.textdomain

• wesnoth.textdomain(domain) → textdomain_constructor

Returns a callable userdata that can be used to construct translatable strings. A typical use is:

local _ = wesnoth.textdomain "example"
wesnoth.alert(_ "This is an example translated string!")

The full syntax for using the result of this function is:

• textdomain_constructor(string [, string_plural, number]) → translatable_string

By passing the optional arguments, you can vary the string based on a number that will be substituted into it. As with all Lua functions, the parentheses are optional when passing a single string argument, as in the above example.

The returned translatable string can be treated in many ways like a regular string. Translatable strings can be compared with other translatable strings or concatenated with each other or with regular strings or integers. The length operator also works, though it should be noted that its value may change if the language is changed. If you need to pass a translatable string to a function that doesn't understand them, it can be converted to a regular string with tostring.

wesnoth.log

• wesnoth.log([logger], message', in_chat)

Logs a message to the console. These messages are normally not visible unless Wesnoth is run from the command-line or (in Windows) with the --wconsole switch. The in_chat argument, however, can be set to true to also echo the message to the in-game chat area.

Possible loggers are info, debug, warning, error, and wml. The wml logger is special and is intended for WML errors; it always goes to chat, so the in_chat argument is ignored and can be omitted. The default logger is info.

wesnoth.as_text

(Version 1.15.10 and later only)

• wesnoth.as_text(value1, value2, ...)

Accept one or more values as arguments and returns them as a string. This is intended for use as an easy way to view the contents of lua tables. Using the returned string for any other purpose is not supported.

wesnoth.simulate_combat

• wesnoth.simulate_combat(attacker, [attacker_weapon_index], defender, [defender_weapon_index]) → attacker stats evaluation, defender stats evaluation, attacker weapon evaluation, defender weapon evaluation

Computes the hitpoint distribution and status chance after a combat between two units. The first unit is the attacker; it does not have to be on the map, though its location should be meaningful. The second unit is the defender; it has to be on the map.

Optional integers can be passed after each unit to select a particular weapon, otherwise the "best" one is selected. When giving the weapon, the parameter is the weapon number (integer, starting at 1) and not the attack definition.

The function returns four tables describing the evaluation of the combat. The first two contain an evaluation of the combatant's stats over the course of the fight, while the second two contains more detailed information on their weapons.

The stats evaluation tables contain the following keys:

• stats.poisoned → probability
• stats.slowed → probability
• stats.untouched → probability

The probability that the unit will be poisoned or slowed, or that it will survive with no damage taken. (A scenario where the unit's hitpoints increase counts as untouched.)

• stats.average_hp → number

The expected value of the unit's hitpoints after the fight.

• stats.hp_chance → array of probabilities

The probability that the unit's hitpoints will be at a specific value after the fight.

The weapon evaluation tables contain the following keys:

num_blows, damage, chance_to_hit, poisons, slows, petrifies, plagues, plague_type, backstabs, rounds, firststrike, drains, drain_constant, drain_percent, attack_num, name

local function display_stats(n, t)
    wesnoth.interface.add_chat_message(string.format(
        "Chance for the %s\n  to be slowed: %f,\n  to be poisoned: %f,\n  to die: %f.\nAverage HP: %f.",
        n, t.slowed, t.poisoned, t.hp_chance[0], t.average_hp))
end
local att_stats, def_stats = wesnoth.simulate_combat(att, att_weapon, def, def_weapon)
display_stats("attacker", att_stats)
display_stats("defender", def_stats)

local att_stats, def_stats, att_weapon, def_weapon = wesnoth.simulate_combat(attacker, att_weapon_number, defender)
wesnoth.interface.add_chat_message(string.format(
    "The attack %s should be countered with %s, which does %d damage, has %d%% chance to hit and forces %d attack rounds due to its berserk ability.",
    att_weapon.name, def_weapon.name or "no weapon", def_weapon.damage, def_weapon.chance_to_hit, def_weapon.rounds))

wesnoth.name_generator

• wesnoth.name_generator("markov", definition, [chain_size, [max_length]]) → generator function
• wesnoth.name_generator("cfg", definition) → generator function
• generator function() → random name

Constructs a name generator for use in generating names using either the Markov chain algorithm used in older versions of Wesnoth or the context-free grammar generator used since 1.13.5. The type parameter indicates which algorithm to use (either markov or cfg). The definition can be a string, just like it would be in a config file, or it can be formatted as a table. Additional parameters may be passed, depending on the type of generator. The function returns a callable userdata, which will return a new name each time it is called (with no parameters).

• Markov chain: A Markov chain generator works by analyzing a list of input names and noticing tendencies in the way the letters are strung together. It can then apply those tendencies to produce new similar names that were not in the original list. Longer lists give better results. The definition is a list of names, formatted either as a comma-separated string or as an array-like table. The Markov generator can take two additional parameters.
  • chain_size: A value greater than 1 for the chain_size causes the analyzer to consider the words in chunks, which is similar to analyzing them syllable by syllable instead of letter by letter. The default chain size is 2, meaning that the analyzer treats words as consisting of 2-character syllables.
  • max_length: Places a cap on the total length of the name. The default value is 12 characters.

local markov_names = wesnoth.name_generator('markov', {'Kaasa', 'Kayya', 'Keyya', 'Kiira', 'Korra'}, 1)
print(markov_names(), markov_names(), markov_names())

• Context-free grammar: A context-free grammar is a way of specifying how strings can be constructed. The definition may be specified as a multi-line string, just as described in the preceding link, or it can be formatted as a table where the keys are non-terminals and the values are what they expand to. The expansion of each non-terminal can be formatted either as a |-separated list as described in the preceding link, or as an array-like table. (Mixing the two forms is permissible too.) The context-free generator has no additional parameters.

local cfg_names = wesnoth.name_generator('cfg', {
  main = {'{prefix}{suffix}', '{prefix}{centre}{suffix}'},
  prefix = 'Kaa|Ka|Ke|Kuu|Ko',
  suffix = 'sa|yya|ra|rra',
  centre = 'err|aash|eez|azz'
})
print(cfg_names(), cfg_names(), cfg_names())

Hooks

wesnoth.persistent_tags

• (game only) wesnoth.persistent_tags.action.read ↔ function(wml content)
• (game only) wesnoth.persistent_tags.action.write ↔ function(add_tag_function)

This is an associative table defining tags that should be persisted in saved games. Each tag is itself a table containing two functions, read and write. The write function is called in on_load and passed a function as a parameter which takes a WML table and adds it the saved game under the specified tag; the read function is called once per matching tag found in the saved game, and is passed a WML table of its contents. Note the asymmetry here: if you're saving an array, the write function is responsible for saving the entire array (and is only called once), while the read function is only responsible for loading one item (and is called several times).

Example:

local inventory = {}

function wesnoth.persistent_tags.inventory.read(cfg)
    inventory[cfg.side] = cfg
end

function wesnoth.persistent_tags.inventory.write(add)
    for i = 1, #wesnoth.sides do
        add(inventory[i])
    end
end

Notice that you don't need to create wesnoth.persistent_tags.inventory as an empty table first; you can simply define the read and write functions.

wesnoth.wml_actions

• (game only) wesnoth.wml_actions.action ↔ function(wml parameters table)

This is a hook table that exposes and defines WML actions. Each function in this table corresponds to a single ActionWML tag, allowing you to invoke tags, define custom tags, and even modify the behavior of built-in tags. The single argument to these functions is a WML table, the content of the tag.

function wesnoth.wml_actions.freeze_unit(cfg)
    local unit_id = cfg.id or wml.error "[freeze_unit] expects an id= attribute."
    local unit = wesnoth.units.get(unit_id)
    if unit then unit.moves = 0 end
    wesnoth.units.modify({ id = unit_id }, { moves = 0 })
end

The new tag can now be used in plain WML code.

[freeze_unit]
    id=Delfador
[/freeze_unit]

You can override functions already assigned to the table. This is useful if you need to extend functionality of core tags. For instance, the following script overrides the [print] tag so that messages are displayed with a bigger font.

function wesnoth.wml_actions.print(cfg)
    local modified_cfg = setmetatable({}, {__index = cfg})
    modified_cfg.size = (cfg.size or 12) + 10
    wesnoth.wml_actions.print(modified_cfg)
end

An action handler should be able to handle being called with either a WML table or a WML vconfig userdata. It is recommended to pass the argument through wml.tovconfig before doing anything with it, both in the action's definition and when calling it directly (in case its definition did not do that). The engine always passes a vconfig when calling a WML action.

wesnoth.wml_conditionals

• (game only) wesnoth.wml_conditionals.action ↔ function(wml parameters table) → boolean result

This is a hook table like wesnoth.wml_actions. You can use it to define new ConditionalWML tags that will be recognized in WML when using [if], [show_if], [while], etc., or more generally when wml.eval_conditional is run.

Use it like this:

function wesnoth.wml_conditionals.foo(cfg)
    local bar = cfg.bar or wml.error("[foo] tag did not have 'bar' attribute")

    return (bar == "baz")
end

If this lua code is executed, it would make the following syntax be valid WML in your add-on:

[if]
   [foo]
      bar = $X
   [/foo]
   [then]
      [message]
         # ...
      [/message]
   [/then]
[/if]

Note that the basic logic tags of ConditionalWML (true, false, and, or, not) do not pass through this table and cannot be overridden.

wesnoth.effects

• (game only) wesnoth.effects.name ↔ function(unit, wml table)
• (game only) wesnoth.effects.name.__descr ↔ description
• (game only) wesnoth.effects.name.__descr ↔ function(unit, wml table) → description

This table contains the implementation of [effect]s. Each value is a callable value that takes a unit and the effect config. It can be a function or a callable table. If it is a callable table, its metatable may have a __descr field which is either a string or a function. Built-in effects are present in this table, and you may register your own custom effects too.

function wesnoth.effects.min_resistance(u, cfg)
	local resistance_new = {}
	local resistance_old = wml.parsed(wml.get_child(cfg, "resistance"))
	for k,v in pairs(resistance_old) do
		if type(k) == "string" and type(v) == "number" and u:resistance_to(k) >= v then
			resistance_new[k] = v
		end
	end
	wesnoth.effects.resistance(u, {
		apply_to = "resistance",
		replace = true,
		T.resistance (resistance_new),
	})
end

The code above adds a new min_resistance effect that will set the resistances to specific values if they are currently below that value. It can then be used like this (for example, in [object]):

[effect]
  apply_to=min_resistance
  [resistance]
    cold=50
  [/resistance]
[/effect]

Note that in order work properly, effects must be registered before any units are created. This means it must be placed into a global or scenario level [lua] tag. In particular, the preload event is too late.

You can also specify description modifiers, which will be used if a custom effect is placed in a [trait] tag. Instead of setting a function as the effect, you set a table with a __call metafunction which does what the function would have done. The table can then have an additional __descr metafunction which updates descriptions as necessary. The built-in effects all use this structure. This metafunction takes the same arguments as the regular effect function, but should not modify the unit. Instead, it returns a string to be appended to the trait's effect description.

Data

Access to most of the game data is available via various tables in the wesnoth module.

wesnoth.colors

(Version 1.15.4 and later only)

• wesnoth.colors.color_name → color info

Access defined color ranges. This can be used to translate the color name available from wesnoth.sides[n].color to RGB values.

Each color info table contains the following keys:

• mid - average shade for recoloring with the team color
• min - minimum shade for recoloring with the team color (this is likely to be black)
• max - maximum shade for recoloring with the team color (this is likely to be almost white)
• minimap - representative color to use on the mini-map
• pango_color - (Version 1.15.13 and later only) a hex string such as #ff0000 suitable for use in formatted text

Each of mid, min, max and minimap have the following keys:

• r - red component of that color
• g - green component of that color
• b - blue component of that color
• a - alpha component of that color (probably fully opaque)

Reference usage in mainline: see data/multiplayer/eras.lua

wesnoth.current

Contains various information about the current game and event state.

• wesnoth.current.side → side number

The number of the currently active side.

• wesnoth.current.turn → turn number

The current turn number.

• wesnoth.current.synced_state → state

Allows you to determine whether the current code runs in a synced context. Returns one of the following strings:

• synced - The current code runs on all mp clients. This is the normal context, in which all gamestate changing actions should take place.
• unsynced - The current code runs only on the local machine, so changing the gamestate here will cause out-of-sync errors. For example, during select events or during the calculation of a game_display hook. Typical things to do here are UI related things, or entering the synced state via [do_command].
• local_choice - The current code was invoked by synchronize_choice and runs only on one local client to calculate the return value for the choice. You cannot enter the synced context with [do_command] now.
• preload - We are currently running a preload event or an even earlier event. This behaves similar to local_choice.

• wesnoth.user_can_invoke_commands → boolean

Indicates whether the player is currently able to take actions in the game.

• wesnoth.current.map → map userdata

The current active game map. See LuaAPI/types/map and LuaAPI/wesnoth/map for information on how this data can be used.

• wesnoth.current.schedule → schedule userdata

The current global time schedule. This is a special object with the following properties:

• #schedule

The Lua length operator will return the number of turns in the schedule.

• schedule[index] ↔ time of day info

Get the information for a particular time of day, or replace it with new info.

• schedule.time_of_day ↔ id

Get the ID of the current active time of day, or switch to a new one. If the time of day occurs more than once in the schedule, the time will be set to the first occurrence.

• schedule.liminal_bonus ↔ bonus

Get the maximum bonus for liminal units in the current schedule. You can also override the default by assigning a different value, or revert to the default by assigning nil.

• wesnoth.current.event_context → table

Contains information on the current active event. Returns a table with the following keys:

• name - The event name. This is the actual event that fired, not the name in the [event] tag, so it never contains commas or variables.
• id - The event's unique ID, if it has one.
• weapon - The first weapon relevant to the event, if any.
• second_weapon - The second weapon relevant to the event, if any.
• damage_inflicted - The damage inflicted in the event, if applicable.
• x1, y1 - The first location relevant to the event, if any.
• x2, y2 - The second location relevant to the event, if any.
• unit_x, unit_y - The location of the first unit relevant t the event, if any. This is the same as x1, y1 in most cases. Currently the only exceptions are enter and exit hex events.

wesnoth.game_config

Contains static global information about the game. Some of this information can also be modified on the fly, but only in the game context, not in the plugin or map generator context.

• wesnoth.game_config.base_income ↔ integer
• wesnoth.game_config.village_income ↔ integer
• wesnoth.game_config.village_support ↔ integer
• wesnoth.game_config.poison_amount ↔ integer
• wesnoth.game_config.rest_heal_amount ↔ integer'
• wesnoth.game_config.recall_cost ↔ integer
• wesnoth.game_config.combat_experience ↔ integer
• wesnoth.game_config.kill_experience ↔ integer

Values of various game settings.

• wesnoth.game_config.global_traits[trait id] →

A table with named fields (trait id strings) holding the wml tables defining the traits. This contains all global traits the engine knows about, but race-specific traits are not included. The known fields and subtags of each element are the ones which were given in the wml definition of the trait.

print(wesnoth.game_config.global_traits.strong.male_name)

• (game only) wesnoth.game_config.do_healing ↔ boolean

Whether healing will occur at the beginning of each side's turn.

• (game_only) wesnoth.game_config.theme ↔ theme id

The currently active in-game theme.

• wesnoth.game_config.debug → boolean

Whether debug mode is currently active. Debug mode is activated by the --debug command-line parameter or the :debug in-game command.

• wesnoth.game_config.debug_lua → boolean

Whether Lua debug is enabled. Lua debug is activated by the --debug-lua command-line parameter. This does not seem to do anything by default.

• wesnoth.game_config.mp_debug → boolean

Whether MP debug is enabled. MP debug is activated in the same way as debug mode, but is only active in multiplayer games.

• wesnoth.game_config.strict_lua → boolean

Whether strict Lua mode is enabled. Strict Lua mode is activated by the --strict-lua command-line parameter and causes all deprecated Lua APIs to be completely removed from the engine.

wesnoth.races

• wesnoth.races.id → race info

Access defined races. Returns a race userdata.

wesnoth.scenario

Contains information about the current scenario

• wesnoth.scenario.turns ↔ turn limit

The current turn limit of the scenario.

• wesnoth.scenario.next ↔ scenario id

The ID of the scenario to transition to when this scenario ends.

• wesnoth.scenario.id → scenario id

The ID of the current scenario.

• wesnoth.scenario.defeat_music ↔ list of music tracks

The music to play if you lose this scenario.

• wesnoth.scenario.victory_music ↔ list of music tracks

The music to play if you win this scenario.

• wesnoth.scenario.show_credits' ↔ boolean

Whether credits should be shown when this scenario ends. Only relevant if wesnoth.scenario.next is nil.

• wesnoth.scenario.end_text ↔ text

The end text to show when the scenario ends. Only relevant if wesnoth.scenario.next is nil.

• wesnoth.scenario.end_text_duration ↔ duration

How long to show the end text for when the scenario ends. Only relevant if wesnoth.scenario.next is nil.

• wesnoth.scenario.difficulty → difficult

The difficulty level this scenario is being played on.

• wesnoth.scenario.type → tag name

The type of this scenario. One of the strings scenario, multiplayer, or test.

• wesnoth.scenario.era → era tag

The [era] tag active in this scenario. Accessing this will throw an error in single-player games.

• wesnoth.scenario.campaign → campaign tag

The [campaign] tag active in this scenario. Accessing this will throw an error in multiplayer or test games, so be sure to check wesnoth.scenario.type first in generic code.

• wesnoth.scenario.resources → list of resource tags

A list of [resource] tags active in this scenario.

• wesnoth.scenario.modifications → list of modification tags

A list of [modification] tags active in this scenario.

• wesnoth.scenario.mp_settings → table

In a multiplayer game, this is a proxy table which gives read only access to all MP-only configuration options which appear as attributes of [multiplayer] tag in a save game file. This allows accessing basically everything that can be set in the create game screen. The following keys exist in the returned table:

• active_mods - A list of all active modification IDs
• hash - A hash of mp data
• mp_campaign - Name of mp campaign
• mp_scenario - ID of this mp scenario
• mp_scenario_name - Name of this mp scenario
• scenario - MP lobby title
• difficulty_define - The campaign difficulty string for an mp campaign
• mp_village_gold
• mp_village_support
• mp_num_turns
• mp_era - The id of the chosen era
• mp_eras - A list of all era ids
• mp_fog
• mp_shroud
• mp_random_start_time
• experience_modifier
• mp_use_map_settings
• mp_countdown - Whether the timer is enabled
• mp_countdown_action_bonus
• mp_countdown_init_time
• mp_countdown_reservoir_time
• mp_countdown_turn_bonus
• observer
• shuffle_sides
• savegame - Whether this is a reloaded game
• side_users - List of how sides are assigned to users (at game start)

wesnoth.terrain_types

(Version 1.15.12 and later only)

• wesnoth.terrain_types[code] → terrain info

Access defined terrain types by their terrain code. Returns a table with the following keys:

• id
• name
• editor_name
• description
• icon
• editor_image
• light
• village
• castle
• keep
• healing

wesnoth.unit_types

• wesnoth.unit_types[id] → unit type info

Access defined unit types by their ID. Returns a unit type userdata.

Submodules

The wesnoth module also contains a number of submodules for working with particular aspects of the game.

wesnoth.game_events

A submodule containing functions for working with event handlers.

wesnoth.map

(Version 1.15.11 and later only)

A submodule containing functions for querying and manipulating the game map.

wesnoth.interface

(Version 1.15.0 and later only)

A submodule containing functions pertaining to the in-game UI.

wesnoth.paths

(Version 1.15.0 and later only)

A submodule containing functions related to pathfinding.

wesnoth.schedule

(Version 1.15.14 and later only)

A submodule containing functions to manipulate the time of day schedule.

wesnoth.sides

(Version 1.15.3 and later only)

A submodule containing functions for manipulating the sides of a scenario.

wesnoth.sync

(Version 1.15.14 and later only)

A submodule containing functions to deal with multiplayer synchronization.

wesnoth.units

(Version 1.15.0 and later only)

A submodule containing functions to manipulate units on the map.