Difference between revisions of "LuaWML"

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(Encoding WML objects into Lua tables: Various improvements, cleanup, linking preferentially to LuaAPI where possible)
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== The '''[lua]''' tag ==
 
== The '''[lua]''' tag ==
  
{{DevFeature}}
+
This tag is a part of [[ActionWML]], thus can be used inside [event] and at other places where [[ActionWML]] can be used. It makes it possible to write actions with the [http://www.lua.org Lua 5.3] language.
  
This tag is a subtag of the '''[event]'''. It makes it possible to write actions with the [http://www.lua.org Lua 5.1] language.
+
It is also possible to put this tag inside a [scenario] [[ScenarioWML]], those tags will be executed immediately when the lua engine loads which is even before the scenario preload event is fired.
 +
 
 +
[lua] is now also allowed in [era], [modification] and [resource], those [lua] tags are then copied into the [scenario]/[multiplayer] when it is played just like [event]s inside [era] or [modification]
  
 
The tag supports only the '''code''' key, which is a string containing the Lua scripts. Since Lua makes usage of the quotes and the { and } symbols, it is certainly wise to enclose the script between stronger quotes, as they prevent the preprocessor from performing macro expansion and tokenization.
 
The tag supports only the '''code''' key, which is a string containing the Lua scripts. Since Lua makes usage of the quotes and the { and } symbols, it is certainly wise to enclose the script between stronger quotes, as they prevent the preprocessor from performing macro expansion and tokenization.
  
 +
<syntaxhighlight lang='wml'>
 
  [lua]
 
  [lua]
 
     code = << wesnoth.message "Hello World!" >>
 
     code = << wesnoth.message "Hello World!" >>
 
  [/lua]
 
  [/lua]
 +
</syntaxhighlight>
 +
 +
The Lua kernel can also be accessed from the [[CommandMode|command mode]]:
 +
 +
:lua local u = wesnoth.get_units({ id = "Konrad" })[1]; u.moves = 5
 +
 +
The '''[args]''' sub-tag can be used to pass a WML object to the script via its variadic local variable "'''...'''".
 +
 +
<syntaxhighlight lang='wml'>
 +
[lua]
 +
    code = << local t = ...; wesnoth.message(tostring(t.text)) >>
 +
    [args]
 +
        text = _ "Hello world!"
 +
    [/args]
 +
[/lua]
 +
</syntaxhighlight>
  
The '''[args]''' tag can be used to pass a WML object to the script via its variadic local variable.
+
== Global environment ==
 +
 
 +
All the Lua scripts of a scenario share the same global environment (aka Lua state). Unlike other parts of the configurable gamestate the Lua state is not stored in savefiles, thus [lua] tags in [scenario] are executed not only before the scenario starts but also each time the game is loaded. Funtions defined in [lua] tags in [scenario] can be used in all [lua] tags in [event]s.
 +
 
 +
<syntaxhighlight lang='wml'>
 +
[scenario]
 +
    [lua]
 +
        code = <<
 +
            function narrator(t)
 +
                -- Behave like the [message] tag.
 +
                wesnoth.fire("message",
 +
                  { speaker = "narrator", message = t.sentence })
 +
            end
 +
        >>
 +
    [/lua]
 +
    [event]
 +
        name = turn 1
 +
        [lua]
 +
            code = << narrator(...) >>
 +
            [args]
 +
                sentence = _ "Hello world!"
 +
            [/args]
 +
        [/lua]
 +
        [lua]
 +
            code = << narrator(...) >>
 +
            [args]
 +
                sentence = _ "How are you today?"
 +
            [/args]
 +
        [/lua]
 +
    [/event]
 +
    ...
 +
[/scenario]
 +
 +
</syntaxhighlight>
 +
 
 +
In the example above, the redundant structure could be hidden behind macros. But it may be better to simply define a new WML tag.
 +
 
 +
<syntaxhighlight lang='wml'>
 +
[scenario]
 +
    [lua]
 +
        code = <<
 +
            -- The function is now placed in the wesnoth.wml_actions table
 +
            -- The tag is [narrator], same as the function name
 +
            function wesnoth.wml_actions.narrator(t)
 +
                -- Behave like the [message] tag.
 +
                wesnoth.fire("message",
 +
                  { speaker = "narrator", message = t.sentence })
 +
            end
 +
        >>
 +
    [/lua]
 +
 +
    [event]
 +
        name = turn 1
 +
        [narrator]
 +
            sentence = _ "Hello world!"
 +
        [/narrator]
 +
        [narrator]
 +
            sentence = _ "How are you today?"
 +
        [/narrator]
 +
    [/event]
 +
[/scenario]
 +
</syntaxhighlight>
 +
 
 +
The global environment is not preserved over save/load cycles. Therefore, storing values in the global environment is generally a bad idea. The only time assigning global variables (including function definitions) makes sense is in a [lua] block directly in [scenario] or during a [[EventWML#Predefined 'name' Key Values|preload]] event, as this event is always run. Therefore, helper functions defined at that time will be available to all the later scripts.
 +
 
 +
The global environment initially contains the following modules: [http://www.lua.org/manual/5.3/manual.html#6.1 basic] (no name), [http://www.lua.org/manual/5.3/manual.html#6.4 string], [http://www.lua.org/manual/5.3/manual.html#6.6 table], and [http://www.lua.org/manual/5.3/manual.html#6.7 math]. A '''wesnoth''' module is also available, it provides access to the [[#Interface to the C++ engine|C++ engine]]. Additionally, the functions clock, date, time and difftime from the [http://www.lua.org/manual/5.3/manual.html#6.9 os] library (keep in mind that they aren't multiplayer- and replay-safe), as well as traceback from the [http://www.lua.org/manual/5.3/manual.html#6.10 debug] library are also available.
 +
 
 +
At the start of a script, the variadic local variable '''...''' (three dots) is a proxy table representing [[#Encoding WML objects into Lua tables|WML data]]. This table is the content of the '''[args]''' sub-tag of the '''[lua]''' tag, if any.
  
 
== Examples ==
 
== Examples ==
Line 19: Line 105:
 
The following WML event is taken from Wesnoth' tutorial. It will serve as an example to present how Lua scripts are embedded into Wesnoth. The event is fired whenever a unit from side 1 (that is, the hero controlled by the user) moves to a tile that is not the one set in the WML variable ''target_hex''.
 
The following WML event is taken from Wesnoth' tutorial. It will serve as an example to present how Lua scripts are embedded into Wesnoth. The event is fired whenever a unit from side 1 (that is, the hero controlled by the user) moves to a tile that is not the one set in the WML variable ''target_hex''.
  
 +
<syntaxhighlight lang='wml'>
 
  # General catch for them moving to the wrong place.
 
  # General catch for them moving to the wrong place.
 
  [event]
 
  [event]
Line 59: Line 146:
 
     [/if]
 
     [/if]
 
  [/event]
 
  [/event]
 +
</syntaxhighlight>
  
 
A Lua script that performs the same action is presented below.
 
A Lua script that performs the same action is presented below.
  
 +
<syntaxhighlight lang='wml'>
 
  [event]
 
  [event]
 
     name=moveto
 
     name=moveto
Line 72: Line 161:
 
     [lua]
 
     [lua]
 
         code = <<
 
         code = <<
             local args = ...
+
 
             if target_hex.is_set and
+
             local event_data = wesnoth.current.event_context
                 (args.x1 ~= target_hex.x or args.y1 ~= target_hex.y)
+
             if wml.variables["target_hex.is_set"] and
 +
                 (event_data.x1 ~= wml.variables["target_hex.x"] or event_data.y1 ~= wml.variables["target_hex.y"])
 
             then
 
             then
 
                 W.redraw()
 
                 W.redraw()
Line 82: Line 172:
 
     [/lua]
 
     [/lua]
 
  [/event]
 
  [/event]
 +
</syntaxhighlight>
  
 
Here is a more detailed explanation of the Lua code. Its first line
 
Here is a more detailed explanation of the Lua code. Its first line
  
local args = ...
+
<syntaxhighlight lang='lua'>
 +
local event_data = wesnoth.current.event_context
 +
</syntaxhighlight>
  
loads the parameter of the script into the ''args'' local variable. Since it is a ''moveto'' event, the ''args'' table contains the destination of the unit in the ''x1'' and ''y1'' fields.
+
puts the event data into the ''event_data'' local variable. Since it is a ''moveto'' event, the ''event_data'' table contains the destination of the unit in the ''x1'' and ''y1'' fields.
  
 
The next two lines then test
 
The next two lines then test
  
if target_hex.is_set and
+
<syntaxhighlight lang='lua'>
     (args.x1 ~= target_hex.x or args.y1 ~= target_hex.y)
+
if wml.variables["target_hex.is_set"] and
 +
     (event_data.x1 ~= wml.variables["target_hex.x"] or event_data.y1 ~= wml.variables["target_hex.y"])
 +
</syntaxhighlight>
  
whether the variable ''target_hex'' matches the event parameters. Since ''target_hex'' is not a local variable, it is taken from the global environment (a table implicitly named ''_G'', so it is actually ''_G.target_hex''). The global environment is not persistent, so it cannot be used to store data. In order to make it useful, it was redirected to the storage of WML variables by the following ''preload'' event.
+
whether the variable ''wml.variables["target_hex"]'' matches the event parameters. Since ''wml.variables'' is not a local variable, it is taken from the global environment. Usually, variables from the global environment are not persistent but the wesnoth engine maps the variable wml.variables to the storage of WML variables.
  
[event]
+
Without using wml.variables, the conditional would have been written
    name=preload
 
    first_time_only=no
 
    [lua]
 
        code = <<
 
            H = wesnoth.dofile("lua/helper.lua")
 
            -- skipping some other initializations
 
            -- ...
 
            H.set_wml_var_metatable(_G)
 
        >>
 
    [/lua]
 
[/event]
 
  
Without a prelude redirecting ''_G'', the conditional would have been written
+
<syntaxhighlight lang='lua'>
 +
if wesnoth.get_variable("target_hex.is_set") and
 +
    (event_data.x1 ~= wesnoth.get_variable("target_hex.x") or event_data.y1 ~= wesnoth.get_variable("target_hex.y")
 +
</syntaxhighlight>
  
if wesnoth.get_variable("target_hex.is_set") and
+
The body of the conditional then performs the [[InterfaceActionsWML#Other interface tags|[redraw]]] action.
    (args.x1 ~= wesnoth.get_variable("target_hex.x") or args.y1 ~= wesnoth.get_variable("target_hex.y")
 
  
The body of the conditional then performs the [[InterfaceActionsWML|redraw]] action.
+
<syntaxhighlight lang='lua'>
 +
W.redraw()
 +
</syntaxhighlight>
  
W.redraw()
+
This short syntax is made possible by a line of the prelude that makes ''W'' a proxy for performing WML actions.
  
Again, this short syntax is made possible by a line of the prelude that makes ''W'' a proxy for performing WML actions.
+
<syntaxhighlight lang='lua'>
 
+
[scenario]
W = H.set_wml_action_metatable({})
+
    [lua]
 +
        code = <<
 +
            H = wesnoth.require "lua/helper.lua"
 +
            W = H.set_wml_action_metatable {}
 +
        >>
 +
    [/lua]
 +
    ...
 +
[/scenario]
 +
</syntaxhighlight>
  
 
Without this shortcut, the first statement would have been written
 
Without this shortcut, the first statement would have been written
  
wesnoth.fire("redraw")
+
<syntaxhighlight lang='lua'>
 +
wesnoth.fire("redraw")
 +
</syntaxhighlight>
 +
or
 +
<syntaxhighlight lang='lua'>
 +
wesnoth.wml_actions.redraw {}
 +
</syntaxhighlight>
  
 
Finally the script displays a message by
 
Finally the script displays a message by
  
narrator_says(_ "*Oops!\nYou moved to the wrong place! After this message, you can press 'u' to undo, then try again.")
+
<syntaxhighlight lang='lua'>
 +
narrator_says(_ "*Oops!\nYou moved to the wrong place! After this message, you can press 'u' to undo, then try again.")
 +
</syntaxhighlight>
  
 
The ''narrator_says'' function is defined in the prelude too, since the construct behind it occurs several times in the tutorial. In plain WML, macros would have been used instead. The definition of the function is
 
The ''narrator_says'' function is defined in the prelude too, since the construct behind it occurs several times in the tutorial. In plain WML, macros would have been used instead. The definition of the function is
  
function narrator_says(m)
+
<syntaxhighlight lang='lua'>
    W.message { speaker="narrator",
+
function narrator_says(m)
                message = m .. _ "\n*Left click or press spacebar to continue..." }
+
    W.message { speaker="narrator",
end
+
                message = m .. _ "\n*Left click or press spacebar to continue..." }
 +
end
 +
</syntaxhighlight>
  
The function fires a [[InterfaceActionsWML|message]] and passes a WML object containing the usual two fields to it. The second field is initialized by concatenating the function argument with another string. Both strings are prefixed by the ''_'' symbol to mark them as translatable. (Note that ''_'' is just a unary function, not a keyword.) Again, this is made possible by a specific line of the prelude:
+
The function fires a [[InterfaceActionsWML#.5Bmessage.5D|[message]]] action and passes a WML object containing the usual two fields to it. The second field is initialized by concatenating the function argument with another string. Both strings are prefixed by the ''_'' symbol to mark them as translatable. (Note that ''_'' is just a unary function, not a keyword.) Again, this is made possible by a specific line of the prelude:
  
_ = wesnoth.textdomain "wesnoth-tutorial"
+
<syntaxhighlight lang='lua'>
 +
_ = wesnoth.textdomain "wesnoth-tutorial"
 +
</syntaxhighlight>
  
 
A longer translation of the tutorial is available at [https://gna.org/patch/download.php?file_id=5483].
 
A longer translation of the tutorial is available at [https://gna.org/patch/download.php?file_id=5483].
  
== Global environment ==
+
== Interface to the engine and helper functions ==
  
All the Lua scripts of a scenario shares the same global environment (aka Lua state). This environment is not preserved over save/load cycles. Therefore, storing values in the global environment is a generally a bad idea (unless it has been redirected to WML variables, see [[#set_wml_var_metatable|set_wml_var_metatable]]). The only time it makes sense to assign global variables is during a [[EventWML|preload]] event, as this event is always run. Therefore, helper functions defined at that time will be available to all the later scripts.
+
<br><div class="navtemplate" style="width: auto; max-width: 75%; margin: 0 auto; border: 1px solid #c60; border-left-width: 8px"><div style="float:left;position:relative;top:-14px;left:-6px">https://raw.github.com/wesnoth/wesnoth/master/data/core/images/items/bones.png</div><p style="margin:0"><strong>This section is in the process of being moved.</strong> The information here remains accurate as of 1.14.0, but for 1.15.0 and later, [[LuaAPI]] is planned to be the definitive source.</p></div><br>
  
The global environment is preloaded with the following modules: [http://www.lua.org/manual/5.1/manual.html#5.1 basic] (no name), [http://www.lua.org/manual/5.1/manual.html#5.4 string], [http://www.lua.org/manual/5.1/manual.html#5.5 table], and [http://www.lua.org/manual/5.1/manual.html#5.6 math]. A '''wesnoth''' module is also available, see below.
+
Functionalities of the game engine are available through the functions contained in the '''wesnoth''' global table. Some of these functions return proxy tables. Writes to fields marked "read-only" are ignored. The '''__cfg''' fields return plain tables; in particular, writes do not modify the original object, and reads return the values from the time the dump was performed.
  
At the start of the script, the variadic local variable '''...''' (three dots) contains a table. It contains the content of the '''[args]''' sub-tag of the '''[lua]''' tag. The table also provides (if they make sense for the current event) the fields '''x1''', '''y1''', '''x2''', and '''y2''', containing map locations, and the sub-tables '''weapon''' and '''second_weapon''' containing attacks.
+
Some helper functions are provided by the '''lua/helper.lua''' library. They are stored inside a table that is returned when loading the library with [[LuaWML:Files#wesnoth.require|wesnoth.require]].
  
== Interface to the C++ engine ==
+
<syntaxhighlight lang='lua'>
 +
helper = wesnoth.require "lua/helper.lua"
 +
</syntaxhighlight>
  
Functionalities of the game engine are available through the functions of the '''wesnoth''' global table.
+
=== WML variables ===
  
==== message ====
+
* [[LuaWML:Variables#wesnoth.get_variable|wesnoth.get_variable]]
 +
* [[LuaWML:Variables#wesnoth.set_variable|wesnoth.set_variable]]
 +
* [[LuaWML:Variables#wesnoth.get_all_vars|wesnoth.get_all_vars]] {{DevFeature1.13|0}}
 +
* [[LuaWML:Variables#wesnoth.wml_matches_filter|wesnoth.wml_matches_filter]] {{DevFeature1.13|8}}
 +
* [[LuaWML:Variables#helper.set_wml_var_metatable|helper.set_wml_var_metatable]]
 +
* [[LuaWML:Variables#helper.get_child|helper.get_child]]
 +
* [[LuaWML:Variables#helper.get_nth_child|helper.get_nth_child]] {{DevFeature1.13|2}}
 +
* [[LuaWML:Variables#helper.child_count|helper.child_count]] {{DevFeature1.13|2}}
 +
* [[LuaWML:Variables#helper.child_range|helper.child_range]]
 +
* [[LuaWML:Variables#helper.child_array|helper.child_array]] {{DevFeature1.13|2}}
 +
* [[LuaWML:Variables#helper.get_variable_array|helper.get_variable_array]]
 +
* [[LuaWML:Variables#helper.get_variable_proxy_array|helper.get_variable_proxy_array]]
 +
* [[LuaWML:Variables#helper.set_variable_array|helper.set_variable_array]]
  
Dumps a string to the lua/info log domain (''--log-info=scripting/lua'' on the command-line) for debugging purpose.
+
=== Events and WML actions ===
  
wesnoth.message "Hello World!"
+
* [[LuaWML:Events#wesnoth.fire|wesnoth.fire]]
 +
* [[LuaWML:Events#wesnoth.wml_actions|wesnoth.wml_actions]]
 +
* [[LuaWML:Events#wesnoth.wml_actions|wesnoth.wml_conditionals]] {{DevFeature1.13|0}}
 +
* [[LuaWML:Events#wesnoth.game_events|wesnoth.game_events]]
 +
* [[LuaWML:Events#wesnoth.persistent_tags|wesnoth.persistent_tags]] {{DevFeature1.13|12}}
 +
* [[LuaWML:Events#wesnoth.fire_event|wesnoth.fire_event]]
 +
* [[LuaWML:Events#wesnoth.fire_event_by_id|wesnoth.fire_event_by_id]] {{DevFeature1.13|6}}
 +
* [[LuaWML:Events#wesnoth.add_event_handler|wesnoth.add_event_handler]] {{DevFeature1.13|0}}
 +
* [[LuaWML:Events#wesnoth.remove_event_handler|wesnoth.remove_event_handler]] {{DevFeature1.13|0}}
 +
* [[LuaWML:Events#wesnoth.eval_conditional|wesnoth.eval_conditional]]
 +
* [[LuaWML:Events#wesnoth.tovconfig|wesnoth.tovconfig]]
 +
* [[LuaWML:Events#helper.set_wml_action_metatable|helper.set_wml_action_metatable]]
 +
* [[LuaWML:Events#helper.wml_error|helper.wml_error]]
 +
* [[LuaWML:Events#helper.literal|helper.literal]]
 +
* [[LuaWML:Events#helper.parsed|helper.parsed]]
 +
* [[LuaWML:Events#helper.shallow_literal|helper.shallow_literal]]
 +
* [[LuaWML:Events#helper.shallow_parsed|helper.shallow_parsed]]
 +
* [[LuaWML:Events#on_event.lua|on_event.on_event]] {{DevFeature1.13|6}}
  
==== fire ====
+
=== User interface ===
 +
* [[LuaWML:Display#wesnoth.get_viewing_side|wesnoth.get_viewing_side]] {{DevFeature1.13|?}}
 +
* [[LuaWML:Display#wesnoth.message|wesnoth.message]]
 +
* [[LuaWML:Display#wesnoth.clear_messages|wesnoth.clear_messages]]
 +
* [[LuaWML:Display#wesnoth.textdomain|wesnoth.textdomain]]
 +
* [[LuaWML:Display#wesnoth.delay|wesnoth.delay]]
 +
* [[LuaWML:Display#wesnoth.float_label|wesnoth.float_label]]
 +
* [[LuaWML:Display#wesnoth.select_unit|wesnoth.select_hex]]
 +
* [[LuaWML:Display#wesnoth.select_unit|wesnoth.select_unit]]
 +
* [[LuaWML:Display#wesnoth.highlight_hex|wesnoth.highlight_hex]]
 +
* [[LuaWML:Display#wesnoth.deselect_hex|wesnoth.deselect_hex]] {{DevFeature1.13|2}}
 +
* [[LuaWML:Display#wesnoth.scroll_to_tile|wesnoth.scroll_to_tile]]
 +
* [[LuaWML:Display#wesnoth.lock_view|wesnoth.lock_view]]
 +
* [[LuaWML:Display#wesnoth.view_locked|wesnoth.view_locked]]
 +
* [[LuaWML:Display#wesnoth.play_sound|wesnoth.play_sound]]
 +
* [[LuaWML:Display#wesnoth.set_music|wesnoth.set_music]]
 +
* [[LuaWML:Display#wesnoth.music_list|wesnoth.music_list]] {{DevFeature1.13|8}}
 +
* [[LuaWML:Display#wesnoth.sound_volume|wesnoth.sound_volume]] {{DevFeature1.13|8}}
 +
* [[LuaWML:Display#wesnoth.show_message_dialog|wesnoth.show_message_dialog]] {{DevFeature1.13|2}}
 +
* [[LuaWML:Display#wesnoth.show_popup_dialog|wesnoth.show_popup_dialog]] {{DevFeature1.13|2}}
 +
* [[LuaWML:Display#wesnoth.show_story|wesnoth.show_story]] {{DevFeature1.13|8}}
 +
* [[LuaWML:Display#wesnoth.show_message_box|wesnoth.show_message_box]] {{DevFeature1.13|8}}
 +
* [[LuaWML:Display#wesnoth.show_menu|wesnoth.show_menu]] {{DevFeature1.13|8}}
 +
* [[LuaWML:Display#wesnoth.show_message_box|wesnoth.alert]] {{DevFeature1.13|8}}
 +
* [[LuaWML:Display#wesnoth.show_message_box|wesnoth.confirm]] {{DevFeature1.13|8}}
 +
* [[LuaWML:Display#wesnoth.show_dialog|wesnoth.show_dialog]]
 +
* [[LuaWML:Display#wesnoth.set_dialog_value|wesnoth.set_dialog_value]]
 +
* [[LuaWML:Display#wesnoth.get_dialog_value|wesnoth.get_dialog_value]]
 +
* [[LuaWML:Display#wesnoth.set_dialog_active|wesnoth.set_dialog_active]]
 +
* [[LuaWML:Display#wesnoth.set_dialog_callback|wesnoth.set_dialog_callback]]
 +
* [[LuaWML:Display#wesnoth.set_dialog_markup|wesnoth.set_dialog_markup]]
 +
* [[LuaWML:Display#wesnoth.set_dialog_focus|wesnoth.set_dialog_focus]] {{DevFeature1.13|2}}
 +
* [[LuaWML:Display#wesnoth.set_dialog_visible|wesnoth.set_dialog_visible]] {{DevFeature1.13|2}}
 +
* [[LuaWML:Display#wesnoth.set_dialog_canvas|wesnoth.set_dialog_canvas]]
 +
* [[LuaWML:Display#wesnoth.add_dialog_tree_node|wesnoth.add_dialog_tree_node]] {{DevFeature1.13|0}}
 +
* [[LuaWML:Display#wesnoth.remove_dialog_item|wesnoth.remove_dialog_item]] {{DevFeature1.13|1}}
 +
* [[LuaWML:Display#wesnoth.get_displayed_unit|wesnoth.get_displayed_unit]]
 +
* [[LuaWML:Display#wesnoth.theme_items|wesnoth.theme_items]]
 +
* [[LuaWML:Display#helper.get_user_choice|helper.get_user_choice]]
 +
* [[LuaWML:Display#wesnoth.is_skipping_messages|wesnoth.is_skipping_messages]] {{DevFeature1.13|2}}
 +
* [[LuaWML:Display#wesnoth.skip_messages|wesnoth.skip_messages]] {{DevFeature1.13|2}}
 +
* [[LuaWML:Display#wesnoth.log|wesnoth.log]] {{DevFeature1.13|5}}
 +
* [[LuaWML:Display#wesnoth.zoom|wesnoth.zoom]] {{DevFeature1.13|8}}
  
Fires a WML action (argument 1); argument 2 is the WML table describing the action, while arguments 3-6 are two locations (not sure what they can be useful for).
+
=== Map and terrains ===
  
wesnoth.fire("message", { speaker="narrator", message=_ "Hello World!" })
+
* [[LuaWML:Tiles#wesnoth.get_map_size|wesnoth.get_map_size]]
 +
* [[LuaWML:Tiles#wesnoth.get_terrain|wesnoth.get_terrain]]
 +
* [[LuaWML:Tiles#wesnoth.set_terrain|wesnoth.set_terrain]]
 +
* [[LuaWML:Tiles#wesnoth.get_terrain_info|wesnoth.get_terrain_info]]
 +
* [[LuaWML:Tiles#wesnoth.get_selected_tile|wesnoth.get_selected_tile]]
 +
* [[LuaWML:Tiles#wesnoth.get_locations|wesnoth.get_locations]]
 +
* [[LuaWML:Tiles#wesnoth.get_villages|wesnoth.get_villages]]
 +
* [[LuaWML:Tiles#wesnoth.match_location|wesnoth.match_location]]
 +
* [[LuaWML:Tiles#wesnoth.add_tile_overlay|wesnoth.add_tile_overlay]]
 +
* [[LuaWML:Tiles#wesnoth.remove_tile_overlay|wesnoth.remove_tile_overlay]]
 +
* [[LuaWML:Tiles#wesnoth.add_fog|wesnoth.add_fog]] {{DevFeature1.13|5}}
 +
* [[LuaWML:Tiles#wesnoth.remove_fog|wesnoth.remove_fog]] {{DevFeature1.13|5}}
 +
* [[LuaWML:Tiles#wesnoth.add_sound_source|wesnoth.add_sound_source]] {{DevFeature1.13|5}}
 +
* [[LuaWML:Tiles#wesnoth.remove_sound_source|wesnoth.remove_sound_source]] {{DevFeature1.13|5}}
 +
* [[LuaWML:Tiles#wesnoth.get_sound_source|wesnoth.get_sound_source]] {{DevFeature1.13|5}}
 +
* [[LuaWML:Tiles#wesnoth.map.get_direction|wesnoth.map.get_direction]] {{DevFeature1.13|8}}
 +
* [[LuaWML:Tiles#wesnoth.map.get_relative_dir|wesnoth.map.get_relative_dir]] {{DevFeature1.13|8}}
 +
* [[LuaWML:Tiles#wesnoth.map.rotate_right_around_center|wesnoth.map.rotate_right_around_center]] {{DevFeature1.13|8}}
 +
* [[LuaWML:Tiles#wesnoth.map.get_adjacent_tiles|wesnoth.map.get_adjacent_tiles]] {{DevFeature1.13|8}}
 +
* [[LuaWML:Tiles#wesnoth.map.tiles_adjacent|wesnoth.map.tiles_adjacent]] {{DevFeature1.13|8}}
 +
* [[LuaWML:Tiles#wesnoth.map.distance_between|wesnoth.map.distance_between]] {{DevFeature1.13|8}}
 +
* [[LuaWML:Tiles#wesnoth.label|wesnoth.label]] {{DevFeature1.13|0}}
 +
* [[LuaWML:Tiles#wesnoth.special_locations|wesnoth.special_locations]] {{DevFeature1.13|12}}
 +
* [[LuaWML:Tiles#items.place_image|items.place_image]]
 +
* [[LuaWML:Tiles#items.place_halo|items.place_halo]]
 +
* [[LuaWML:Tiles#items.remove|items.remove]]
  
==== get_variable ====
+
=== Time of day schedule ===
  
Loads a variable with the given WML name (argument 1) and converts it into a Lua object. Returns ''nil'' if the name does not point to anything, a scalar for a WML attribute, and a table for a WML object. Argument 2, if ''true'', prevents the recursive conversion if the name points to an object; an empty table is returned in this case.
+
* [[LuaWML:Time#wesnoth.get_time_of_day|wesnoth.get_time_of_day]]
 +
* [[LuaWML:Time#wesnoth.add_time_area|wesnoth.add_time_area]] {{DevFeature1.13|0}}
 +
* [[LuaWML:Time#wesnoth.remove_time_area|wesnoth.remove_time_area]] {{DevFeature1.13|0}}
  
wesnoth.fire("store_unit", { variable="my_unit", { "filter", { id="hero" } } })
+
=== Units ===
local heros_hp = wesnoth.get_variable("my_unit[0].hitpoints")
 
  
==== set_variable ====
+
* [[LuaWML:Units#wesnoth.get_units|wesnoth.get_units]]
 +
* [[LuaWML:Units#wesnoth.get_unit|wesnoth.get_unit]]
 +
* [[LuaWML:Units#wesnoth.match_unit|wesnoth.match_unit]]
 +
* [[LuaWML:Units#wesnoth.put_unit|wesnoth.put_unit]]
 +
* [[LuaWML:Units#wesnoth.erase_unit|wesnoth.erase_unit]] {{DevFeature1.13|2}}
 +
* [[LuaWML:Units#wesnoth.get_recall_units|wesnoth.get_recall_units]]
 +
* [[LuaWML:Units#wesnoth.put_recall_unit|wesnoth.put_recall_unit]]
 +
* [[LuaWML:Units#wesnoth.create_unit|wesnoth.create_unit]]
 +
* [[LuaWML:Units#wesnoth.copy_unit|wesnoth.copy_unit]]
 +
* [[LuaWML:Units#wesnoth.extract_unit|wesnoth.extract_unit]]
 +
* [[LuaWML:Units#wesnoth.add_modification|wesnoth.add_modification]]
 +
* [[LuaWML:Units#wesnoth.remove_modifications|wesnoth.remove_modifications]] {{DevFeature1.13|?}}
 +
* [[LuaWML:Units#wesnoth.unit_resistance|wesnoth.unit_resistance]]
 +
* [[LuaWML:Units#wesnoth.unit_defense|wesnoth.unit_defense]]
 +
* [[LuaWML:Units#wesnoth.unit_movement_cost|wesnoth.unit_movement_cost]]
 +
* [[LuaWML:Units#wesnoth.unit_vision_cost|wesnoth.unit_vision_cost]]
 +
* [[LuaWML:Units#wesnoth.unit_jamming_cost|wesnoth.unit_jamming_cost]]
 +
* [[LuaWML:Units#wesnoth.unit_ability|wesnoth.unit_ability]]
 +
* [[LuaWML:Units#wesnoth.unit_types|wesnoth.unit_types]]
 +
* [[LuaWML:Units#wesnoth.races|wesnoth.races]]
 +
* [[LuaWML:Units#wesnoth.get_traits|wesnoth.get_traits]]
 +
* [[LuaWML:Units#wesnoth.advance_unit|wesnoth.advance_unit]] {{DevFeature1.13|?}}
 +
* [[LuaWML:Units#wesnoth.add_known_unit|wesnoth.add_known_unit]] {{DevFeature1.13|?}}
 +
* [[LuaWML:Units#wesnoth.simulate_combat|wesnoth.simulate_combat]]
 +
* [[LuaWML:Units#wesnoth.transform_unit|wesnoth.transform_unit]]
 +
* [[LuaWML:Units#wesnoth.create_animator|wesnoth.create_animator]] {{DevFeature1.13|7}}
 +
* [[LuaWML:Units#wesnoth.effects|wesnoth.effects]] {{DevFeature1.13|2}}
  
Converts and stores a Lua object (argument 2) to a WML variable (argument 1). A WML object is created for a table, an attribute otherwise.
+
=== Sides ===
  
wesnoth.set_variable("my_unit.hitpoints", heros_hp + 10)
+
* [[LuaWML:Sides#wesnoth.sides|wesnoth.sides]]
 +
* [[LuaWML:Sides#wesnoth.get_sides|wesnoth.get_sides]]
 +
* [[LuaWML:Sides#wesnoth.get_village_owner|wesnoth.get_village_owner]]
 +
* [[LuaWML:Sides#wesnoth.set_village_owner|wesnoth.set_village_owner]]
 +
* [[LuaWML:Sides#wesnoth.is_enemy|wesnoth.is_enemy]]
 +
* [[LuaWML:Sides#wesnoth.match_side|wesnoth.match_side]]
 +
* [[LuaWML:Sides#wesnoth.get_starting_location|wesnoth.get_starting_location]]
 +
* [[LuaWML:Sides#wesnoth.set_side_id|wesnoth.set_side_id]] {{DevFeature1.13|7}}
 +
* [[LuaWML:Sides#wesnoth.place_shroud|wesnoth.place_shroud]] {{DevFeature1.13|7}}
 +
* [[LuaWML:Sides#wesnoth.remove_shroud|wesnoth.remove_shroud]] {{DevFeature1.13|7}}
 +
* [[LuaWML:Sides#wesnoth.is_fogged|wesnoth.is_fogged]] {{DevFeature1.13|7}}
 +
* [[LuaWML:Sides#wesnoth.is_shrouded|wesnoth.is_shrouded]] {{DevFeature1.13|7}}
 +
* [[LuaWML:Sides#wesnoth.switch_ai|wesnoth.switch_ai]] {{DevFeature1.13|7}}
 +
* [[LuaWML:Sides#wesnoth.append_ai|wesnoth.append_ai]] {{DevFeature1.13|7}}
 +
* [[LuaWML:Sides#wesnoth.add_ai_component|wesnoth.add_ai_component]] {{DevFeature1.13|7}}
 +
* [[LuaWML:Sides#wesnoth.change_ai_component|wesnoth.change_ai_component]] {{DevFeature1.13|7}}
 +
* [[LuaWML:Sides#wesnoth.delete_ai_component|wesnoth.delete_ai_component]] {{DevFeature1.13|7}}
 +
* [[LuaWML:Sides#helper.all_teams|helper.all_teams]]
 +
* [[LuaWML:Sides#helper.get_side_variable|helper.get_side_variable]] {{DevFeature1.13|?}}
 +
* [[LuaWML:Sides#helper.set_side_variable|helper.set_side_variable]] {{DevFeature1.13|?}}
  
==== textdomain ====
+
=== Pathfinder ===
  
Creates a function proxy for lazily translating strings from the given domain.
+
* [[LuaWML:Pathfinder#wesnoth.find_path|wesnoth.find_path]]
 +
* [[LuaWML:Pathfinder#wesnoth.find_vacant_tile|wesnoth.find_vacant_tile]]
 +
* [[LuaWML:Pathfinder#wesnoth.find_reach|wesnoth.find_reach]]
 +
* [[LuaWML:Pathfinder#wesnoth.find_cost_map|wesnoth.find_cost_map]]
 +
* [[LuaWML:Pathfinder#helper.distance_between|helper.distance_between]]
 +
* [[LuaWML:Pathfinder#helper.adjacent_tiles|helper.adjacent_tiles]]
  
_ = wesnoth.textdomain("my-campaign")
+
=== Lua files ===
wesnoth.set_variable("my_unit.description", _ "the unit formerly known as Hero")
 
  
==== dofile ====
+
* [[LuaWML:Files#wesnoth.dofile|wesnoth.dofile]]
 +
* [[LuaWML:Files#wesnoth.require|wesnoth.require]]
 +
* [[LuaWML:Files#wesnoth.have_file|wesnoth.have_file]] {{DevFeature1.13|5}}
 +
* [[LuaWML:Files#wesnoth.read_file|wesnoth.read_file]] {{DevFeature1.13|5}}
  
Replaces [http://www.lua.org/manual/5.1/manual.html#5.1 basic.dofile] for loading files. Loads the given filename (relative to the content directory) and executes it in an unprotected environment (that is, exceptions propagate to the caller). Returns the values returned by the executed script.
+
=== Location sets ===
  
helper = wesnoth.dofile "lua/helper.lua"
+
* [[LuaWML:Location_set#location_set.create|location_set.create]]
 +
* [[LuaWML:Location_set#location_set.of_pairs|location_set.of_pairs]]
 +
* [[LuaWML:Location_set#location_set.of_wml_var|location_set.of_wml_var]]
 +
* [[LuaWML:Location_set#location_set:empty|location_set:empty]]
 +
* [[LuaWML:Location_set#location_set:size|location_set:size]]
 +
* [[LuaWML:Location_set#location_set:clear|location_set:clear]]
 +
* [[LuaWML:Location_set#location_set:get|location_set:get]]
 +
* [[LuaWML:Location_set#location_set:insert|location_set:insert]]
 +
* [[LuaWML:Location_set#location_set:remove|location_set:remove]]
 +
* [[LuaWML:Location_set#location_set:of_pairs|location_set:of_pairs]]
 +
* [[LuaWML:Location_set#location_set:of_wml_var|location_set:of_wml_var]]
 +
* [[LuaWML:Location_set#location_set:to_pairs|location_set:to_pairs]]
 +
* [[LuaWML:Location_set#location_set:to_stable_pairs|location_set:to_stable_pairs]]
 +
* [[LuaWML:Location_set#location_set:to_wml_var|location_set:to_wml_var]]
 +
* [[LuaWML:Location_set#location_set:union|location_set:union]]
 +
* [[LuaWML:Location_set#location_set:inter|location_set:inter]]
 +
* [[LuaWML:Location_set#location_set:iter|location_set:iter]]
 +
* [[LuaWML:Location_set#location_set:stable_iter|location_set:stable_iter]]
 +
* [[LuaWML:Location_set#location_set:filter|location_set:filter]]
 +
* [[LuaWML:Location_set#location_set:union_merge|location_set:union_merge]]
 +
* [[LuaWML:Location_set#location_set:inter_merge|location_set:inter_merge]]
  
==== register_wml_action ====
+
=== Miscellaneous ===
  
Registers the second argument as a handler for the given action tag. When the game encounters this tag an event, it fires the action handler and passes the content of the WML object as the first argument.
+
* [[LuaWML:Misc#wesnoth.game_config|wesnoth.game_config]]
 +
* [[LuaWML:Misc#wesnoth.get_era|wesnoth.get_era]]
 +
* [[LuaWML:Misc#wesnoth.current|wesnoth.current]]
 +
* [[LuaWML:Misc#wesnoth.synchronize_choice|wesnoth.synchronize_choice]]
 +
* [[LuaWML:Misc#wesnoth.synchronize_choices|wesnoth.synchronize_choices]] {{DevFeature1.13|?}}
 +
* [[LuaWML:Misc#wesnoth.unsynced|wesnoth.unsynced]] {{DevFeature1.13|?}}
 +
* [[LuaWML:Misc#wesnoth.get_image_size|wesnoth.get_image_size]]
 +
* [[LuaWML:Misc#wesnoth.compare_versions|wesnoth.compare_versions]]
 +
* [[LuaWML:Misc#wesnoth.have_file|wesnoth.have_file]]
 +
* [[LuaWML:Misc#wesnoth.debug|wesnoth.debug]]
 +
* [[LuaWML:Misc#wesnoth.get_time_stamp|wesnoth.get_time_stamp]]
 +
* [[LuaWML:Misc#wesnoth.random|wesnoth.random]]  {{DevFeature1.13|2}}
 +
* [[LuaWML:Misc#wesnoth.eval_formula|wesnoth.eval_formula]] {{DevFeature1.13|5}}
 +
* [[LuaWML:Misc#wesnoth.compile_formula|wesnoth.compile_formula]] {{DevFeature1.13|5}}
 +
* [[LuaWML:Misc#wesnoth.name_generator|wesnoth.name_generator]] {{DevFeature1.13|5}}
 +
* [[LuaWML:Misc#wesnoth.set_next_scenario|wesnoth.set_next_scenario]] {{DevFeature1.13|5}}
 +
* [[LuaWML:Misc#wesnoth.format|wesnoth.format]] {{DevFeature1.13|8}}
 +
* [[LuaWML:Misc#wesnoth.format_conjunct_list|wesnoth.format_conjunct_list]] {{DevFeature1.13|8}}
 +
* [[LuaWML:Misc#wesnoth.format_disjunct_list|wesnoth.format_disjunct_list]] {{DevFeature1.13|8}}
 +
* [[LuaWML:Misc#wesnoth.wesnoth.end_turn|wesnoth.end_turn]] {{DevFeature1.13|?}}
 +
* [[LuaWML:Misc#wml.tag|wml.tag]]
 +
* [[LuaWML:Misc#helper.modify_unit|helper.modify_unit]]
 +
* [[LuaWML:Misc#helper.move_unit_fake|helper.move_unit_fake]]
 +
* [[LuaWML:Misc#helper.rand|helper.rand]]
 +
* [[LuaWML:Misc#helper.round|helper.round]]
 +
* [[LuaWML:Misc#helper.shuffle|helper.shuffle]]
  
wesnoth.register_wml_action("freeze_unit",
+
=== Functions that should not be used ===
    function(t)
 
        helper.modify_unit({ id = t.id }, { moves = 0 })
 
    end
 
)
 
  
[freeze_unit]
+
If you take a look at Wesnoth's own lua files, you might find some undocumented functions use in the implementations of WML tags. Where possible, you should avoid using them, as they might be changed or removed with no compatibility for further releases. Instead, use the corresponding wml tags (in lua you can use <tt>wesnoth.wml_actions.tag_name(cfg)</tt>, though keep in mind that this won't substitute variables in the config).
    id=Delfador
 
[/freeze_unit]
 
  
==== get_units ====
+
If uncertain whether an undocumented feature is safe to use, ask on the forums, Discord, or IRC. It may turn out that someone simply forgot to add it to the wiki.
  
Returns an array of all the units matching the WML filter passed as the first argument.
+
* wesnoth.redraw
 +
* wesnoth.set_menu_item
 +
* wesnoth.clear_menu_item
 +
* wesnoth.modify_ai
 +
* wesnoth.print
 +
* wesnoth.end_level
  
local leaders_on_side_two = get_units({ side = 2, canrecruit = true })
+
== Encoding WML objects into Lua tables ==
local name_of_leader = leaders_on_side_two[1].name
 
  
Units are proxy tables with the following fields:
+
Function [[LuaWML:Events#wesnoth.fire|wesnoth.fire]] expects a table representing a WML object as its second argument (if needed). Function [[LuaWML:Variables#wesnoth.set_variable|wesnoth.set_variable]] allows to modify whole WML objects, again by passing it a table. Function [[LuaWML:Variables#wesnoth.get_variable|wesnoth.get_variable]] transforms a WML object into a table, if its second argument is not set to ''true''. All these tables have the same format.
* '''x''', '''y''': integers (read only)
 
* '''side''': integer (read/write)
 
* '''id''', '''side_id''': strings (read only)
 
* '''name''': translatable string (read only)
 
* '''hitpoints''', '''max_hitpoints''', '''experience''', '''max_experience''', '''max_moves''': integers (read only)
 
* '''moves''': integer (read/write)
 
* '''resting''': boolean (read/write)
 
* '''petrified''', '''canrecruit''': booleans (read only)
 
* '''role''', '''facing''': strings (read/write)
 
* '''__cfg''': WML table (read only)
 
  
==== get_side ====
+
Scalar fields are transformed into WML attributes. For instance, the following Lua table
  
Returns the team with given number.
+
<syntaxhighlight lang='lua'>
 +
{
 +
    a_bool = true,
 +
    an_int = 42,
 +
    a_float = 1.25,
 +
    a_string = "scout",
 +
    a_translation = _ "Hello World!"
 +
}
 +
</syntaxhighlight>
  
local team = wesnoth.get_side(1)
+
is equivalent to the content of the following WML object
team.gold = team.gold + 50
 
  
Teams are proxy tables with the following fields:
+
<syntaxhighlight lang='wml'>
* '''gold''', '''village_gold''', '''base_income''': integers (read/write)
+
[dummy]
* '''total_income''': integer (read only)
+
    a_bool = "yes"
* '''objectives''', '''user_team_name''': translatable strings (read/write)
+
    an_int = 42
* '''objectives_changed''': boolean (read/write)
+
    a_float = 1.25
* '''team_name''': string (read/write)
+
    a_string = "scout"
* '''__cfg''': WML table (read only)
+
    a_translation = _ "Hello World!"
 +
[/dummy]
 +
</syntaxhighlight>
  
==== get_unit_type_ids ====
+
WML child objects are not stored as Lua named fields, since several of them can have the same tag. Moreover, their tags can conflict with the attribute keys. So child objects are stored as pairs string + table in the unnamed fields in definition order. This means that for every subtag appearing in the wml code there is an additional table "layer" in the corresponding WML table of the form <code>{[1] = "tag_name", [2] = {}}</code> which is equivalent to <code>{"tag_name", {}}</code>. [1] etc are the unnamed fields (as opposed to wml attributes). The table under [2] in this subtable then holds the wml attributes from inside the wml subtag. So every subtag other than the toplevel tag corresponds to two nested tables each. For instance, the following Lua table
  
Returns an array containing all the unit type IDs the engine knows about.
+
<syntaxhighlight lang='lua'>
 +
{
 +
    foo = 42,
 +
    { "bar", { v = 1, w = 2 } },
 +
    { "foo", { x = false } },
 +
    { "bar", { y = "foo" } },
 +
    { "foobar", { z = 5, { "barfoo", {} } } }
 +
}
 +
</syntaxhighlight>
  
local unit_types = wesnoth.get_unit_type_ids()
+
is equivalent to the content of the following WML object
wesnoth.message(string.format("%d unit types registered. First one is %s.", #unit_types, unit_types[1]))
 
  
==== get_unit_type ====
+
<syntaxhighlight lang='wml'>
 +
[dummy]
 +
    foo = 42
 +
    [bar]
 +
        v = 1
 +
        w = 2
 +
    [/bar]
 +
    [foo]
 +
        x = no
 +
    [/foo]
 +
    [bar]
 +
        y = foo
 +
    [bar]
 +
    [foobar]
 +
        z = 5
 +
        [barfoo]
 +
        [/barfoo]
 +
    [/foobar]
 +
[/dummy]
 +
</syntaxhighlight>
  
Returns the unit type with the corresponding ID.
+
Both tables above are also equivalent to this WML table, where all unnamed fields are displayed:
  
local lich_cost = wesnoth.get_unit_type("Ancient Lich").cost
+
<syntaxhighlight lang='lua'>
 +
{
 +
    foo = 42,
 +
    [1] = { [1] = "bar", [2] = { v = 1, w = 2 } },
 +
    [2] = { [1] = "foo", [2] = { x = false } },
 +
    [3] = { [1] = "bar", [2] = { y = "foo" } },
 +
    [4] = { [1] = "foobar", [2] = { z = 5, [1] = { [1] = "barfoo", [2] = {} } } }
 +
}
 +
</syntaxhighlight>
  
Unit types are proxy tables with the following fields:
+
So assuming ''cfg'' contains the above WML object, the following accesses are possible:
* '''id''': string
 
* '''name''': translatable string (read only)
 
* '''max_moves''', '''max_experience''', '''max_hitpoints''', '''level''', '''cost''': integers (read only)
 
* '''__cfg''': WML table (read only)
 
  
==== get_terrain ====
+
<syntaxhighlight lang=lua>
 +
a_int = cfg.foo        -- "dummy.foo", 42
 +
a_string = cfg[3][2].y -- "dummy.bar[1].y", "foo"
 +
a_table = cfg[4][2]    -- "dummy.foobar", { z = 5, { "barfoo", {} } }
 +
</syntaxhighlight>
  
Returns the terrain code for the given location.
+
For creating valid wml table in lua it is usully easier to use ''T = helper.set_wml_tag_metatable {}'' asuming you did that you can create the above wml document with
 +
<syntaxhighlight lang=lua>
 +
{
 +
    foo = 42,
 +
    T.bar {
 +
        v = 1,
 +
        w = 1,
 +
    },
 +
    T.foo {
 +
        x = false,
 +
    },
 +
    T.bar {
 +
        y = "foo",
 +
    },
 +
    T.foobar {
 +
        z = 5,
 +
        T.barfoo {
 +
        },
 +
    },
 +
}
 +
</syntaxhighlight>
  
local is_grassland = wesnoth.get_terrain(12, 15) == "Gg"
+
Consider using the [[LuaAPI/wml#wml.get_child|wml.get_child]] and [[LuaAPI/wml#wml.child_range|wml.child_range]] helper functions to ease the access to subtags.
  
==== set_terrain ====
+
{{DevFeature1.13|5}} As a convenience, attributes with array values (tables with only integer keys) are concatenated into a string when converting a Lua table into WML. For example, the following Lua code:
  
Modifies the terrain at the given location.
+
<syntaxhighlight lang=lua>
 +
{
 +
    x = {1, 2, 3, 4},
 +
    y = {7, 8, 9, 10}
 +
}
 +
</syntaxhighlight>
  
function create_village(x, y)
+
produces the following WML table:
    wesnoth.set_terrain(x, y, "Gg^Vh")
 
end
 
  
==== get_terrain_info ====
+
<syntaxhighlight lang=wml>
 +
[dummy]
 +
    x=1,2,3,4
 +
    y=7,8,9,10
 +
[/dummy]
 +
</syntaxhighlight>
  
Returns the terrain details for the given terrain code.
+
Functions registered in [[LuaWML:Events#wesnoth.wml_actions|wesnoth.wml_actions]] and other similar tables that provide hooks that the engine calls will receive their data either in lua tables encoding a WML object or as a [[LuaAPI/wml#wml.tovconfig|WML vconfig userdata]], which has the same structure but is read-only. Accessing fields or children on a vconfig performs variable substitution on the fly. Its '''__parsed''' and '''__literal''' fields provide translations to plain, writable tables. '''__literal''' returns the original text of the data (including dollar symbols in attributes and '''[insert_tag]''' children), while '''__parsed''' performs a full variable substitution.
  
local is_keep = wesnoth.get_terrain_info(wesnoth.get_terrain(12, 15)).keep
+
For instance, if you cannot stand any longer the fact that '''first_time_only''' is set to yes by default for the '''[event]''' tag, you can redefine it. But we have to be careful not to cause variable substitution, since the engine would perform a second variable substitution afterwards.
  
Terrain info is a plain table with the following fields:
+
<syntaxhighlight lang=lua>
* '''id''': string
+
local old_event_handler = wesnoth.wml_actions.event
* '''name''', '''description''': translatable strings
+
function wesnoth.wml_actions.event(cfg)
* '''castle''', '''keep''', '''village''': booleans
+
    -- Get the plain text from the user.
* '''healing''': integer
+
    local new_cfg = helper.literal(cfg)
 +
    -- The expression below is equivalent to cfg.__parsed.first_time_only,
 +
    -- only faster. It is needed, since the first_time_only attribute may
 +
    -- reference variables.
 +
    local first = cfg.first_time_only
 +
    -- Modify the default behavior of first_time_only.
 +
    if first == nil then first = false end
 +
    new_cfg.first_time_only = first
 +
    -- Call the engine handler.
 +
    old_event_handler(new_cfg)
 +
end
 +
</syntaxhighlight>
  
==== get_village_owner ====
+
(Note: The above example will only affect nested events. Toplevel events will still default to ''first_time_only=yes''.)
 +
(Note2: You should not do that since it will break other addons that rely on the first_time_only=no default value.)
 +
<!-- This should probably be replaced with a better example. -->
  
Returns the side that owns the village at the given location.
+
'''pairs''' and '''ipairs''' also work on vconfig objects (contrary to the above statement). However, '''pairs''' works a little differently than on plain configs (tables) - it returns only string keys (attributes in WML terms) and not integer keys (tags in WML terms).
  
local owned_by_side_1 = wesnoth.get_village_owner(12, 15) == 1
+
Another approach for handling userdata and tables in the same way, would be to convert the former into the latter beforehand. The [[LuaAPI/wml#wml.parsed|wml.parsed]] and [[LuaAPI/wml#wml.literal|wml.literal]] helpers take care of this for you.
  
==== set_village_owner ====
+
The vconfig userdata provides two other special fields: '''__shallow_parsed''' and '''__shallow_literal'''. They return a table corresponding to the WML userdata with variable substitution performed on the attributes (or not). [insert_tag] tags have also been parsed, so the number of children is faithful. But contrarily to '''__parsed''' and '''__literal''', the process is not recursive: all the children are still WML userdata and variable substitution can still happen for them. These shallow translators are meant as optimized versions of the deep ones, when only the toplevel attributes need to be writable.
  
Gives ownership of the village at the given location to the given side (or remove ownership if none).
+
== Skeleton of a lua tag ==
  
wesnoth.set_village_owner(12, 15, 1)
+
The following [lua] tag is a skeleton for a prelude enabling Lua in your WML events. It creates a table ''H'' containing the functions from helper.lua . It sets up a table ''T'' so be used for easier creation of valid WML tables. It also sets up a table ''V'' so that any access to it is redirected to the persistent WML storage. Finally, it loads a textdomain to be accessed through the ''_'' variable.
  
==== get_map_size ====
+
<syntaxhighlight lang='wml'>
 +
[scenario]
 +
    [lua]
 +
        code = <<
 +
            H = wesnoth.require "lua/helper.lua"
 +
            T = wml.tag
 +
            V = wml.variables
 +
            local _ = wesnoth.textdomain "my-campaign"
  
Returns the width and the height of the map.
+
            -- Define your global constants here.
 +
            -- ...
  
local w,h = wesnoth.get_map_size()
 
  
== Encoding WML objects into Lua tables ==
+
            -- Define your global functions here.
 +
            -- ...
 +
        >>
 +
    [/lua]
 +
    ...
 +
[/scenario]
 +
</syntaxhighlight>
  
Function [[#fire|wesnoth.fire]] expects a table representing a WML object as its second argument (if needed). Function [[#set_variable|wesnoth.set_variable]] allows to modify whole WML objects, again by passing it a table. Function [[#get_variable|wesnoth.get_variable]] transforms a WML object into a table, if its second argument is not set to ''true''. All these tables have the same format.
+
It may be worth putting the whole Lua script above inside a separate file and having the [lua] tag load it:
  
Scalar fields are transformed into WML attributes. For instance, the following Lua table
+
<syntaxhighlight lang='wml'>
 +
[scenario]
 +
    [lua]
 +
        code = << wesnoth.dofile "~add-ons/Whatever/file.lua" >>
 +
    [/lua]
 +
    ...
 +
[/scenario]
 +
</syntaxhighlight>
  
{
+
== Remarks on Random Numbers ==
    a_bool = true,
 
    an_int = 42,
 
    a_float = 1.25,
 
    a_string = "scout",
 
    a_translation = _ "Hello World!"
 
}
 
  
is equivalent to the content of the following WML object
+
The math.random function is not safe for replays and multiplayer games, since the random values will be different each time and on all the clients. Instead, the Lua code should use the [[LuaWML:Misc#wesnoth.random|wesnoth.random]] function to synchronize random values. It has the same interface as math.random but is multiplayer-safe.
  
[dummy]
+
Also available is [[LuaWML:Misc#helper.rand|helper.rand()]], which takes the same argument in the same format as [[InternalActionsWML#.5Bset_variable.5D|[set_variable]]] rand=.
    a_bool = "yes"
 
    an_int = "42"
 
    a_float = "1.25"
 
    a_string = "scout"
 
    a_translation = _ "Hello World!"
 
[/dummy]
 
  
WML child objects are not stored as Lua named fields, since several of them can have the same tag. Moreover, their tags can conflict with the attribute keys. So child objects are stored as pairs string + table in the unnamed fields in definition order. For instance, the following Lua table
+
<syntaxhighlight lang='lua'>
 +
local random_variable = helper.rand("1,2,3")
 +
</syntaxhighlight>
  
{
+
== Random Lua table iteration ==
    foo = 42,
 
    { "bar", { v = 1, w = 2 } },
 
    { "foo", { x = false } },
 
    { "bar", { y = "foo" } },
 
    { "foobar", { { "barfoo", {} } } }
 
}
 
  
is equivalent to the content of the following WML object
+
Table iteration order ('''pairs''') is not strictly defined in Lua. If your code depends on the order of iteration, different clients may have different data in a multiplayer game. For example:
  
[dummy]
+
<syntaxhighlight lang='lua'>
    foo = 42
+
  local table = { ["Mage"] = true, ["Wose"] = true }
    [bar]
+
  local concat = ""
        v = 1
+
  local bad_usage = next(table) -- wrong, leads to OOS
        w = 2
+
  for k, _ in pairs(table) do -- wrong, leads to OOS
    [/bar]
+
    concat = concat .. k
    [foo]
+
  end
        x = no
+
</syntaxhighlight>
    [/foo]
 
    [bar]
 
        y = foo
 
    [bar]
 
    [foobar]
 
        [barfoo]
 
        [/barfoo]
 
    [/foobar]
 
[/dummy]
 
  
== Helper functions ==
+
To avoid the problem, sort the table keys before iterating. Or alternatively, use Lua "arrays" and the '''ipairs''' function, which have a strictly defined order and never lead to OOS. Example of correct code:
  
The following functions are provided by the '''lua/helper.lua''' library. They are stored inside a table that is returned when loading the file by [[#dofile|wesnoth.dofile]].
+
<syntaxhighlight lang='lua'>
 +
  local array = { "Mage", "Wose" }
 +
  local good_usage = table[1] -- correct
 +
  local concat = ""
 +
  for _, v in ipairs(array) do -- correct
 +
    concat = concat .. v
 +
  end
 +
</syntaxhighlight>
  
helper = wesnoth.dofile "lua/helper.lua"
+
[[Category: Lua Reference|*]]
 
+
[[Category: WML Reference]]
==== set_wml_action_metatable ====
 
 
 
Sets the metable of a table so that it can be used to fire WML actions. Returns the table. The fields of the table are then simple wrappers around a call to [[#fire|wesnoth.fire]].
 
 
 
W = helper.set_wml_action_metatable {}
 
W.message { speaker = "narrator", message = "?" }
 
 
 
==== set_wml_var_metatable ====
 
 
 
Sets the metable of a table so that it can be used to access WML variables. Returns the table. The fields of the tables are then proxies to the WML objects with the same names; reading/writing to them will directly access the WML variables.
 
 
 
helper.set_wml_var_metatable(_G)
 
my_persistent_variable = 42
 
 
 
==== modify_unit ====
 
 
 
Modifies all the units satisfying the given filter (argument 1) with some WML attributes/objects (argument 2). This is a Lua implementation of the [http://www.wesnoth.org/macro-reference.xhtml MODIFY_UNIT] macro.
 
 
 
helper.modify_unit({ id="Delfador" }, { moves=0 })
 
 
 
==== move_unit_fake ====
 
 
 
Fakes the move of a unit satisfying the given filter (argument 1) to the given position (argument 2). This is a Lua implementation of the [http://www.wesnoth.org/macro-reference.xhtml MOVE_UNIT] macro.
 
 
 
helper.move_unit_fake({ id="Delfador" }, 14, 8)
 
 
 
== Skeleton of a preload event ==
 
 
 
The following event is a skeleton for a prelude enabling Lua in your WML events. It creates a table ''H'' containing the functions from helper.lua and a table ''W'' that serves as a proxy for firing WML actions. It also sets up the global environment so that any access to an undefined global variable is redirected to the persistent WML storage.
 
 
 
[event]
 
    name=preload
 
    first_time_only=no
 
    [lua]
 
        code = <<
 
            H = wesnoth.dofile("lua/helper.lua")
 
            W = H.set_wml_action_metatable({})
 
            _ = wesnoth.textdomain "my-campaign"
 
 
            -- Define your global constants here.
 
            -- ...
 
 
            H.set_wml_var_metatable(_G)
 
 
            -- Define your global functions here.
 
            -- ...
 
        >>
 
    [/lua]
 
[/event]
 

Revision as of 03:15, 19 November 2019

[edit]WML Tags

A:

abilities, about, add_ai_behavior, advance, advanced_preference, advancefrom, advancement, advances, affect_adjacent, ai, allied_with, allow_end_turn, allow_extra_recruit, allow_recruit, allow_undo, and, animate, animate_unit, animation, aspect, attack, attack_anim, attacks, avoid;

B:

base_unit, berserk, binary_path, break, brush;

C:

campaign, cancel_action, candidate_action, capture_village, case, chance_to_hit, change_theme, chat, choose, clear_global_variable, clear_menu_item, clear_variable, color_adjust, color_range, command (action, replay), continue, criteria;

D:

damage, death, deaths, default, defend, defends, defense, delay, deprecated_message, destination, difficulty, disable, disallow_end_turn, disallow_extra_recruit, disallow_recruit, do, do_command, drains, draw_weapon_anim;

E:

editor_group, editor_music, editor_times, effect, else (action, animation), elseif, endlevel, end_turn (action, replay), enemy_of, engine, entry, era, event, extra_anim;

F:

facet, facing, fake_unit, false, feedback, female, filter (concept, event), filter_adjacent, filter_adjacent_location, filter_attack, filter_attacker, filter_base_value, filter_condition, filter_defender, filter_enemy, filter_location, filter_opponent, filter_own, filter_owner, filter_radius, filter_recall, filter_second, filter_second_attack, filter_self, filter_side, filter_vision, filter_weapon, filter_wml, find_path, fire_event, firststrike, floating_text, for, foreach, frame, full_heal;

G:

game_config, get_global_variable, goal, gold, gold_carryover;

H:

harm_unit, has_ally, has_attack, has_unit, have_location, have_unit, heal_on_hit, heal_unit, healed_anim, healing_anim, heals, hide_help, hide_unit, hides;

I:

idle_anim, if (action, animation), illuminates, image, init_side, insert_tag, inspect, item, item_group;

J:

jamming_costs, join;

K:

kill, killed;

L:

label, language, leader, leader_goal, leadership, leading_anim, levelin_anim, levelout_anim, lift_fog, limit, literal, load_resource, locale, lock_view, lua;

M:

male, menu_item, message, micro_ai, missile_frame, modification, modifications, modify_ai, modify_side, modify_turns, modify_unit, modify_unit_type, move, move_unit, move_unit_fake, move_units_fake, movement_anim, movement costs, movetype, multiplayer, multiplayer_side, music;

N:

not, note;

O:

object, objective, objectives, on_undo, open_help, option, options, or;

P:

part, petrifies, petrify, place_shroud, plague, poison, portrait, post_movement_anim, pre_movement_anim, primary_attack, primary_unit, print, put_to_recall_list;

R:

race, random_placement, recall (action, replay), recalls, recruit, recruit_anim, recruiting_anim, recruits, redraw, regenerate, remove_event, remove_item, remove_object, remove_shroud, remove_sound_source, remove_time_area, remove_unit_overlay, repeat, replace_map, replace_schedule, replay, replay_start, reset_fog, resistance (ability, unit), resistance_defaults, resource, return, role, rule;

S:

save, scenario, scroll, scroll_to, scroll_to_unit, secondary_attack, secondary_unit, section, select_unit, sequence, set_extra_recruit, set_global_variable, set_menu_item, set_recruit, set_specials, set_variable, set_variables, sheath_weapon_anim, show_if (message, set_menu_item), show_objectives, side, skirmisher, slow, snapshot, sound, sound_source, source (replay, teleport), special_note, specials, split, stage, standing_anim, statistics, status, store_gold, store_items, store_locations, store_map_dimensions, store_reachable_locations, store_relative_direction, store_side, store_starting_location, store_time_of_day, store_turns, store_unit, store_unit_defense, store_unit_type, store_unit_type_ids, store_villages, story, swarm, switch, sync_variable;

T:

target, team, teleport (ability, action), teleport_anim, terrain, terrain_defaults, terrain_graphics, terrain_mask, terrain_type, test, test_condition, text_input, textdomain, theme, then, tile, time, time_area, topic, toplevel, trait, transform_unit, traveler, true, tunnel, tutorial;

U:

unhide_unit, unit, unit_overlay, unit_type, unit_worth, units, unlock_view, unpetrify, unstore_unit, unsynced;

V:

value, variable, variables, variant, variation, victory_anim, village, vision_costs, volume;

W:

while, wml_message, wml_schema;

Z:

zoom;

The [lua] tag

This tag is a part of ActionWML, thus can be used inside [event] and at other places where ActionWML can be used. It makes it possible to write actions with the Lua 5.3 language.

It is also possible to put this tag inside a [scenario] ScenarioWML, those tags will be executed immediately when the lua engine loads which is even before the scenario preload event is fired.

[lua] is now also allowed in [era], [modification] and [resource], those [lua] tags are then copied into the [scenario]/[multiplayer] when it is played just like [event]s inside [era] or [modification]

The tag supports only the code key, which is a string containing the Lua scripts. Since Lua makes usage of the quotes and the { and } symbols, it is certainly wise to enclose the script between stronger quotes, as they prevent the preprocessor from performing macro expansion and tokenization.

 [lua]
     code = << wesnoth.message "Hello World!" >>
 [/lua]

The Lua kernel can also be accessed from the command mode:

:lua local u = wesnoth.get_units({ id = "Konrad" })[1]; u.moves = 5

The [args] sub-tag can be used to pass a WML object to the script via its variadic local variable "...".

 [lua]
     code = << local t = ...; wesnoth.message(tostring(t.text)) >>
     [args]
         text = _ "Hello world!"
     [/args]
 [/lua]

Global environment

All the Lua scripts of a scenario share the same global environment (aka Lua state). Unlike other parts of the configurable gamestate the Lua state is not stored in savefiles, thus [lua] tags in [scenario] are executed not only before the scenario starts but also each time the game is loaded. Funtions defined in [lua] tags in [scenario] can be used in all [lua] tags in [event]s.

 [scenario]
     [lua]
         code = <<
             function narrator(t)
                 -- Behave like the [message] tag.
                 wesnoth.fire("message",
                   { speaker = "narrator", message = t.sentence })
             end
         >>
     [/lua]
     [event]
         name = turn 1
         [lua]
             code = << narrator(...) >>
             [args]
                 sentence = _ "Hello world!"
             [/args]
         [/lua]
         [lua]
             code = << narrator(...) >>
             [args]
                 sentence = _ "How are you today?"
             [/args]
         [/lua]
     [/event]
     ...
 [/scenario]

In the example above, the redundant structure could be hidden behind macros. But it may be better to simply define a new WML tag.

 [scenario]
     [lua]
         code = <<
             -- The function is now placed in the wesnoth.wml_actions table
             -- The tag is [narrator], same as the function name
             function wesnoth.wml_actions.narrator(t)
                 -- Behave like the [message] tag.
                 wesnoth.fire("message",
                   { speaker = "narrator", message = t.sentence })
             end
         >>
     [/lua]
 
     [event]
         name = turn 1
         [narrator]
             sentence = _ "Hello world!"
         [/narrator]
         [narrator]
             sentence = _ "How are you today?"
         [/narrator]
     [/event]
 [/scenario]

The global environment is not preserved over save/load cycles. Therefore, storing values in the global environment is generally a bad idea. The only time assigning global variables (including function definitions) makes sense is in a [lua] block directly in [scenario] or during a preload event, as this event is always run. Therefore, helper functions defined at that time will be available to all the later scripts.

The global environment initially contains the following modules: basic (no name), string, table, and math. A wesnoth module is also available, it provides access to the C++ engine. Additionally, the functions clock, date, time and difftime from the os library (keep in mind that they aren't multiplayer- and replay-safe), as well as traceback from the debug library are also available.

At the start of a script, the variadic local variable ... (three dots) is a proxy table representing WML data. This table is the content of the [args] sub-tag of the [lua] tag, if any.

Examples

The following WML event is taken from Wesnoth' tutorial. It will serve as an example to present how Lua scripts are embedded into Wesnoth. The event is fired whenever a unit from side 1 (that is, the hero controlled by the user) moves to a tile that is not the one set in the WML variable target_hex.

 # General catch for them moving to the wrong place.
 [event]
     name=moveto
     first_time_only=no
     [allow_undo][/allow_undo]
     [filter]
         side=1
     [/filter]
 
     [if]
         [variable]
             name=target_hex.is_set
             equals=yes
         [/variable]
         [then]
             [if]
                 [variable]
                     name=x1
                     equals=$target_hex.x
                 [/variable]
                 [variable]
                     name=y1
                     equals=$target_hex.y
                 [/variable]
                 [then]
                 [/then]
                 [else]
                     [redraw][/redraw]
                     [message]
                         speaker=narrator
                         message=_ "*Oops!
 You moved to the wrong place! After this message, you can press 'u' to undo, then try again." +
                         _ "
 *Left click or press spacebar to continue..."
                     [/message]
                 [/else]
             [/if]
         [/then]
     [/if]
 [/event]

A Lua script that performs the same action is presented below.

 [event]
     name=moveto
     first_time_only=no
     [allow_undo][/allow_undo]
     [filter]
         side=1
     [/filter]
 
     [lua]
         code = <<

             local event_data = wesnoth.current.event_context
             if wml.variables["target_hex.is_set"] and
                (event_data.x1 ~= wml.variables["target_hex.x"] or event_data.y1 ~= wml.variables["target_hex.y"])
             then
                 W.redraw()
                 narrator_says(_ "*Oops!\nYou moved to the wrong place! After this message, you can press 'u' to undo, then try again.")
             end
         >>
     [/lua]
 [/event]

Here is a more detailed explanation of the Lua code. Its first line

local event_data = wesnoth.current.event_context

puts the event data into the event_data local variable. Since it is a moveto event, the event_data table contains the destination of the unit in the x1 and y1 fields.

The next two lines then test

if wml.variables["target_hex.is_set"] and
    (event_data.x1 ~= wml.variables["target_hex.x"] or event_data.y1 ~= wml.variables["target_hex.y"])

whether the variable wml.variables["target_hex"] matches the event parameters. Since wml.variables is not a local variable, it is taken from the global environment. Usually, variables from the global environment are not persistent but the wesnoth engine maps the variable wml.variables to the storage of WML variables.

Without using wml.variables, the conditional would have been written

if wesnoth.get_variable("target_hex.is_set") and
    (event_data.x1 ~= wesnoth.get_variable("target_hex.x") or event_data.y1 ~= wesnoth.get_variable("target_hex.y")

The body of the conditional then performs the [redraw] action.

W.redraw()

This short syntax is made possible by a line of the prelude that makes W a proxy for performing WML actions.

 [scenario]
     [lua]
         code = <<
             H = wesnoth.require "lua/helper.lua"
             W = H.set_wml_action_metatable {}
         >>
     [/lua]
     ...
 [/scenario]

Without this shortcut, the first statement would have been written

wesnoth.fire("redraw")

or

wesnoth.wml_actions.redraw {}

Finally the script displays a message by

narrator_says(_ "*Oops!\nYou moved to the wrong place! After this message, you can press 'u' to undo, then try again.")

The narrator_says function is defined in the prelude too, since the construct behind it occurs several times in the tutorial. In plain WML, macros would have been used instead. The definition of the function is

function narrator_says(m)
    W.message { speaker="narrator",
                message = m .. _ "\n*Left click or press spacebar to continue..." }
end

The function fires a [message] action and passes a WML object containing the usual two fields to it. The second field is initialized by concatenating the function argument with another string. Both strings are prefixed by the _ symbol to mark them as translatable. (Note that _ is just a unary function, not a keyword.) Again, this is made possible by a specific line of the prelude:

_ = wesnoth.textdomain "wesnoth-tutorial"

A longer translation of the tutorial is available at [1].

Interface to the engine and helper functions



Functionalities of the game engine are available through the functions contained in the wesnoth global table. Some of these functions return proxy tables. Writes to fields marked "read-only" are ignored. The __cfg fields return plain tables; in particular, writes do not modify the original object, and reads return the values from the time the dump was performed.

Some helper functions are provided by the lua/helper.lua library. They are stored inside a table that is returned when loading the library with wesnoth.require.

helper = wesnoth.require "lua/helper.lua"

WML variables

Events and WML actions

User interface

Map and terrains

Time of day schedule

Units

Sides

Pathfinder

Lua files

Location sets

Miscellaneous

Functions that should not be used

If you take a look at Wesnoth's own lua files, you might find some undocumented functions use in the implementations of WML tags. Where possible, you should avoid using them, as they might be changed or removed with no compatibility for further releases. Instead, use the corresponding wml tags (in lua you can use wesnoth.wml_actions.tag_name(cfg), though keep in mind that this won't substitute variables in the config).

If uncertain whether an undocumented feature is safe to use, ask on the forums, Discord, or IRC. It may turn out that someone simply forgot to add it to the wiki.

  • wesnoth.redraw
  • wesnoth.set_menu_item
  • wesnoth.clear_menu_item
  • wesnoth.modify_ai
  • wesnoth.print
  • wesnoth.end_level

Encoding WML objects into Lua tables

Function wesnoth.fire expects a table representing a WML object as its second argument (if needed). Function wesnoth.set_variable allows to modify whole WML objects, again by passing it a table. Function wesnoth.get_variable transforms a WML object into a table, if its second argument is not set to true. All these tables have the same format.

Scalar fields are transformed into WML attributes. For instance, the following Lua table

{
    a_bool = true,
    an_int = 42,
    a_float = 1.25,
    a_string = "scout",
    a_translation = _ "Hello World!"
}

is equivalent to the content of the following WML object

[dummy]
    a_bool = "yes"
    an_int = 42
    a_float = 1.25
    a_string = "scout"
    a_translation = _ "Hello World!"
[/dummy]

WML child objects are not stored as Lua named fields, since several of them can have the same tag. Moreover, their tags can conflict with the attribute keys. So child objects are stored as pairs string + table in the unnamed fields in definition order. This means that for every subtag appearing in the wml code there is an additional table "layer" in the corresponding WML table of the form {[1] = "tag_name", [2] = {}} which is equivalent to {"tag_name", {}}. [1] etc are the unnamed fields (as opposed to wml attributes). The table under [2] in this subtable then holds the wml attributes from inside the wml subtag. So every subtag other than the toplevel tag corresponds to two nested tables each. For instance, the following Lua table

{
    foo = 42,
    { "bar", { v = 1, w = 2 } },
    { "foo", { x = false } },
    { "bar", { y = "foo" } },
    { "foobar", { z = 5, { "barfoo", {} } } }
}

is equivalent to the content of the following WML object

[dummy]
    foo = 42
    [bar]
        v = 1
        w = 2
    [/bar]
    [foo]
        x = no
    [/foo]
    [bar]
        y = foo
    [bar]
    [foobar]
        z = 5
        [barfoo]
        [/barfoo]
    [/foobar]
[/dummy]

Both tables above are also equivalent to this WML table, where all unnamed fields are displayed:

{
    foo = 42,
    [1] = { [1] = "bar", [2] = { v = 1, w = 2 } },
    [2] = { [1] = "foo", [2] = { x = false } },
    [3] = { [1] = "bar", [2] = { y = "foo" } },
    [4] = { [1] = "foobar", [2] = { z = 5, [1] = { [1] = "barfoo", [2] = {} } } }
}

So assuming cfg contains the above WML object, the following accesses are possible:

a_int = cfg.foo        -- "dummy.foo", 42
a_string = cfg[3][2].y -- "dummy.bar[1].y", "foo"
a_table = cfg[4][2]    -- "dummy.foobar", { z = 5, { "barfoo", {} } }

For creating valid wml table in lua it is usully easier to use T = helper.set_wml_tag_metatable {} asuming you did that you can create the above wml document with

{
    foo = 42,
    T.bar {
         v = 1,
         w = 1,
    },
    T.foo {
        x = false,
    },
    T.bar {
         y = "foo",
    },
    T.foobar {
         z = 5,
         T.barfoo {
         },
    },
}

Consider using the wml.get_child and wml.child_range helper functions to ease the access to subtags.

(Version 1.13.5 and later only) As a convenience, attributes with array values (tables with only integer keys) are concatenated into a string when converting a Lua table into WML. For example, the following Lua code:

{
    x = {1, 2, 3, 4},
    y = {7, 8, 9, 10}
}

produces the following WML table:

[dummy]
    x=1,2,3,4
    y=7,8,9,10
[/dummy]

Functions registered in wesnoth.wml_actions and other similar tables that provide hooks that the engine calls will receive their data either in lua tables encoding a WML object or as a WML vconfig userdata, which has the same structure but is read-only. Accessing fields or children on a vconfig performs variable substitution on the fly. Its __parsed and __literal fields provide translations to plain, writable tables. __literal returns the original text of the data (including dollar symbols in attributes and [insert_tag] children), while __parsed performs a full variable substitution.

For instance, if you cannot stand any longer the fact that first_time_only is set to yes by default for the [event] tag, you can redefine it. But we have to be careful not to cause variable substitution, since the engine would perform a second variable substitution afterwards.

local old_event_handler = wesnoth.wml_actions.event
function wesnoth.wml_actions.event(cfg)
    -- Get the plain text from the user.
    local new_cfg = helper.literal(cfg)
    -- The expression below is equivalent to cfg.__parsed.first_time_only,
    -- only faster. It is needed, since the first_time_only attribute may
    -- reference variables.
    local first = cfg.first_time_only
    -- Modify the default behavior of first_time_only.
    if first == nil then first = false end
    new_cfg.first_time_only = first
    -- Call the engine handler.
    old_event_handler(new_cfg)
end

(Note: The above example will only affect nested events. Toplevel events will still default to first_time_only=yes.) (Note2: You should not do that since it will break other addons that rely on the first_time_only=no default value.)

pairs and ipairs also work on vconfig objects (contrary to the above statement). However, pairs works a little differently than on plain configs (tables) - it returns only string keys (attributes in WML terms) and not integer keys (tags in WML terms).

Another approach for handling userdata and tables in the same way, would be to convert the former into the latter beforehand. The wml.parsed and wml.literal helpers take care of this for you.

The vconfig userdata provides two other special fields: __shallow_parsed and __shallow_literal. They return a table corresponding to the WML userdata with variable substitution performed on the attributes (or not). [insert_tag] tags have also been parsed, so the number of children is faithful. But contrarily to __parsed and __literal, the process is not recursive: all the children are still WML userdata and variable substitution can still happen for them. These shallow translators are meant as optimized versions of the deep ones, when only the toplevel attributes need to be writable.

Skeleton of a lua tag

The following [lua] tag is a skeleton for a prelude enabling Lua in your WML events. It creates a table H containing the functions from helper.lua . It sets up a table T so be used for easier creation of valid WML tables. It also sets up a table V so that any access to it is redirected to the persistent WML storage. Finally, it loads a textdomain to be accessed through the _ variable.

[scenario]
    [lua]
        code = <<
            H = wesnoth.require "lua/helper.lua"
            T = wml.tag
            V = wml.variables
            local _ = wesnoth.textdomain "my-campaign"

            -- Define your global constants here.
            -- ...


            -- Define your global functions here.
            -- ...
        >>
    [/lua]
    ... 
[/scenario]

It may be worth putting the whole Lua script above inside a separate file and having the [lua] tag load it:

[scenario]
    [lua]
        code = << wesnoth.dofile "~add-ons/Whatever/file.lua" >>
    [/lua]
    ...
[/scenario]

Remarks on Random Numbers

The math.random function is not safe for replays and multiplayer games, since the random values will be different each time and on all the clients. Instead, the Lua code should use the wesnoth.random function to synchronize random values. It has the same interface as math.random but is multiplayer-safe.

Also available is helper.rand(), which takes the same argument in the same format as [set_variable] rand=.

 local random_variable = helper.rand("1,2,3")

Random Lua table iteration

Table iteration order (pairs) is not strictly defined in Lua. If your code depends on the order of iteration, different clients may have different data in a multiplayer game. For example:

  local table = { ["Mage"] = true, ["Wose"] = true }
  local concat = ""
  local bad_usage = next(table) -- wrong, leads to OOS
  for k, _ in pairs(table) do -- wrong, leads to OOS
    concat = concat .. k
  end

To avoid the problem, sort the table keys before iterating. Or alternatively, use Lua "arrays" and the ipairs function, which have a strictly defined order and never lead to OOS. Example of correct code:

  local array = { "Mage", "Wose" }
  local good_usage = table[1] -- correct
  local concat = ""
  for _, v in ipairs(array) do -- correct
    concat = concat .. v
  end