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 ==
  
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 5.2] language.
+
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.
  
 
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.
 
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.
  
{{DevFeature1.13|0}}
+
[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]
[lua] is now also allowed in [era] and [modification] 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.
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== Global environment ==
 
== Global environment ==
  
All the Lua scripts of a scenario share the same global environment (aka Lua state). For instance, a function defined in an event can be used in all the events that happen after it.
+
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'>
 
<syntaxhighlight lang='wml'>
  [event]
+
  [scenario]
    name = preload
 
    first_time_only = no
 
 
     [lua]
 
     [lua]
 
         code = <<
 
         code = <<
Line 50: Line 47:
 
         >>
 
         >>
 
     [/lua]
 
     [/lua]
  [/event]
+
    [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]
 
   
 
   
[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]
 
 
</syntaxhighlight>
 
</syntaxhighlight>
  
Line 72: Line 70:
  
 
<syntaxhighlight lang='wml'>
 
<syntaxhighlight lang='wml'>
  [event]
+
  [scenario]
    name = preload
 
    first_time_only = no
 
 
     [lua]
 
     [lua]
 
         code = <<
 
         code = <<
Line 86: Line 82:
 
         >>
 
         >>
 
     [/lua]
 
     [/lua]
[/event]
 
 
   
 
   
[event]
+
    [event]
    name = turn 1
+
        name = turn 1
    [narrator]
+
        [narrator]
        sentence = _ "Hello world!"
+
            sentence = _ "Hello world!"
    [/narrator]
+
        [/narrator]
    [narrator]
+
        [narrator]
        sentence = _ "How are you today?"
+
            sentence = _ "How are you today?"
     [/narrator]
+
        [/narrator]
  [/event]
+
     [/event]
 +
  [/scenario]
 
</syntaxhighlight>
 
</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 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/5.1/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, 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/5.1/manual.html#5.8 os] library (keep in mind that they aren't multiplayer- and replay-safe), as well as traceback from the [http://www.lua.org/manual/5.1/manual.html#5.9 debug] library are also available.
+
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.
 
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.
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     [lua]
 
     [lua]
 
         code = <<
 
         code = <<
 +
 
             local event_data = wesnoth.current.event_context
 
             local event_data = wesnoth.current.event_context
             if V.target_hex.is_set and
+
             if wml.variables["target_hex.is_set"] and
                 (event_data.x1 ~= V.target_hex.x or event_data.y1 ~= V.target_hex.y)
+
                 (event_data.x1 ~= wml.variables["target_hex.x"] or event_data.y1 ~= wml.variables["target_hex.y"])
 
             then
 
             then
 
                 W.redraw()
 
                 W.redraw()
Line 188: Line 185:
  
 
<syntaxhighlight lang='lua'>
 
<syntaxhighlight lang='lua'>
if V.target_hex.is_set and
+
if wml.variables["target_hex.is_set"] and
     (event_data.x1 ~= V.target_hex.x or event_data.y1 ~= V.target_hex.y)
+
     (event_data.x1 ~= wml.variables["target_hex.x"] or event_data.y1 ~= wml.variables["target_hex.y"])
 
</syntaxhighlight>
 
</syntaxhighlight>
  
whether the variable ''V.target_hex'' matches the event parameters. Since ''V'' is not a local variable, it is taken from the global environment. Usually, variables from the global environment are not persistent (they get lost on reloading), so it shouldn't be used to store data. In order to have an easy way to access the usual persistent Wml variables, the global variable ''V''  was mapped 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.
 
 
<syntaxhighlight lang='wml'>
 
[event]
 
    name=preload
 
    first_time_only=no
 
    [lua]
 
        code = <<
 
            H = wesnoth.require "lua/helper.lua"
 
            -- skipping some other initializations
 
            -- ...
 
            V = H.set_wml_var_metatable {}
 
        >>
 
    [/lua]
 
[/event]
 
</syntaxhighlight>
 
  
Without a prelude redirecting ''V'', the conditional would have been written
+
Without using wml.variables, the conditional would have been written
  
 
<syntaxhighlight lang='lua'>
 
<syntaxhighlight lang='lua'>
Line 222: Line 204:
 
</syntaxhighlight>
 
</syntaxhighlight>
  
Again, this short syntax is made possible by a line of the prelude that makes ''W'' a proxy for performing WML actions.
+
This short syntax is made possible by a line of the prelude that makes ''W'' a proxy for performing WML actions.
  
 
<syntaxhighlight lang='lua'>
 
<syntaxhighlight lang='lua'>
W = H.set_wml_action_metatable {}
+
[scenario]
 +
    [lua]
 +
        code = <<
 +
            H = wesnoth.require "lua/helper.lua"
 +
            W = H.set_wml_action_metatable {}
 +
        >>
 +
    [/lua]
 +
    ...
 +
[/scenario]
 
</syntaxhighlight>
 
</syntaxhighlight>
  
Line 232: Line 222:
 
<syntaxhighlight lang='lua'>
 
<syntaxhighlight lang='lua'>
 
wesnoth.fire("redraw")
 
wesnoth.fire("redraw")
 +
</syntaxhighlight>
 +
or
 +
<syntaxhighlight lang='lua'>
 +
wesnoth.wml_actions.redraw {}
 
</syntaxhighlight>
 
</syntaxhighlight>
  
Line 258: Line 252:
  
 
== Interface to the engine and helper functions ==
 
== Interface to the engine and helper functions ==
 +
 +
<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>
  
 
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.
 
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.
Line 272: Line 268:
 
* [[LuaWML:Variables#wesnoth.set_variable|wesnoth.set_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.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.set_wml_var_metatable|helper.set_wml_var_metatable]]
 
* [[LuaWML:Variables#helper.get_child|helper.get_child]]
 
* [[LuaWML:Variables#helper.get_child|helper.get_child]]
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* [[LuaWML:Events#wesnoth.wml_actions|wesnoth.wml_conditionals]] {{DevFeature1.13|0}}
 
* [[LuaWML:Events#wesnoth.wml_actions|wesnoth.wml_conditionals]] {{DevFeature1.13|0}}
 
* [[LuaWML:Events#wesnoth.game_events|wesnoth.game_events]]
 
* [[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|wesnoth.fire_event]]
 
* [[LuaWML:Events#wesnoth.fire_event_by_id|wesnoth.fire_event_by_id]] {{DevFeature1.13|6}}
 
* [[LuaWML:Events#wesnoth.fire_event_by_id|wesnoth.fire_event_by_id]] {{DevFeature1.13|6}}
Line 300: Line 298:
 
* [[LuaWML:Events#helper.shallow_literal|helper.shallow_literal]]
 
* [[LuaWML:Events#helper.shallow_literal|helper.shallow_literal]]
 
* [[LuaWML:Events#helper.shallow_parsed|helper.shallow_parsed]]
 
* [[LuaWML:Events#helper.shallow_parsed|helper.shallow_parsed]]
 +
* [[LuaWML:Events#on_event.lua|on_event.on_event]] {{DevFeature1.13|6}}
  
 
=== User interface ===
 
=== User interface ===
 
+
* [[LuaWML:Display#wesnoth.get_viewing_side|wesnoth.get_viewing_side]] {{DevFeature1.13|?}}
 
* [[LuaWML:Display#wesnoth.message|wesnoth.message]]
 
* [[LuaWML:Display#wesnoth.message|wesnoth.message]]
 
* [[LuaWML:Display#wesnoth.clear_messages|wesnoth.clear_messages]]
 
* [[LuaWML:Display#wesnoth.clear_messages|wesnoth.clear_messages]]
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* [[LuaWML:Display#wesnoth.show_popup_dialog|wesnoth.show_popup_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_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.show_dialog|wesnoth.show_dialog]]
 
* [[LuaWML:Display#wesnoth.set_dialog_value|wesnoth.set_dialog_value]]
 
* [[LuaWML:Display#wesnoth.set_dialog_value|wesnoth.set_dialog_value]]
Line 364: Line 367:
 
* [[LuaWML:Tiles#wesnoth.map.tiles_adjacent|wesnoth.map.tiles_adjacent]] {{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.map.distance_between|wesnoth.map.distance_between]] {{DevFeature1.13|8}}
* [[LuaWML:Tiles#wesnoth.label|wesnoth.map.label]] {{DevFeature1.13|0}}
+
* [[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_image|items.place_image]]
 
* [[LuaWML:Tiles#items.place_halo|items.place_halo]]
 
* [[LuaWML:Tiles#items.place_halo|items.place_halo]]
Line 388: Line 392:
 
* [[LuaWML:Units#wesnoth.extract_unit|wesnoth.extract_unit]]
 
* [[LuaWML:Units#wesnoth.extract_unit|wesnoth.extract_unit]]
 
* [[LuaWML:Units#wesnoth.add_modification|wesnoth.add_modification]]
 
* [[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_resistance|wesnoth.unit_resistance]]
 
* [[LuaWML:Units#wesnoth.unit_defense|wesnoth.unit_defense]]
 
* [[LuaWML:Units#wesnoth.unit_defense|wesnoth.unit_defense]]
Line 397: Line 402:
 
* [[LuaWML:Units#wesnoth.races|wesnoth.races]]
 
* [[LuaWML:Units#wesnoth.races|wesnoth.races]]
 
* [[LuaWML:Units#wesnoth.get_traits|wesnoth.get_traits]]
 
* [[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.simulate_combat|wesnoth.simulate_combat]]
 
* [[LuaWML:Units#wesnoth.transform_unit|wesnoth.transform_unit]]
 
* [[LuaWML:Units#wesnoth.transform_unit|wesnoth.transform_unit]]
Line 420: Line 427:
 
* [[LuaWML:Sides#wesnoth.add_ai_component|wesnoth.add_ai_component]] {{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.change_ai_component|wesnoth.change_ai_component]] {{DevFeature1.13|7}}
* [[LuaWML:Sides#wesnoth.add_ai_component|wesnoth.add_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.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|?}}
  
 
=== Pathfinder ===
 
=== Pathfinder ===
Line 469: Line 478:
 
* [[LuaWML:Misc#wesnoth.current|wesnoth.current]]
 
* [[LuaWML:Misc#wesnoth.current|wesnoth.current]]
 
* [[LuaWML:Misc#wesnoth.synchronize_choice|wesnoth.synchronize_choice]]
 
* [[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.get_image_size|wesnoth.get_image_size]]
 
* [[LuaWML:Misc#wesnoth.compare_versions|wesnoth.compare_versions]]
 
* [[LuaWML:Misc#wesnoth.compare_versions|wesnoth.compare_versions]]
Line 479: Line 490:
 
* [[LuaWML:Misc#wesnoth.name_generator|wesnoth.name_generator]] {{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.set_next_scenario|wesnoth.set_next_scenario]] {{DevFeature1.13|5}}
* [[LuaWML:Misc#helper.set_wml_tag_metatable|helper.set_wml_tag_metatable]]
+
* [[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.modify_unit|helper.modify_unit]]
 
* [[LuaWML:Misc#helper.move_unit_fake|helper.move_unit_fake]]
 
* [[LuaWML:Misc#helper.move_unit_fake|helper.move_unit_fake]]
Line 485: Line 500:
 
* [[LuaWML:Misc#helper.round|helper.round]]
 
* [[LuaWML:Misc#helper.round|helper.round]]
 
* [[LuaWML:Misc#helper.shuffle|helper.shuffle]]
 
* [[LuaWML:Misc#helper.shuffle|helper.shuffle]]
 +
 +
=== 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 <tt>wesnoth.wml_actions.tag_name(cfg)</tt>, 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 ==
 
== Encoding WML objects into Lua tables ==
Line 507: Line 535:
 
[dummy]
 
[dummy]
 
     a_bool = "yes"
 
     a_bool = "yes"
     an_int = "42"
+
     an_int = 42
     a_float = "1.25"
+
     a_float = 1.25
 
     a_string = "scout"
 
     a_string = "scout"
 
     a_translation = _ "Hello World!"
 
     a_translation = _ "Hello World!"
Line 591: Line 619:
 
</syntaxhighlight>
 
</syntaxhighlight>
  
Consider using the [[LuaWML:Variables#helper.get_child|helper.get_child]] and [[LuaWML:Variables#helper.child_range|helper.child_range]] to ease the access to subtags.
+
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.
  
 
{{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:
 
{{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:
Line 611: Line 639:
 
</syntaxhighlight>
 
</syntaxhighlight>
  
Functions registered in [[LuaWML:Events#wesnoth.wml_actions|wesnoth.wml_actions]] receive their data in a userdata object which has the exact same structure as above. It is read-only however. Accessing fields or children performs variable substitution on the fly. Its '''__parsed''' and '''__literal''' fields provide translations to plain tables (therefore writable). '''__literal''' returns the original text of the data (including dollar symbols in attributes and [insert_tag] children), while '''__parsed''' performs a variable substitution.
+
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.
  
 
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.
 
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.
Line 619: Line 647:
 
function wesnoth.wml_actions.event(cfg)
 
function wesnoth.wml_actions.event(cfg)
 
     -- Get the plain text from the user.
 
     -- Get the plain text from the user.
     local new_cfg = cfg.__literal
+
     local new_cfg = helper.literal(cfg)
 
     -- The expression below is equivalent to cfg.__parsed.first_time_only,
 
     -- The expression below is equivalent to cfg.__parsed.first_time_only,
 
     -- only faster. It is needed, since the first_time_only attribute may
 
     -- only faster. It is needed, since the first_time_only attribute may
Line 633: Line 661:
  
 
(Note: The above example will only affect nested events. Toplevel events will still default to ''first_time_only=yes''.)
 
(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. -->
 
<!-- This should probably be replaced with a better example. -->
  
Note that, since the object is a userdata and not a table, '''pairs''' and '''ipairs''' are unfortunately not usable on it. So scripts have to work at a lower level. For instance, the following function returns the first sub-tag with a given name and it works both on WML tables and WML userdata:
+
'''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).
 
 
<syntaxhighlight lang=lua>
 
function get_child(cfg, name)
 
    for i = 1, #cfg do
 
        local v = cfg[i]
 
        if v[1] == name then return v[2] end
 
    end
 
end
 
</syntaxhighlight>
 
  
{{DevFeature1.13|2}} '''pairs''' and '''ipairs''' now 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 [[LuaAPI/wml#wml.parsed|wml.parsed]] and [[LuaAPI/wml#wml.literal|wml.literal]] helpers take care of this for you.
 
 
Another approach for handling userdata and tables in the same way, would be to convert the former into the latter beforehand:
 
 
 
<syntaxhighlight lang=lua>
 
if getmetatable(cfg) == "wml object" then cfg = cfg.__parsed end
 
</syntaxhighlight>
 
  
The WML 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.
+
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 preload event ==
+
== Skeleton of a lua tag ==
  
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 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.
+
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.  
  
 
<syntaxhighlight lang='wml'>
 
<syntaxhighlight lang='wml'>
[event]
+
[scenario]
    name=preload
 
    first_time_only=no
 
 
     [lua]
 
     [lua]
 
         code = <<
 
         code = <<
 
             H = wesnoth.require "lua/helper.lua"
 
             H = wesnoth.require "lua/helper.lua"
            W = H.set_wml_action_metatable {}
+
             T = wml.tag
             T = H.set_wml_tag_metatable {}
+
             V = wml.variables
             V = H.set_wml_var_metatable {}
+
             local _ = wesnoth.textdomain "my-campaign"
             _ = wesnoth.textdomain "my-campaign"
 
  
 
             -- Define your global constants here.
 
             -- Define your global constants here.
Line 680: Line 691:
 
         >>
 
         >>
 
     [/lua]
 
     [/lua]
[/event]
+
    ...
 +
[/scenario]
 
</syntaxhighlight>
 
</syntaxhighlight>
  
It may be worth putting the whole Lua script above inside a separate file and having the ''preload'' event load it:
+
It may be worth putting the whole Lua script above inside a separate file and having the [lua] tag load it:
  
 
<syntaxhighlight lang='wml'>
 
<syntaxhighlight lang='wml'>
[event]
+
[scenario]
    name=preload
 
    first_time_only=no
 
 
     [lua]
 
     [lua]
 
         code = << wesnoth.dofile "~add-ons/Whatever/file.lua" >>
 
         code = << wesnoth.dofile "~add-ons/Whatever/file.lua" >>
 
     [/lua]
 
     [/lua]
[/event]
+
    ...
 +
[/scenario]
 
</syntaxhighlight>
 
</syntaxhighlight>
  
 
== Remarks on Random Numbers ==
 
== 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 [[LuaWML:Misc#helper.rand|helper.rand()]] function to synchronize random values. It takes the same argument in the same format as [[InternalActionsWML#.5Bset_variable.5D|[set_variable]]] rand=.
+
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.
 +
 
 +
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=.
  
 
<syntaxhighlight lang='lua'>
 
<syntaxhighlight lang='lua'>
 
  local random_variable = helper.rand("1,2,3")
 
  local random_variable = helper.rand("1,2,3")
 
</syntaxhighlight>
 
</syntaxhighlight>
 
Also available is [[LuaWML:Misc#wesnoth.random|wesnoth.random]], which has the same interface as math.random but is multiplayer-safe.
 
  
 
== Random Lua table iteration ==
 
== Random Lua table iteration ==
  
Table iteration order is not strictly defined in Lua. If your code depends on the order of iteration, make sure you sort the table keys beforehand and iterate over the sorted array only. Otherwise you'll get OOS, as different clients will have different local views on how to iterate the table.
+
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:
  
 
<syntaxhighlight lang='lua'>
 
<syntaxhighlight lang='lua'>
Line 716: Line 727:
 
     concat = concat .. k
 
     concat = concat .. k
 
   end
 
   end
 +
</syntaxhighlight>
  
 +
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:
 +
 +
<syntaxhighlight lang='lua'>
 
   local array = { "Mage", "Wose" }
 
   local array = { "Mage", "Wose" }
 
   local good_usage = table[1] -- correct
 
   local good_usage = table[1] -- correct
Line 723: Line 738:
 
     concat = concat .. v
 
     concat = concat .. v
 
   end
 
   end
 
 
 
</syntaxhighlight>
 
</syntaxhighlight>
 
Lua arrays have a strictly defined order and never lead to OOS. In other words, `ipars` is always safe, while `pairs` should only be used if the order of iteration doesn't change anything.
 
  
 
[[Category: Lua Reference|*]]
 
[[Category: Lua Reference|*]]
 
[[Category: WML Reference]]
 
[[Category: WML Reference]]

Latest 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, 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
This page was last edited on 19 November 2019, at 03:15.