EventWML

The [event] Tag

This tag is a subtag of the [scenario], [unit] and [era] tags which is used to describe a set of actions which trigger at a certain point in a scenario. When used in a [scenario] tag (also includes [multiplayer], [tutorial] and [test]), the event only occurs in that scenario. When used in a [unit] type definition, the event will occur in all scenarios in which a unit of that type appears in. When used in an [era], the event will occur in any scenario which is played using that era.

This tag has keys and child tags that control when and if the event actions will be triggered. Most important of these is the name key. Without it, no error will be raised but the event will never fire. Therefore, from a practical standpoint, it can be considered mandatory. All of the others can be used or not and the event actions will fire either way.

The 'name' Key (Mandatory)

Usage:

name=<value>

This is not like a normal 'name' key. It is a basic description of when the event will trigger. It also has a very large number of predefined values, one of which must be used for the key to be valid.

Lexicon side note: It is not uncommon to refer to these values as the 'trigger' for an event and, furthermore, to call an event by its 'trigger' name. For example, in an event containing name=moveto, a person might refer to the event as a 'moveto event' and/or refer to the 'moveto trigger' in the event or even talk about the 'event trigger' when referring to the moveto value of the 'name' key in that event. Some or all of this usage can, in fact, be found throughout this page.

The name key can accept a list of comma separated values describing when the event will be triggered.* These values may be either predefined event types or custom event names not matching any predefined type.

For example:

name=attacker_misses,defender_misses

* Note that unless you use first_time_only=no, the event will fire only once, not once for each listed type.

Predefined 'name' Key Values

All predefined event types are listed here along with a description of when this value will cause the event to be triggered. Any value not listed here is a custom event name which can be triggered only by a [fire_event] tag somewhere else. Spaces in event names can be interchanged with underscores (for example, name=new turn and name=new_turn are equivalent).

preload Template:DevFeature: Triggers before a scenario 'prestarts' and when loading a savegame -- before anything is shown on the screen at all. Can be used to set up the Lua environment: loading libraries, defining helper functions, etc.
Note: Unlike prestart and start, the preload event must be able to fire more than once! This is because it is triggered each time a savegame is loaded in addition to the initial time when it loads before the scenario 'prestart'. This means that it is effectively mandatory to have the first_time_only=no key value in a preload event.

prestart: Triggers before a scenario 'starts' -- before anything is shown on the screen at all. Can be used to set up things like village ownership. For things displayed on-screen such as character dialog, use start instead.
Note: This value makes the first_time_only key irrelevant since, by definition, it can only fire once.

start: Triggers after the map is shown but before the scenario begins -- before players can 'do' anything.
Note: This value makes the first_time_only key irrelevant since, by definition, it can only fire once.

new turn: Triggers whenever the last player ends their turn. See also first_time_only=no. When the last player ends their turn, before any events of this type trigger, the value of the WML variable turn_number is set to the number of the turn that is beginning.

side turn: Triggers when a side is about to start its turn. Before events of this type trigger, the value of the WML variable side_number is set to the number of the side of the player about to take their turn. This is before any healing takes place for that side, before calculating income, and before restoring unit movement and status.

ai turn: Triggered just before the AI is invoked for a side. This is called after side turn, and thus the WML variable side_number still holds the number of this side.

turn refresh: Like side turn, triggers just before a side is taking control but after healing, calculating income, and restoring unit movement and status.

turn X: For X equals a number greater than 1, this event triggers at the start of turn X. The value of X cannot be 1 but, if that effect is needed, use name=new turn and first_time_only=yes to achieve the equivalent of what turn 1 would do.

time over: Triggers on turn turns. (turns is specified in [scenario])

enemies defeated: Triggers when all units with canrecruit=yes (that is, all leaders) not allied with side 1 are killed.

victory: In this scenario, any tag of the form [endlevel] result=victory [/endlevel] will be automatically preceded by all actions in this tag. It helps debugging if the victory event allows you to safely advance to any of the possible next maps after using the ":n" command. Scenarios where key units are picked up before the victory, or where some action chosen earlier determines which map to advance to, make it hard to quickly test scenarios in a campaign. (See also: [endlevel], DirectActionsWML)

defeat: In this scenario, any tag of the form [endlevel] result=defeat [/endlevel] will be automatically preceded by all actions in this tag. (See also [endlevel], DirectActionsWML)

Filters can be applied to the following event triggers (see FilterWML; see also below). The actions specified in the event tag will be executed only if the filter returns true. These event triggers are all actions by units (moveto, attack) or things that happen to units (recruit, advance). When one of these events is triggered, the position of the active unit (referred to as the primary unit) is stored in the variables x1 and y1 and the position of any unit that primary unit does something to is stored in the variables x2 and y2 (this unit is referred to as the secondary unit below). These units are also automatically stored in the variables 'unit' and 'second_unit' as if they had been stored using the [store_unit] tag. see SingleUnitWML

moveto: Triggers after the primary unit moves. Typically this is used when the primary unit gets to a particular location and a filter for the location of the primary unit is included; remember that this is the location that the primary unit lands on, not the location it started on or any location it travels on.
An [allow_undo] tag anywhere within a moveto event will cancel any lack of undo functionality the event would have caused. Note that undo functionality will only move the unit back to its former location; it will not other changes to the game caused by the event. Thus it is up to the scenario designer to use this tag correctly. Template:DevFeature $x2 and $y2 refer to the hex the unit came from.

sighted: Triggers when the primary unit becomes visible to the secondary unit in particular after not being visible to the secondary unit's side (so if the secondary unit's side doesn't have shroud or fog, the event never triggers). This happens both when the primary unit moves into view during its turn, and when the secondary unit moves to a location where it can see the primary unit. (This editor hasn't tested whether the event triggers multiple times if the primary unit moves into view of multiple units at once, or if not, which one gets chosen to be the secondary unit here.) (Note: it appears that when a sighted event is triggered because an enemy unit moves into your field of view, the game engine cannot determine which unit (on your side) sees the unit that moved, and so it fires a name=sighted event without setting $second_unit. This means that, for example, using speaker=second_unit inside a message tag may fail.)

attack: Triggers when the primary unit attacks the secondary unit.

attack end: Similar to attack, but is triggered after the fight instead of before. Note that if either unit is killed during the fight, this event triggers before any die events.

attacker hits: Triggers when the the primary unit (the attacker) hits the secondary unit (the defender). The value of the WML variable damage_inflicted is set to the number of hitpoints inflicted by the attacker.

attacker misses: Same as attacker_hits, but is triggered when the attacker misses.

defender hits: Triggers when the primary unit (the attacker) is hit in retaliation by the secondary unit (the defender). The value of the WML variable damage_inflicted is set to the number of hitpoints inflicted by the defender.

defender misses: Same as defender_hits, but is triggered when the defender misses.

stone: Triggers when the primary unit is hit by an attack with the 'stones' ability (See stones, AbilitiesWML) by the secondary unit (the unit with the 'stones' ability).

last breath: Triggers when the primary unit is killed by the secondary unit, but before the death animation is triggered.

die: Triggers when the primary unit is killed by the secondary unit.

capture: Triggers when the primary unit captures a village. The village may have been previously neutral, or previously owned by another side; merely moving into your own villages does not constitute a capture.

recruit: Triggers when the primary unit is recruited. (That is, when a unit is recruited it will trigger this event and this event's filter will filter that unit.).

prerecruit: Triggers when the primary unit is recruited but before it is displayed.

recall: Triggers after a unit is recalled.

prerecall: Triggers when a unit is recalled but before it is displayed.

advance: Triggers just before the primary unit is going to advance to another unit.

post advance: Triggers just after the primary unit has advanced to another unit.

select: Triggers when the primary unit is selected. Also triggers when ending a move, as the game keeps the moving unit selected by selecting it again at the end of movement. Note: in networked multiplayer, these events are only executed by the client on which the event is triggered, leading to out of sync errors if you modify the game state in the event.

menu item X: Triggers when a WML menu item with id=X is selected. Note: if the menu item has a [command], this event may be executed before or after the command; there is no guarantee.

=== Custom events.

An event with a custom name may be invoked using the [fire_event] tag. Normally you'll use such custom events as named subroutines to be called by events with predefined types. One common case of this, for example, is that more than one sighted events might fire the same custom event that changes the scenario objectives.

Optional Keys and Tags

These keys and tags are more complex ways to filter when an event should trigger:

first_time_only

Whether the event should be removed from the scenario after it is triggered. There are two possible values for this key:

first_time_only=yes

Default behavior if key is omitted. The event will trigger the first time it can and never again.

first_time_only=no

The event will every time the criteria are met instead of only the first time.

[filter]

The event will only trigger if the primary unit matches this filter.

StandardUnitFilter: selection criteria

[filter_second]

Like [filter], but for the secondary unit.

StandardUnitFilter: selection criteria

[filter_attack]

Can be used to set additional filtering criteria for the primary unit and the secondary unit that are not generally available in a standard unit filter. Can be used in events attack, attacker_hits, attacker_misses, defender_hits, defender_misses and attack_end. For more information and other filter keys, see FilterWML.

name: the name of the weapon used.
range: the range of the weapon used.
special: filter on the attack's special power.

[filter_second_attack]

Like [filter_attack], but for the secondary unit.

name: the name of the weapon used.
range: the range of the weapon used.
special: filter on the attack's special power.

[event]

A special case 'action', the [event] tag may be used to create a nested event.

delayed_variable_substitution

This key is only relevant inside of a nested event and controls when variable substitution will occur in those special case actions.

Actions triggered by [event]

After the trigger conditions have been met, all action tags within the [event] tag are executed in the order they are written in.

There are 3 main types of actions:

direct actions (DirectActionsWML) which have a direct effect on gameplay
display actions (InterfaceActionsWML) which show something to the user
internal actions (InternalActionsWML) which are used by WML internally

Several actions use standard filters to find out which units to execute the command on. These are denoted by the phrases "standard unit filter" and "standard location filter".

Nested Events

There is one special type of action: event creation. By placing an [event] tag inside another [event] tag, the nested event is spawned (created) when the parent (outer) event is encountered (when executing the contents of the parent event).

(See Examples)

Delayed Variable Substitution

Variable substitution for a nested event can happen either when it is spawned by the parent event or when it is triggered itself. This is controlled with the key delayed_variable_substitution which is used in the nested event.

If this key is set to yes, the variables in the nested event will contain values from the turn in which the nested event was triggered. This is the default behavior if the key is omitted. If set to no, the variables in the nested event are set at the time the parent event is triggered.

This behavior can be fine tuned with a special syntax when referencing variables. Instead of the normal $variable syntax, use $|variable to cause a variable to contain values relevant to the turn in which the nested event was triggered even when delayed_variable_substitution is set to no. In this way you can have a mix of variables relevant to the parent and nested event trigger times.

(See Examples)

Multiplayer safety

It is only possible to use [message] with input and random numbers in events that are synchronous. This limitation is caused because that WML requires data from remote hosts which is only available after network synchronisation.

List of event that are synchronous:

moveto
sighted
attack
attack_end
attacker_hits
attacker_misses
defender_hits
defender_misses
stone
last breath
die
capture
recruit
prerecruit
recall
prerecall
advance
post_advance
events fired from WML event handler that is synchronous
new turn Template:DevFeature
side turn Template:DevFeature
turn X Template:DevFeature
turn refresh Template:DevFeature

There is also event that are synchronous if fired by engine but they can be fired by wml tags too from non-synchronous event. So when you are using them you must be extra careful. For example [unsotre_unit] unit may trigger unit advancement that will fire advance and post advance events.

A Trap for the Unwary

It is perfectly possible (and, in fact, useful) to have multiple events with the same predefined name and thus the same trigger condition. However, it is not defined what order such events will fire in, so you need to code so the order will not matter.

Because of the above, you need to beware of using macros to generate events. If you include a macro expanding to an event definition twice, the event will be executed twice (not once) each time the trigger condition fires. Consider this code:

#define DOUBLE
    [event]
        name=multiply_by_2
        {VARIABLE_OP 2_becomes_4 multiply 2}
    [/event]
#enddef

{DOUBLE}
{DOUBLE}

{VARIABLE 2_becomes_4 2}
		
[fire_event]
    name=multiply_by_2
[/fire_event]

{DEBUG_MSG "$2_becomes_4 should be 4"}

After it executes, the debug message will reveal that the variable has been set to 8, not 4.

Miscellaneous Notes and Examples

Primary/Secondary Unit Speaker Example

In events, the primary unit can be referred to as unit and the secondary unit can be referred to as second_unit in [message] tags using the speaker key. For example:

[event]
    name=die
    [message]
        speaker=second_unit
        message= _ "Hahaha! I finally killed you!"
    [/message]

    [message]
        speaker=unit
        message= _ "It's not over yet! I'll come back to haunt you!"
    [/message]
[/event]

Nested Event Example

An event is created for a portal that opens on turn 10. The parent (or 'outer') event executes on turn 10 at which point the nested moveto event is created. This nested event executes when a player steps on a certain spot.

[event]
    name=turn 10

    [event]
        name=moveto

        [filter]
            x,y=5,8
        [/filter]

        # moving to 5,8 will trigger this event only on turn 10 and after
    [/event]
[/event]

An equivalent way of doing this would be to create a single moveto event with an [if] statement to check for turn number but using nested [event] tags is a convenient shortcut to accomplish this task without resorting to [if] statements.

Delayed Variable Substitution Example

This code will display the turn on which the nested moveto event happens.

[event]
    name=turn 10

    [event]
        name=moveto
        delayed_variable_substitution=yes

        [filter]
            x,y=5,8
        [/filter]

        {DEBUG_MSG "Turn $turn_number"} 
   [/event]
[/event]

Since this is the default behavior for the delayed_variable_substitution key, the following example is identical.

[event]
    name=turn 10

    [event]
        name=moveto

        [filter]
            x,y=5,8
        [/filter]

        {DEBUG_MSG "Turn $turn_number"} 
   [/event]
[/event]

This code will always display "Turn 10" when the nested moveto event happens. This is because the variable substitution is done when the parent event is triggered and spawns the nested event, not when the nested event is triggered.

[event]
    name=turn 10

    [event]
        name=moveto
        delayed_variable_substitution=no

        [filter]
            x,y=5,8
        [/filter]

        {DEBUG_MSG "Turn $turn_number"} 
   [/event]
[/event]

Finally, this example is identical to the first two, in that it will display the turn on which the nested moveto event happens despite the fact that the delayed_variable_substitution key is set to no. This is because the special $|variable syntax is used.

[event]
    name=turn 10

    [event]
        name=moveto
        delayed_variable_substitution=no

        [filter]
            x,y=5,8
        [/filter]

        {DEBUG_MSG "Turn $|turn_number"} 
   [/event]
[/event]