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{{WML Tags}}
 
{{WML Tags}}
  
== Configuring the Default AI Using WML ==
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== Customizing the Default AI Using WML ==
  
This page describes how the behavior of the default (RCA) AI can be configured using simple WML commands.  The descriptions below assume a basic understanding of how the RCA AI evaluates moves, what '''candidate actions''', '''aspects''' and '''goals''' are and how they interact.  If you do not know these things yet, check out the [[RCA_AI]] page.
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This page describes how the behavior of the default (RCA) AI can be customized using simple WML commands.  The descriptions below assume a basic understanding of how the RCA AI evaluates moves, what '''candidate actions''', '''aspects''' and '''goals''' are, and how they interact.  If you do not know these things yet, check out the [[RCA AI]] page.
  
This page focuses mostly on descriptions of the various AI configuration parameters and how to set them up at the beginning of a scenario, although for many of them (for example, for all [[simple aspects]]) the methods for changing them mid-scenario are almost identical.  See [[Modifying AI Components]] for instructions for some of the more complex AI configuration tasks.
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This page contains:
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* Descriptions of the aspects and goals of the default AI
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* Instructions for setting them up at the beginning of the scenario in a [side] tag
  
== The [ai] Tag: Defining Aspects and Goals ==
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This page does not contain:
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* Instructions for [[LuaAI#Dynamic_Lua_Aspects|setting up aspects dynamically using Lua]].
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* Instructions for [[Modifying_AI_Components#Modifying_Standard_Aspects|changing aspects and goals mid scenario]], although for many of them (for example, for all [[Wesnoth_AI_Framework#The_.5Bai.5D_Tag_.E2.80.94_Aspects|standard aspects]]) the methods are almost identical
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* Instructions for some of the [[Modifying_AI_Components|more complex AI customization tasks]].
  
The [ai] tag is used inside a [side] or [modify_side] tag.  Its contents are the [[RCA_AI|RCA_AI's]] [[RCA_AI#Aspects|aspects]] and [[RCA_AI#Goals|goals]] that can be used to customize certain aspects of the AI. You can use multiple [ai] tags and have them apply during different turns or times of day, for example to set an undead side's caution higher and aggression lower during the day, or to boost the aggressiveness of a side when it receives reinforcements on a specific turn.
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== Defining Aspects and Goals of the RCA AI ==
  
Examples of simple uses of the [ai] tag to set AI parameters (aspects) are
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[[RCA_AI#Use_of_Aspects_in_the_RCA_AI|Aspects]] and [[RCA_AI#Use_of_Goals_and_Targets_in_the_RCA_AI|goals]] of the [[RCA_AI|default (RCA) AI]] can be defined at the beginning of a scenario with [ai] tags inside the [side] tags.  They are used to customize certain aspects of the AIThe [ai] tag, when used for this purpose, takes the [[#List_of_AI_Aspects|aspects themselves]] as arguments, as well as the following general keys:
[ai]
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* '''time_of_day''': (string) The time(s) of day when the AI should use the parameters given in this [ai] tag. Possible values are listed in [https://github.com/wesnoth/wesnoth/blob/master/data/core/macros/schedules.cfg data/core/macros/schedules.cfg] (see also [[TimeWML]]).  Note that it is the ''id'' (not the ''name'') of the time of day that needs to be used here.  Also note that this aspect did not work for a long time due to a bug (versions 1.7.4 - 1.11.6).  It has been fixed for BfW 1.11.7.
    aggression=0.99
 
  [/ai]
 
or
 
[ai]
 
    [avoid]
 
        [filter]
 
            side=2,3
 
        [/filter]
 
        radius=2
 
    [/avoid]
 
[/ai]
 
  
'''Important Note:''' if you use a different AI engine ([[FormulaAI]] or [[LuaAI]]) or a [[Micro_AIs|Micro AI]] for a side, setting aspects in the [side] tag might not work due to a bug in the AI setup mechanism (or it might; there's no general rule that catches all cases).  In that case, you might have to use [modify_side] in a ''prestart'' or ''start'' event instead.  If unsure, you can use ':inspect' in debug mode to verify whether an aspect was changed successfully.
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* '''turns''': (string) During which turns the AI should use the parameters given in this [ai] tag. This takes the same syntax of dashes (-) and commas (,) as is described under Filtering Locations in [[FilterWML]], except of course they apply to turns not locations.
  
The following general keys/tags can be used in an '''[ai]''' tag:
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* '''ai_algorithm''': (string) Allows an alternate AI algorithm (cannot be created with WML) to be used. Besides the default, the game only comes with ''idle_ai'', which makes the AI do nothing and can be used to create a passive, unmoving side. Cannot be applied only to a set of turns or a given time of day using the keys ''turns'' and ''time_of_day'', but must be given either in an [ai] tag without the aforementioned keys or in the [side] tag outside all [ai] tags. {{DevFeature1.13|5}} In 1.13, the meaning of '''ai_algorithm''' has changed and no longer selects a native AI that's built into the engine, as the RCA AI has now become the core system and no alternatives exist anymore. Instead, it selects a predefined ''[ai]'' definition, such as those defined in ''data/ai/ais''. Since these are defined in WML, you can easily build your own.
* '''time_of_day''': (string) The time(s) of day when the AI should use the parameters given in this [ai] tag. Possible values are listed in data/core/macros/schedules.cfg (see also [[TimeWML]]). Note that it is the ID (not the name) of the time of day that needs to be used here. Also note that this aspect did not work for a long time due to a bug (versions 1.7.4 - 1.11.6).  It has been fixed for BfW 1.11.7.
 
  
* '''turns''': (string) During which turns the AI should use the parameters given in this [ai] tag. This takes the same syntax of dashes (-) and commas (,) as is described under Filtering Locations in [[FilterWML]], except of course they apply to turns not locations.
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An example of a simple use of the [ai] tag to set AI parameters (aspects) is
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<syntaxhighlight lang=wml>
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[ai]
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    time_of_day=dusk
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    aggression=0.99
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    caution=0.01
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    [avoid]
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        [filter]
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            side=2,3
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        [/filter]
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        radius=2
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    [/avoid]
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[/ai]
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</syntaxhighlight>
  
* '''ai_algorithm''': (string) Allows an alternate AI algorithm (cannot be created with WML) to be used. Besides the default, the game only comes with ''idle_ai'', which makes the AI do nothing and can be used to create a passive, unmoving side. Cannot be applied only to a set of turns or a given time of day using the keys ''turns'' and ''time_of_day'', but must be given either in an [ai] tag without the aforementioned keys or in the [side] tag outside all [ai] tags.
 
  
In addition to these general keys, the aspects themselves make up the remaining keys and tags of the [ai] tagThese are described in the following sections.
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'''Important Note:''' If you use a different AI engine ([[FormulaAI]] or [[LuaAI]]) for a side, setting aspects in the [side] tag might not work due to a bug in the AI setup mechanism (or it might; there's no general rule that catches all cases).  In that case, you might have to use [modify_side][ai] in a ''prestart'' or ''start'' event insteadIf unsure, you can use <code>:inspect</code> in debug mode to verify whether an aspect was changed successfully.
  
 
==List of AI Aspects==
 
==List of AI Aspects==
  
* '''advancements''': (string) Defines a list of unit types to which AI units can advance. If a unit type is listed here, units that can advance to this type will ''only'' advance to this type, even if they have, in principle, several advancement options.  As an example, if this aspect is set to "Javelineer,Elvish Hero", then all Spearmen advance to Javelineers, and all Elvish Fighters advance to Elvish Heroes.  All other units follow their usual advancement choices as determined by the AI.  '''Important notes:'''
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* '''advancements''': (string) Defines a list of unit types to which AI units can advance. If a unit type is listed here, units that can advance to this type will <u>only</u> advance to this type, even if they have, in principle, several advancement options.  As an example, if this aspect is set to 'Javelineer,Elvish Hero', then all Spearmen advance to Javelineers, and all Elvish Fighters advance to Elvish Heroes.  All other units follow their usual advancement choices as determined by the AI.  '''Important notes:'''
** This is a simplified version of the more complex (and arguably more useful) application of a dynamic Lua 'advancements' aspect, as described [[AiWML#Dynamic_advancements_Aspect|below]].
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** This is a simplified version of the more complex (and arguably more useful) application of a dynamic Lua ''advancements'' aspect, as described [[LuaAI#The_advancements_Aspect|here]].
** The 'advancements' aspect only takes effect during the AI turn, that is, on offense only, not on defense.
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** The ''advancements'' aspect only takes effect during the AI turn, that is, on offense only, not on defense.
 
** Listing more than one advancement unit type for a given unit still results in only one of the types being used (generally the one listed last).
 
** Listing more than one advancement unit type for a given unit still results in only one of the types being used (generally the one listed last).
  
* '''aggression'''=0.4: (double: ranging from -infinity to 1.0)  This key affects how the AI selects its attack targets.  The higher the value, the more likely the AI is to attack even if odds are not in its favor.  Applies to combat CA only.
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* '''aggression'''=0.4: (double: ranging from -infinity to 1.0)  This key affects how the AI selects its attack targets.  The higher the value, the more likely the AI is to attack even if odds are not in its favor.  Applies to ''combat'' CA only.
 
** '''Important: do not set aggression to values greater than 1''' as this makes the AI ''prefer'' attacks in which it receives more damage (see below) unless that is specifically the effect you want to achieve.
 
** '''Important: do not set aggression to values greater than 1''' as this makes the AI ''prefer'' attacks in which it receives more damage (see below) unless that is specifically the effect you want to achieve.
 
** In the attack evaluation, each attack (this includes attack combinations of several AI units against the same enemy unit) is assigned a score.  The attack with the highest score is done first.  Then the next attack is evaluated, until no attack with a score greater than 0 is found any more.  (Note that this ''attack score'' is different from the ''combat CA score'', which is always 100,000 as long as an individual attack score >0 is found.  The combat CA score is zero if the highest attack score is <=0).
 
** In the attack evaluation, each attack (this includes attack combinations of several AI units against the same enemy unit) is assigned a score.  The attack with the highest score is done first.  Then the next attack is evaluated, until no attack with a score greater than 0 is found any more.  (Note that this ''attack score'' is different from the ''combat CA score'', which is always 100,000 as long as an individual attack score >0 is found.  The combat CA score is zero if the highest attack score is <=0).
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*** Roughly speaking, 'aggression=0' results in the AI valuing its units approximately as much as the enemy units.  This is not a one-to-one relation, but can be used as an approximate guideline.
 
*** Roughly speaking, 'aggression=0' results in the AI valuing its units approximately as much as the enemy units.  This is not a one-to-one relation, but can be used as an approximate guideline.
 
*** Very large negative values of ''aggression'' mean that the value of the AI's units is much more important than that of the enemy units.  As a result, the AI never attacks unless it will receive no damage in exchange.
 
*** Very large negative values of ''aggression'' mean that the value of the AI's units is much more important than that of the enemy units.  As a result, the AI never attacks unless it will receive no damage in exchange.
*** The rating for damage received in an attack actually becomes a positive contribution to the score for values of aggression larger than 1.  This usually does result in sensible behavior and values greater than 1 should therefore not be used.
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*** The rating for damage received in an attack actually becomes a positive contribution to the score for values of aggression larger than 1.  This usually does not result in sensible behavior and values greater than 1 should therefore not be used.
 
** Note: ''aggression'' is always set to 1.0 for attacks on units that pose a direct threat to the AI's leader.  Currently this only means units adjacent to the leader.
 
** Note: ''aggression'' is always set to 1.0 for attacks on units that pose a direct threat to the AI's leader.  Currently this only means units adjacent to the leader.
  
*'''[attacks]''': Filters the units considered for combat, both on the AI and the enemy sides.  Applies to the combat CA only.  It cannot be set in the same way as the other aspects and is therefore described in a [[AiWML#Filtering_Combat_with_the_.27attacks.27_Aspect|separate section]] below.
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*'''[attacks]''': Filters the units considered for combat, both on the AI and the enemy sides.  Applies to the ''combat'' and ''high_xp_attacks'' CAs only.  It cannot be set in the same way as the other aspects and is therefore described in a [[#Filtering_Combat_with_the_attacks_Aspect|separate section]] below.
  
* '''[avoid]''': Makes the AI avoid specific locations.  The AI never moves a unit to these locations except for trying to move its leader to a keep or toward [leader_goal]s, and thus applies to all CAs except move-leader-to-goals and move-leader-to-keep.
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* '''[avoid]''': Makes the AI avoid specific locations.  The AI never moves a unit to these locations except for trying to move its leader to a keep or toward [leader_goal]s, and thus applies to all CAs except ''move-leader-to-goals'' and ''move-leader-to-keep''.
 
** '''[[StandardLocationFilter]]''': The locations for the AI to avoid.  Do not use a [filter_location] tag.
 
** '''[[StandardLocationFilter]]''': The locations for the AI to avoid.  Do not use a [filter_location] tag.
  
* '''caution'''=0.25: (double) Defines how cautious the AI is in several ways.  It determines whether the leader should move toward [leader_goal], if attacks are worth moving onto less favorable terrain, whether units should retreat, and whether the AI should move units toward targets individually, as groups or not at all.  Affects several CAs (listed in the order of their [[AiWML#Evaluating_AI_Moves_--_Candidate_Actions_.28CAs.29|evaluation scores]]):
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* '''caution'''=0.25: (double) Defines how cautious the AI is in several ways.  It determines whether the leader should move toward [leader_goal], if attacks are worth moving onto less favorable terrain, whether units should retreat, and whether the AI should move units toward targets individually, as groups or not at all.  Affects several CAs (listed in the order of their [[RCA_AI#The_Candidate_Actions_.28CAs.29_of_the_main_loop_Stage_in_the_RCA_AI|evaluation scores]]):
** Move-leader-to-goals CA: If ''max_risk'' is not set in [leader_goal], its default value is '1-caution'.  This determines whether the leader takes the next step toward his goal.  See description of [leader_goal].
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** ''Move-leader-to-goals CA'': If ''max_risk'' is not set in [leader_goal], its default value is '1-caution'.  This determines whether the leader takes the next step toward his goal.  See description of [leader_goal].
** Combat CA:  
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** ''Combat'' CA:  
 
*** During the evaluation of attacks, the AI considers whether the attacking units could get onto more favorable terrain if they didn't attack but moved somewhere else instead.  The difference between the two terrain ratings, together with a number of other factors, determines the "exposure" rating of the units.  This exposure is then subtracted from the 'attack score' as described for ''aggression'' above.
 
*** During the evaluation of attacks, the AI considers whether the attacking units could get onto more favorable terrain if they didn't attack but moved somewhere else instead.  The difference between the two terrain ratings, together with a number of other factors, determines the "exposure" rating of the units.  This exposure is then subtracted from the 'attack score' as described for ''aggression'' above.
*** The exposure rating also contains a multiplication by ''caution'', meaning that 'caution=0' results in exposure not being taken into account, and that it becomes more and more important for larger values.  In other words, the higher the values of ''caution'', the more reluctant is the AI to attack from unfavorable terrain.  (Note that exposure is one of the negative contributions to the attack score as described for ''aggression'', and therefore is ignored if 'aggression=1' is set.)
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*** The exposure rating also contains a multiplication by ''caution'', meaning that 'caution=0' results in exposure not being taken into account, and that it becomes more and more important for larger values.  In other words, the higher the values of ''caution'', the more reluctant is the AI to attack from unfavorable terrain.  (Note that exposure is one of the negative contributions to the attack score as described for ''aggression'', and therefore is also ignored if 'aggression=1' is set.)
 
*** If the AI leader is used in an attack, the AI ''always'' uses 'caution=2' for the evaluation of that attack.
 
*** If the AI leader is used in an attack, the AI ''always'' uses 'caution=2' for the evaluation of that attack.
** Retreat CA:  
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** ''Retreat'' CA:  
*** If caution is greater than 0, there is an evaluation of forces for the map location a unit stands on. This is basically the sum of damage that can be done to that location by either side, reduced by terrain defense and relative hitpoints if attackers don't have full health. A retreat takes place, if<br>caution * their_power > our_power<br>There is also a terrain factor involved if the attacker is not on optimal terrain, similar to the exposure described above for the combat CA.
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*** If caution is greater than 0, there is an evaluation of forces for the map location a unit stands on. This is basically the sum of damage that can be done to that location by either side, reduced by terrain defense and relative hitpoints if attackers don't have full health. A retreat takes place, if <tt>caution &times; their_power > our_power</tt>. There is also a terrain factor involved if the attacker is not on optimal terrain, similar to the exposure described above for the combat CA.
 
*** So let's say the AI has its default caution of 0.25. Then the enemy forces have to be at least 4 times as strong before the unit retreats. For a caution of 1, as soon as the enemy is stronger, the unit retreats.  
 
*** So let's say the AI has its default caution of 0.25. Then the enemy forces have to be at least 4 times as strong before the unit retreats. For a caution of 1, as soon as the enemy is stronger, the unit retreats.  
 
*** The AI never retreats if caution is set to 0 or lower.
 
*** The AI never retreats if caution is set to 0 or lower.
** Move-to-targets CA:
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** ''Move-to-targets'' CA:
*** If grouping for the AI is enabled and the path along which to move toward a target is considered to be dangerous, caution has an influence, too. "Dangerous" mainly means that there is a good chance for a unit to be killed if it's by itself.  In that case, the AI compares its units to the enemy units and based on the result moves forward or not. All units that can reach the next location of the move are considered.  The formula for deciding whether to move toward the target as a group is<br>our_strength / their_strength > 0.5 + caution<br>If this condition holds true, units are moved toward the goal as a group, otherwise they try to group together in a location favorable for a attack on the enemy during the next turn.
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*** If grouping for the AI is enabled and the path along which to move toward a target is considered to be dangerous, caution has an influence, too. "Dangerous" mainly means that there is a good chance for a unit to be killed if it's by itself.  In that case, the AI compares its units to the enemy units and based on the result moves forward or not. All units that can reach the next location of the move are considered.  The formula for deciding whether to move toward the target as a group is <tt>our_strength / their_strength > 0.5 + caution</tt>. If this condition holds true, units are moved toward the goal as a group, otherwise they try to group together in a location favorable for a attack on the enemy during the next turn.
 
***So if caution is 0.5, the AI side needs to be at least as strong as the enemy. If it is 0, the AI moves toward the target, even if the enemy is up to twice as strong as the AI. Setting caution to 1.5 means the AI needs to be at least twice as strong as the enemy.
 
***So if caution is 0.5, the AI side needs to be at least as strong as the enemy. If it is 0, the AI moves toward the target, even if the enemy is up to twice as strong as the AI. Setting caution to 1.5 means the AI needs to be at least twice as strong as the enemy.
 
*** The AI also considers retreating units during the move-to-target phase based on criteria similar to those for the retreat CA.
 
*** The AI also considers retreating units during the move-to-target phase based on criteria similar to those for the retreat CA.
  
* '''[goal]'''="": Defines units or locations as [[AiWML#AI_Targets_and_Goals|targets]] for the AI.  See the dedicated section on the [[AiWML#The_.5Bgoal.5D_Tag|[goal] tag]] below for details.  Applies to move-to-targets CA only.
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* '''[goal]'''="": Defines units or locations as [[#AI_Targets_and_Goals|move targets]] (not attack targets!) for the AI.  '''Applies to ''move-to-targets'' CA only'''. <-- That is '''extremely important''' to understand, in particular the fact that the [goal] tag has '''no influence whatsoever on attacks'''.    See the dedicated section on the [[#The_.5Bgoal.5D_Tag|[goal] tag]] below for details.
  
* '''grouping'''="offensive": (string) How the AI should try to group units.  Applies to move-to-targets CA only.  Possible values:
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* '''grouping'''="offensive": (string) How the AI should try to group units.  Applies to ''move-to-targets'' CA only.  Possible values:
 
** ''offensive'': Makes the AI try to group units together before attacking.
 
** ''offensive'': Makes the AI try to group units together before attacking.
 
** ''defensive'': Makes the AI group units together very conservatively, only advancing them much beyond its castle if it has overwhelming force.
 
** ''defensive'': Makes the AI group units together very conservatively, only advancing them much beyond its castle if it has overwhelming force.
 
** ''no'': Makes the AI use no grouping behavior.
 
** ''no'': Makes the AI use no grouping behavior.
  
* '''leader_aggression'''="-4.0": Exactly as aggression, but for units which can recruit.  Applies to combat CA only.  Note that the move-leader-to-keep CA has a higher score than the combat CA.  A leader therefore usually only attacks if he is on his keep at the beginning of the turn, otherwise he moves toward the closest keep instead, even with ''leader_aggression=1''.
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* '''leader_aggression'''="-4.0": Exactly as aggression, but for units which can recruit.  Applies to ''combat'' CA only.  Note that the move-leader-to-keep CA has a higher score than the combat CA.  A leader therefore usually only attacks if he is on his keep at the beginning of the turn, otherwise he moves toward the closest keep instead, even with ''leader_aggression=1''.
  
* '''[leader_goal]'''="": Makes the AI try to move its leader to a specific location.  Applies to move-leader-to-goals CA only.
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* '''[leader_goal]'''="": Makes the AI try to move its leader to a specific location.  Applies to ''move-leader-to-goals'' CA only.
 
** '''x''', '''y''': The location toward which the AI should move its leader.
 
** '''x''', '''y''': The location toward which the AI should move its leader.
** '''auto_remove'''=no: (bool)  If 'no' (default), the AI moves the leader to the goal, after which he stays there until [leader_goal] is [[AiWML#Adding_and_Deleting_Aspects_with_the_.5Bmodify_ai.5D_Tag|removed manually]].  If 'yes', the leader_goal is removed upon the leader getting there.  Important: this ''only'' works if ''id'' is set correctly (see the next bullet).
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** '''auto_remove'''=no: (bool)  If 'no' (default), the AI moves the leader to the goal, after which he stays there until [leader_goal] is [[Modifying_AI_Components#Modifying_Standard_Aspects|removed manually]].  If 'yes', the leader_goal is removed upon the leader getting there.  Important: this ''only'' works if ''id'' is set correctly (see the next bullet).
** '''id'''="": (string)  An internal id key of the [leader_goal] tag.  An id is required for ''auto_remove'' to work.  However, setting this id does not automatically set the id of the [leader_goal] [[AiWML#A_Bit_More_on_Simple_vs._Composite_Aspects|facet]].  Thus, in principle for this to work, you need to set the id of the facet as described [[AiWML#Adding_and_Deleting_Aspects_with_the_.5Bmodify_ai.5D_Tag|below]] ''and'' set the ''id'' key in [leader_value] to the same value.  Since you are probably only going to use one [leader_goal] tag at a time, there is a much simpler way: setting 'id=0' (which refers to the first facet) or 'id=*' (which means all facets) in [leader_goal] allows ''auto_remove'' to work without the extra step of setting the facet id.
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** '''id'''="": (string)  An internal id key of the [leader_goal] tag.  An id is required for ''auto_remove'' to work.  However, setting this id does not automatically set the id of the [leader_goal] [[Wesnoth_AI_Framework#The_.5Bai.5D_Tag_.E2.80.94_Aspects|facet]].  Thus, in principle for this to work, you need to set the id of the facet as described [[Modifying_AI_Components#Modifying_Standard_Aspects|here]] ''and'' set the ''id'' key in [leader_value] to the same value.  Since you are probably only going to use one [leader_goal] tag at a time, there is a much simpler way: setting 'id=0' (which refers to the first facet) or 'id=*' (which means all facets) in [leader_goal] allows ''auto_remove'' to work without the extra step of setting the facet id. {{DevFeature1.13|5}} Setting this now also sets the id of the [leader_goal] facet, allowing auto_remove to work with multiple leader goals without using the fully-expanded aspect syntax.
 
**'''max_risk'''=1-caution: (double: meaningful values are >=0)  How much risk the leader may be exposed to by moving toward the goal.  For evaluating this risk, the AI multiplies the leader's hitpoints by this number.  The leader is only moved toward the goal if the resulting value is larger than the expected damage the leader is going to take during the next enemy turn.  Thus, 'max_risk=0' means he will only move if no attack on him is possible at the target hex of the move.  'max_risk=1' (or larger) results in him moving even if he's almost certainly going to die.
 
**'''max_risk'''=1-caution: (double: meaningful values are >=0)  How much risk the leader may be exposed to by moving toward the goal.  For evaluating this risk, the AI multiplies the leader's hitpoints by this number.  The leader is only moved toward the goal if the resulting value is larger than the expected damage the leader is going to take during the next enemy turn.  Thus, 'max_risk=0' means he will only move if no attack on him is possible at the target hex of the move.  'max_risk=1' (or larger) results in him moving even if he's almost certainly going to die.
  
* '''leader_ignores_keep'''=no: (bool) If 'yes', AI leaders do not move to the closest keep at the beginning of the turn.  Instead, they participate in the move_to_targets candidate action (and all other CAs in which they already participated anyway, of course).  For practical purposes this means that:
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* '''leader_ignores_keep'''=no: (bool) If 'yes', AI leaders do not move to the closest keep at the beginning of the turn.  Instead, they participate in the ''move_to_targets'' candidate action (and all other CAs in which they already participated anyway, of course).  For practical purposes this means that:
 
** Leaders participate in all the moves and attacks in the same way as any other unit of the AI side.
 
** Leaders participate in all the moves and attacks in the same way as any other unit of the AI side.
 
** AI leaders do not recruit except on the first turn if they start on a keep, or if they accidentally end up on a keep.  Thus, if a leader is supposed to recruit first and then participate in the action, leader_ignores_keep should be set to 'no' at the beginning of the scenario, and be changed to 'yes' in an event later.
 
** AI leaders do not recruit except on the first turn if they start on a keep, or if they accidentally end up on a keep.  Thus, if a leader is supposed to recruit first and then participate in the action, leader_ignores_keep should be set to 'no' at the beginning of the scenario, and be changed to 'yes' in an event later.
  
* '''leader_value'''=3: (double) A number 0 or higher which determines the value of enemy leaders as [[AiWML#AI_Targets_and_Goals|targets]].  Affects move-to-targets CA only (and therefore specifically does not apply to attacks).
+
* '''leader_value'''=3: (double) A number 0 or higher which determines the value of enemy leaders as [[#AI_Targets_and_Goals|targets]].  Affects ''move-to-targets CA'' only (and therefore specifically does not apply to attacks).
  
* '''passive_leader'''=no: (bool) If 'yes', the AI leader never moves or attacks, not even to move back to the keep (unless 'passive_leader_shares_keep=yes' is set) or to attack adjacent units, except to obey [leader_goal]s.  Affects all CAs except recruitment and move-leader-to-goals.
+
* '''passive_leader'''=no: (bool) If 'yes', the AI leader never moves or attacks, not even to move back to the keep (unless 'passive_leader_shares_keep=yes' is set) or to attack adjacent units, except to obey [leader_goal]s.  Affects all CAs except ''recruitment'' and ''move-leader-to-goals''.
  
 
* '''passive_leader_shares_keep'''=no: (bool) If 'yes', lets the AI leader moves off the keep to share it with allied leaders (if they can reach it next turn) if 'passive_leader=yes' is set.  He also returns to keep to recruit when possible and attacks adjacent enemy units.
 
* '''passive_leader_shares_keep'''=no: (bool) If 'yes', lets the AI leader moves off the keep to share it with allied leaders (if they can reach it next turn) if 'passive_leader=yes' is set.  He also returns to keep to recruit when possible and attacks adjacent enemy units.
  
* '''recruitment_ignore_bad_combat'''=no: (bool) If 'yes', the AI does not analyze the enemy units on the map to see if the unit to be recruited is suitable for fighting them.  Affects recruitment CA only.
+
*'''recruitment_diversity''', '''recruitment_instructions''', '''recruitment_more''', '''recruitment_pattern''', '''recruitment_randomness''', '''recruitment_save_gold''': These aspects can be used to customize recruiting with the new recruitment CA introduced in Wesnoth 1.11They are described on a [[AI_Recruitment|separate page]].
 
 
*'''recruitment_instruction'''="": Limits the number of units of a given type that the AI can have on the map simultaneously.  Applies to the recruitment CA only.  It cannot be set in the same way as the other aspects and is therefore described in a [[AiWML#Limiting_Recruiting_with_the_.27recruitment_instruction.27_Aspect|separate section]] below.
 
 
 
* '''recruitment_pattern'''="": (string) This key takes a comma separated list containing the usages of the units that can be recruited. Common usages are: 'scout', 'fighter', 'archer', 'healer' and 'mixed fighter'. This tells the AI with what probability it should recruit different types of units. The AI considers all units with the specified usage(s) and ''only'' those, so make sure the units you want recruited are really covered by the pattern, or use an empty pattern (the default) to have it consider all available units. The usage is listed in the unit type config files (see data/core/units/ for mainline units; see also [[UnitTypeWML]]).  Affects recruitment CA only.
 
** For example, "recruitment_pattern=fighter,fighter,archer" means that the AI recruits on average twice as many fighters as archers, and does not recruit scouts (other than scouts for capturing villages, which are recruited independently), healers or mixed fighters.  It does ''not'' mean that it recruits two fighters first, then an archer, then two fighters again, etc.
 
 
 
* '''scout_village_targeting'''=3: (double) The AI multiplies the value of village [[AiWML#AI_Targets_and_Goals|targets]] for scouts by this value.  Affects move-to-targets CA only.
 
 
 
* '''simple_targeting'''=no: (bool) If 'yes', the AI moves its units toward [[AiWML#AI_Targets_and_Goals|targets]] one by one (sequentially), without considering whether another unit might be better suited for the current move or target. If 'no' (the default), all units are considered for all targetsThis is slower, but might result in better moves.  Affects move-to-targets CA only.
 
 
 
* '''support_villages'''=no: (bool) Trigger a code path that tries to protect those villages that are threatened by the enemy.  This seems to cause the AI to 'sit around' a lot, so it's only used if it's explicitly enabled.  Affects move-to-targets CA only.
 
 
 
* '''village_value'''=1: (double) A number 0 or higher which determines how much the AI tries to go for villages as [[AiWML#AI_Targets_and_Goals|targets]]. Affects move-to-targets CA only.
 
 
 
* '''villages_per_scout'''=4: (int) A number 0 or higher which determines how many scouts the AI recruits. If 0, the AI doesn't recruit scouts to capture villages.  Affects recruitment CA only.
 
 
 
=== Deprecated AI Targeting Aspects ===
 
  
The following AI targeting parameters (aspects) currently still work, but have been superseded by the [[AiWML#The_.5Bgoal.5D_Tag|[goal] tag]].  They should not be used any more as they will likely be removed at some pointThese tags specify [[AiWML#AI_Targets_and_Goals|targets]] and only apply to the move-to-targets CA.
+
* '''scout_village_targeting'''=3: (double) The AI multiplies the value of village [[#AI_Targets_and_Goals|targets]] for scouts by this valueAffects ''move-to-targets'' CA only.
  
* '''[target]'''="": '''Deprecated'''. Any number of [target] tags can be used to set targets for the AI. For anything related to 'values', set them relative to other targets. An AI is willing to dedicate twice as many resources and travel twice as far to get to a target worth '2.0' as for a target worth '1.0'.  Applies to move-to-targets CA only.
+
* '''simple_targeting'''=no: (bool) If 'yes', the AI moves its units toward [[#AI_Targets_and_Goals|targets]] one by one (sequentially), without considering whether another unit might be better suited for the current move or target. If 'no' (the default), all units are considered for all targets. This is slower, but might result in better moves. Affects ''move-to-targets'' CA only.
** '''[[StandardUnitFilter]]''': Do not use a [filter] tag.
 
** '''value'''=1: (double)  A number greater than 0 (default=1) which determines how much the AI tries to move toward units which pass the filter.
 
  
* '''[protect_location]'''="": '''Deprecated'''. Gives the AI a location to protect. Note that the AI does ''not'' station any units around the location, it only sends units to attack any enemy units that come within the guarding radius of the targetApplies to move-to-targets CA only.
+
* '''support_villages'''=no: (bool) Trigger a code path that tries to protect those villages that are threatened by the enemy.  This seems to cause the AI to 'sit around' a lot, so it's only used if it's explicitly enabled. Affects ''move-to-targets'' CA only.
** '''x''', '''y''': Standard coordinates. These indicate the location the AI is protecting.
 
** '''radius''': The radius around it to protect (0 indicates a single hex).
 
** '''value''': The importance of protecting this location.
 
  
* '''[protect_unit]'''="": '''Deprecated'''. Gives the AI a set of units to protect. Note once again that the AI does not place units around the protected units if there are no enemies nearby.  Applies to move-to-targets CA only.
+
* '''village_value'''=1: (double) A number 0 or higher which determines how much the AI tries to go for villages as [[#AI_Targets_and_Goals|targets]]. Affects ''move-to-targets'' CA only.
** '''[[StandardUnitFilter]]''': The unit(s) to protect. Do not use a [filter] tag.
 
** '''radius''': The radius around it to protect (0 indicates a single hex).
 
** '''value''': The importance of protecting this unit.
 
  
* '''protect_leader'''=2.0 and '''protect_leader_radius'''=10: '''Deprecated'''. Target any enemy units that come within 'protect_leader_radius' of the AI leader with a value of 'protect_leader'.  Applies to move-to-targets CA only.
+
* '''villages_per_scout'''=4: (int) A number 0 or higher which determines how many scouts the AI recruits. If 0, the AI doesn't recruit scouts to capture villages. Affects ''recruitment'' CA only.
  
 
=== Removed AI Aspects ===
 
=== Removed AI Aspects ===
  
The following AI parameters (aspects) can still be set, their values can be retrieved, and they can be viewed in the gamestate inspector dialog, but they do not seem to have an effect in the RCA AI code any more.  Some other parameters will also likely be removed in the future.  We will update this list accordingly.
+
The following AI parameters (aspects) can still be set, their values can be retrieved, and they can be viewed in the gamestate inspector dialog, but they do not have an effect in the RCA AI code any more.  Some other parameters will also likely be removed in the future.  We will update this list accordingly. {{DevFeature1.13|5}} Except for attack_depth, these have now all been removed.
  
 
* '''attack_depth'''=5: (int)
 
* '''attack_depth'''=5: (int)
 
* '''number_of_possible_recruits_to_force_recruit'''=3.1: (double)
 
* '''number_of_possible_recruits_to_force_recruit'''=3.1: (double)
 +
* '''recruitment''': This aspect was used to customize the recruitment of the old default AI (the one used before the RCA AI).  This recruitment code is not used in the RCA AI any more.  Setting recruitment instructions with this aspect is therefore meaningless.  Use the '''recruitment_instructions''' aspect instead.
 +
** It is, in principle, still possible to use this aspect together with the [[Wesnoth_AI_Framework#Recruitment_Stage|recruitment stage]], but this is discouraged for the reasons given at this link.
 +
* '''recruitment_ignore_bad_combat'''=no: (bool)
 
* '''recruitment_ignore_bad_movement'''=no: (bool)
 
* '''recruitment_ignore_bad_movement'''=no: (bool)
  
 
==AI Targets and Goals==
 
==AI Targets and Goals==
  
AI targets are used in the move-to-targets candidate action (CA) to move the AI's units toward selected units or locations.  The AI engine automatically selects all enemy leaders, enemy units that pose a threat to the AI leader and unowned or enemy-owned villages as targets and assigns them certain base values.  Additional targets can be defined using the [goal] tag.
+
AI targets are used in the ''move-to-targets'' candidate action (CA) to move the AI's units toward selected units or locations.  The AI engine automatically selects all enemy leaders, enemy units that pose a threat to the AI leader and unowned or enemy-owned villages as targets and assigns them certain [[RCA_AI#RCA_AI_Aspect_and_Goal_Configuration|base values]].  Additional targets can be defined using the [goal] tag.
  
It is '''very important''' to realize that these targets apply to the move-to-targets CA only and have no influence on other CAs.  In particular, they have no effect whatsoever on which enemies the AI attacks.  This is often a source of confusion for scenario creators and is essential to understand.  More background information about AI targets and goals can be found [[RCA_AI#Goals|here]].  The sections below only describe how to modify goals and targets in WML.
+
It is '''very important''' to realize that these targets apply to the ''move-to-targets'' CA only and have no influence on other CAs.  In particular, they have no effect whatsoever on which enemies the AI attacks.  This is often a source of confusion for scenario creators.  More background information on RCA AI targets and goals can be found [[RCA_AI#Use_of_Goals_and_Targets_in_the_RCA_AI|here]].  The sections below only describe how to set up goals in order to add targets for the ''move-to-targets'' CA.
  
 
===The [goal] Tag===
 
===The [goal] Tag===
  
The [goal] tag specifies target units or locations toward which the AI should move its units in the move-to-targets CA.  The following keys/tags can be used:
+
The [goal] tag specifies target units or locations toward which the AI should move its units in the ''move-to-targets'' CA.  The following keys/tags can be used:
 
* '''name'''="target": (string)  The following values are possible and result in different types of targets, as shown in the examples below:
 
* '''name'''="target": (string)  The following values are possible and result in different types of targets, as shown in the examples below:
** ''target'':  The (default) target goal specifies target units (not necessarily enemy units) toward which the AI should move its units.
+
** ''target'':  The (default) target goal specifies target units (not necessarily enemy units) toward which the AI should move its units. {{DevFeature1.13|5}} target_unit is now a synonym for this.
 
** ''target_location'': Specifies target locations toward which the AI should move its units.
 
** ''target_location'': Specifies target locations toward which the AI should move its units.
 
** ''protect_location'': Specifies locations that the AI should protect. Enemy units within the specified distance (''protect_radius'') of one of these locations are marked as targets with the provided value.  Note that the AI will ''not'' station any units around the protected locations.  It will only send units toward enemy units that come within ''protect_radius'' of them.
 
** ''protect_location'': Specifies locations that the AI should protect. Enemy units within the specified distance (''protect_radius'') of one of these locations are marked as targets with the provided value.  Note that the AI will ''not'' station any units around the protected locations.  It will only send units toward enemy units that come within ''protect_radius'' of them.
 
** ''protect_unit'': Specifies units (of all sides) that the AI should protect. Enemy units within ''protect_radius'' of one of these units are marked as targets with the provided value.  Note once again that the AI will not place units around the protected units if there are no enemies nearby.
 
** ''protect_unit'': Specifies units (of all sides) that the AI should protect. Enemy units within ''protect_radius'' of one of these units are marked as targets with the provided value.  Note once again that the AI will not place units around the protected units if there are no enemies nearby.
 
** ''protect_my_unit'': ('''deprecated''') <s>Specifies units from the AI's own side that the AI should protect. (This is basically the ''protect_unit'' goal with an implied ''side='' in the filter, restricting matching units to the AI's side.) Enemy units within ''protect_radius'' of one of these units are marked as targets with the provided value.  Note once again that the AI will not place units around the protected units if there are no enemies nearby.</s>
 
** ''protect_my_unit'': ('''deprecated''') <s>Specifies units from the AI's own side that the AI should protect. (This is basically the ''protect_unit'' goal with an implied ''side='' in the filter, restricting matching units to the AI's side.) Enemy units within ''protect_radius'' of one of these units are marked as targets with the provided value.  Note once again that the AI will not place units around the protected units if there are no enemies nearby.</s>
 +
** ''lua_goal'': A dynamically calculated goal written in Lua. See [[LuaAI#Lua_Goals_and_Targets|here]] for details on how this works.
  
 
* '''[criteria]'''="": Contains a [[StandardUnitFilter]] (for ''target'', ''protect_unit'' or ''protect_my_unit'') or [[StandardLocationFilter]] (for ''target_location'' or ''protect_location'') describing the targets.
 
* '''[criteria]'''="": Contains a [[StandardUnitFilter]] (for ''target'', ''protect_unit'' or ''protect_my_unit'') or [[StandardLocationFilter]] (for ''target_location'' or ''protect_location'') describing the targets.
Line 170: Line 155:
  
 
'''target:'''
 
'''target:'''
[ai]
+
<syntaxhighlight lang='wml'>
    [goal]
+
[ai]
        [criteria] #NOTE: this is a SUF, because we're targeting a unit
+
    [goal]
            side=3
+
        [criteria] #NOTE: this is a SUF, because we're targeting a unit
        [/criteria]
+
            side=3
        value=5
+
        [/criteria]
    [/goal]
+
        value=5
[/ai]
+
    [/goal]
 +
[/ai]
 +
</syntaxhighlight>
  
 
'''target_location:'''
 
'''target_location:'''
[ai]
+
<syntaxhighlight lang='wml'>
    [goal]
+
[ai]
        name=target_location
+
    [goal]
        [criteria] #NOTE: this is a SLF, because we're targeting a location
+
        name=target_location
            x,y=42,20
+
        [criteria] #NOTE: this is a SLF, because we're targeting a location
        [/criteria]
+
            x,y=42,20
        value=5
+
        [/criteria]
    [/goal]
+
        value=5
[/ai]
+
    [/goal]
 +
[/ai]
 +
</syntaxhighlight>
  
 
'''protect_location:'''
 
'''protect_location:'''
[ai]
+
<syntaxhighlight lang='wml'>
    [goal]
+
[ai]
        name=protect_location
+
    [goal]
        [criteria] #NOTE: this is a SLF, because we're protecting a location
+
        name=protect_location
            x,y=42,20
+
        [criteria] #NOTE: this is a SLF, because we're protecting a location
        [/criteria]
+
            x,y=42,20
        protect_radius=16
+
        [/criteria]
        value=5
+
        protect_radius=16
    [/goal]
+
        value=5
[/ai]
+
    [/goal]
 +
[/ai]
 +
</syntaxhighlight>
  
 
'''protect_unit:'''
 
'''protect_unit:'''
[ai]
+
<syntaxhighlight lang='wml'>
    [goal]
+
[ai]
        name=protect_unit
+
    [goal]
        [criteria] #NOTE: this is a SUF, because we're protecting a unit
+
        name=protect_unit
            side=3
+
        [criteria] #NOTE: this is a SUF, because we're protecting a unit
        [/criteria]
+
            side=3
        protect_radius=16
+
        [/criteria]
        value=5
+
        protect_radius=16
    [/goal]
+
        value=5
[/ai]
+
    [/goal]
 +
[/ai]
 +
</syntaxhighlight>
  
 
'''How to use protect_unit to protect the own leader''' (We are side 2)
 
'''How to use protect_unit to protect the own leader''' (We are side 2)
[ai]
+
<syntaxhighlight lang='wml'>
    [goal]
+
[ai]
        name=protect_unit
+
    [goal]
        [criteria]
+
        name=protect_unit
            side=2
+
        [criteria]
            canrecruit=yes
+
            side=2
        [/criteria]
+
            canrecruit=yes
        protect_radius=8
+
        [/criteria]
 +
        protect_radius=8
 
         value=5
 
         value=5
    [/goal]
+
    [/goal]
[/ai]
+
[/ai]
 +
</syntaxhighlight>
 +
 
 +
=== Deprecated AI Targeting Aspects ===
  
To modify goals from WML events, several helper macros are available in [http://www.wesnoth.org/macro-reference.xhtml#file:ai.cfg data/core/macros/ai.cfg].
+
The following AI targeting parameters currently still work, but have been superseded by the [[#The_.5Bgoal.5D_Tag|[goal] tag]]. They should not be used any more as they will likely be removed at some point. These tags only apply to the move-to-targets CA.
 +
 
 +
* '''[target]'''="": '''Deprecated'''. Any number of [target] tags can be used to set targets for the AI. For anything related to 'values', set them relative to other targets. An AI is willing to dedicate twice as many resources and travel twice as far to get to a target worth '2.0' as for a target worth '1.0'.  Applies to move-to-targets CA only.
 +
** '''[[StandardUnitFilter]]''': Do not use a [filter] tag.
 +
** '''value'''=1: (double)  A number greater than 0 (default=1) which determines how much the AI tries to move toward units which pass the filter.
  
== Filtering Combat with the 'attacks' Aspect==
+
* '''[protect_location]'''="": '''Deprecated'''. Gives the AI a location to protect. Note that the AI does ''not'' station any units around the location, it only sends units to attack any enemy units that come within the guarding radius of the target.  Applies to move-to-targets CA only.
 +
** '''x''', '''y''': Standard coordinates. These indicate the location the AI is protecting.
 +
** '''radius''': The radius around it to protect (0 indicates a single hex). {{DevFeature1.13|5}} This key has been changed to protect_radius, though it's preferred to change old code to use the [goal] tag instead.
 +
** '''value''': The importance of protecting this location.
  
The ''attacks'' aspect lets us filter the units considered during the combat candidate action.  Units on the AI side can be selected with the '''[filter_own]''' tag and enemy units are filtered via '''[filter_enemy]''', both of which take a [[StandardUnitFilter]].  Only units defined in these tags are considered as attacker/target pairs. To define, for example, an ''attacks'' aspect in which units from the elvish sorceress line are the only attackers, and undead units are the only targets, use either
+
* '''[protect_unit]'''="": '''Deprecated'''. Gives the AI a set of units to protect. Note once again that the AI does not place units around the protected units if there are no enemies nearby.  Applies to move-to-targets CA only.
[ai]
+
** '''[[StandardUnitFilter]]''': The unit(s) to protect. Do not use a [filter] tag.
    [aspect]
+
** '''radius''': The radius around it to protect (0 indicates a single hex). {{DevFeature1.13|5}} This key has been changed to protect_radius, though it's preferred to change old code to use the [goal] tag instead.
        id=attacks
+
** '''value''': The importance of protecting this unit.
        [facet]
+
 
            invalidate_on_gamestate_change=yes
+
* '''protect_leader'''=2.0 and '''protect_leader_radius'''=10: '''Deprecated'''. Target any enemy units that come within 'protect_leader_radius' of the AI leader with a value of 'protect_leader'.  Applies to move-to-targets CA only.
            [filter_own]
+
 
                type=Elvish Sorceress,Elvish Enchantress,Elvish Sylph
+
== Filtering which Units Participate in which Actions==
            [/filter_own]
+
 
            [filter_enemy]
+
{{DevFeature1.15|3}}
                race=undead
 
            [/filter_enemy]
 
        [/facet]
 
    [/aspect]
 
[/ai]
 
or
 
    [modify_ai]
 
        side=2
 
        action=add
 
        path=aspect[attacks].facet[]
 
        [facet]
 
            invalidate_on_gamestate_change=yes
 
            [filter_own]
 
                type=Elvish Sorceress,Elvish Enchantress,Elvish Sylph
 
            [/filter_own]
 
            [filter_enemy]
 
                race=undead
 
            [/filter_enemy]
 
        [/facet]
 
    [/modify_ai]
 
Several important notes:
 
* See [[AiWML#A_Bit_More_on_Simple_vs._Composite_Aspects|A Bit More on Simple vs. Composite Aspects]] and [[AiWML#Adding_and_Deleting_Aspects_with_the_.5Bmodify_ai.5D_Tag|Adding and Deleting Aspects with the [modify_ai] Tag]] below for explanations of the syntax used in these examples.
 
* This only works if 'invalidate_on_gamestate_change=yes' is set, so that the available attacker/target pairs are recalculated after each move.  This is also explained at [[AiWML#A_Bit_More_on_Simple_vs._Composite_Aspects|A Bit More on Simple vs. Composite Aspects]].
 
* If [filter_own] or [filter_enemy] are omitted, the selection defaults to all units of the respective sides.
 
* '''Most importantly''': The above examples result in the sorceresses-on-undead attacks being the ''only'' attacks done by the AI. No other attacks are executed, no matter how advantageous their outcomes might be.  There is no simple way to get around that.  An example of dealing with this (executing all attacks of a certain kind first, then doing whatever possible attacks are left afterward) by setting up an additional Lua candidate action can be found in [[Micro_AIs | Micro AI]] test scenario 'Protect the Wizard' in ''/data/ai/micro_ais/''.
 
  
== Limiting Recruiting with the 'recruitment_instruction' Aspect==
+
Each [[RCA_AI#The_Candidate_Actions_.28CAs.29_of_the_main_loop_Stage_in_the_RCA_AI|candidate action of the default AI]] can be restricted to apply to only a subset of the AI units. This is done by adding a '''[filter_own]''' tag to the '''[[Wesnoth_AI_Framework#The_.5Bai.5D_Tag_.E2.80.94_Candidate_Actions|[candidate_action]]]''' tag definition.
  
The number of units that can be recruited by the AI can be limited using the ''recruitment_instruction'' aspect. To define, for example, a ''recruitment_instruction'' aspect in which only two bowmen and one swordsman can be recruited, use
+
Typical use cases:
[ai]
+
* Restricting an action to certain units so that other units are not used to this. For example, village grabbing could be restricted to scout units only, so that slower units do not take detours on their way toward the enemies. See the example below.
    [aspect]
+
* Excluding units from a certain action in order to have them available for other actions afterward. For example, one might want to add a custom candidate action which moves healers behind injured units (or use the existing [[Micro_AIs|Micro AI]] for this). Ideally, this should happen after ''all'' other units have moved, specifically also after the move-to-targets candidate action (MtT CA) is done. In the default setting, however, the MtT CA would also move the healers. Thus, we would want to exclude them using a '''[filter_own]''' tag.
        id=recruitment
+
* Adding two instances of the same candidate action with different scores to force the order in which units participate in this action. For example, one could add another instance of the move-leader-to-keep CA with a '''[filter_own]''' tag restricting it to one leader, in order to make this leader move to a keep (and therefore recruit) first.
        [facet]
 
            [value]
 
                name=ai_default::recruitment
 
                [limit]
 
                    type=Swordsman
 
                    max=1
 
                [/limit]
 
                [limit]
 
                    type=Bowman
 
                    max=2
 
                [/limit]
 
            [/value]
 
        [/facet]
 
    [/aspect]
 
[/ai]
 
For all the possible keys and syntax, see [[AI_Recruitment#Aspect_recruitment_instruction|here]].
 
  
Several important notes:
+
Note that for the combat AI, using the attacks aspect to filter units as described in the next section '''is slightly more efficient'''. Thus, that should be the preferred method if there are many units on the map.
* This aspect may currently result in no recruiting happening at all after the listed units have reached their limit, if those units seem more desirable to the AI than the rest of the recruit list.  This is due to a [https://gna.org/bugs/index.php?19662 bug] and will be fixed soon.
 
* See [[AiWML#A_Bit_More_on_Simple_vs._Composite_Aspects|A Bit More on Simple vs. Composite Aspects]] below for an explanation of the syntax used in this example.
 
* The [[AiWML#Using_.5Bmodify_ai.5D_to_Change_Goals.2C_Candidate_Actions_and_Stages|[modify_ai] tag]] can also be used, equivalently to what is shown above for the [[AiWML#Filtering_Combat_with_the_.27attacks.27_Aspect|''attacks'' aspect]].
 
* 'name=ai_default::recruitment' needs to be set exactly like this, so that the ''ai_default::recruitment'' stage is used.
 
* A separate '''[limit]''' tag needs to be used for each unit type.
 
* The number set by the '''max''' key limits the number of units that the side can have simultaneously.  Thus, if one of the bowmen dies in the example above, another can be recruited.  This is the same behavior as one gets with the LIMIT_CONTEMPORANEOUS_RECRUITS macro.
 
* Units for which no [limit] tag is defined can be recruited in arbitrary amounts.
 
  
==Dynamic Lua Aspects==
+
Example:
 +
<syntaxhighlight lang='wml'>
 +
[candidate_action]
 +
id=villages
 +
engine=cpp
 +
name=ai_default_rca::get_villages_phase
 +
max_score=60000
 +
score=60000
 +
[filter_own]
 +
type=Wolf Rider
 +
[/filter_own]
 +
[/candidate_action]
 +
</syntaxhighlight>
  
Aspects can also be defined dynamically using Lua.  Here is an example of defining aggression so that it increases slowly from turn to turn:
 
[aspect]
 
    id=aggression
 
    engine=lua
 
   
 
    code=<<
 
        local value = wesnoth.current.turn / 10.
 
        return value
 
    >>     
 
[/aspect]
 
  
===Dynamic advancements Aspect===
+
== Filtering Combat with the ''attacks'' Aspect==
  
The advancements aspect can be used with a function <code>advance(x, y)</code>, where (x, y) is the current location of the unit about to advance. You may use <code>wesnoth.get_unit(x, y)</code> to retrieve the unit object itselfFor example, the following code advance the Spearman with id=Bob to a Swordsman, while all other Spearmen are advanced to Javelineers.
+
The ''attacks'' aspect lets us filter the units considered by the ''combat'' and ''high_xp_attacks'' candidate actions.  Units on the AI side can be selected with the '''[filter_own]''' tag and enemy units are filtered via '''[filter_enemy]''', both of which take a [[StandardUnitFilter]]. Only units defined in these tags are considered as attacker/target pairsTo define, for example, an ''attacks'' aspect in which units from the elvish sorceress line are the only attackers, and undead units are the only targets, use
[ai]
+
<syntaxhighlight lang='wml'>
    [aspect]
+
[ai]
        id=advancements
+
    [aspect]
        engine=lua
+
        id=attacks
+
        [facet]
        code=<<
+
            invalidate_on_gamestate_change=yes
            function advance(x, y)
+
            [filter_own]
                local unit = wesnoth.get_unit(x, y)
+
                type=Elvish Sorceress,Elvish Enchantress,Elvish Sylph
                if (unit.id == 'Bob') then
+
            [/filter_own]
                    return 'Swordsman'
+
            [filter_enemy]
                else
+
                race=undead
                    return 'Javelineer'
+
            [/filter_enemy]
                end
+
        [/facet]
            end
+
    [/aspect]
            return advance
+
[/ai]
        >>
+
</syntaxhighlight>
    [/aspect]
+
Several important notes:
[/ai]
+
* The ''attacks'' aspect is a ''composite'' aspect and cannot be defined using the simple syntax of the other ''standard'' aspects.  See [[Wesnoth_AI_Framework#The_.5Bai.5D_Tag_.E2.80.94_Aspects|here]] for a description of the syntax of the example.
Note that the return value of <code>advance(x, y)</code> could also be a listSee [[AiWML#The_.5Bai.5D_Tag:_Defining_Aspects|above]] for several important notes on the advancements aspect.
+
* This only works if <code>invalidate_on_gamestate_change=yes</code> is set.  The reason is that the ''attacks'' aspect internally contains information about all available attacker/target pairs.  These need to be recalculated after each moveThis is explained [[Wesnoth_AI_Framework#Some_more_on_the_invalidation_keys|here]].
 +
* If [filter_own] or [filter_enemy] are omitted, the selection defaults to all units of the respective sides.
 +
* '''Most importantly''': The above example results in sorceress-line vs undead attacks being the <u>only</u> attacks done by the AI.  No other attacks are executed, no matter how advantageous their outcomes may be.  There is no simple way around that, but it can be accomplished by one of the following means:
 +
** Setting up the [filter_own] or [filter_enemy] [[StandardUnitFilter]]s to adapt dynamically to the situation on the map.
 +
** Adding a Lua candidate action which dynamically adjusts the aspect depending on the current situation on the map.  An example of dealing with this is given in the [[Micro_AIs#Micro_AI_Test_and_Demo_Scenarios|Micro AI test scenario]] [https://github.com/wesnoth/wesnoth/blob/master/data/ai/micro_ais/scenarios/protect_unit.cfg ''Protect Unit''].
 +
** Using [[LuaAI#Dynamic_Lua_Aspects|dynamic Lua aspects]] is in principle also possible, but far from easy due to the complex tables this aspect returns.
  
== Adding, Deleting or Changing Aspects and Goals Mid Game ==
+
{{DevFeature1.13|5}}
  
The previous sections of this page demonstrate how to set up aspects and goals at the beginning of a scenario using the [ai] tag inside [side] tags. The standard aspects can also be [[Modifying_AI_Components#Using_.5Bmodify_side.5D_to_Change_Aspects_Mid_Scenario|changed while a game is in progress]] using the [ai] tag inside a [modify_side] tag with the same syntax.  However, that does not work for composite aspects and all other AI components.  For these, the [modify_ai] tag needs to be used.  It has a more complex styntax and is described at [[Modifying_AI_Components]].
+
Though the above code still works in 1.13.5 and later (and will continue to work indefinitely), it can also be simplified a little:
 +
<syntaxhighlight lang='wml'>
 +
[ai]
 +
    [attacks]
 +
        invalidate_on_gamestate_change=yes
 +
        [filter_own]
 +
            type=Elvish Sorceress,Elvish Enchantress,Elvish Sylph
 +
        [/filter_own]
 +
        [filter_enemy]
 +
            race=undead
 +
        [/filter_enemy]
 +
    [/attacks]
 +
[/ai]
 +
</syntaxhighlight>
  
== See Also ==
 
* [[Practical_Guide_to_Modifying_AI_Behavior]]
 
* [[ReferenceWML]]
 
  
 +
'''See also:''' [[Wesnoth AI]]
 
[[Category: WML Reference]]
 
[[Category: WML Reference]]
 
[[Category:AI]]
 
[[Category:AI]]

Revision as of 16:51, 22 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;

Customizing the Default AI Using WML

This page describes how the behavior of the default (RCA) AI can be customized using simple WML commands. The descriptions below assume a basic understanding of how the RCA AI evaluates moves, what candidate actions, aspects and goals are, and how they interact. If you do not know these things yet, check out the RCA AI page.

This page contains:

  • Descriptions of the aspects and goals of the default AI
  • Instructions for setting them up at the beginning of the scenario in a [side] tag

This page does not contain:

Defining Aspects and Goals of the RCA AI

Aspects and goals of the default (RCA) AI can be defined at the beginning of a scenario with [ai] tags inside the [side] tags. They are used to customize certain aspects of the AI. The [ai] tag, when used for this purpose, takes the aspects themselves as arguments, as well as the following general keys:

  • time_of_day: (string) The time(s) of day when the AI should use the parameters given in this [ai] tag. Possible values are listed in data/core/macros/schedules.cfg (see also TimeWML). Note that it is the id (not the name) of the time of day that needs to be used here. Also note that this aspect did not work for a long time due to a bug (versions 1.7.4 - 1.11.6). It has been fixed for BfW 1.11.7.
  • turns: (string) During which turns the AI should use the parameters given in this [ai] tag. This takes the same syntax of dashes (-) and commas (,) as is described under Filtering Locations in FilterWML, except of course they apply to turns not locations.
  • ai_algorithm: (string) Allows an alternate AI algorithm (cannot be created with WML) to be used. Besides the default, the game only comes with idle_ai, which makes the AI do nothing and can be used to create a passive, unmoving side. Cannot be applied only to a set of turns or a given time of day using the keys turns and time_of_day, but must be given either in an [ai] tag without the aforementioned keys or in the [side] tag outside all [ai] tags. (Version 1.13.5 and later only) In 1.13, the meaning of ai_algorithm has changed and no longer selects a native AI that's built into the engine, as the RCA AI has now become the core system and no alternatives exist anymore. Instead, it selects a predefined [ai] definition, such as those defined in data/ai/ais. Since these are defined in WML, you can easily build your own.

An example of a simple use of the [ai] tag to set AI parameters (aspects) is

[ai]
    time_of_day=dusk
    aggression=0.99
    caution=0.01
    [avoid]
        [filter]
            side=2,3
        [/filter]
        radius=2
    [/avoid]
[/ai]


Important Note: If you use a different AI engine (FormulaAI or LuaAI) for a side, setting aspects in the [side] tag might not work due to a bug in the AI setup mechanism (or it might; there's no general rule that catches all cases). In that case, you might have to use [modify_side][ai] in a prestart or start event instead. If unsure, you can use :inspect in debug mode to verify whether an aspect was changed successfully.

List of AI Aspects

  • advancements: (string) Defines a list of unit types to which AI units can advance. If a unit type is listed here, units that can advance to this type will only advance to this type, even if they have, in principle, several advancement options. As an example, if this aspect is set to 'Javelineer,Elvish Hero', then all Spearmen advance to Javelineers, and all Elvish Fighters advance to Elvish Heroes. All other units follow their usual advancement choices as determined by the AI. Important notes:
    • This is a simplified version of the more complex (and arguably more useful) application of a dynamic Lua advancements aspect, as described here.
    • The advancements aspect only takes effect during the AI turn, that is, on offense only, not on defense.
    • Listing more than one advancement unit type for a given unit still results in only one of the types being used (generally the one listed last).
  • aggression=0.4: (double: ranging from -infinity to 1.0) This key affects how the AI selects its attack targets. The higher the value, the more likely the AI is to attack even if odds are not in its favor. Applies to combat CA only.
    • Important: do not set aggression to values greater than 1 as this makes the AI prefer attacks in which it receives more damage (see below) unless that is specifically the effect you want to achieve.
    • In the attack evaluation, each attack (this includes attack combinations of several AI units against the same enemy unit) is assigned a score. The attack with the highest score is done first. Then the next attack is evaluated, until no attack with a score greater than 0 is found any more. (Note that this attack score is different from the combat CA score, which is always 100,000 as long as an individual attack score >0 is found. The combat CA score is zero if the highest attack score is <=0).
    • The attack score is a complex combination of many different aspects of the attacks. Positive (additive) contributions to the score are things like the value (cost and XP) of the target, the chance to kill the target, whether it is already wounded, how much damage the attack is likely to inflict, etc. Negative (additive) factors include how much damage the AI's units are likely to take, how valuable they are, how exposed they will be after the attack, etc. There are also multiplicative factors that are used if the attack target is a threat to the AI's leader etc.
    • All the negative contributions to the score are multiplied by '(1-aggression)'. This means that:
      • If 'aggression=1', no negative contributions are added to the score. Thus, the AI disregards damage done to its own units and selects attacks based solely on the damage it can do to enemy units. If the AI can inflict 1 damage and take 0, or inflict 2 damage and take 20, it will take the latter option.
      • The smaller the value of aggression, the more weight is put on value of and potential damage to the AI's units as compared to the attack target.
      • Roughly speaking, 'aggression=0' results in the AI valuing its units approximately as much as the enemy units. This is not a one-to-one relation, but can be used as an approximate guideline.
      • Very large negative values of aggression mean that the value of the AI's units is much more important than that of the enemy units. As a result, the AI never attacks unless it will receive no damage in exchange.
      • The rating for damage received in an attack actually becomes a positive contribution to the score for values of aggression larger than 1. This usually does not result in sensible behavior and values greater than 1 should therefore not be used.
    • Note: aggression is always set to 1.0 for attacks on units that pose a direct threat to the AI's leader. Currently this only means units adjacent to the leader.
  • [attacks]: Filters the units considered for combat, both on the AI and the enemy sides. Applies to the combat and high_xp_attacks CAs only. It cannot be set in the same way as the other aspects and is therefore described in a separate section below.
  • [avoid]: Makes the AI avoid specific locations. The AI never moves a unit to these locations except for trying to move its leader to a keep or toward [leader_goal]s, and thus applies to all CAs except move-leader-to-goals and move-leader-to-keep.
  • caution=0.25: (double) Defines how cautious the AI is in several ways. It determines whether the leader should move toward [leader_goal], if attacks are worth moving onto less favorable terrain, whether units should retreat, and whether the AI should move units toward targets individually, as groups or not at all. Affects several CAs (listed in the order of their evaluation scores):
    • Move-leader-to-goals CA: If max_risk is not set in [leader_goal], its default value is '1-caution'. This determines whether the leader takes the next step toward his goal. See description of [leader_goal].
    • Combat CA:
      • During the evaluation of attacks, the AI considers whether the attacking units could get onto more favorable terrain if they didn't attack but moved somewhere else instead. The difference between the two terrain ratings, together with a number of other factors, determines the "exposure" rating of the units. This exposure is then subtracted from the 'attack score' as described for aggression above.
      • The exposure rating also contains a multiplication by caution, meaning that 'caution=0' results in exposure not being taken into account, and that it becomes more and more important for larger values. In other words, the higher the values of caution, the more reluctant is the AI to attack from unfavorable terrain. (Note that exposure is one of the negative contributions to the attack score as described for aggression, and therefore is also ignored if 'aggression=1' is set.)
      • If the AI leader is used in an attack, the AI always uses 'caution=2' for the evaluation of that attack.
    • Retreat CA:
      • If caution is greater than 0, there is an evaluation of forces for the map location a unit stands on. This is basically the sum of damage that can be done to that location by either side, reduced by terrain defense and relative hitpoints if attackers don't have full health. A retreat takes place, if caution × their_power > our_power. There is also a terrain factor involved if the attacker is not on optimal terrain, similar to the exposure described above for the combat CA.
      • So let's say the AI has its default caution of 0.25. Then the enemy forces have to be at least 4 times as strong before the unit retreats. For a caution of 1, as soon as the enemy is stronger, the unit retreats.
      • The AI never retreats if caution is set to 0 or lower.
    • Move-to-targets CA:
      • If grouping for the AI is enabled and the path along which to move toward a target is considered to be dangerous, caution has an influence, too. "Dangerous" mainly means that there is a good chance for a unit to be killed if it's by itself. In that case, the AI compares its units to the enemy units and based on the result moves forward or not. All units that can reach the next location of the move are considered. The formula for deciding whether to move toward the target as a group is our_strength / their_strength > 0.5 + caution. If this condition holds true, units are moved toward the goal as a group, otherwise they try to group together in a location favorable for a attack on the enemy during the next turn.
      • So if caution is 0.5, the AI side needs to be at least as strong as the enemy. If it is 0, the AI moves toward the target, even if the enemy is up to twice as strong as the AI. Setting caution to 1.5 means the AI needs to be at least twice as strong as the enemy.
      • The AI also considers retreating units during the move-to-target phase based on criteria similar to those for the retreat CA.
  • [goal]="": Defines units or locations as move targets (not attack targets!) for the AI. Applies to move-to-targets CA only. <-- That is extremely important to understand, in particular the fact that the [goal] tag has no influence whatsoever on attacks. See the dedicated section on the [goal] tag below for details.
  • grouping="offensive": (string) How the AI should try to group units. Applies to move-to-targets CA only. Possible values:
    • offensive: Makes the AI try to group units together before attacking.
    • defensive: Makes the AI group units together very conservatively, only advancing them much beyond its castle if it has overwhelming force.
    • no: Makes the AI use no grouping behavior.
  • leader_aggression="-4.0": Exactly as aggression, but for units which can recruit. Applies to combat CA only. Note that the move-leader-to-keep CA has a higher score than the combat CA. A leader therefore usually only attacks if he is on his keep at the beginning of the turn, otherwise he moves toward the closest keep instead, even with leader_aggression=1.
  • [leader_goal]="": Makes the AI try to move its leader to a specific location. Applies to move-leader-to-goals CA only.
    • x, y: The location toward which the AI should move its leader.
    • auto_remove=no: (bool) If 'no' (default), the AI moves the leader to the goal, after which he stays there until [leader_goal] is removed manually. If 'yes', the leader_goal is removed upon the leader getting there. Important: this only works if id is set correctly (see the next bullet).
    • id="": (string) An internal id key of the [leader_goal] tag. An id is required for auto_remove to work. However, setting this id does not automatically set the id of the [leader_goal] facet. Thus, in principle for this to work, you need to set the id of the facet as described here and set the id key in [leader_value] to the same value. Since you are probably only going to use one [leader_goal] tag at a time, there is a much simpler way: setting 'id=0' (which refers to the first facet) or 'id=*' (which means all facets) in [leader_goal] allows auto_remove to work without the extra step of setting the facet id. (Version 1.13.5 and later only) Setting this now also sets the id of the [leader_goal] facet, allowing auto_remove to work with multiple leader goals without using the fully-expanded aspect syntax.
    • max_risk=1-caution: (double: meaningful values are >=0) How much risk the leader may be exposed to by moving toward the goal. For evaluating this risk, the AI multiplies the leader's hitpoints by this number. The leader is only moved toward the goal if the resulting value is larger than the expected damage the leader is going to take during the next enemy turn. Thus, 'max_risk=0' means he will only move if no attack on him is possible at the target hex of the move. 'max_risk=1' (or larger) results in him moving even if he's almost certainly going to die.
  • leader_ignores_keep=no: (bool) If 'yes', AI leaders do not move to the closest keep at the beginning of the turn. Instead, they participate in the move_to_targets candidate action (and all other CAs in which they already participated anyway, of course). For practical purposes this means that:
    • Leaders participate in all the moves and attacks in the same way as any other unit of the AI side.
    • AI leaders do not recruit except on the first turn if they start on a keep, or if they accidentally end up on a keep. Thus, if a leader is supposed to recruit first and then participate in the action, leader_ignores_keep should be set to 'no' at the beginning of the scenario, and be changed to 'yes' in an event later.
  • leader_value=3: (double) A number 0 or higher which determines the value of enemy leaders as targets. Affects move-to-targets CA only (and therefore specifically does not apply to attacks).
  • passive_leader=no: (bool) If 'yes', the AI leader never moves or attacks, not even to move back to the keep (unless 'passive_leader_shares_keep=yes' is set) or to attack adjacent units, except to obey [leader_goal]s. Affects all CAs except recruitment and move-leader-to-goals.
  • passive_leader_shares_keep=no: (bool) If 'yes', lets the AI leader moves off the keep to share it with allied leaders (if they can reach it next turn) if 'passive_leader=yes' is set. He also returns to keep to recruit when possible and attacks adjacent enemy units.
  • recruitment_diversity, recruitment_instructions, recruitment_more, recruitment_pattern, recruitment_randomness, recruitment_save_gold: These aspects can be used to customize recruiting with the new recruitment CA introduced in Wesnoth 1.11. They are described on a separate page.
  • scout_village_targeting=3: (double) The AI multiplies the value of village targets for scouts by this value. Affects move-to-targets CA only.
  • simple_targeting=no: (bool) If 'yes', the AI moves its units toward targets one by one (sequentially), without considering whether another unit might be better suited for the current move or target. If 'no' (the default), all units are considered for all targets. This is slower, but might result in better moves. Affects move-to-targets CA only.
  • support_villages=no: (bool) Trigger a code path that tries to protect those villages that are threatened by the enemy. This seems to cause the AI to 'sit around' a lot, so it's only used if it's explicitly enabled. Affects move-to-targets CA only.
  • village_value=1: (double) A number 0 or higher which determines how much the AI tries to go for villages as targets. Affects move-to-targets CA only.
  • villages_per_scout=4: (int) A number 0 or higher which determines how many scouts the AI recruits. If 0, the AI doesn't recruit scouts to capture villages. Affects recruitment CA only.

Removed AI Aspects

The following AI parameters (aspects) can still be set, their values can be retrieved, and they can be viewed in the gamestate inspector dialog, but they do not have an effect in the RCA AI code any more. Some other parameters will also likely be removed in the future. We will update this list accordingly. (Version 1.13.5 and later only) Except for attack_depth, these have now all been removed.

  • attack_depth=5: (int)
  • number_of_possible_recruits_to_force_recruit=3.1: (double)
  • recruitment: This aspect was used to customize the recruitment of the old default AI (the one used before the RCA AI). This recruitment code is not used in the RCA AI any more. Setting recruitment instructions with this aspect is therefore meaningless. Use the recruitment_instructions aspect instead.
    • It is, in principle, still possible to use this aspect together with the recruitment stage, but this is discouraged for the reasons given at this link.
  • recruitment_ignore_bad_combat=no: (bool)
  • recruitment_ignore_bad_movement=no: (bool)

AI Targets and Goals

AI targets are used in the move-to-targets candidate action (CA) to move the AI's units toward selected units or locations. The AI engine automatically selects all enemy leaders, enemy units that pose a threat to the AI leader and unowned or enemy-owned villages as targets and assigns them certain base values. Additional targets can be defined using the [goal] tag.

It is very important to realize that these targets apply to the move-to-targets CA only and have no influence on other CAs. In particular, they have no effect whatsoever on which enemies the AI attacks. This is often a source of confusion for scenario creators. More background information on RCA AI targets and goals can be found here. The sections below only describe how to set up goals in order to add targets for the move-to-targets CA.

The [goal] Tag

The [goal] tag specifies target units or locations toward which the AI should move its units in the move-to-targets CA. The following keys/tags can be used:

  • name="target": (string) The following values are possible and result in different types of targets, as shown in the examples below:
    • target: The (default) target goal specifies target units (not necessarily enemy units) toward which the AI should move its units. (Version 1.13.5 and later only) target_unit is now a synonym for this.
    • target_location: Specifies target locations toward which the AI should move its units.
    • protect_location: Specifies locations that the AI should protect. Enemy units within the specified distance (protect_radius) of one of these locations are marked as targets with the provided value. Note that the AI will not station any units around the protected locations. It will only send units toward enemy units that come within protect_radius of them.
    • protect_unit: Specifies units (of all sides) that the AI should protect. Enemy units within protect_radius of one of these units are marked as targets with the provided value. Note once again that the AI will not place units around the protected units if there are no enemies nearby.
    • protect_my_unit: (deprecated) Specifies units from the AI's own side that the AI should protect. (This is basically the protect_unit goal with an implied side= in the filter, restricting matching units to the AI's side.) Enemy units within protect_radius of one of these units are marked as targets with the provided value. Note once again that the AI will not place units around the protected units if there are no enemies nearby.
    • lua_goal: A dynamically calculated goal written in Lua. See here for details on how this works.
  • value=0: (double) The value of the goal.
  • protect_radius=20: (int) The protection radius. Applies to protect_location, protect_unit and protect_my_unit.

Examples of [goal] Tag Usage

target:

[ai]
    [goal]
        [criteria] #NOTE: this is a SUF, because we're targeting a unit
            side=3
        [/criteria]
        value=5
    [/goal]
[/ai]

target_location:

[ai]
    [goal]
        name=target_location
        [criteria] #NOTE: this is a SLF, because we're targeting a location
            x,y=42,20
        [/criteria]
        value=5
    [/goal]
[/ai]

protect_location:

[ai]
    [goal]
        name=protect_location
        [criteria] #NOTE: this is a SLF, because we're protecting a location
            x,y=42,20
        [/criteria]
        protect_radius=16
        value=5
    [/goal]
[/ai]

protect_unit:

[ai]
    [goal]
        name=protect_unit
        [criteria] #NOTE: this is a SUF, because we're protecting a unit
            side=3
        [/criteria]
        protect_radius=16
        value=5
    [/goal]
[/ai]

How to use protect_unit to protect the own leader (We are side 2)

[ai]
    [goal]
        name=protect_unit
        [criteria]
            side=2
            canrecruit=yes
        [/criteria]
        protect_radius=8
        value=5
    [/goal]
[/ai]

Deprecated AI Targeting Aspects

The following AI targeting parameters currently still work, but have been superseded by the [goal] tag. They should not be used any more as they will likely be removed at some point. These tags only apply to the move-to-targets CA.

  • [target]="": Deprecated. Any number of [target] tags can be used to set targets for the AI. For anything related to 'values', set them relative to other targets. An AI is willing to dedicate twice as many resources and travel twice as far to get to a target worth '2.0' as for a target worth '1.0'. Applies to move-to-targets CA only.
    • StandardUnitFilter: Do not use a [filter] tag.
    • value=1: (double) A number greater than 0 (default=1) which determines how much the AI tries to move toward units which pass the filter.
  • [protect_location]="": Deprecated. Gives the AI a location to protect. Note that the AI does not station any units around the location, it only sends units to attack any enemy units that come within the guarding radius of the target. Applies to move-to-targets CA only.
    • x, y: Standard coordinates. These indicate the location the AI is protecting.
    • radius: The radius around it to protect (0 indicates a single hex). (Version 1.13.5 and later only) This key has been changed to protect_radius, though it's preferred to change old code to use the [goal] tag instead.
    • value: The importance of protecting this location.
  • [protect_unit]="": Deprecated. Gives the AI a set of units to protect. Note once again that the AI does not place units around the protected units if there are no enemies nearby. Applies to move-to-targets CA only.
    • StandardUnitFilter: The unit(s) to protect. Do not use a [filter] tag.
    • radius: The radius around it to protect (0 indicates a single hex). (Version 1.13.5 and later only) This key has been changed to protect_radius, though it's preferred to change old code to use the [goal] tag instead.
    • value: The importance of protecting this unit.
  • protect_leader=2.0 and protect_leader_radius=10: Deprecated. Target any enemy units that come within 'protect_leader_radius' of the AI leader with a value of 'protect_leader'. Applies to move-to-targets CA only.

Filtering which Units Participate in which Actions

(Version 1.15.3 and later only)

Each candidate action of the default AI can be restricted to apply to only a subset of the AI units. This is done by adding a [filter_own] tag to the [candidate_action] tag definition.

Typical use cases:

  • Restricting an action to certain units so that other units are not used to this. For example, village grabbing could be restricted to scout units only, so that slower units do not take detours on their way toward the enemies. See the example below.
  • Excluding units from a certain action in order to have them available for other actions afterward. For example, one might want to add a custom candidate action which moves healers behind injured units (or use the existing Micro AI for this). Ideally, this should happen after all other units have moved, specifically also after the move-to-targets candidate action (MtT CA) is done. In the default setting, however, the MtT CA would also move the healers. Thus, we would want to exclude them using a [filter_own] tag.
  • Adding two instances of the same candidate action with different scores to force the order in which units participate in this action. For example, one could add another instance of the move-leader-to-keep CA with a [filter_own] tag restricting it to one leader, in order to make this leader move to a keep (and therefore recruit) first.

Note that for the combat AI, using the attacks aspect to filter units as described in the next section is slightly more efficient. Thus, that should be the preferred method if there are many units on the map.

Example:

[candidate_action]
	id=villages
	engine=cpp
	name=ai_default_rca::get_villages_phase
	max_score=60000
	score=60000
	[filter_own]
		type=Wolf Rider
	[/filter_own]
[/candidate_action]


Filtering Combat with the attacks Aspect

The attacks aspect lets us filter the units considered by the combat and high_xp_attacks candidate actions. Units on the AI side can be selected with the [filter_own] tag and enemy units are filtered via [filter_enemy], both of which take a StandardUnitFilter. Only units defined in these tags are considered as attacker/target pairs. To define, for example, an attacks aspect in which units from the elvish sorceress line are the only attackers, and undead units are the only targets, use

[ai]
    [aspect]
        id=attacks
        [facet]
            invalidate_on_gamestate_change=yes
            [filter_own]
                type=Elvish Sorceress,Elvish Enchantress,Elvish Sylph
            [/filter_own]
            [filter_enemy]
                race=undead
            [/filter_enemy]
        [/facet]
    [/aspect]
[/ai]

Several important notes:

  • The attacks aspect is a composite aspect and cannot be defined using the simple syntax of the other standard aspects. See here for a description of the syntax of the example.
  • This only works if invalidate_on_gamestate_change=yes is set. The reason is that the attacks aspect internally contains information about all available attacker/target pairs. These need to be recalculated after each move. This is explained here.
  • If [filter_own] or [filter_enemy] are omitted, the selection defaults to all units of the respective sides.
  • Most importantly: The above example results in sorceress-line vs undead attacks being the only attacks done by the AI. No other attacks are executed, no matter how advantageous their outcomes may be. There is no simple way around that, but it can be accomplished by one of the following means:
    • Setting up the [filter_own] or [filter_enemy] StandardUnitFilters to adapt dynamically to the situation on the map.
    • Adding a Lua candidate action which dynamically adjusts the aspect depending on the current situation on the map. An example of dealing with this is given in the Micro AI test scenario Protect Unit.
    • Using dynamic Lua aspects is in principle also possible, but far from easy due to the complex tables this aspect returns.

(Version 1.13.5 and later only)

Though the above code still works in 1.13.5 and later (and will continue to work indefinitely), it can also be simplified a little:

[ai]
    [attacks]
        invalidate_on_gamestate_change=yes
        [filter_own]
            type=Elvish Sorceress,Elvish Enchantress,Elvish Sylph
        [/filter_own]
        [filter_enemy]
            race=undead
        [/filter_enemy]
    [/attacks]
[/ai]


See also: Wesnoth AI