{{tag>dragonscript behavior}}
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[[:start|Start Page]] >> [[main|DragonScript Scripting Language]] >> [[dragengine:modules:dragonscript:abstractions|Abstraction Layers: How you want to build your Game]] >> [[dragengine:modules:dragonscript:behavior_elements|Behavior Elements]] >> **ECBehaviorLookAt**
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  * [[behaviors_use_cases|Behaviors Explained: By Use-Case]]
  * [[behaviors_a_to_z|Behaviors Explained: From A to Z]]

====== ECBehaviorLookAt ======

Behavior adding support to actors to know what element they are looking at.

Behavior uses one collider collision test located attached ECBehaviorColliderAI facing forward. If no [[behavior_colliderai|ECBehaviorColliderAI]] is present [[behavior_collider|ECBehaviorCollider]] is used instead.

If [[behavior_component|ECBehaviorComponent]] is present and a test bone is set the collision test will be  attached to the component bone. This is simple and good solution for FPS type games.

If no component and bone is used and [[behavior_locomotion|ECBehaviorLocomotion]] is present then the test parameters will be updated to match the locomotion looking direction.

====== Instance Counts ======
This behavior can be used only once on an element.

====== Element Class Properties ======
Element class properties have the prefix ''lookAt.'' .

===== range =====
Set range in meters. Elements will only be detected this far.
  * Full name: ''lookAt.range''
  * Type: float
  * Default Value: 2
  * Restriction: At least 0
  * Example (*.deeclass) <code xml><float name='lookAt.range'>3</float></code>

===== origin =====
Set origin from where the test ray is cast.
  * Full name: ''lookAt.origin''
  * Type: 3-component float vector
  * Default Value: (0,1.6,0)
  * Example (*.deeclass) <code xml><vector name='lookAt.origin' x='0' y='1.6' z='0.2'/></code>

===== bone =====
Set bone from where the test ray is cast.
  * Full name: ''lookAt.bone''
  * Type: string
  * Default Value: empty string
  * Example (*.deeclass) <code xml><string name='lookAt.bone'>head</string></code>

====== Events ======

This behavior has these events:

===== enabledChanged =====

Enabled changed.

===== lookAtChanged =====

Looking at element changed.

====== Behavior Tree Actions ======

This behavior adds these behavior tree actions if behavior tree is present.

===== lookAt.check =====

Check one or more look-at parameters. Action succeeds if all parameter value matches their respective look-at parameter otherwise action fails. This action is typically used as first action in a sequence to run the sequence only if a look-at parameter matches (or not).

^Parameter^Value^Description^
|enabled|''true'', ''false''|Look-at is enabled|
|lookAt|''true'', ''false''|Is looking at element|
|lookAt.distance.less|float|Distance to look-at element is less than value meters|
|lookAt.distance.greater|float|Distance to look-at element is greater than value meters|
|lookAt.player|''true'', ''false''|Is looking at player|
|wait| |If present action returns BTResult.running instead of BTResult.failed to wait until the checks are all fulfilled|

This is an example of using this action:
<code xml>
<sequence>
  <action name='lookAt.check'>
    <parameter name='lookAt.player'>true</parameter>
  </action>
  <!-- actions here run only if looking at player -->
</sequence>
</code>

====== Behavior Tree Conditions ======

This behavior adds these behavior tree conditions if behavior tree is present.

===== lookAt.check =====

Check one or more look-at parameters. Conditions returns true if all parameter value match their respective look-at parameter. This condition is typically used to run an action or sequence of actions as long as look-at conditions are true.

^Parameter^Value^Description^
|enabled|''true'', ''false''|Look-at is enabled|
|lookAt.lookAt|''true'', ''false''|Is looking at element|
|lookAt.lookAt.distance.less|float|Distance to look-at element is less than value meters|
|lookAt.lookAt.distance.greater|float|Distance to look-at element is greater than value meters|
|lookAt.lookAt.player|''true'', ''false''|Is looking at player|

This is an example of using this condition:
<code xml>
<action name='myAction' id='doing something'>
  <parameter name='lookAt.enabled'>true</parameter>
  <condition>lookAt.check</condition>
</action>
</code>

====== State Machine Actions ======

Same as [[#behavior_tree_actions|Behavior Tree Actions]].

====== State Machine Conditions ======

Same as [[#behavior_tree_conditions|Behavior Tree Conditions]].

====== State Machine Events ======

This behavior sends these state machine events.

===== lookAt.enabled =====

Look-at has been enabled.

===== lookAt.disabled =====

Look-at has been disabled.

===== lookAt.lookAt =====

Looking at an element. Send if looking at an element when previously not looking at an element or looking at a different element.

===== lookAt.noLookAt =====

Not looking at an element. Send if not looking at an element when previously has been looking at an element.

====== Required Behaviors ======

This behavior requires no other behaviors.

====== Optional Behaviors ======

  * [[behavior_colliderai|ECBehaviorColliderAI]]: Cast test ray relative to collider
  * [[behavior_collider|ECBehaviorCollider]]: Cast test ray relative to collider
  * [[behavior_component|ECBehaviorComponent]]: Cast test ray from bone from component
  * [[behavior_locomotion|ECBehaviorLocomotion]]: Use lcomotion looking state to direct test ray cast direction
  * [[behavior_behaviortree|ECBehaviorBehaviorTree]]: Add actions and conditions for behavior trees to use.
  * [[behavior_statemachine|ECBehaviorStateMachine]]: Add actions and conditions for state machine to use and events to send to the state machine.

====== Persistency ======

This behavior does not required element class to be persistable (setPersistable).

====== API Documentation ======

#@LinkApiDocDEDS2_HTML~classDragengine_1_1Scenery_1_1ECBehaviorLookAt.html,ECBehaviorLookAt~@#.

Since DragonScript Module Version ''1.0''

====== Use Cases ======

  * Detect what element the player or an NPC is looking at.

====== Element Class Example ======

This example defines an element which look-at support.

<code>
class MyElement extends BehaviorElementClass
  public var ECBehaviorComponent component
  public var ECBehaviorCollider collider
  public var ECBehaviorColliderAI colliderAI
  public var ECBehaviorLocomotion locomotion
  public var ECBehaviorLookAt lookAt
  func new()
    component = ECBehaviorComponent.new(this, null)
    collider = ECBehaviorCollider.new(this, component)
    colliderAI = ECBehaviorColliderAI.new(this, collider)
    locomotion = ECBehaviorLocomotion.new(this, colliderAI)
    lookAt = ECBehaviorLookAt.new(this, colliderAI, component, locomotion)
  end
end
</code>

====== Behavior Factory ======

Using element class supporting adding behaviors the behavior can be added like this:
<code xml>
<?xml version='1.0' encoding='UTF-8'?>
<elementClass name='MyClass' class='GenericBehaviorElement'>
  <behavior type='ECBehaviorComponent'/>
  <behavior type='ECBehaviorCollider'/>
  <behavior type='ECBehaviorColliderAI'/>
  <behavior type='ECBehaviorLocomotion'/>
  
  <behavior type='ECBehaviorLookAt'>
    <!-- optional: set collision filter. default value '3:0 1 2 3' which means
                   category BaseGameApp.CollisionFilterBit.actorAI
                   filter BaseGameApp.CollisionFilterBit.geometry,
                          BaseGameApp.CollisionFilterBit.dynamic,
                          BaseGameApp.CollisionFilterBit.actorAI.
                   format is '', 'category' or 'category:filter' where category and filter
                   are a list of bits to set. -->
    <string name='collisionFilter'>3:0 1 2 3</string>
    
    <!-- optional: use component with id instead of empty string -->
    <string name='component'>second</string>
    
    <!-- optional: use behavior tree with id instead of empty string -->
    <string name='behaviorTree'>second</string>
    
    <!-- optional: use state machine with id instead of empty string -->
    <string name='stateMachine'>second</string>
    
    <!-- set element properties. omit property prefix if used inside behavior tag -->
    <string name='.name'>Color 1</string>
  </behavior>
  
  <!-- for adding multiple behaviors use unique identifiers -->
  <behavior type='ECBehaviorLookAt' id='second'/>
</elementClass>
</code>

====== Live Examples ======

  * [[https://github.com/LordOfDragons/deexamples|DEExamples Repository]]