Behavior adding support to grab an ECBehaviorGrabSpot.

Grab spots are typically used for physics interaction like VR hand use but can be used also with mouse interaction. The actual grabbing interaction, exact grab location and orientation as well as attaching logic is handled by other behaviors using listening. This behavior also tracks if what grab spot an actor is grabbing. Hence at most one grab spot can be grabbed by this behavior at each time.

Elements able to be grabbed have to use the ECBehaviorGrabSpot behavior. Both the grab spot and the grabber have to persist the other behavior. During restoring no notifications are triggered this way.

To detect grab spots a touch sensor is added with a default sphere shape. By default the touch sensor is disabled and has to be enabled if the game logic allows grabbing. The collision filter category is set to BaseGameApp.CollisionFilterBit.trigger and the collision filter mask is set to BaseGameApp.CollisionFilterBit.dynamic.

This behavior can be added multiple times to an element. Use the behavior identifier to tell them apart.

Element class properties have the prefix grabber. or grabber(id). if id is not empty.

Shape of collider used to detect grab spots.

• Full name: grabber.shape or grabber(id).shape
• Type: string (shape format). See “Shape List Encoding” in CodecPropertyString.
• Default Value: empty string
• Example (*.deeclass):

  <string name='grabber(right).shape'>box:extends,0.1,0.1,0.1</string>

Attach position relative to parent element or bone.

• Full name: grabber.position or grabber(id).position
• Type: 3-component float vector
• Default Value: (0, 0, 0)
• Example (*.deeclass):

  <vector name='grabber(right).position' x='0' y='0' z='0.1'/>

Attach orientation in euler degrees relative to parent element or bone.

• Full name: grabber.rotation or grabber(id).rotation
• Type: 3-component float vector
• Default Value: (0, 0, 0)
• Example (*.deeclass):

  <vector name='grabber(right).rotation' x='-45' y='0' z='0'/>

Name of bone to attach to or empty string to attach to the parent element.

• Full name: grabber.bone or grabber(id).bone
• Type: string
• Default Value: empty string
• Example (*.deeclass):

  <string name='grabber(right).bone'>attach hand.r</string>

Grabber grabbed grab spot.

Grabber released grab spot.

Start touching grab spot.

Stop touching grab spot.

Grab spot can be touched if all listeners return true.

Grabber enabled changed.

This behavior does require other behaviors.

• ECBehaviorCollider: If used attaches grab spot touch collider to collider
• ECBehaviorVRHand: If used attaches grab spot touch collider to VR hand collider

This behavior does support element class to be persistable (setPersistable).

ECBehaviorGrabber.

Since DragonScript Module Version 1.9

• Grab objects in VR

The following example creates an element class with support to test what element the player is pointing at:

class MyElement extends BehaviorElementClass
   public var ECBehaviorVRPlayspace vrPlayspace
   public var ECBehaviorVRHand vrHandRight
   public var ECBehaviorVRHand vrHandLeft
   public var ECBehaviorGrabber vrRightHandGrabber
   public var ECBehaviorGrabber vrLeftHandGrabber
   
   public func new()
      // Create playspace
      vrPlayspace = ECBehaviorVRPlayspace.new(this)
      
      // Create hand controllers. The InputDeviceType indicates what device type
      // to monitor. vrRightHand and vrLeftHand can exist only once
      vrHandRight = ECBehaviorVRHand.new(this, vrPlayspace, InputDeviceType.vrRightHand, "right")
      vrHandLeft = ECBehaviorVRHand.new(this, vrPlayspace, InputDeviceType.vrLeftHand, "left")
      
      // Create grabbers for each hand
      vrRightHandGrabber = ECBehaviorGrabber.new(this, vrRightHand, "right")
      vrLeftHandGrabber = ECBehaviorGrabber.new(this, vrLeftHand, "left")
  end
end

The BaseVRActorClass provides full VR support including ECBehaviorGrabber for both hands.

Using element class supporting adding behaviors the behavior can be added like this:

<?xml version='1.0' encoding='UTF-8'?>
<elementClass name='MyClass' class='GenericBehaviorElement'>
  <behavior type='ECBehaviorVRPlayspace'/>
  <behavior type='ECBehaviorVRHand' id='right'/>
  <behavior type='ECBehaviorVRHand' id='left'/>
 
  <behavior type='ECBehaviorGrabber' id='right'>
    <!-- optional: use vr hand with id instead of empty string -->
    <string name='vrHand'>right</string>
 
    <!-- optional: set collision filter. default value '4:1' which means
                   category BaseGameApp.CollisionFilterBit.trigger
                   filter BaseGameApp.CollisionFilterBit.dynamic.
                   format is '', 'category' or 'category:filter' where category and filter
                   are a list of bits to set. -->
    <string name='collisionFilter'>4:1 2</string>
 
    <!-- set element properties. omit property prefix if used inside behavior tag -->
    <string name='.bone'>hand.r</string>
  </behavior>
 
  <!-- for adding multiple behaviors use unique identifiers -->
  <behavior type='ECBehaviorCustomColor' id='left'>
    <string name='vrHand'>left</string>
    <string name='.bone'>hand.l</string>
  </behavior>
</elementClass>

• DEExamples Repository: ExampleVR project.