Behavior Tree BlackboardVariable<T>Value changes references despite editor assignment

Unity Engine
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1

Hi, I have encountered what I believe to be a bug in the Behavior package where the blackboard variable source object gets swapped by some magic (hard to trace process).

Here’s my setup:

  • I have a Character and a bunch of abilities that all inherit from CharacterAbility
  • Attached to the character is a BehaviorAgent that drives input to the abilities for NPCs
  • I have made a simple custom Condition node that has a BlackboardVariable<CharacterAbility> to check if that particular implementation of the CharacterAbility is Authorized to be executed.
Condition Code 
[Serializable, Unity.Properties.GeneratePropertyBag]
[Condition(name: "AbilityReady", story: "Is [Ability] Ready?", category: "Conditions", id: "1aca371128344d88ef24165aa09d1b2c")]
public partial class AbilityReadyCondition : Condition {
    [SerializeReference] public BlackboardVariable<CharacterAbility> Ability;
    public override bool IsTrue() {
        return Ability.Value.AbilityAuthorized;
    }
}
  • I have assigned an ability called CharacterDash2D from my Blackboard to this node
    image
    image928×253 24 KB

Here’s where I encounter an undesirable behavior:

  • At runtime, when the Behavior Agent runs into this Condition, it appears have swapped the reference from the CharacterDash2D to another CharacterAbility attached to the Agent, namely Orientation2D the first one attached to the GameObject, almost as if it does a GetComponent<CharacterAbility> call.
    As can be seen in the image below from debugging the value of the blackboard variable

    image
    image1170×571 40 KB

  • I also confirmed that this behavior is consistent by rearranging my components on the GameObject, and it seems like it will consistently grab the top component by base type CharacterAbility despite having explicitly assigned the CharacterDash2D as the BlackboardVariable and also in the BehaviorAgent Inspector.

    image
    image538×192 21.7 KB

This is at least to me an undesirable behavior and I assume it’s a bug, but I at least wanted to bring attention to this.

2

Hi @alexennerfelt,

This does indeed look like a bug, thanks for the report.
I will bring it up with the team.

Cheers,
Darren

3

Thank you @Darren_Kelly,

I’ll make a temporary solution until I hear anything further :slight_smile:

4

No problem, a good workaround for now would be to have the abilities on separate empty objects in the hierarchy.

5

I’ll just make a specific condition for the DashAbility for now, I have about 30 different prefabs for npcs, so I’d rather wait for a bugfix than restructuring all of them.

6

Hi alexennerfelt,

Just letting you know that a PR landed to address this issue. It should be available in the next release (1.0.4).

Thanks for your patience.