Check if ARCamera first time detect the marker and "spawn" the 3d object

Question

i'm trying to make a simple AR app, the flow of the app i try to make is, camera detect first marker > do something, camera detect 2nd marker > do something different

the problem is i already googled with combination of keyword i can think of, and also i also look for the documentation but nothing really i can found that help with my problem

my initial though is to just use a script on the said marker and put the "do something" on void OnEnable, but the object is enable anyway, so its useless

anyone can lend me a rope ?

Answer 1

DefaultTrackingEventHandler is the script handling the tracking. In the sample scene for multiple markes, it is attached to ImageTarget.

That script registers to the TrackableBehaviour and propagates the tracking found/lost via the OnTrackingFound/Lost methods.

In the sample scene, those methods collect the collider and renderer of the child object and enables/disables.

What you can do is to propagate further the info to other listeners. In this case you could enable a script that runs an update checking for a condition until it is met and disable the script and matching trackable behaviour.

public class DefaultTrackableEventHandler : MonoBehaviour,
                                            ITrackableEventHandler
{
    private TrackableBehaviour mTrackableBehaviour;
    [SerializedField] private MyConditionClass actionMb = null;
    protected virtual void Start()
    {
        mTrackableBehaviour = GetComponent<TrackableBehaviour>();
        if (mTrackableBehaviour)
        {
            mTrackableBehaviour.RegisterTrackableEventHandler(this);
        }
    }

    public void OnTrackableStateChanged(
                                    TrackableBehaviour.Status previousStatus,
                                    TrackableBehaviour.Status newStatus)
    {
        if (newStatus == TrackableBehaviour.Status.DETECTED ||
            newStatus == TrackableBehaviour.Status.TRACKED ||
            newStatus == TrackableBehaviour.Status.EXTENDED_TRACKED)
        {

            OnTrackingFound();
        }
        else
        {
            OnTrackingLost();
        }
    }

    protected virtual void OnTrackingFound()
    {
        // Was already successfully done
        if(this.actionMb.ConditionMet == true){ return; }
        this.actionMb.enable = true;
    }


    protected virtual void OnTrackingLost()
    {
        // Was already successfully done
        if(this.actionMb.ConditionMet == true){ return; }
        this.actionMb.enable = false;
    }
}

public abstract class MyConditionClass : MonoBehaviour
{   
    public bool ConditionMet{ get; private set; }
    protected abstract bool CheckCondition();
    protected virtual void Update(){
        if(ConditionMet == true){ return; }
        ConditionMet = CheckCondition();
    }
}  

public class MyConditionClassForInput : MyConditionClass 
{   
    protected override bool CheckCondition(){
        return (Input.GetKeyDown(KeyCode.Space));
    }
}

So you have a base class containing the data that should be common to all conditions, like whether the condition was already met as shown. and the Update running a condition check.

Then you have sub class that implements the condition check (has to since abstract).