Spatial Anchors Callbacks

Depending on your application's requirement, you may want to track when anchors are created, updated, or removed. This can be done using the MLAnchors.Request.TryGetResult() API to query when a change was made.

Some applications may query Spatial Anchors once while others may want to perform the search more frequently.

Example

The example below shows a simple implementation of using the MLAnchors TryGetResult() API to call Unity Events when spatial anchors are modified.

caution

This feature requires the SPATIAL_ANCHORS permission to be enabled in your project's Manifest Settings. (Edit > Project Settings > Magic Leap > Manifest Settings)

using System;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.XR.MagicLeap;

public class SpatialAnchorCallbacksExample : MonoBehaviour
{
    [Tooltip("How often, in seconds, to search for anchors.")]
    public float SearchInterval = 10;

#if UNITY_MAGICLEAP || UNITY_ANDROID

    public Action<MLAnchors.Anchor> OnAnchorAdded;
    public Action<MLAnchors.Anchor> OnAnchorUpdated;
    public Action<MLAnchors.Anchor> OnAnchorRemoved;

    private MLAnchors.Request _mlAnchorsRequest;
    private MLAnchors.Request.Params _anchorRequestParams;
    //The timestamp when anchors were last searched for
    private float _lastTick;

    //Cached list of the anchors anchor values that were tracked during the last search.
    private readonly List<MLAnchors.Anchor> _trackedAnchorValues = new List<MLAnchors.Anchor>();
    //Cached list of the anchors that are returned via MLAnchors.Request.TryGetResult()
    private readonly HashSet<string> _resultAnchorIds = new HashSet<string>();

    void Start()
    {
        // Initialize Magic leap Spatial Anchor Requests.
        _mlAnchorsRequest = new MLAnchors.Request();
        // Setting Max result or radius to zero means the search will not be constrained.
        _anchorRequestParams = new MLAnchors.Request.Params(Vector3.zero, 0, 0, false);
    }

    void Update()
    {
        // Only search when the update time lapsed 
        if(Time.time- _lastTick < SearchInterval)
            return;
        _lastTick = Time.time;
        _resultAnchorIds.Clear();

        // Starts the search using the parameters above.
        MLResult startStatus = _mlAnchorsRequest.Start(_anchorRequestParams);
        // Query the search for anchors.
        MLResult resultStatus = _mlAnchorsRequest.TryGetResult(out MLAnchors.Request.Result result);

        // Iterate through the anchors found in the search and add it to the current anchor list.
        for (int i = 0; i < result.anchors.Length; ++i)
        {
            MLAnchors.Anchor anchor = result.anchors[i];
            string anchorId = anchor.Id;
            // Track the found anchor's id in our resultAnchorId list.
            _resultAnchorIds.Add(anchorId);
            //Check if the anchor is already tracked.
            int indexOf = _trackedAnchorValues.FindIndex(x => x.Id == anchorId);
            if (indexOf <= 0)
            {
                // If the anchor is new call the OnCreate event and add it to our list.
                _trackedAnchorValues.Add(anchor);
                OnAnchorAdded?.Invoke(anchor);
            }
            else 
            {
                // Update the value of the tracked anchor.
                _trackedAnchorValues[indexOf] = anchor;
                OnAnchorUpdated?.Invoke(anchor);
            }
        }

        //Iterate through the retrieved anchors and update the tracked anchors list
        for (int i = _trackedAnchorValues.Count - 1; i >= 0; i--)
        {
            var trackedAnchor = _trackedAnchorValues[i];
            if (!_resultAnchorIds.Contains(trackedAnchor.Id))
            {
                _trackedAnchorValues.Remove(trackedAnchor);
                OnAnchorRemoved?.Invoke(trackedAnchor);
            }
        }
        
    }
#endif
}