three.jsaframeartoolkitar.js

How to detect when a marker is found in AR.js


I'm trying to detect when a marker if found/lost in ar.js, while using a-frame.

From what I see in the source code, when the marker is found, a 'getMarker' event should be fired, moreover artoolkit seems to dispatch a markerFound event.

I tried to listen to those events on the <a-scene>, or on the <a-marker>, but it seems I'm either mistaken, or i need to get deeper to the arController, or arToolkit objects.

When i log the scene, or the marker, i only get references to the attributes, which don't seem to have the above objects attached.(like marker.arController, or marker.getAttribute('artoolkitmarker').arController)

Did anybody tried this and have any tips how to do this ?


Solution

  • PR303 introduces events when a marker is found and lost

    You can use them by simply adding an event listener:

    anchorRef.addEventListener("markerFound", (e)=>{ // your code here}
    

    with a simple setup like this:

    <a-marker id="anchor">
      <a-entity>
    </a-marker>
    

    example here. Please note, that as of sep 18', you need to use the dev branch to use the above.


    ORIGINAL ANWSER - in case you want to do it manually

    Detecting if the marker is found is possible by checking if the marker is visible when needed (other event, or on tick): if(document.querySelector("a-marker").object3D.visible == true)

    For example:

    init: function() {
       this.marker = document.querySelector("a-marker")
       this.markerVisible = false
    },
    tick: function() {
       if (!this.marker) return
       if (this.marker.object3D.visible) {
          if (!this.markerVisible) {
             // marker detected
             this.markerVisible = true
          }
       } else {
          if (this.markerVisbile) {
             // lost sight of the marker
             this.markerVisible = false
          }
       }
    }
    


    As adrian li noted, it doesn't work with a-marker-camera, only with a-markers