Engine API Reference - v1.77.0
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    Class XrAnchor

    An anchor keeps track of a position and rotation that is fixed relative to the real world. This allows the application to adjust the location of virtual objects placed in the scene in a way that helps with maintaining the illusion that the placed objects are really present in the user's environment.

    Hierarchy (View Summary)

    Index

    Accessors

    persistent uuid

    Methods

    destroy fire forget getPosition getRotation hasEvent off on once persist

    Events

    EVENT_CHANGE EVENT_DESTROY EVENT_FORGET EVENT_PERSIST

    Accessors

    • get uuid(): null | string

      Gets the UUID string of a persisted anchor or null if the anchor is not persisted.

      Returns null | string

    Methods

    • Fire an event, all additional arguments are passed on to the event listener.

      Parameters

      • name: string

        Name of event to fire.

      • Optionalarg1: any

        First argument that is passed to the event handler.

      • Optionalarg2: any

        Second argument that is passed to the event handler.

      • Optionalarg3: any

        Third argument that is passed to the event handler.

      • Optionalarg4: any

        Fourth argument that is passed to the event handler.

      • Optionalarg5: any

        Fifth argument that is passed to the event handler.

      • Optionalarg6: any

        Sixth argument that is passed to the event handler.

      • Optionalarg7: any

        Seventh argument that is passed to the event handler.

      • Optionalarg8: any

        Eighth argument that is passed to the event handler.

      Returns EventHandler

      Self for chaining.

      obj.fire('test', 'This is the message');

    • Removes the persistent UUID of an anchor from the underlying system. This effectively makes the anchor non-persistent, so it will not be restored in future WebXR sessions.

      Parameters

      • Optionalcallback: XrAnchorForgetCallback

        Optional callback function to be called when the anchor has been forgotten or if an error occurs.

      Returns void

      // Forget the anchor and log the result or error
      anchor.forget((err) => {
          if (err) {
              console.error('Failed to forget anchor:', err);
          } else {
              console.log('Anchor has been forgotten');
          }
      });

    • Test if there are any handlers bound to an event name.

      Parameters

      • name: string

        The name of the event to test.

      Returns boolean

      True if the object has handlers bound to the specified event name.

      obj.on('test', function () { }); // bind an event to 'test'
      obj.hasEvent('test'); // returns true
      obj.hasEvent('hello'); // returns false

    • Detach an event handler from an event. If callback is not provided then all callbacks are unbound from the event, if scope is not provided then all events with the callback will be unbound.

      Parameters

      • Optionalname: string

        Name of the event to unbind.

      • Optionalcallback: HandleEventCallback

        Function to be unbound.

      • Optionalscope: any

        Scope that was used as the this when the event is fired.

      Returns EventHandler

      Self for chaining.

      const handler = function () {
      };
      obj.on('test', handler);

      obj.off(); // Removes all events
      obj.off('test'); // Removes all events called 'test'
      obj.off('test', handler); // Removes all handler functions, called 'test'
      obj.off('test', handler, this); // Removes all handler functions, called 'test' with scope this

    • Attach an event handler to an event.

      Parameters

      • name: string

        Name of the event to bind the callback to.

      • callback: HandleEventCallback

        Function that is called when event is fired. Note the callback is limited to 8 arguments.

      • Optionalscope: any = ...

        Object to use as 'this' when the event is fired, defaults to current this.

      Returns EventHandle

      Can be used for removing event in the future.

      obj.on('test', function (a, b) {
          console.log(a + b);
      });
      obj.fire('test', 1, 2); // prints 3 to the console

      const evt = obj.on('test', function (a, b) {
          console.log(a + b);
      });
      // some time later
      evt.off();

    • Attach an event handler to an event. This handler will be removed after being fired once.

      Parameters

      • name: string

        Name of the event to bind the callback to.

      • callback: HandleEventCallback

        Function that is called when event is fired. Note the callback is limited to 8 arguments.

      • Optionalscope: any = ...

        Object to use as 'this' when the event is fired, defaults to current this.

      Returns EventHandle

      • can be used for removing event in the future.
      obj.once('test', function (a, b) {
          console.log(a + b);
      });
      obj.fire('test', 1, 2); // prints 3 to the console
      obj.fire('test', 1, 2); // not going to get handled

    • Persists the anchor between WebXR sessions by generating a universally unique identifier (UUID) for the anchor. This UUID can be used later to restore the anchor from the underlying system. Note that the underlying system may have a limit on the number of anchors that can be persisted per origin.

      Parameters

      • Optionalcallback: XrAnchorPersistCallback

        Optional callback function to be called when the persistent UUID has been generated or if an error occurs.

      Returns void

      // Persist the anchor and log the UUID or error
      anchor.persist((err, uuid) => {
          if (err) {
              console.error('Failed to persist anchor:', err);
          } else {
              console.log('Anchor persisted with UUID:', uuid);
          }
      });

    Events

    EVENT_CHANGE: string = 'change'

    Fired when an anchor's position and/or rotation is changed.

    anchor.on('change', () => {
        // anchor has been updated
        entity.setPosition(anchor.getPosition());
        entity.setRotation(anchor.getRotation());
    });
    EVENT_DESTROY: string = 'destroy'

    Fired when an anchor is destroyed.

    // once anchor is destroyed
    anchor.once('destroy', () => {
        // destroy its related entity
        entity.destroy();
    });
    EVENT_FORGET: string = 'forget'

    Fired when an anchor has been forgotten.

    anchor.on('forget', () => {
        // anchor has been forgotten
    });
    EVENT_PERSIST: string = 'persist'

    Fired when an anchor has has been persisted. The handler is passed the UUID string that can be used to restore this anchor.

    anchor.on('persist', (uuid) => {
        // anchor has been persisted
    });

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