Engine API Reference - v2.7.1
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    Class XrImageTracking

    Image Tracking provides the ability to track real world images using provided image samples and their estimated sizes. The underlying system will assume that the tracked image can move and rotate in the real world and will try to provide transformation estimates and its tracking state.

    Hierarchy (View Summary)

    Index

    Accessors

    available images supported

    Methods

    add fire hasEvent off on once remove

    Events

    EVENT_ERROR

    Accessors

    • get available(): boolean

      True if Image Tracking is available. This information is only available when the XR session has started, and will be true if image tracking is supported and images were provided and they have been processed successfully.

      Returns boolean

    Methods

    • Add an image for image tracking. A width can also be provided to help the underlying system estimate the appropriate transformation. Modifying the tracked images list is only possible before an AR session is started.

      Parameters

      • image:
            | Blob
            | ImageBitmap
            | HTMLCanvasElement
            | HTMLImageElement
            | SVGImageElement
            | HTMLVideoElement
            | ImageData

        Image that is matching real world image as close as possible. Resolution of images should be at least 300x300. High resolution does not improve tracking performance. The color of the image is irrelevant, so grayscale images can be used. Images with too many geometric features or repeating patterns will reduce tracking stability.

      • width: number

        Width (in meters) of image in the real world. Providing this value as close to the real value will improve tracking quality.

      Returns null | XrTrackedImage

      Tracked image object that will contain tracking information. Returns null if image tracking is not supported or if the XR manager is not active.

      // image of a book cover that has width of 20cm (0.2m)
      app.xr.imageTracking.add(bookCoverImg, 0.2);

    • 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');

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

      const evt = obj.on('test', (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', (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

    Events

    EVENT_ERROR: string = 'error'

    Fired when the XR session is started, but image tracking failed to process the provided images. The handler is passed the Error object.

    app.xr.imageTracking.on('error', (err) => {
        console.error(err.message);
    });

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