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 tracked image can move and rotate in the real world and will try to provide transformation estimates and its tracking state.

Hierarchy (View Summary)

Accessors

available images supported

Methods

add fire hasEvent off on once remove

Events

EVENT_ERROR

Accessors

available

  • 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

images

supported

Methods

add

  • add(
        image:
            | Blob
            | ImageBitmap
            | HTMLCanvasElement
            | HTMLImageElement
            | SVGImageElement
            | HTMLVideoElement
            | ImageData,
        width: number,
    ): XrTrackedImage

  • 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. Color of 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 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.

    Example

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

fire

  • fire(
        name: string,
        arg1?: any,
        arg2?: any,
        arg3?: any,
        arg4?: any,
        arg5?: any,
        arg6?: any,
        arg7?: any,
        arg8?: any,
    ): EventHandler

  • 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.

    Example

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

hasEvent

  • hasEvent(name: string): boolean

  • 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.

    Example

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

off

  • off(name?: string, callback?: HandleEventCallback, scope?: object): EventHandler

  • 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: object

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

    Returns EventHandler

    Self for chaining.

    Example

    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

on

  • on(name: string, callback: HandleEventCallback, scope?: object): EventHandle

  • 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: object = ...

      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.

    Example

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

    Example

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

once

  • once(name: string, callback: HandleEventCallback, scope?: object): EventHandle

  • 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: object = ...

      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.

    Example

    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

remove

Events

StaticEVENT_ERROR

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.

Example

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

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