How to use the @pixi/math.ObservablePoint function in @pixi/math

* sprite.
         *
         * By default, this is `(0,0)` (or `texture.defaultAnchor`
         * if you have modified that), which means the position
         * `(x,y)` of this `Sprite` will be the top-left corner.
         *
         * Note: Updating `texture.defaultAnchor` after
         * constructing a `Sprite` does _not_ update its anchor.
         *
         * {@link https://docs.cocos2d-x.org/cocos2d-x/en/sprites/manipulation.html}
         *
         * @default `texture.defaultAnchor`
         * @member {PIXI.ObservablePoint}
         * @private
         */
        this._anchor = new ObservablePoint(
            this._onAnchorUpdate,
            this,
            (texture ? texture.defaultAnchor.x : 0),
            (texture ? texture.defaultAnchor.y : 0)
        );

        /**
         * The texture that the sprite is using
         *
         * @private
         * @member {PIXI.Texture}
         */
        this._texture = null;

        /**
         * The width of the sprite (this is initially set by the texture)

{
        super();

        /**
         * The anchor sets the origin point of the texture.
         * The default is 0,0 or taken from the {@link PIXI.Texture#defaultAnchor|Texture}
         * passed to the constructor. A value of 0,0 means the texture's origin is the top left.
         * Setting the anchor to 0.5,0.5 means the texture's origin is centered.
         * Setting the anchor to 1,1 would mean the texture's origin point will be the bottom right corner.
         * Note: Updating the {@link PIXI.Texture#defaultAnchor} after a Texture is
         * created does _not_ update the Sprite's anchor values.
         *
         * @member {PIXI.ObservablePoint}
         * @private
         */
        this._anchor = new ObservablePoint(
            this._onAnchorUpdate,
            this,
            (texture ? texture.defaultAnchor.x : 0),
            (texture ? texture.defaultAnchor.y : 0)
        );

        /**
         * The texture that the sprite is using
         *
         * @private
         * @member {PIXI.Texture}
         */
        this._texture = null;

        /**
         * The width of the sprite (this is initially set by the texture)

this._maxLineHeight = 0;

        /**
         * Letter spacing. This is useful for setting the space between characters.
         * @member {number}
         * @private
         */
        this._letterSpacing = 0;

        /**
         * Text anchor. read-only
         *
         * @member {PIXI.ObservablePoint}
         * @private
         */
        this._anchor = new ObservablePoint(() => { this.dirty = true; }, this, 0, 0);

        /**
         * The dirty state of this object.
         *
         * @member {boolean}
         */
        this.dirty = false;

        /**
         * If true PixiJS will Math.floor() x/y values when rendering, stopping pixel interpolation.
         * Advantages can include sharper image quality (like text) and faster rendering on canvas.
         * The main disadvantage is movement of objects may appear less smooth.
         * To set the global default, change {@link PIXI.settings.ROUND_PIXELS}
         *
         * @member {boolean}
         * @default false

this._maxLineHeight = 0;

        /**
         * Letter spacing. This is useful for setting the space between characters.
         * @member {number}
         * @private
         */
        this._letterSpacing = 0;

        /**
         * Text anchor. read-only
         *
         * @member {PIXI.ObservablePoint}
         * @private
         */
        this._anchor = new ObservablePoint(() => { this.dirty = true; }, this, 0, 0);

        /**
         * The dirty state of this object.
         *
         * @member {boolean}
         */
        this.dirty = false;

        this.updateText();
    }

constructor(velocity = [0, 0], kernelSize = 5, offset = 0) {
        super(vertex, fragment);
        this.uniforms.uVelocity = new Float32Array(2);
        this._velocity = new ObservablePoint(this.velocityChanged, this);
        this.velocity = velocity;

        /**
         * The kernelSize of the blur, higher values are slower but look better.
         * Use odd value greater than 5.
         * @member {number}
         * @default 5
         */
        this.kernelSize = kernelSize;
        this.offset = offset;
    }

*/
        this.position = new Point(0, 0);

        /**
         * The scale factor of the object.
         *
         * @member {PIXI.Point}
         */
        this.scale = new Point(1, 1);

        /**
         * The skew amount, on the x and y axis.
         *
         * @member {PIXI.ObservablePoint}
         */
        this.skew = new ObservablePoint(this.updateSkew, this, 0, 0);

        /**
         * The pivot point of the displayObject that it rotates around
         *
         * @member {PIXI.Point}
         */
        this.pivot = new Point(0, 0);

        /**
         * The rotation value of the object, in radians
         *
         * @member {Number}
         * @private
         */
        this._rotation = 0;