/**
 * An observable point is a point that triggers a callback when the point's position is changed.
 *
 * @class
 * @memberof PIXI
 *
 * @param cb {function} The function to be called when the point changes
 * @param scope {object} The scope to be applied to the cb
 * @param [x=0] {number} position of the point on the x axis
 * @param [y=0] {number} position of the point on the y axis
 */
function ObservablePoint(cb, scope, x, y)
{
    this._x = x || 0;
    this._y = y || 0;

    this.cb = cb;
    this.scope = scope;
}

ObservablePoint.prototype.constructor = ObservablePoint;
module.exports = ObservablePoint;



Object.defineProperties(ObservablePoint.prototype, {
    /**
     * The position of the displayObject on the x axis relative to the local coordinates of the parent.
     *
     * @member {number}
     * @memberof PIXI.ObservablePoint#
     */
    x: {
        get: function ()
        {
            return this._x;
        },
        set: function (value)
        {
            this._x = value;
            this.cb.call(this.scope);
        }
    },
    /**
     * The position of the displayObject on the x axis relative to the local coordinates of the parent.
     *
     * @member {number}
     * @memberof PIXI.ObservablePoint#
     */
    y: {
        get: function ()
        {
            return this._y;
        },
        set: function (value)
        {
            this._y = value;
            this.cb.call(this.scope);
        }
    }
});

/**
 * Sets the point to a new x and y position.
 * If y is omitted, both x and y will be set to x.
 *
 * @param [x=0] {number} position of the point on the x axis
 * @param [y=0] {number} position of the point on the y axis
 */
ObservablePoint.prototype.set = function (x, y)
{
    this._x = x || 0;
    this._y = y || ( (y !== 0) ? this._x : 0 );

    this.transform._versionLocal++; // TODO: Pretty sure this doesn't exist.
};