# Source: src/ol/interaction/mousewheelzoominteraction.js

    // FIXME works for View2D only

    goog.provide('ol.interaction.MouseWheelZoom');

    goog.require('goog.asserts');
    goog.require('goog.events.MouseWheelEvent');
    goog.require('goog.events.MouseWheelHandler.EventType');
    goog.require('goog.math');
    goog.require('ol');
    goog.require('ol.Coordinate');
    goog.require('ol.interaction.Interaction');

    /**
     * @classdesc
     * Allows the user to zoom the map by scrolling the mouse wheel.
     *
     * @constructor
     * @extends {ol.interaction.Interaction}
     * @param {olx.interaction.MouseWheelZoomOptions=} opt_options Options.
     * @todo api
     */
    ol.interaction.MouseWheelZoom = function(opt_options) {

      var options = goog.isDef(opt_options) ? opt_options : {};

      goog.base(this);

      /**
       * @private
       * @type {number}
       */
      this.delta_ = 0;

      /**
       * @private
       * @type {number}
       */
      this.duration_ = goog.isDef(options.duration) ? options.duration : 250;

      /**
       * @private
       * @type {?ol.Coordinate}
       */
      this.lastAnchor_ = null;

      /**
       * @private
       * @type {number|undefined}
       */
      this.startTime_ = undefined;

      /**
       * @private
       * @type {number|undefined}
       */
      this.timeoutId_ = undefined;

    };
    goog.inherits(ol.interaction.MouseWheelZoom, ol.interaction.Interaction);

    /**
     * @inheritDoc
     */
    ol.interaction.MouseWheelZoom.prototype.handleMapBrowserEvent =
        function(mapBrowserEvent) {
      var stopEvent = false;
      if (mapBrowserEvent.type ==
          goog.events.MouseWheelHandler.EventType.MOUSEWHEEL) {
        var map = mapBrowserEvent.map;
        var mouseWheelEvent = mapBrowserEvent.browserEvent;
        goog.asserts.assertInstanceof(mouseWheelEvent, goog.events.MouseWheelEvent);

        this.lastAnchor_ = mapBrowserEvent.coordinate;
        this.delta_ += mouseWheelEvent.deltaY;

        if (!goog.isDef(this.startTime_)) {
          this.startTime_ = goog.now();
        }

        var duration = ol.MOUSEWHEELZOOM_TIMEOUT_DURATION;
        var timeLeft = Math.max(duration - (goog.now() - this.startTime_), 0);

        goog.global.clearTimeout(this.timeoutId_);
        this.timeoutId_ = goog.global.setTimeout(
            goog.bind(this.doZoom_, this, map), timeLeft);

        mapBrowserEvent.preventDefault();
        stopEvent = true;
      }
      return !stopEvent;
    };

    /**
     * @private
     * @param {ol.Map} map Map.
     */
    ol.interaction.MouseWheelZoom.prototype.doZoom_ = function(map) {
      var maxDelta = ol.MOUSEWHEELZOOM_MAXDELTA;
      var delta = goog.math.clamp(this.delta_, -maxDelta, maxDelta);

      // FIXME works for View2D only
      var view = map.getView().getView2D();

      map.render();
      ol.interaction.Interaction.zoomByDelta(map, view, -delta, this.lastAnchor_,
          this.duration_);

      this.delta_ = 0;
      this.lastAnchor_ = null;
      this.startTime_ = undefined;
      this.timeoutId_ = undefined;
    };