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

    // FIXME works for View2D only

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

    goog.require('goog.asserts');
    goog.require('goog.style');
    goog.require('ol.Coordinate');
    goog.require('ol.ViewHint');
    goog.require('ol.interaction.Interaction');
    goog.require('ol.interaction.Pointer');

    /**
     * @classdesc
     * Allows the user to zoom the map by pinching with two fingers
     * on a touch screen.
     *
     * @constructor
     * @extends {ol.interaction.Pointer}
     * @param {olx.interaction.PinchZoomOptions=} opt_options Options.
     * @todo api
     */
    ol.interaction.PinchZoom = function(opt_options) {

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

      goog.base(this);

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

      /**
       * @private
       * @type {number}
       */
      this.duration_ = goog.isDef(options.duration) ? options.duration : 400;

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

      /**
       * @private
       * @type {number}
       */
      this.lastScaleDelta_ = 1;

    };
    goog.inherits(ol.interaction.PinchZoom, ol.interaction.Pointer);

    /**
     * @inheritDoc
     */
    ol.interaction.PinchZoom.prototype.handlePointerDrag =
        function(mapBrowserEvent) {
      goog.asserts.assert(this.targetPointers.length >= 2);
      var scaleDelta = 1.0;

      var touch0 = this.targetPointers[0];
      var touch1 = this.targetPointers[1];
      var dx = touch0.clientX - touch1.clientX;
      var dy = touch0.clientY - touch1.clientY;

      // distance between touches
      var distance = Math.sqrt(dx * dx + dy * dy);

      if (goog.isDef(this.lastDistance_)) {
        scaleDelta = this.lastDistance_ / distance;
      }
      this.lastDistance_ = distance;
      if (scaleDelta != 1.0) {
        this.lastScaleDelta_ = scaleDelta;
      }

      var map = mapBrowserEvent.map;
      // FIXME works for View2D only
      var view = map.getView().getView2D();
      var view2DState = view.getView2DState();

      // scale anchor point.
      var viewportPosition = goog.style.getClientPosition(map.getViewport());
      var centroid =
          ol.interaction.Pointer.centroid(this.targetPointers);
      centroid[0] -= viewportPosition.x;
      centroid[1] -= viewportPosition.y;
      this.anchor_ = map.getCoordinateFromPixel(centroid);

      // scale, bypass the resolution constraint
      map.render();
      ol.interaction.Interaction.zoomWithoutConstraints(
          map, view, view2DState.resolution * scaleDelta, this.anchor_);

    };

    /**
     * @inheritDoc
     */
    ol.interaction.PinchZoom.prototype.handlePointerUp =
        function(mapBrowserEvent) {
      if (this.targetPointers.length < 2) {
        var map = mapBrowserEvent.map;
        var view = map.getView();
        view.setHint(ol.ViewHint.INTERACTING, -1);
        // FIXME works for View2D only
        var view2D = view.getView2D();
        var view2DState = view2D.getView2DState();
        // Zoom to final resolution, with an animation, and provide a
        // direction not to zoom out/in if user was pinching in/out.
        // Direction is > 0 if pinching out, and < 0 if pinching in.
        var direction = this.lastScaleDelta_ - 1;
        ol.interaction.Interaction.zoom(map, view2D, view2DState.resolution,
            this.anchor_, this.duration_, direction);
        return false;
      } else {
        return true;
      }
    };

    /**
     * @inheritDoc
     */
    ol.interaction.PinchZoom.prototype.handlePointerDown =
        function(mapBrowserEvent) {
      if (this.targetPointers.length >= 2) {
        var map = mapBrowserEvent.map;
        this.anchor_ = null;
        this.lastDistance_ = undefined;
        this.lastScaleDelta_ = 1;
        if (!this.handlingDownUpSequence) {
          map.getView().setHint(ol.ViewHint.INTERACTING, 1);
        }
        map.render();
        return true;
      } else {
        return false;
      }
    };