text: /**
   * @module ol/interaction/PinchZoom
   */
  import {inherits} from '../util.js';
  import ViewHint from '../ViewHint.js';
  import {FALSE} from '../functions.js';
  import {zoom, zoomWithoutConstraints} from '../interaction/Interaction.js';
  import PointerInteraction, {centroid as centroidFromPointers} from '../interaction/Pointer.js';
  
  
  /**
   * @typedef {Object} Options
   * @property {number} [duration=400] Animation duration in milliseconds.
   * @property {boolean} [constrainResolution=false] Zoom to the closest integer
   * zoom level after the pinch gesture ends.
   */
  
  
  /**
   * @classdesc
   * Allows the user to zoom the map by pinching with two fingers
   * on a touch screen.
   *
   * @constructor
   * @extends {module:ol/interaction/Pointer}
   * @param {module:ol/interaction/PinchZoom~Options=} opt_options Options.
   * @api
   */
  const PinchZoom = function(opt_options) {
  
    PointerInteraction.call(this, {
      handleDownEvent: handleDownEvent,
      handleDragEvent: handleDragEvent,
      handleUpEvent: handleUpEvent
    });
  
    const options = opt_options ? opt_options : {};
  
    /**
     * @private
     * @type {boolean}
     */
    this.constrainResolution_ = options.constrainResolution || false;
  
    /**
     * @private
     * @type {module:ol/coordinate~Coordinate}
     */
    this.anchor_ = null;
  
    /**
     * @private
     * @type {number}
     */
    this.duration_ = options.duration !== undefined ? options.duration : 400;
  
    /**
     * @private
     * @type {number|undefined}
     */
    this.lastDistance_ = undefined;
  
    /**
     * @private
     * @type {number}
     */
    this.lastScaleDelta_ = 1;
  
  };
  
  inherits(PinchZoom, PointerInteraction);
  
  
  /**
   * @param {module:ol/MapBrowserPointerEvent} mapBrowserEvent Event.
   * @this {module:ol/interaction/PinchZoom}
   */
  function handleDragEvent(mapBrowserEvent) {
    let scaleDelta = 1.0;
  
    const touch0 = this.targetPointers[0];
    const touch1 = this.targetPointers[1];
    const dx = touch0.clientX - touch1.clientX;
    const dy = touch0.clientY - touch1.clientY;
  
    // distance between touches
    const distance = Math.sqrt(dx * dx + dy * dy);
  
    if (this.lastDistance_ !== undefined) {
      scaleDelta = this.lastDistance_ / distance;
    }
    this.lastDistance_ = distance;
  
  
    const map = mapBrowserEvent.map;
    const view = map.getView();
    const resolution = view.getResolution();
    const maxResolution = view.getMaxResolution();
    const minResolution = view.getMinResolution();
    let newResolution = resolution * scaleDelta;
    if (newResolution > maxResolution) {
      scaleDelta = maxResolution / resolution;
      newResolution = maxResolution;
    } else if (newResolution < minResolution) {
      scaleDelta = minResolution / resolution;
      newResolution = minResolution;
    }
  
    if (scaleDelta != 1.0) {
      this.lastScaleDelta_ = scaleDelta;
    }
  
    // scale anchor point.
    const viewportPosition = map.getViewport().getBoundingClientRect();
    const centroid = centroidFromPointers(this.targetPointers);
    centroid[0] -= viewportPosition.left;
    centroid[1] -= viewportPosition.top;
    this.anchor_ = map.getCoordinateFromPixel(centroid);
  
    // scale, bypass the resolution constraint
    map.render();
    zoomWithoutConstraints(view, newResolution, this.anchor_);
  }
  
  
  /**
   * @param {module:ol/MapBrowserPointerEvent} mapBrowserEvent Event.
   * @return {boolean} Stop drag sequence?
   * @this {module:ol/interaction/PinchZoom}
   */
  function handleUpEvent(mapBrowserEvent) {
    if (this.targetPointers.length < 2) {
      const map = mapBrowserEvent.map;
      const view = map.getView();
      view.setHint(ViewHint.INTERACTING, -1);
      const resolution = view.getResolution();
      if (this.constrainResolution_ ||
          resolution < view.getMinResolution() ||
          resolution > view.getMaxResolution()) {
        // 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.
        const direction = this.lastScaleDelta_ - 1;
        zoom(view, resolution, this.anchor_, this.duration_, direction);
      }
      return false;
    } else {
      return true;
    }
  }
  
  
  /**
   * @param {module:ol/MapBrowserPointerEvent} mapBrowserEvent Event.
   * @return {boolean} Start drag sequence?
   * @this {module:ol/interaction/PinchZoom}
   */
  function handleDownEvent(mapBrowserEvent) {
    if (this.targetPointers.length >= 2) {
      const map = mapBrowserEvent.map;
      this.anchor_ = null;
      this.lastDistance_ = undefined;
      this.lastScaleDelta_ = 1;
      if (!this.handlingDownUpSequence) {
        map.getView().setHint(ViewHint.INTERACTING, 1);
      }
      return true;
    } else {
      return false;
    }
  }
  
  
  /**
   * @inheritDoc
   */
  PinchZoom.prototype.shouldStopEvent = FALSE;
  export default PinchZoom;
  