text: // Copyright 2014 The Closure Library Authors. All Rights Reserved.
  //
  // Licensed under the Apache License, Version 2.0 (the "License");
  // you may not use this file except in compliance with the License.
  // You may obtain a copy of the License at
  //
  //      http://www.apache.org/licenses/LICENSE-2.0
  //
  // Unless required by applicable law or agreed to in writing, software
  // distributed under the License is distributed on an "AS-IS" BASIS,
  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  // See the License for the specific language governing permissions and
  // limitations under the License.
  
  /**
   * @fileoverview This class aims to smooth out inconsistencies between browser
   * handling of wheel events by providing an event that is similar to that
   * defined in the standard, but also easier to consume.
   *
   * It is based upon the WheelEvent, which allows for up to 3 dimensional
   * scrolling events that come in units of either pixels, lines or pages.
   * http://www.w3.org/TR/2014/WD-DOM-Level-3-Events-20140925/#interface-WheelEvent
   *
   * The significant difference here is that it also provides reasonable pixel
   * deltas for clients that do not want to treat line and page scrolling events
   * specially.
   *
   * Clients of this code should be aware that some input devices only fire a few
   * discrete events (such as a mouse wheel without acceleration) whereas some can
   * generate a large number of events for a single interaction (such as a
   * touchpad with acceleration). There is no signal in the events to reliably
   * distinguish between these.
   *
   * @see ../demos/wheelhandler.html
   */
  
  goog.provide('goog.events.WheelEvent');
  
  goog.require('goog.asserts');
  goog.require('goog.events.BrowserEvent');
  
  
  
  /**
   * A common class for wheel events. This is used with the WheelHandler.
   *
   * @param {Event} browserEvent Browser event object.
   * @param {goog.events.WheelEvent.DeltaMode} deltaMode The delta mode units of
   *     the wheel event.
   * @param {number} deltaX The number of delta units the user in the X axis.
   * @param {number} deltaY The number of delta units the user in the Y axis.
   * @param {number} deltaZ The number of delta units the user in the Z axis.
   * @constructor
   * @extends {goog.events.BrowserEvent}
   * @final
   */
  goog.events.WheelEvent = function(
      browserEvent, deltaMode, deltaX, deltaY, deltaZ) {
    goog.events.WheelEvent.base(this, 'constructor', browserEvent);
    goog.asserts.assert(browserEvent, 'Expecting a non-null browserEvent');
  
    /** @type {goog.events.WheelEvent.EventType} */
    this.type = goog.events.WheelEvent.EventType.WHEEL;
  
    /**
     * An enum corresponding to the units of this event.
     * @type {goog.events.WheelEvent.DeltaMode}
     */
    this.deltaMode = deltaMode;
  
    /**
     * The number of delta units in the X axis.
     * @type {number}
     */
    this.deltaX = deltaX;
  
    /**
     * The number of delta units in the Y axis.
     * @type {number}
     */
    this.deltaY = deltaY;
  
    /**
     * The number of delta units in the Z axis.
     * @type {number}
     */
    this.deltaZ = deltaZ;
  
    // Ratio between delta and pixel values.
    var pixelRatio = 1;  // Value for DeltaMode.PIXEL
    switch (deltaMode) {
      case goog.events.WheelEvent.DeltaMode.PAGE:
        pixelRatio *= goog.events.WheelEvent.PIXELS_PER_PAGE_;
        break;
      case goog.events.WheelEvent.DeltaMode.LINE:
        pixelRatio *= goog.events.WheelEvent.PIXELS_PER_LINE_;
        break;
    }
  
    /**
     * The number of delta pixels in the X axis. Code that doesn't want to handle
     * different deltaMode units can just look here.
     * @type {number}
     */
    this.pixelDeltaX = this.deltaX * pixelRatio;
  
    /**
     * The number of pixels in the Y axis. Code that doesn't want to
     * handle different deltaMode units can just look here.
     * @type {number}
     */
    this.pixelDeltaY = this.deltaY * pixelRatio;
  
    /**
     * The number of pixels scrolled in the Z axis. Code that doesn't want to
     * handle different deltaMode units can just look here.
     * @type {number}
     */
    this.pixelDeltaZ = this.deltaZ * pixelRatio;
  };
  goog.inherits(goog.events.WheelEvent, goog.events.BrowserEvent);
  
  
  /**
   * Enum type for the events fired by the wheel handler.
   * @enum {string}
   */
  goog.events.WheelEvent.EventType = {
    /** The user has provided wheel-based input. */
    WHEEL: 'wheel'
  };
  
  
  /**
   * Units for the deltas in a WheelEvent.
   * @enum {number}
   */
  goog.events.WheelEvent.DeltaMode = {
    /** The units are in pixels. From DOM_DELTA_PIXEL. */
    PIXEL: 0,
    /** The units are in lines. From DOM_DELTA_LINE. */
    LINE: 1,
    /** The units are in pages. From DOM_DELTA_PAGE. */
    PAGE: 2
  };
  
  
  /**
   * A conversion number between line scroll units and pixel scroll units. The
   * actual value per line can vary a lot between devices and font sizes. This
   * number can not be perfect, but it should be reasonable for converting lines
   * scroll events into pixels.
   * @const {number}
   * @private
   */
  goog.events.WheelEvent.PIXELS_PER_LINE_ = 15;
  
  
  /**
   * A conversion number between page scroll units and pixel scroll units. The
   * actual value per page can vary a lot as many different devices have different
   * screen sizes, and the window might not be taking up the full screen. This
   * number can not be perfect, but it should be reasonable for converting page
   * scroll events into pixels.
   * @const {number}
   * @private
   */
  goog.events.WheelEvent.PIXELS_PER_PAGE_ =
      30 * goog.events.WheelEvent.PIXELS_PER_LINE_;
  