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