Use a specialized new tab page in TOUCH_UI builds

chrome/browser/resources/touch_ntp/touchhandler.js

+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+/**
+ * @fileoverview Touch Handler. Class that handles all touch events and
+ * uses them to interpret higher level gestures and behaviors. TouchEvent is a
+ * built in mobile safari type:
+ * http://developer.apple.com/safari/library/documentation/UserExperience/Reference/TouchEventClassReference/TouchEvent/TouchEvent.html.
+ * This class is intended to work with all webkit browsers, tested on Chrome and
+ * iOS.
+ *
+ * The following types of gestures are currently supported.  See the definition
+ * of TouchHandler.EventType for details.
+ *
+ * Single Touch:
+ *      This provides simple single-touch events.  Any secondary touch is
+ *      ignored.
+ *
+ * Drag:
+ *      A single touch followed by some movement. This behavior will handle all
+ *      of the required events and report the properties of the drag to you
+ *      while the touch is happening and at the end of the drag sequence. This
+ *      behavior will NOT perform the actual dragging (redrawing the element)
+ *      for you, this responsibility is left to the client code.
+ *
+ * Long press:
+ *     When your element is touched and held without any drag occuring, the
+ *     LONG_PRESS event will fire.
+ */
+
+// Use an anonymous function to enable strict mode just for this file (which
+// will be concatenated with other files when embedded in Chrome)
+var TouchHandler = (function() {
+  'use strict';
+
+  /**
+   * A TouchHandler attaches to an Element, listents for low-level touch (or
+   * mouse) events and dispatching higher-level events on the element.
+   * @param {!Element} element The element to listen on and fire events
+   * for.
+   * @constructor
+   */
+  function TouchHandler(element) {
+    /**
+     * @type {!Element}
+     * @private
+     */
+    this.element_ = element;
+
+    /**
+     * The absolute sum of all touch y deltas.
+     * @type {number}
+     * @private
+     */
+    this.totalMoveY_ = 0;
+
+    /**
+     * The absolute sum of all touch x deltas.
+     * @type {number}
+     * @private
+     */
+    this.totalMoveX_ = 0;
+
+    /**
+     * An array of tuples where the first item is the horizontal component of a
+     * recent relevant touch and the second item is the touch's time stamp. Old
+     * touches are removed based on the max tracking time and when direction
+     * changes.
+      * @type {!Array.<number>}
+      * @private
+      */
+    this.recentTouchesX_ = [];
+
+    /**
+     * An array of tuples where the first item is the vertical component of a
+     * recent relevant touch and the second item is the touch's time stamp. Old
+     * touches are removed based on the max tracking time and when direction
+     * changes.
+     * @type {!Array.<number>}
+     * @private
+     */
+    this.recentTouchesY_ = [];
+
+    /**
+     * Used to keep track of all events we subscribe to so we can easily clean
+     * up
+     * @type {EventTracker}
+     * @private
+     */
+    this.events_ = new EventTracker();
+  }
+
+
+  /**
+   * DOM Events that may be fired by the TouchHandler at the element
+   */
+  TouchHandler.EventType = {
+    // Fired whenever the element is touched as the only touch to the device.
+    // enableDrag defaults to false, set to true to permit dragging.
+    TOUCH_START: 'touchhandler:touch_start',
+
+    // Fired when an element is held for a period of time.  Prevents dragging
+    // from occuring (even if enableDrag was set to true).
+    LONG_PRESS: 'touchhandler:long_press',
+
+    // If enableDrag was set to true at TOUCH_START, DRAG_START will fire when
+    // the touch first moves sufficient distance.  enableDrag is set to true but
+    // can be reset to false to cancel the drag.
+    DRAG_START: 'touchhandler:drag_start',
+
+    // If enableDrag was true after DRAG_START, DRAG_MOVE will fire whenever the
+    // touch is moved.
+    DRAG_MOVE: 'touchhandler:drag_move',
+
+    // Fired just before TOUCH_END when a drag is released.  Correlates 1:1 with
+    // a DRAG_START.
+    DRAG_END: 'touchhandler:drag_end',
+
+    // Fired whenever a touch that is being tracked has been released.
+    // Correlates 1:1 with a TOUCH_START.
+    TOUCH_END: 'touchhandler:touch_end'
+  };
+
+
+  /**
+   * The type of event sent by TouchHandler
+   * @constructor
+   * @param {string} type The type of event (one of Grabber.EventType).
+   * @param {boolean} bubbles Whether or not the event should bubble.
+   * @param {number} clientX The X location of the touch.
+   * @param {number} clientY The Y location of the touch.
+   * @param {!Element} touchedElement The element at the current location of the
+   *        touch.
+   */
+  TouchHandler.Event = function(type, bubbles, clientX, clientY,
+      touchedElement) {
+    var event = document.createEvent('Event');
+    event.initEvent(type, bubbles, true);
+    event.__proto__ = TouchHandler.Event.prototype;
+
+    /**
+     * The X location of the touch affected
+     * @type {number}
+     */
+    event.clientX = clientX;
+
+    /**
+     * The Y location of the touch affected
+     * @type {number}
+     */
+    event.clientY = clientY;
+
+    /**
+     * The element at the current location of the touch.
+     * @type {!Element}
+     */
+    event.touchedElement = touchedElement;
+
+    return event;
+  };
+
+  TouchHandler.Event.prototype = {
+    __proto__: Event.prototype,
+
+    /**
+     * For TOUCH_START and DRAG START events, set to true to enable dragging or
+     * false to disable dragging.
+     * @type {boolean|undefined}
+     */
+    enableDrag: undefined,
+
+    /**
+     * For DRAG events, provides the horizontal component of the
+     * drag delta. Drag delta is defined as the delta of the start touch
+     * position and the current drag position.
+     * @type {number|undefined}
+     */
+    dragDeltaX: undefined,
+
+    /**
+     * For DRAG events, provides the vertical component of the
+     * drag delta.
+     * @type {number|undefined}
+     */
+    dragDeltaY: undefined
+  };
+
+  /**
+   * Minimum movement of touch required to be considered a drag.
+   * @type {number}
+   * @private
+   */
+  TouchHandler.MIN_TRACKING_FOR_DRAG_ = 8;
+
+
+  /**
+   * The maximum number of ms to track a touch event. After an event is older
+   * than this value, it will be ignored in velocity calculations.
+   * @type {number}
+   * @private
+   */
+  TouchHandler.MAX_TRACKING_TIME_ = 250;
+
+
+  /**
+   * The maximum number of touches to track.
+   * @type {number}
+   * @private
+   */
+  TouchHandler.MAX_TRACKING_TOUCHES_ = 5;
+
+
+  /**
+   * The maximum velocity to return, in pixels per millisecond, that is used
+   * to guard against errors in calculating end velocity of a drag. This is a
+   * very fast drag velocity.
+   * @type {number}
+   * @private
+   */
+  TouchHandler.MAXIMUM_VELOCITY_ = 5;
+
+
+  /**
+   * The velocity to return, in pixel per millisecond, when the time stamps on
+   * the events are erroneous. The browser can return bad time stamps if the
+   * thread is blocked for the duration of the drag. This is a low velocity to
+   * prevent the content from moving quickly after a slow drag. It is less
+   * jarring if the content moves slowly after a fast drag.
+   * @type {number}
+   * @private
+   */
+  TouchHandler.VELOCITY_FOR_INCORRECT_EVENTS_ = 1;
+
+  /**
+   * The time, in milliseconds, that a touch must be held to be considered
+   * 'long'.
+   * @type {number}
+   * @private
+   */
+  TouchHandler.TIME_FOR_LONG_PRESS_ = 500;
+
+  TouchHandler.prototype = {
+    /**
+     * If defined, the identifer of the single touch that is active.  Note that
+     * 0 is a valid touch identifier - it should not be treated equivalently to
+     * undefined.
+     * @type {number|undefined}
+     * @private
+     */
+    activeTouch_: undefined,
+
+    /**
+     * @type {boolean|undefined}
+     * @private
+     */
+    tracking_: undefined,
+
+    /**
+     * @type {number|undefined}
+     * @private
+     */
+    startTouchX_: undefined,
+
+    /**
+     * @type {number|undefined}
+     * @private
+     */
+    startTouchY_: undefined,
+
+    /**
+     * @type {number|undefined}
+     * @private
+     */
+    endTouchX_: undefined,
+
+    /**
+     * @type {number|undefined}
+     * @private
+     */
+    endTouchY_: undefined,
+
+    /**
+     * Time of the touchstart event.
+     * @type {number|undefined}
+     * @private
+     */
+    startTime_: undefined,
+
+    /**
+     * The time of the touchend event.
+     * @type {number|undefined}
+     * @private
+     */
+    endTime_: undefined,
+
+    /**
+     * @type {number|undefined}
+     * @private
+     */
+    lastTouchX_: undefined,
+
+    /**
+     * @type {number|undefined}
+     * @private
+     */
+    lastTouchY_: undefined,
+
+    /**
+     * @type {number|undefined}
+     * @private
+     */
+    lastMoveX_: undefined,
+
+    /**
+     * @type {number|undefined}
+     * @private
+     */
+    lastMoveY_: undefined,
+
+    /**
+     * @type {number|undefined}
+     * @private
+     */
+    longPressTimeout_: undefined,
+
+    /**
+     * If defined and true, the next click event should be swallowed
+     * @type {boolean|undefined}
+     * @private
+     */
+    swallowNextClick_: undefined,
+
+    /**
+     * Start listenting for events.
+     * @param {boolean=} opt_capture True if the TouchHandler should listen to
+     *      during the capture phase.
+     */
+    enable: function(opt_capture) {
+      var capture = !!opt_capture;
+
+      // Just listen to start events for now. When a touch is occuring we'll
+      // want to be subscribed to move and end events on the document, but we
+      // don't want to incur the cost of lots of no-op handlers on the document.
+      this.events_.add(this.element_, 'touchstart', this.onStart_.bind(this),
+                       capture);
+      this.events_.add(this.element_, 'mousedown',
+                       this.mouseToTouchCallback_(this.onStart_.bind(this)),
+                       capture);
+
+      // If the element is long-pressed, we may need to swallow a click
+      this.events_.add(this.element_, 'click', this.onClick_.bind(this), true);
+    },
+
+    /**
+     * Stop listening to all events.
+     */
+    disable: function() {
+      this.stopTouching_();
+      this.events_.removeAll();
+    },
+
+    /**
+     * Wraps a callback with translations of mouse events to touch events.
+     * NOTE: These types really should be function(Event) but then we couldn't
+     * use this with bind (which operates on any type of function).  Doesn't
+     * JSDoc support some sort of polymorphic types?
+     * @param {Function} callback The event callback.
+     * @return {Function} The wrapping callback.
+     * @private
+     */
+    mouseToTouchCallback_: function(callback) {
+      return function(e) {
+        // Note that there may be synthesizes mouse events caused by touch
+        // events (a mouseDown after a touch-click).  We leave it up to the
+        // client to worry about this if it matters to them (typically a short
+        // mouseDown/mouseUp without a click is no big problem and it's not
+        // obvious how we identify such synthesized events in a general way).
+        var touch = {
+          // any fixed value will do for the identifier - there will only
+          // ever be a single active 'touch' when using the mouse.
+          identifier: 0,
+          clientX: e.clientX,
+          clientY: e.clientY,
+          target: e.target
+        };
+        e.touches = [];
+        e.targetTouches = [];
+        e.changedTouches = [touch];
+        if (e.type != 'mouseup') {
+          e.touches[0] = touch;
+          e.targetTouches[0] = touch;
+        }
+        callback(e);
+      };
+    },
+
+    /**
+     * Begin tracking the touchable element, it is eligible for dragging.
+     * @private
+     */
+    beginTracking_: function() {
+      this.tracking_ = true;
+    },
+
+    /**
+     * Stop tracking the touchable element, it is no longer dragging.
+     * @private
+     */
+    endTracking_: function() {
+      this.tracking_ = false;
+      this.dragging_ = false;
+      this.totalMoveY_ = 0;
+      this.totalMoveX_ = 0;
+    },
+
+    /**
+     * Reset the touchable element as if we never saw the touchStart
+     * Doesn't dispatch any end events - be careful of existing listeners.
+     */
+    cancelTouch: function() {
+      this.stopTouching_();
+      this.endTracking_();
+      // If clients needed to be aware of this, we could fire a cancel event
+      // here.
+    },
+
+    /**
+     * Record that touching has stopped
+     * @private
+     */
+    stopTouching_: function() {
+      // Mark as no longer being touched
+      this.activeTouch_ = undefined;
+
+      // If we're waiting for a long press, stop
+      window.clearTimeout(this.longPressTimeout_);
+
+      // Stop listening for move/end events until there's another touch.
+      // We don't want to leave handlers piled up on the document.
+      // Note that there's no harm in removing handlers that weren't added, so
+      // rather than track whether we're using mouse or touch we do both.
+      this.events_.remove(document, 'touchmove');
+      this.events_.remove(document, 'touchend');
+      this.events_.remove(document, 'touchcancel');
+      this.events_.remove(document, 'mousemove');
+      this.events_.remove(document, 'mouseup');
+    },
+
+    /**
+     * Touch start handler.
+     * @param {!TouchEvent} e The touchstart event.
+     * @private
+     */
+    onStart_: function(e) {
+      // Only process single touches.  If there is already a touch happening, or
+      // two simultaneous touches then just ignore them.
+      if (e.touches.length > 1)
+        // Note that we could cancel an active touch here.  That would make
+        // simultaneous touch behave similar to near-simultaneous. However, if
+        // the user is dragging something, an accidental second touch could be
+        // quite disruptive if it cancelled their drag.  Better to just ignore
+        // it.
+        return;
+
+      // It's still possible there could be an active "touch" if the user is
+      // simultaneously using a mouse and a touch input.
+      if (this.activeTouch_ !== undefined)
+        return;
+
+      var touch = e.targetTouches[0];
+      this.activeTouch_ = touch.identifier;
+
+      // We've just started touching so shouldn't swallow any upcoming click
+      if (this.swallowNextClick_)
+        this.swallowNextClick_ = false;
+
+      // Sign up for end/cancel notifications for this touch.
+      // Note that we do this on the document so that even if the user drags
+      // their finger off the element, we'll still know what they're doing.
+      if (e.type == 'mousedown') {
+        this.events_.add(document, 'mouseup',
+            this.mouseToTouchCallback_(this.onEnd_.bind(this)), false);
+      } else {
+        this.events_.add(document, 'touchend', this.onEnd_.bind(this), false);
+        this.events_.add(document, 'touchcancel', this.onEnd_.bind(this),
+            false);
+      }
+
+      // This timeout is cleared on touchEnd and onDrag
+      // If we invoke the function then we have a real long press
+      window.clearTimeout(this.longPressTimeout_);
+      this.longPressTimeout_ = window.setTimeout(
+          this.onLongPress_.bind(this),
+          TouchHandler.TIME_FOR_LONG_PRESS_);
+
+      // Dispatch the TOUCH_START event
+      if (!this.dispatchEvent_(TouchHandler.EventType.TOUCH_START, touch))
+        // Dragging was not enabled, nothing more to do
+        return;
+
+      // We want dragging notifications
+      if (e.type == 'mousedown') {
+        this.events_.add(document, 'mousemove',
+            this.mouseToTouchCallback_(this.onMove_.bind(this)), false);
+      } else {
+        this.events_.add(document, 'touchmove', this.onMove_.bind(this), false);
+      }
+
+      this.startTouchX_ = this.lastTouchX_ = touch.clientX;
+      this.startTouchY_ = this.lastTouchY_ = touch.clientY;
+      this.startTime_ = e.timeStamp;
+
+      this.recentTouchesX_ = [];
+      this.recentTouchesY_ = [];
+      this.recentTouchesX_.push(touch.clientX, e.timeStamp);
+      this.recentTouchesY_.push(touch.clientY, e.timeStamp);
+
+      this.beginTracking_();
+    },
+
+    /**
+     * Given a list of Touches, find the one matching our activeTouch
+     * identifier. Note that Chrome currently always uses 0 as the identifier.
+     * In that case we'll end up always choosing the first element in the list.
+     * @param {TouchList} touches The list of Touch objects to search.
+     * @return {!Touch|undefined} The touch matching our active ID if any.
+     * @private
+     */
+    findActiveTouch_: function(touches) {
+      assert(this.activeTouch_ !== undefined, 'Expecting an active touch');
+      // A TouchList isn't actually an array, so we shouldn't use
+      // Array.prototype.filter/some, etc.
+      for (var i = 0; i < touches.length; i++) {
+        if (touches[i].identifier == this.activeTouch_)
+          return touches[i];
+      }
+      return undefined;
+    },
+
+    /**
+     * Touch move handler.
+     * @param {!TouchEvent} e The touchmove event.
+     * @private
+     */
+    onMove_: function(e) {
+      if (!this.tracking_)
+        return;
+
+      // Our active touch should always be in the list of touches still active
+      assert(this.findActiveTouch_(e.touches), 'Missing touchEnd');
+
+      var that = this;
+      var touch = this.findActiveTouch_(e.changedTouches);
+      if (!touch)
+        return;
+
+      var clientX = touch.clientX;
+      var clientY = touch.clientY;
+
+      var moveX = this.lastTouchX_ - clientX;
+      var moveY = this.lastTouchY_ - clientY;
+      this.totalMoveX_ += Math.abs(moveX);
+      this.totalMoveY_ += Math.abs(moveY);
+      this.lastTouchX_ = clientX;
+      this.lastTouchY_ = clientY;
+
+      if (!this.dragging_ && (this.totalMoveY_ >
+          TouchHandler.MIN_TRACKING_FOR_DRAG_ ||
+          this.totalMoveX_ >
+          TouchHandler.MIN_TRACKING_FOR_DRAG_)) {
+        // If we're waiting for a long press, stop
+        window.clearTimeout(this.longPressTimeout_);
+
+        // Dispatch the DRAG_START event and record whether dragging should be
+        // allowed or not.  Note that this relies on the current value of
+        // startTouchX/Y - handlers may use the initial drag delta to determine
+        // if dragging should be permitted.
+        this.dragging_ = this.dispatchEvent_(
+            TouchHandler.EventType.DRAG_START, touch);
+
+        if (this.dragging_) {
+          // Update the start position here so that drag deltas have better
+          // values but don't touch the recent positions so that velocity
+          // calculations can still use touchstart position in the time and
+          // distance delta.
+          this.startTouchX_ = clientX;
+          this.startTouchY_ = clientY;
+          this.startTime_ = e.timeStamp;
+        } else {
+          this.endTracking_();
+        }
+      }
+
+      if (this.dragging_) {
+        this.dispatchEvent_(TouchHandler.EventType.DRAG_MOVE, touch);
+
+        this.removeTouchesInWrongDirection_(this.recentTouchesX_,
+            this.lastMoveX_, moveX);
+        this.removeTouchesInWrongDirection_(this.recentTouchesY_,
+            this.lastMoveY_, moveY);
+        this.removeOldTouches_(this.recentTouchesX_, e.timeStamp);
+        this.removeOldTouches_(this.recentTouchesY_, e.timeStamp);
+        this.recentTouchesX_.push(clientX, e.timeStamp);
+        this.recentTouchesY_.push(clientY, e.timeStamp);
+      }
+
+      this.lastMoveX_ = moveX;
+      this.lastMoveY_ = moveY;
+    },
+
+    /**
+     * Filters the provided recent touches array to remove all touches except
+     * the last if the move direction has changed.
+     * @param {!Array.<number>} recentTouches An array of tuples where the first
+     *     item is the x or y component of the recent touch and the second item
+     *     is the touch time stamp.
+     * @param {number|undefined} lastMove The x or y component of the previous
+     *     move.
+     * @param {number} recentMove The x or y component of the most recent move.
+     * @private
+     */
+    removeTouchesInWrongDirection_: function(recentTouches, lastMove,
+        recentMove) {
+      if (lastMove && recentMove && recentTouches.length > 2 &&
+          (lastMove > 0 ^ recentMove > 0)) {
+        recentTouches.splice(0, recentTouches.length - 2);
+      }
+    },
+
+    /**
+     * Filters the provided recent touches array to remove all touches older
+     * than the max tracking time or the 5th most recent touch.
+     * @param {!Array.<number>} recentTouches An array of tuples where the first
+     *     item is the x or y component of the recent touch and the second item
+     *     is the touch time stamp.
+     * @param {number} recentTime The time of the most recent event.
+     * @private
+     */
+    removeOldTouches_: function(recentTouches, recentTime) {
+      while (recentTouches.length && recentTime - recentTouches[1] >
+          TouchHandler.MAX_TRACKING_TIME_ ||
+          recentTouches.length >
+              TouchHandler.MAX_TRACKING_TOUCHES_ * 2) {
+        recentTouches.splice(0, 2);
+      }
+    },
+
+    /**
+     * Touch end handler.
+     * @param {!TouchEvent} e The touchend event.
+     * @private
+     */
+    onEnd_: function(e) {
+      var that = this;
+      assert(this.activeTouch_ !== undefined, 'Expect to already be touching');
+
+      // If the touch we're tracking isn't changing here, ignore this touch end.
+      var touch = this.findActiveTouch_(e.changedTouches);
+      if (!touch) {
+        // In most cases, our active touch will be in the 'touches' collection,
+        // but we can't assert that because occasionally two touchend events can
+        // occur at almost the same time with both having empty 'touches' lists.
+        // I.e., 'touches' seems like it can be a bit more up-to-date than the
+        // current event.
+        return;
+      }
+
+      // This is touchEnd for the touch we're monitoring
+      assert(!this.findActiveTouch_(e.touches),
+             'Touch ended also still active');
+
+      // Indicate that touching has finished
+      this.stopTouching_();
+
+      if (this.tracking_) {
+        var clientX = touch.clientX;
+        var clientY = touch.clientY;
+
+        if (this.dragging_) {
+          this.endTime_ = e.timeStamp;
+          this.endTouchX_ = clientX;
+          this.endTouchY_ = clientY;
+
+          this.removeOldTouches_(this.recentTouchesX_, e.timeStamp);
+          this.removeOldTouches_(this.recentTouchesY_, e.timeStamp);
+
+          this.dispatchEvent_(TouchHandler.EventType.DRAG_END, touch);
+
+          // Note that in some situations we can get a click event here as well.
+          // For now this isn't a problem, but we may want to consider having
+          // some logic that hides clicks that appear to be caused by a touchEnd
+          // used for dragging.
+        }
+
+        this.endTracking_();
+      }
+
+      // Note that we dispatch the touchEnd event last so that events at
+      // different levels of semantics nest nicely (similar to how DOM
+      // drag-and-drop events are nested inside of the mouse events that trigger
+      // them).
+      this.dispatchEvent_(TouchHandler.EventType.TOUCH_END, touch);
+    },
+
+    /**
+     * Get end velocity of the drag. This method is specific to drag behavior,
+     * so if touch behavior and drag behavior is split then this should go with
+     * drag behavior. End velocity is defined as deltaXY / deltaTime where
+     * deltaXY is the difference between endPosition and the oldest recent
+     * position, and deltaTime is the difference between endTime and the oldest
+     * recent time stamp.
+     * @return {Object} The x and y velocity.
+     */
+    getEndVelocity: function() {
+      // Note that we could move velocity to just be an end-event parameter.
+      var velocityX = this.recentTouchesX_.length ?
+          (this.endTouchX_ - this.recentTouchesX_[0]) /
+          (this.endTime_ - this.recentTouchesX_[1]) : 0;
+      var velocityY = this.recentTouchesY_.length ?
+          (this.endTouchY_ - this.recentTouchesY_[0]) /
+          (this.endTime_ - this.recentTouchesY_[1]) : 0;
+
+      velocityX = this.correctVelocity_(velocityX);
+      velocityY = this.correctVelocity_(velocityY);
+
+      return {
+        x: velocityX,
+        y: velocityY
+      };
+    },
+
+    /**
+     * Correct erroneous velocities by capping the velocity if we think it's too
+     * high, or setting it to a default velocity if know that the event data is
+     * bad.
+     * @param {number} velocity The x or y velocity component.
+     * @return {number} The corrected velocity.
+     * @private
+     */
+    correctVelocity_: function(velocity) {
+      var absVelocity = Math.abs(velocity);
+
+      // We add to recent touches for each touchstart and touchmove. If we have
+      // fewer than 3 touches (6 entries), we assume that the thread was blocked
+      // for the duration of the drag and we received events in quick succession
+      // with the wrong time stamps.
+      if (absVelocity > TouchHandler.MAXIMUM_VELOCITY_) {
+        absVelocity = this.recentTouchesY_.length < 3 ?
+            TouchHandler.VELOCITY_FOR_INCORRECT_EVENTS_ :
+                TouchHandler.MAXIMUM_VELOCITY_;
+      }
+      return absVelocity * (velocity < 0 ? -1 : 1);
+    },
+
+    /**
+     * Handler when an element has been pressed for a long time
+     * @private
+     */
+    onLongPress_: function() {
+      // Swallow any click that occurs on this element without an intervening
+      // touch start event.  This simple click-busting technique should be
+      // sufficient here since a real click should have a touchstart first.
+      this.swallowNextClick_ = true;
+
+      // Dispatch to the LONG_PRESS
+      this.dispatchEventXY_(TouchHandler.EventType.LONG_PRESS, this.element_,
+          this.startTouchX_, this.startTouchY_);
+    },
+
+    /**
+     * Click handler - used to swallow clicks after a long-press
+     * @param {!Event} e The click event.
+     * @private
+     */
+    onClick_: function(e) {
+      if (this.swallowNextClick_) {
+        e.preventDefault();
+        e.stopPropagation();
+        this.swallowNextClick_ = false;
+      }
+    },
+
+    /**
+     * Dispatch a TouchHandler event to the element
+     * @param {string} eventType The event to dispatch.
+     * @param {Touch} touch The touch triggering this event.
+     * @return {boolean|undefined} The value of enableDrag after dispatching
+     *         the event.
+     * @private
+     */
+    dispatchEvent_: function(eventType, touch) {
+
+      // Determine which element was touched.  For mouse events, this is always
+      // the event/touch target.  But for touch events, the target is always the
+      // target of the touchstart (and it's unlikely we can change this
+      // since the common implementation of touch dragging relies on it). Since
+      // touch is our primary scenario (which we want to emulate with mouse),
+      // we'll treat both cases the same and not depend on the target.
+      var touchedElement;
+      if (eventType == TouchHandler.EventType.TOUCH_START) {
+        touchedElement = touch.target;
+      } else {
+        touchedElement = this.element_.ownerDocument.
+            elementFromPoint(touch.clientX, touch.clientY);
+      }
+
+      return this.dispatchEventXY_(eventType, touchedElement, touch.clientX,
+          touch.clientY);
+    },
+
+    /**
+     * Dispatch a TouchHandler event to the element
+     * @param {string} eventType The event to dispatch.
+       @param {number} clientX The X location for the event.
+       @param {number} clientY The Y location for the event.
+     * @return {boolean|undefined} The value of enableDrag after dispatching
+     *         the event.
+     * @private
+     */
+    dispatchEventXY_: function(eventType, touchedElement, clientX, clientY) {
+      var isDrag = (eventType == TouchHandler.EventType.DRAG_START ||
+          eventType == TouchHandler.EventType.DRAG_MOVE ||
+          eventType == TouchHandler.EventType.DRAG_END);
+
+      // Drag events don't bubble - we're really just dragging the element,
+      // not affecting its parent at all.
+      var bubbles = !isDrag;
+
+      var event = new TouchHandler.Event(eventType, bubbles, clientX, clientY,
+          touchedElement);
+
+      // Set enableDrag when it can be overridden
+      if (eventType == TouchHandler.EventType.TOUCH_START)
+        event.enableDrag = false;
+      else if (eventType == TouchHandler.EventType.DRAG_START)
+        event.enableDrag = true;
+
+      if (isDrag) {
+        event.dragDeltaX = clientX - this.startTouchX_;
+        event.dragDeltaY = clientY - this.startTouchY_;
+      }
+
+      this.element_.dispatchEvent(event);
+      return event.enableDrag;
+    }
+  };
+
+  return TouchHandler;
+})();