The Tor Browser: browser/metro/base/content/input.js@7e26c7da4463 (annotated)

browser/metro/base/content/input.js@7e26c7da4463 (annotated)

browser/metro/base/content/input.js

Wed, 31 Dec 2014 06:55:50 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Wed, 31 Dec 2014 06:55:50 +0100
changeset 2: 7e26c7da4463
permissions: -rw-r--r--

Added tag UPSTREAM_283F7C6 for changeset ca08bd8f51b2

 // -*- Mode: js2; tab-width: 2; indent-tabs-mode: nil; js2-basic-offset: 2; js2-skip-preprocessor-directives: t; js2-strict-trailing-comma-warning: nil -*-
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 Components.utils.import("resource://gre/modules/Geometry.jsm");
 /*
  * Drag scrolling related constants
  */
 // maximum drag distance in inches while axis locking can still be reverted
 const kAxisLockRevertThreshold = 0.8;
 // Same as NS_EVENT_STATE_ACTIVE from mozilla/EventStates.h
 const kStateActive = 0x00000001;
 // After a drag begins, kinetic panning is stopped if the drag doesn't become
 // a pan in 300 milliseconds.
 const kStopKineticPanOnDragTimeout = 300;
 // Min/max velocity of kinetic panning. This is in pixels/millisecond.
 const kMinVelocity = 0.4;
 const kMaxVelocity = 6;
 /*
  * prefs
  */
 // Display rects around selection ranges. Useful in debugging
 // selection problems.
 const kDebugSelectionDisplayPref = "metro.debug.selection.displayRanges";
 // Dump range rect data to the console. Very useful, but also slows
 // things down a lot.
 const kDebugSelectionDumpPref = "metro.debug.selection.dumpRanges";
 // Dump message manager event traffic for selection.
 const kDebugSelectionDumpEvents = "metro.debug.selection.dumpEvents";
 const kAsyncPanZoomEnabled = "layers.async-pan-zoom.enabled"
 /**
  * TouchModule
  *
  * Handles all touch-related input such as dragging and tapping.
  *
  * The Fennec chrome DOM tree has elements that are augmented dynamically with
  * custom JS properties that tell the TouchModule they have custom support for
  * either dragging or clicking.  These JS properties are JS objects that expose
  * an interface supporting dragging or clicking (though currently we only look
  * to drag scrollable elements).
  *
  * A custom dragger is a JS property that lives on a scrollable DOM element,
  * accessible as myElement.customDragger.  The customDragger must support the
  * following interface:  (The `scroller' argument is given for convenience, and
  * is the object reference to the element's scrollbox object).
  *
  *   dragStart(cX, cY, target, scroller)
  *     Signals the beginning of a drag.  Coordinates are passed as
  *     client coordinates. target is copied from the event.
  *
  *   dragStop(dx, dy, scroller)
  *     Signals the end of a drag.  The dx, dy parameters may be non-zero to
  *     indicate one last drag movement.
  *
  *   dragMove(dx, dy, scroller, isKinetic)
  *     Signals an input attempt to drag by dx, dy.
  *
  * There is a default dragger in case a scrollable element is dragged --- see
  * the defaultDragger prototype property.
  */
 var TouchModule = {
   _debugEvents: false,
   _isCancelled: false,
   _isCancellable: false,
   init: function init() {
     this._dragData = new DragData();
     this._dragger = null;
     this._targetScrollbox = null;
     this._targetScrollInterface = null;
     this._kinetic = new KineticController(this._dragBy.bind(this),
                                           this._kineticStop.bind(this));
     // capture phase events
     window.addEventListener("CancelTouchSequence", this, true);
     window.addEventListener("keydown", this, true);
     window.addEventListener("MozMouseHittest", this, true);
     // bubble phase
     window.addEventListener("contextmenu", this, false);
     window.addEventListener("touchstart", this, false);
     window.addEventListener("touchmove", this, false);
     window.addEventListener("touchend", this, false);
     Services.obs.addObserver(this, "Gesture:SingleTap", false);
     Services.obs.addObserver(this, "Gesture:DoubleTap", false);
   },
   /*
    * Events
    */
   handleEvent: function handleEvent(aEvent) {
     switch (aEvent.type) {
       case "contextmenu":
         this._onContextMenu(aEvent);
         break;
       case "CancelTouchSequence":
         this.cancelPending();
         break;
       default: {
         if (this._debugEvents) {
           if (aEvent.type != "touchmove")
             Util.dumpLn("TouchModule:", aEvent.type, aEvent.target);
         }
         switch (aEvent.type) {
           case "touchstart":
             this._onTouchStart(aEvent);
             break;
           case "touchmove":
             this._onTouchMove(aEvent);
             break;
           case "touchend":
             this._onTouchEnd(aEvent);
             break;
           case "keydown":
             this._handleKeyDown(aEvent);
             break;
           case "MozMouseHittest":
             // Used by widget to hit test chrome vs content. Make sure the XUl scrollbars
             // are counted as "chrome". Since the XUL scrollbars have sub-elements we walk
             // the parent chain to ensure we catch all of those as well.
             let onScrollbar = false;
             for (let node = aEvent.originalTarget; node instanceof XULElement; node = node.parentNode) {
               if (node.tagName == 'scrollbar') {
                 onScrollbar = true;
                 break;
               }
             }
             if (onScrollbar || aEvent.target.ownerDocument == document) {
               aEvent.preventDefault();
             }
             aEvent.stopPropagation();
             break;
         }
       }
     }
   },
   _handleKeyDown: function _handleKeyDown(aEvent) {
     const TABKEY = 9;
     if (aEvent.keyCode == TABKEY && !InputSourceHelper.isPrecise) {
       if (Util.isEditable(aEvent.target) &&
           aEvent.target.selectionStart != aEvent.target.selectionEnd) {
         SelectionHelperUI.closeEditSession(false);
       }
       setTimeout(function() {
         let element = Browser.selectedBrowser.contentDocument.activeElement;
         // We only want to attach monocles if we have an input, text area,
         // there is selection, and the target element changed.
         // Sometimes the target element won't change even though selection is
         // cleared because of focus outside the browser.
         if (Util.isEditable(element) &&
             !SelectionHelperUI.isActive &&
             element.selectionStart != element.selectionEnd &&
             // not e10s friendly
             aEvent.target != element) {
               let rect = element.getBoundingClientRect();
               SelectionHelperUI.attachEditSession(Browser.selectedBrowser,
                                                   rect.left + rect.width / 2,
                                                   rect.top + rect.height / 2);
         }
       }, 50);
     }
   },
   observe: function BrowserUI_observe(aSubject, aTopic, aData) {
     switch (aTopic) {
       case "Gesture:SingleTap":
       case "Gesture:DoubleTap":
         Browser.selectedBrowser.messageManager.sendAsyncMessage(aTopic, JSON.parse(aData));
         break;
     }
   },
   sample: function sample(aTimeStamp) {
     this._waitingForPaint = false;
   },
   /**
    * This gets invoked by the input handler if another module grabs.  We should
    * reset our state or something here.  This is probably doing the wrong thing
    * in its current form.
    */
   cancelPending: function cancelPending() {
     this._doDragStop();
     // Kinetic panning may have already been active or drag stop above may have
     // made kinetic panning active.
     this._kinetic.end();
     this._targetScrollbox = null;
     this._targetScrollInterface = null;
   },
   _onContextMenu: function _onContextMenu(aEvent) {
     // bug 598965 - chrome UI should stop to be pannable once the
     // context menu has appeared.
     if (ContextMenuUI.popupState) {
       this.cancelPending();
     }
   },
   /** Begin possible pan and send tap down event. */
   _onTouchStart: function _onTouchStart(aEvent) {
     if (aEvent.touches.length > 1)
       return;
     this._isCancelled = false;
     this._isCancellable = true;
     if (aEvent.defaultPrevented) {
       this._isCancelled = true;
       return;
     }
     let dragData = this._dragData;
     if (dragData.dragging) {
       // Somehow a mouse up was missed.
       this._doDragStop();
     }
     dragData.reset();
     this.dX = 0;
     this.dY = 0;
     // walk up the DOM tree in search of nearest scrollable ancestor.  nulls are
     // returned if none found.
     let [targetScrollbox, targetScrollInterface, dragger]
       = ScrollUtils.getScrollboxFromElement(aEvent.originalTarget);
     // stop kinetic panning if targetScrollbox has changed
     if (this._kinetic.isActive() && this._dragger != dragger)
       this._kinetic.end();
     this._targetScrollbox = targetScrollInterface ? targetScrollInterface.element : targetScrollbox;
     this._targetScrollInterface = targetScrollInterface;
     if (!this._targetScrollbox) {
       return;
     }
     // Don't allow kinetic panning if APZC is enabled and the pan element is the deck
     let deck = document.getElementById("browsers");
     if (Services.prefs.getBoolPref(kAsyncPanZoomEnabled) &&
         this._targetScrollbox == deck) {
       return;
     }
     // XXX shouldn't dragger always be valid here?
     if (dragger) {
       let draggable = dragger.isDraggable(targetScrollbox, targetScrollInterface);
       dragData.locked = !draggable.x || !draggable.y;
       if (draggable.x || draggable.y) {
         this._dragger = dragger;
         if (dragger.freeDrag)
           dragData.alwaysFreeDrag = dragger.freeDrag();
         this._doDragStart(aEvent, draggable);
       }
     }
   },
   /** Send tap up event and any necessary full taps. */
   _onTouchEnd: function _onTouchEnd(aEvent) {
     if (aEvent.touches.length > 0 || this._isCancelled || !this._targetScrollbox)
       return;
     // onMouseMove will not record the delta change if we are waiting for a
     // paint. Since this is the last input for this drag, we override the flag.
     this._waitingForPaint = false;
     this._onTouchMove(aEvent);
     let dragData = this._dragData;
     this._doDragStop();
   },
   /**
    * If we're in a drag, do what we have to do to drag on.
    */
   _onTouchMove: function _onTouchMove(aEvent) {
     if (aEvent.touches.length > 1)
       return;
     if (this._isCancellable) {
       // only the first touchmove is cancellable.
       this._isCancellable = false;
       if (aEvent.defaultPrevented) {
         this._isCancelled = true;
       }
     }
     if (this._isCancelled)
       return;
     let touch = aEvent.changedTouches[0];
     if (!this._targetScrollbox) {
       return;
     }
     let dragData = this._dragData;
     if (dragData.dragging) {
       let oldIsPan = dragData.isPan();
       dragData.setDragPosition(touch.screenX, touch.screenY);
       dragData.setMousePosition(touch);
       // Kinetic panning is sensitive to time. It is more stable if it receives
       // the mousemove events as they come. For dragging though, we only want
       // to call _dragBy if we aren't waiting for a paint (so we don't spam the
       // main browser loop with a bunch of redundant paints).
       //
       // Here, we feed kinetic panning drag differences for mouse events as
       // come; for dragging, we build up a drag buffer in this.dX/this.dY and
       // release it when we are ready to paint.
       //
       let [sX, sY] = dragData.panPosition();
       this.dX += dragData.prevPanX - sX;
       this.dY += dragData.prevPanY - sY;
       if (dragData.isPan()) {
         // Only pan when mouse event isn't part of a click. Prevent jittering on tap.
         this._kinetic.addData(sX - dragData.prevPanX, sY - dragData.prevPanY);
         // dragBy will reset dX and dY values to 0
         this._dragBy(this.dX, this.dY);
         // Let everyone know when mousemove begins a pan
         if (!oldIsPan && dragData.isPan()) {
           let event = document.createEvent("Events");
           event.initEvent("PanBegin", true, false);
           this._targetScrollbox.dispatchEvent(event);
           Browser.selectedBrowser.messageManager.sendAsyncMessage("Browser:PanBegin", {});
         }
       }
     }
   },
   /**
    * Inform our dragger of a dragStart.
    */
   _doDragStart: function _doDragStart(aEvent, aDraggable) {
     let touch = aEvent.changedTouches[0];
     let dragData = this._dragData;
     dragData.setDragStart(touch.screenX, touch.screenY, aDraggable);
     this._kinetic.addData(0, 0);
     this._dragStartTime = Date.now();
     if (!this._kinetic.isActive()) {
       this._dragger.dragStart(touch.clientX, touch.clientY, touch.target, this._targetScrollInterface);
     }
   },
   /** Finish a drag. */
   _doDragStop: function _doDragStop() {
     let dragData = this._dragData;
     if (!dragData.dragging)
       return;
     dragData.endDrag();
     // Note: it is possible for kinetic scrolling to be active from a
     // mousedown/mouseup event previous to this one. In this case, we
     // want the kinetic panner to tell our drag interface to stop.
     if (dragData.isPan()) {
       if (Date.now() - this._dragStartTime > kStopKineticPanOnDragTimeout)
         this._kinetic._velocity.set(0, 0);
       // Start kinetic pan if we aren't using async pan zoom or the scroll
       // element is not browsers.
       let deck = document.getElementById("browsers");
       if (!Services.prefs.getBoolPref(kAsyncPanZoomEnabled) ||
           this._targetScrollbox != deck) {
         this._kinetic.start();
       }
     } else {
       this._kinetic.end();
       if (this._dragger)
         this._dragger.dragStop(0, 0, this._targetScrollInterface);
       this._dragger = null;
     }
   },
   /**
    * Used by _onTouchMove() above and by KineticController's timer to do the
    * actual dragMove signalling to the dragger.  We'd put this in _onTouchMove()
    * but then KineticController would be adding to its own data as it signals
    * the dragger of dragMove()s.
    */
   _dragBy: function _dragBy(dX, dY, aIsKinetic) {
     let dragged = true;
     let dragData = this._dragData;
     if (!this._waitingForPaint || aIsKinetic) {
       let dragData = this._dragData;
       dragged = this._dragger.dragMove(dX, dY, this._targetScrollInterface, aIsKinetic,
                                        dragData._mouseX, dragData._mouseY);
       if (dragged && !this._waitingForPaint) {
         this._waitingForPaint = true;
         mozRequestAnimationFrame(this);
       }
       this.dX = 0;
       this.dY = 0;
     }
     if (!dragData.isPan())
       this._kinetic.pause();
     return dragged;
   },
   /** Callback for kinetic scroller. */
   _kineticStop: function _kineticStop() {
     // Kinetic panning could finish while user is panning, so don't finish
     // the pan just yet.
     let dragData = this._dragData;
     if (!dragData.dragging) {
       if (this._dragger)
         this._dragger.dragStop(0, 0, this._targetScrollInterface);
       this._dragger = null;
       let event = document.createEvent("Events");
       event.initEvent("PanFinished", true, false);
       this._targetScrollbox.dispatchEvent(event);
     }
   },
   toString: function toString() {
     return '[TouchModule] {'
       + '\n\tdragData=' + this._dragData + ', '
       + 'dragger=' + this._dragger + ', '
       + '\n\ttargetScroller=' + this._targetScrollInterface + '}';
   },
 };
 var ScrollUtils = {
   // threshold in pixels for sensing a tap as opposed to a pan
   get tapRadius() {
     let dpi = Util.displayDPI;
     delete this.tapRadius;
     return this.tapRadius = Services.prefs.getIntPref("ui.dragThresholdX") / 240 * dpi;
   },
   /**
    * Walk up (parentward) the DOM tree from elem in search of a scrollable element.
    * Return the element and its scroll interface if one is found, two nulls otherwise.
    *
    * This function will cache the pointer to the scroll interface on the element itself,
    * so it is safe to call it many times without incurring the same XPConnect overhead
    * as in the initial call.
    */
   getScrollboxFromElement: function getScrollboxFromElement(elem) {
     let scrollbox = null;
     let qinterface = null;
     // if element is content or the startui page, get the browser scroll interface
     if (elem.ownerDocument == Browser.selectedBrowser.contentDocument) {
       elem = Browser.selectedBrowser;
     }
     for (; elem; elem = elem.parentNode) {
       try {
         if (elem.anonScrollBox) {
           scrollbox = elem.anonScrollBox;
           qinterface = scrollbox.boxObject.QueryInterface(Ci.nsIScrollBoxObject);
         } else if (elem.scrollBoxObject) {
           scrollbox = elem;
           qinterface = elem.scrollBoxObject;
           break;
         } else if (elem.customDragger) {
           scrollbox = elem;
           break;
         } else if (elem.boxObject) {
           let qi = (elem._cachedSBO) ? elem._cachedSBO
                                      : elem.boxObject.QueryInterface(Ci.nsIScrollBoxObject);
           if (qi) {
             scrollbox = elem;
             scrollbox._cachedSBO = qinterface = qi;
             break;
           }
         }
       } catch (e) { /* we aren't here to deal with your exceptions, we'll just keep
                        traversing until we find something more well-behaved, as we
                        prefer default behaviour to whiny scrollers. */ }
     }
     return [scrollbox, qinterface, (scrollbox ? (scrollbox.customDragger || this._defaultDragger) : null)];
   },
   /** Determine if the distance moved can be considered a pan */
   isPan: function isPan(aPoint, aPoint2) {
     return (Math.abs(aPoint.x - aPoint2.x) > this.tapRadius ||
             Math.abs(aPoint.y - aPoint2.y) > this.tapRadius);
   },
   /**
    * The default dragger object used by TouchModule when dragging a scrollable
    * element that provides no customDragger.  Simply performs the expected
    * regular scrollBy calls on the scroller.
    */
   _defaultDragger: {
     isDraggable: function isDraggable(target, scroller) {
       let sX = {}, sY = {},
           pX = {}, pY = {};
       scroller.getPosition(pX, pY);
       scroller.getScrolledSize(sX, sY);
       let rect = target.getBoundingClientRect();
       return { x: (sX.value > rect.width  || pX.value != 0),
                y: (sY.value > rect.height || pY.value != 0) };
     },
     dragStart: function dragStart(cx, cy, target, scroller) {
       scroller.element.addEventListener("PanBegin", this._showScrollbars, false);
     },
     dragStop: function dragStop(dx, dy, scroller) {
       scroller.element.removeEventListener("PanBegin", this._showScrollbars, false);
       return this.dragMove(dx, dy, scroller);
     },
     dragMove: function dragMove(dx, dy, scroller) {
       if (scroller.getPosition) {
         try {
           let oldX = {}, oldY = {};
           scroller.getPosition(oldX, oldY);
           scroller.scrollBy(dx, dy);
           let newX = {}, newY = {};
           scroller.getPosition(newX, newY);
           return (newX.value != oldX.value) || (newY.value != oldY.value);
         } catch (e) { /* we have no time for whiny scrollers! */ }
       }
       return false;
     },
     _showScrollbars: function _showScrollbars(aEvent) {
       let scrollbox = aEvent.target;
       scrollbox.setAttribute("panning", "true");
       let hideScrollbars = function() {
         scrollbox.removeEventListener("PanFinished", hideScrollbars, false);
         scrollbox.removeEventListener("CancelTouchSequence", hideScrollbars, false);
         scrollbox.removeAttribute("panning");
       }
       // Wait for panning to be completely finished before removing scrollbars
       scrollbox.addEventListener("PanFinished", hideScrollbars, false);
       scrollbox.addEventListener("CancelTouchSequence", hideScrollbars, false);
     }
   }
 };
 /**
  * DragData handles processing drags on the screen, handling both
  * locking of movement on one axis, and click detection.
  */
 function DragData() {
   this._domUtils = Cc["@mozilla.org/inspector/dom-utils;1"].getService(Ci.inIDOMUtils);
   this._lockRevertThreshold = Util.displayDPI * kAxisLockRevertThreshold;
   this.reset();
 };
 DragData.prototype = {
   reset: function reset() {
     this.dragging = false;
     this.sX = null;
     this.sY = null;
     this.locked = false;
     this.stayLocked = false;
     this.alwaysFreeDrag = false;
     this.lockedX = null;
     this.lockedY = null;
     this._originX = null;
     this._originY = null;
     this.prevPanX = null;
     this.prevPanY = null;
     this._isPan = false;
   },
   /** Depending on drag data, locks sX,sY to X-axis or Y-axis of start position. */
   _lockAxis: function _lockAxis(sX, sY) {
     if (this.locked) {
       if (this.lockedX !== null)
         sX = this.lockedX;
       else if (this.lockedY !== null)
         sY = this.lockedY;
       return [sX, sY];
     }
     else {
       return [this._originX, this._originY];
     }
   },
   setMousePosition: function setMousePosition(aEvent) {
     this._mouseX = aEvent.clientX;
     this._mouseY = aEvent.clientY;
   },
   setDragPosition: function setDragPosition(sX, sY) {
     // Check if drag is now a pan.
     if (!this._isPan) {
       this._isPan = ScrollUtils.isPan(new Point(this._originX, this._originY), new Point(sX, sY));
       if (this._isPan) {
         this._resetActive();
       }
     }
     // If now a pan, mark previous position where panning was.
     if (this._isPan) {
       let absX = Math.abs(this._originX - sX);
       let absY = Math.abs(this._originY - sY);
       if (absX > this._lockRevertThreshold || absY > this._lockRevertThreshold)
         this.stayLocked = true;
       // After the first lock, see if locking decision should be reverted.
       if (!this.stayLocked) {
         if (this.lockedX && absX > 3 * absY)
           this.lockedX = null;
         else if (this.lockedY && absY > 3 * absX)
           this.lockedY = null;
       }
       if (!this.locked) {
         // look at difference from origin coord to lock movement, but only
         // do it if initial movement is sufficient to detect intent
         // divide possibilty space into eight parts.  Diagonals will allow
         // free movement, while moving towards a cardinal will lock that
         // axis.  We pick a direction if you move more than twice as far
         // on one axis than another, which should be an angle of about 30
         // degrees from the axis
         if (absX > 2.5 * absY)
           this.lockedY = sY;
         else if (absY > absX)
           this.lockedX = sX;
         this.locked = true;
       }
     }
     // Never lock if the dragger requests it
     if (this.alwaysFreeDrag) {
       this.lockedY = null;
       this.lockedX = null;
     }
     // After pan lock, figure out previous panning position. Base it on last drag
     // position so there isn't a jump in panning.
     let [prevX, prevY] = this._lockAxis(this.sX, this.sY);
     this.prevPanX = prevX;
     this.prevPanY = prevY;
     this.sX = sX;
     this.sY = sY;
   },
   setDragStart: function setDragStart(screenX, screenY, aDraggable) {
     this.sX = this._originX = screenX;
     this.sY = this._originY = screenY;
     this.dragging = true;
     // If the target area is pannable only in one direction lock it early
     // on the right axis
     this.lockedX = !aDraggable.x ? screenX : null;
     this.lockedY = !aDraggable.y ? screenY : null;
     this.stayLocked = this.lockedX || this.lockedY;
     this.locked = this.stayLocked;
   },
   endDrag: function endDrag() {
     this._resetActive();
     this.dragging = false;
   },
   /** Returns true if drag should pan scrollboxes.*/
   isPan: function isPan() {
     return this._isPan;
   },
   /** Return true if drag should be parsed as a click. */
   isClick: function isClick() {
     return !this._isPan;
   },
   /**
    * Returns the screen position for a pan. This factors in axis locking.
    * @return Array of screen X and Y coordinates
    */
   panPosition: function panPosition() {
     return this._lockAxis(this.sX, this.sY);
   },
   /** dismiss the active state of the pan element */
   _resetActive: function _resetActive() {
     let target = document.documentElement;
     // If the target is active, toggle (turn off) the active flag. Otherwise do nothing.
     if (this._domUtils.getContentState(target) & kStateActive)
       this._domUtils.setContentState(target, kStateActive);
   },
   toString: function toString() {
     return '[DragData] { sX,sY=' + this.sX + ',' + this.sY + ', dragging=' + this.dragging + ' }';
   }
 };
 /**
  * KineticController - a class to take drag position data and use it
  * to do kinetic panning of a scrollable object.
  *
  * aPanBy is a function that will be called with the dx and dy
  * generated by the kinetic algorithm.  It should return true if the
  * object was panned, false if there was no movement.
  *
  * There are two complicated things done here.  One is calculating the
  * initial velocity of the movement based on user input.  Two is
  * calculating the distance to move every frame.
  */
 function KineticController(aPanBy, aEndCallback) {
   this._panBy = aPanBy;
   this._beforeEnd = aEndCallback;
   // These are used to calculate the position of the scroll panes during kinetic panning. Think of
   // these points as vectors that are added together and multiplied by scalars.
   this._position = new Point(0, 0);
   this._velocity = new Point(0, 0);
   this._acceleration = new Point(0, 0);
   this._time = 0;
   this._timeStart = 0;
   // How often do we change the position of the scroll pane?  Too often and panning may jerk near
   // the end. Too little and panning will be choppy. In milliseconds.
   this._updateInterval = Services.prefs.getIntPref("browser.ui.kinetic.updateInterval");
   // Constants that affect the "friction" of the scroll pane.
   this._exponentialC = Services.prefs.getIntPref("browser.ui.kinetic.exponentialC");
   this._polynomialC = Services.prefs.getIntPref("browser.ui.kinetic.polynomialC") / 1000000;
   // Number of milliseconds that can contain a swipe. Movements earlier than this are disregarded.
   this._swipeLength = Services.prefs.getIntPref("browser.ui.kinetic.swipeLength");
   this._reset();
 }
 KineticController.prototype = {
   _reset: function _reset() {
     this._active = false;
     this._paused = false;
     this.momentumBuffer = [];
     this._velocity.set(0, 0);
   },
   isActive: function isActive() {
     return this._active;
   },
   _startTimer: function _startTimer() {
     let self = this;
     let lastp = this._position;  // track last position vector because pan takes deltas
     let v0 = this._velocity;  // initial velocity
     let a = this._acceleration;  // acceleration
     let c = this._exponentialC;
     let p = new Point(0, 0);
     let dx, dy, t, realt;
     function calcP(v0, a, t) {
       // Important traits for this function:
       //   p(t=0) is 0
       //   p'(t=0) is v0
       //
       // We use exponential to get a smoother stop, but by itself exponential
       // is too smooth at the end. Adding a polynomial with the appropriate
       // weight helps to balance
       return v0 * Math.exp(-t / c) * -c + a * t * t + v0 * c;
     }
     this._calcV = function(v0, a, t) {
       return v0 * Math.exp(-t / c) + 2 * a * t;
     }
     let callback = {
       sample: function kineticHandleEvent(timeStamp) {
         // Someone called end() on us between timer intervals
         // or we are paused.
         if (!self.isActive() || self._paused)
           return;
         // To make animation end fast enough but to keep smoothness, average the ideal
         // time frame (smooth animation) with the actual time lapse (end fast enough).
         // Animation will never take longer than 2 times the ideal length of time.
         realt = timeStamp - self._initialTime;
         self._time += self._updateInterval;
         t = (self._time + realt) / 2;
         // Calculate new position.
         p.x = calcP(v0.x, a.x, t);
         p.y = calcP(v0.y, a.y, t);
         dx = Math.round(p.x - lastp.x);
         dy = Math.round(p.y - lastp.y);
         // Test to see if movement is finished for each component.
         if (dx * a.x > 0) {
           dx = 0;
           lastp.x = 0;
           v0.x = 0;
           a.x = 0;
         }
         // Symmetric to above case.
         if (dy * a.y > 0) {
           dy = 0;
           lastp.y = 0;
           v0.y = 0;
           a.y = 0;
         }
         if (v0.x == 0 && v0.y == 0) {
           self.end();
         } else {
           let panStop = false;
           if (dx != 0 || dy != 0) {
             try { panStop = !self._panBy(-dx, -dy, true); } catch (e) {}
             lastp.add(dx, dy);
           }
           if (panStop)
             self.end();
           else
             mozRequestAnimationFrame(this);
         }
       }
     };
     this._active = true;
     this._paused = false;
     mozRequestAnimationFrame(callback);
   },
   start: function start() {
     function sign(x) {
       return x ? ((x > 0) ? 1 : -1) : 0;
     }
     function clampFromZero(x, closerToZero, furtherFromZero) {
       if (x >= 0)
         return Math.max(closerToZero, Math.min(furtherFromZero, x));
       return Math.min(-closerToZero, Math.max(-furtherFromZero, x));
     }
     let mb = this.momentumBuffer;
     let mblen = this.momentumBuffer.length;
     let lastTime = mb[mblen - 1].t;
     let distanceX = 0;
     let distanceY = 0;
     let swipeLength = this._swipeLength;
     // determine speed based on recorded input
     let me;
     for (let i = 0; i < mblen; i++) {
       me = mb[i];
       if (lastTime - me.t < swipeLength) {
         distanceX += me.dx;
         distanceY += me.dy;
       }
     }
     let currentVelocityX = 0;
     let currentVelocityY = 0;
     if (this.isActive()) {
       // If active, then we expect this._calcV to be defined.
       let currentTime = Date.now() - this._initialTime;
       currentVelocityX = Util.clamp(this._calcV(this._velocity.x, this._acceleration.x, currentTime), -kMaxVelocity, kMaxVelocity);
       currentVelocityY = Util.clamp(this._calcV(this._velocity.y, this._acceleration.y, currentTime), -kMaxVelocity, kMaxVelocity);
     }
     if (currentVelocityX * this._velocity.x <= 0)
       currentVelocityX = 0;
     if (currentVelocityY * this._velocity.y <= 0)
       currentVelocityY = 0;
     let swipeTime = Math.min(swipeLength, lastTime - mb[0].t);
     this._velocity.x = clampFromZero((distanceX / swipeTime) + currentVelocityX, Math.abs(currentVelocityX), kMaxVelocity);
     this._velocity.y = clampFromZero((distanceY / swipeTime) + currentVelocityY, Math.abs(currentVelocityY), kMaxVelocity);
     if (Math.abs(this._velocity.x) < kMinVelocity)
       this._velocity.x = 0;
     if (Math.abs(this._velocity.y) < kMinVelocity)
       this._velocity.y = 0;
     // Set acceleration vector to opposite signs of velocity
     this._acceleration.set(this._velocity.clone().map(sign).scale(-this._polynomialC));
     this._position.set(0, 0);
     this._initialTime = mozAnimationStartTime;
     this._time = 0;
     this.momentumBuffer = [];
     if (!this.isActive() || this._paused)
       this._startTimer();
     return true;
   },
   pause: function pause() {
     this._paused = true;
   },
   end: function end() {
     if (this.isActive()) {
       if (this._beforeEnd)
         this._beforeEnd();
       this._reset();
     }
   },
   addData: function addData(dx, dy) {
     let mbLength = this.momentumBuffer.length;
     let now = Date.now();
     if (this.isActive()) {
       // Stop active movement when dragging in other direction.
       if (dx * this._velocity.x < 0 || dy * this._velocity.y < 0)
         this.end();
     }
     this.momentumBuffer.push({'t': now, 'dx' : dx, 'dy' : dy});
   }
 };
 /*
  * Simple gestures support
  */
 var GestureModule = {
   _debugEvents: false,
   init: function init() {
     window.addEventListener("MozSwipeGesture", this, true);
   },
   /*
    * Events
    *
    * Dispatch events based on the type of mouse gesture event. For now, make
    * sure to stop propagation of every gesture event so that web content cannot
    * receive gesture events.
    *
    * @param nsIDOMEvent information structure
    */
   handleEvent: function handleEvent(aEvent) {
     try {
       aEvent.stopPropagation();
       aEvent.preventDefault();
       if (this._debugEvents) Util.dumpLn("GestureModule:", aEvent.type);
       switch (aEvent.type) {
         case "MozSwipeGesture":
           if (this._onSwipe(aEvent)) {
             let event = document.createEvent("Events");
             event.initEvent("CancelTouchSequence", true, true);
             aEvent.target.dispatchEvent(event);
           }
           break;
       }
     } catch (e) {
       Util.dumpLn("Error while handling gesture event", aEvent.type,
                   "\nPlease report error at:", e);
       Cu.reportError(e);
     }
   },
   _onSwipe: function _onSwipe(aEvent) {
     switch (aEvent.direction) {
       case Ci.nsIDOMSimpleGestureEvent.DIRECTION_LEFT:
         return this._tryCommand("cmd_forward");
       case Ci.nsIDOMSimpleGestureEvent.DIRECTION_RIGHT:
         return this._tryCommand("cmd_back");
     }
     return false;
   },
   _tryCommand: function _tryCommand(aId) {
      if (document.getElementById(aId).getAttribute("disabled") == "true")
        return false;
      CommandUpdater.doCommand(aId);
      return true;
   },
 };
 /**
  * Helper to track when the user is using a precise pointing device (pen/mouse)
  * versus an imprecise one (touch).
  */
 var InputSourceHelper = {
   isPrecise: false,
   init: function ish_init() {
     Services.obs.addObserver(this, "metro_precise_input", false);
     Services.obs.addObserver(this, "metro_imprecise_input", false);
   },
   _precise: function () {
     if (!this.isPrecise) {
       this.isPrecise = true;
       this._fire("MozPrecisePointer");
     }
   },
   _imprecise: function () {
     if (this.isPrecise) {
       this.isPrecise = false;
       this._fire("MozImprecisePointer");
     }
   },
   observe: function BrowserUI_observe(aSubject, aTopic, aData) {
     switch (aTopic) {
       case "metro_precise_input":
         this._precise();
         break;
       case "metro_imprecise_input":
         this._imprecise();
         break;
     }
   },
   fireUpdate: function fireUpdate() {
     if (this.isPrecise) {
       this._fire("MozPrecisePointer");
     } else {
       this._fire("MozImprecisePointer");
     }
   },
   _fire: function (name) {
     let event = document.createEvent("Events");
     event.initEvent(name, true, true);
     window.dispatchEvent(event);
   }
 };