gecko/mobile/chrome/content/InputHandler.js

// -*- Mode: js2; tab-width: 2; indent-tabs-mode: nil; js2-basic-offset: 2; js2-skip-preprocessor-directives: t; js2-strict-trailing-comma-warning: nil -*-
/*
 * ***** BEGIN LICENSE BLOCK *****
 * Version: MPL 1.1/GPL 2.0/LGPL 2.1
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (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.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * The Original Code is Mozilla Mobile Browser.
 *
 * The Initial Developer of the Original Code is
 * Mozilla Corporation.
 * Portions created by the Initial Developer are Copyright (C) 2008, 2009
 * the Initial Developer. All Rights Reserved.
 *
 * Contributor(s):
 *   Stuart Parmenter <stuart@mozilla.com>
 *   Brad Lassey <blassey@mozilla.com>
 *   Mark Finkle <mfinkle@mozilla.com>
 *   Gavin Sharp <gavin.sharp@gmail.com>
 *   Ben Combee <combee@mozilla.com>
 *
 * Alternatively, the contents of this file may be used under the terms of
 * either the GNU General Public License Version 2 or later (the "GPL"), or
 * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
 * in which case the provisions of the GPL or the LGPL are applicable instead
 * of those above. If you wish to allow use of your version of this file only
 * under the terms of either the GPL or the LGPL, and not to allow others to
 * use your version of this file under the terms of the MPL, indicate your
 * decision by deleting the provisions above and replace them with the notice
 * and other provisions required by the GPL or the LGPL. If you do not delete
 * the provisions above, a recipient may use your version of this file under
 * the terms of any one of the MPL, the GPL or the LGPL.
 *
 * ***** END LICENSE BLOCK ***** */

function getScrollboxFromElement(elem) {
  // check element for scrollable interface, if not found check parent until we get to root
  let scrollbox = null;

  while (elem.parentNode) {
    try {
      if ("scrollBoxObject" in elem && elem.scrollBoxObject) {
        scrollbox = elem.scrollBoxObject;
        break;
      }
      else if (elem.boxObject) {
        scrollbox = elem.boxObject.QueryInterface(Ci.nsIScrollBoxObject);
        break;
      }
    }
    catch (e) {
      // an exception is OK, we just don't want to propogate it
    }
    elem = elem.parentNode;
  }
  return scrollbox;
}

/**
 * Everything that is registed in _modules gets called with each event that the
 * InputHandler is registered to listen for.
 *
 * When one of the handlers decides it wants to handle the event, it should call
 * grab() on its owner which will cause it to receive all of the events until it
 * calls ungrab().  Calling grab will notify the other handlers via a
 * cancelPending() notification.  This tells them to stop what they're doing and
 * give up hope for being the one to process the events.
 */

function InputHandler() {
  /* the list of modules that will handle input */
  this._modules = [];

  /* which module, if any, has all events directed to it */
  this._grabbed = null;

  /* when true, don't process any events */
  this._ignoreEvents = false;

  /* if set, allow a click event to get through */
  this._allowNextClick = false;

  /* used to stop everything if mouse leaves window on desktop */
  window.addEventListener("mouseout", this, true);

  /* these handle dragging of both chrome elements and content */
  window.addEventListener("mousedown", this, true);
  window.addEventListener("mouseup", this, true);
  window.addEventListener("mousemove", this, true);
  window.addEventListener("click", this, true);
  window.addEventListener("mouseout", this, true);

  let stack = document.getElementById("browser-container");
  stack.addEventListener("DOMMouseScroll", this, true);

  let browserCanvas = document.getElementById("browser-canvas");
  browserCanvas.addEventListener("keydown", this, true);
  browserCanvas.addEventListener("keyup", this, true);

  let useEarlyMouseMoves = gPrefService.getBoolPref("browser.ui.panning.fixup.mousemove");

  this._modules.push(new ChromeInputModule(this, browserCanvas));
  this._modules.push(new ContentPanningModule(this, browserCanvas, useEarlyMouseMoves));
  this._modules.push(new ContentClickingModule(this));
  this._modules.push(new ScrollwheelModule(this));
}

InputHandler.prototype = {
  grab: function grab(obj) {
    // do nothing if we have a grab and it's the one requested
    // grab(null) is allowed because of mouseout handling
    if ((obj == null) || (this._grabbed != obj)) {

      // only send events to this object
      this._grabbed = obj;

      // call cancel on all modules
      for each(mod in this._modules) {
        if (mod != obj)
          mod.cancelPending();
      }
    }
  },

  ungrab: function ungrab(obj) {
    if (this._grabbed == obj)
      this._grabbed = null;
  },

  startListening: function startListening() {
    this._ignoreEvents = false;
  },

  stopListening: function stopListening() {
    this._ignoreEvents = true;
  },

  allowNextClick: function allowNextClick() {
    this._allowNextClick = true;
  },

  handleEvent: function handleEvent(aEvent) {
    if (this._ignoreEvents)
      return;

    // to allow supressing most clicks we don't generate ourselves,
    // filter them here unless handler code has asked us to allow it
    // through one time
    if (aEvent.type == "click") {
      if (this._allowNextClick) {
        this._allowNextClick = false;
      }
      else {
        aEvent.stopPropagation();
        aEvent.preventDefault();
        return;
      }
    }

    if (this._grabbed) {
      this._grabbed.handleEvent(aEvent);
    }
    else {
      for each(mod in this._modules) {
        mod.handleEvent(aEvent);
        // if event got grabbed, don't pass to other handlers
        if (this._grabbed)
          break;
      }
    }
  }
};

/**
 * Drag Data is used by both chrome and content input modules
 */

function DragData(owner, dragRadius, dragStartTimeoutLength) {
  this._owner = owner;
  this._dragRadius = dragRadius;
  this.reset();
}

DragData.prototype = {
  reset: function reset() {
    this.dragging = false;
    this.sX = null;
    this.sY = null;
    this.alreadyLocked = false;
    this.lockedX = null;
    this.lockedY = null;
    this._originX = null;
    this._originY = null;
  },

  setDragPosition: function setDragPosition(screenX, screenY) {
    this.sX = screenX;
    this.sY = screenY;
  },

  setDragStart: function setDragStart(screenX, screenY) {
    this.setDragPosition(screenX, screenY);
    this._originX = screenX;
    this._originY = screenY;
    this.dragging = true;
  },

  lockMouseMove: function lockMouseMove(sX, sY) {
    if (this.lockedX !== null)
      sX = this.lockedX;
    else if (this.lockedY !== null)
      sY = this.lockedY;
    return [sX, sY];
  },

  lockAxis: function lockAxis(sX, sY) {
    if (this.alreadyLocked)
      return this.lockMouseMove(sX, sY);

    // look at difference from stored coord to lock movement, but only
    // do it if initial movement is sufficient to detect intent
    let absX = Math.abs(this.sX - sX);
    let absY = Math.abs(this.sY - sY);

    // lock panning if we move more than half of the drag radius and that direction
    // contributed more than 2/3rd to the radial movement
    if ((absX > (this._dragRadius / 2)) && ((absX * absX) > (2 * absY * absY))) {
      this.lockedY = this.sY;
      sY = this.sY;
    }
    else if ((absY > (this._dragRadius / 2)) && ((absY * absY) > (2 * absX * absX))) {
      this.lockedX = this.sX;
      sX = this.sX;
    }
    this.alreadyLocked = true;

    return [sX, sY];
  },

  isPointOutsideRadius: function isPointOutsideRadius(sX, sY) {
    if (this._originX == undefined)
      return false;
    return (Math.pow(sX - this._originX, 2) + Math.pow(sY - this._originY, 2)) >
      (2 * Math.pow(this._dragRadius, 2));
  }
};

/**
 * Panning code for chrome elements
 */

function ChromeInputModule(owner, browserCanvas) {
  this._owner = owner;
  this._browserCanvas = browserCanvas;
  this._dragData = new DragData(this, 50, 200);
  this._targetScrollbox = null;
  this._clickEvents = [];
}

ChromeInputModule.prototype = {
  handleEvent: function handleEvent(aEvent) {
    switch (aEvent.type) {
      case "mousedown":
        this._onMouseDown(aEvent);
        break;
      case "mousemove":
        this._onMouseMove(aEvent);
        break;
      case "mouseup":
        this._onMouseUp(aEvent);
        break;
    }
  },

  /* If someone else grabs events ahead of us, cancel any pending
   * timeouts we may have.
   */
  cancelPending: function cancelPending() {
    this._dragData.reset();
    this._targetScrollbox = null;
  },

  // called from DragData.setDragStart only
  _dragStart: function _dragStart(sX, sY) {
    let dragData = this._dragData;

    dragData.setDragStart(sX, sY);

    [sX, sY] = dragData.lockAxis(sX, sY);
  },

  _dragStop: function _dragStop(sX, sY) {
    let dragData = this._dragData;
    [sX, sY] = dragData.lockMouseMove(sX, sY);
    if (this._targetScrollbox)
      this._targetScrollbox.scrollBy(dragData.sX - sX, dragData.sY - sY);
    this._targetScrollbox = null;
  },

  _dragMove: function _dragMove(sX, sY) {
    let dragData = this._dragData;
    if (dragData.isPointOutsideRadius(sX, sY))
      this._clickEvents = [];

    [sX, sY] = dragData.lockMouseMove(sX, sY);
    if (this._targetScrollbox)
      this._targetScrollbox.scrollBy(dragData.sX - sX, dragData.sY - sY);
    dragData.setDragPosition(sX, sY);
  },

  _onMouseDown: function _onMouseDown(aEvent) {
    // exit early for events in the content area
    if (aEvent.target === this._browserCanvas) {
      return;
    }

    let dragData = this._dragData;

    this._targetScrollbox = getScrollboxFromElement(aEvent.target);
    if (!this._targetScrollbox)
      return;

    // absorb the event for the scrollable XUL element and make all future events grabbed too
    this._owner.grab(this);
    aEvent.stopPropagation();
    aEvent.preventDefault();

    this._dragStart(aEvent.screenX, aEvent.screenY);
    this._onMouseMove(aEvent); // treat this as a mouse move too

    // store away the event for possible sending later if a drag doesn't happen
    let clickEvent = document.createEvent("MouseEvent");
    clickEvent.initMouseEvent(aEvent.type, aEvent.bubbles, aEvent.cancelable,
                              aEvent.view, aEvent.detail,
                              aEvent.screenX, aEvent.screenY, aEvent.clientX, aEvent.clientY,
                              aEvent.ctrlKey, aEvent.altKey, aEvent.shiftKeyArg, aEvent.metaKeyArg,
                              aEvent.button, aEvent.relatedTarget);
    this._clickEvents.push({event: clickEvent, target: aEvent.target, time: Date.now()});
  },

  _onMouseUp: function _onMouseUp(aEvent) {
    // only process if original mousedown was on a scrollable element
    if (!this._targetScrollbox) {
      this._owner.allowNextClick();
      return;
    }

    // keep an eye out for mouseups that didn't start with a mousedown
    if (!(this._clickEvents.length % 2)) {
      this._clickEvents = [];
    }
    else {
      let clickEvent = document.createEvent("MouseEvent");
      clickEvent.initMouseEvent(aEvent.type, aEvent.bubbles, aEvent.cancelable,
                                aEvent.view, aEvent.detail,
                                aEvent.screenX, aEvent.screenY, aEvent.clientX, aEvent.clientY,
                                aEvent.ctrlKey, aEvent.altKey, aEvent.shiftKeyArg, aEvent.metaKeyArg,
                                aEvent.button, aEvent.relatedTarget);
      this._clickEvents.push({event: clickEvent, target: aEvent.target, time: Date.now()});

      this._sendSingleClick();
      this._targetScrollbox = null;
    }

    aEvent.stopPropagation();
    aEvent.preventDefault();

    let dragData = this._dragData;
    if (dragData.dragging)
      this._dragStop(aEvent.screenX, aEvent.screenY);

    dragData.reset(); // be sure to reset the timer
    this._targetScrollbox = null;
    this._owner.ungrab(this);
  },

  _onMouseMove: function _onMouseMove(aEvent) {
    let dragData = this._dragData;

    // only process if original mousedown was on a scrollable element
    if (!this._targetScrollbox)
      return;

    aEvent.stopPropagation();
    aEvent.preventDefault();

    let sX = aEvent.screenX;
    let sY = aEvent.screenY;

    if (!dragData.sX)
      dragData.setDragPosition(aEvent.screenX, aEvent.screenY);

    [sX, sY] = dragData.lockMouseMove(aEvent.screenX, aEvent.screenY);

    if (!dragData.dragging)
      return;

    [sX, sY] = dragData.lockMouseMove(sX, sY);
    this._dragMove(sX, sY);
  },

  // resend original events with our handler out of the loop
  _sendSingleClick: function _sendSingleClick() {
    this._owner.grab(this);
    this._owner.stopListening();

    // send original mouseDown/mouseUps again
    this._redispatchChromeMouseEvent(this._clickEvents[0].event);
    this._redispatchChromeMouseEvent(this._clickEvents[1].event);

    this._owner.startListening();
    this._owner.ungrab(this);

    this._clickEvents = [];
  },

  _redispatchChromeMouseEvent: function _redispatchChromeMouseEvent(aEvent) {
    if (!(aEvent instanceof MouseEvent)) {
      Cu.reportError("_redispatchChromeMouseEvent called with a non-mouse event");
      return;
    }

    // Redispatch the mouse event, ignoring the root scroll frame
    let cwu = Browser.windowUtils;
    cwu.sendMouseEvent(aEvent.type, aEvent.clientX, aEvent.clientY,
                       aEvent.button, aEvent.detail, 0, true);
  }
};

/**
 * Kinetic panning code for content
 */

function KineticData(owner) {
  this._owner = owner;
  this._kineticTimer = null;
  this.reset();
}

KineticData.prototype = {
  /* const */ _updateInterval : 33, // this would put us at roughly 30fps

  reset: function reset() {
    if (this._kineticTimer != null) {
      this._kineticTimer.cancel();
      this._kineticTimer = null;
    }

    this.momentumBuffer = [];
    this._speedX = 0;
    this._speedY = 0;
  },

  _startKineticTimer: function _startKineticTimer() {
    let callback = {
      _self: this,
      notify: function kineticTimerCallback(timer) {
        let self = this._self;

        const decelerationRate = 0.15;

        // dump("             speeds: " + self._speedX + " " + self._speedY + "\n");

        if (self._speedX == 0 && self._speedY == 0) {
          self.endKinetic();
          return;
        } else {
          let dx = Math.round(self._speedX * self._updateInterval);
          let dy = Math.round(self._speedY * self._updateInterval);
          // dump("dx, dy: " + dx + " " + dy + "\n");

          let panned = self._owner._dragBy(dx, dy);
          if (!panned) {
            self.endKinetic();
            return;
          }
        }

        if (self._speedX < 0) {
          self._speedX = Math.min(self._speedX + decelerationRate, 0);
        } else if (self._speedX > 0) {
          self._speedX = Math.max(self._speedX - decelerationRate, 0);
        }
        if (self._speedY < 0) {
          self._speedY = Math.min(self._speedY + decelerationRate, 0);
        } else if (self._speedY > 0) {
          self._speedY = Math.max(self._speedY - decelerationRate, 0);
        }

        if (self._speedX == 0 && self._speedY == 0)
          self.endKinetic();
      }
    };

    this._kineticTimer = Cc["@mozilla.org/timer;1"].createInstance(Ci.nsITimer);
    //initialize our timer with updateInterval
    this._kineticTimer.initWithCallback(callback,
                                        this._updateInterval,
                                        this._kineticTimer.TYPE_REPEATING_SLACK);
  },


  startKinetic: function startKinetic(sX, sY) {
    let mb = this.momentumBuffer;
    let mblen = this.momentumBuffer.length;

    // If we don't have at least 2 events we can't really do kinetic panning
    if (mblen < 2)
      return false;

    let tempX = 0;
    let tempY = 0;

    // build arrays of each movement's speed in pixels/ms
    let prev = mb[0];
    for (let i = 1; i < mblen; i++) {
      let me = mb[i];

      let timeDiff = me.t - prev.t;
      tempX += (me.sx - prev.sx) / timeDiff;
      tempY += (me.sy - prev.sy) / timeDiff;

      prev = me;
    }

    // average the speeds out (this could probably be a bit smarter)
    this._speedX = tempX / mblen;
    this._speedY = tempY / mblen;

    // fire off our kinetic timer which will do all the work
    this._startKineticTimer();

    return true;
  },

  endKinetic: function endKinetic() {
    ws.dragStop();
    this.reset();

    // Make sure that sidebars don't stay partially open
    // XXX this should live somewhere else
    let [leftVis,] = ws.getWidgetVisibility("tabs-container", false);
    let [rightVis,] = ws.getWidgetVisibility("browser-controls", false);
    if (leftVis != 0 && leftVis != 1) {
      let w = document.getElementById("tabs-container").getBoundingClientRect().width;
      if (leftVis >= 0.6666)
        ws.panBy(-w, 0, true);
      else
        ws.panBy(leftVis * w, 0, true);
    }
    else if (rightVis != 0 && rightVis != 1) {
      let w = document.getElementById("browser-controls").getBoundingClientRect().width;
      if (rightVis >= 0.6666)
        ws.panBy(w, 0, true);
      else
        ws.panBy(-rightVis * w, 0, true);
    }
    
    // unfreeze the toolbar if we have hide the sidebar
    let visibleNow = ws.isWidgetVisible("tabs-container") || ws.isWidgetVisible("browser-controls");
    if (!visibleNow)
      ws.unfreeze('toolbar-main')
  },

  addData: function addData(sx, sy) {
    let mbLength = this.momentumBuffer.length;
    // avoid adding duplicates which would otherwise slow down the speed
    let now = Date.now();

    if (mbLength > 0) {
      let mbLast = this.momentumBuffer[mbLength - 1];
      if ((mbLast.sx == sx && mbLast.sy == sy) || mbLast.t == now) {
	return;
      }
    }

    this.momentumBuffer.push({'t': now, 'sx' : sx, 'sy' : sy});
  }
};

function ContentPanningModule(owner, browserCanvas, useEarlyMouseMoves) {
  this._owner = owner;
  this._browserCanvas = browserCanvas;
  this._dragData = new DragData(this, 50, 200);
  this._kineticData = new KineticData(this);
  this._useEarlyMouseMoves = useEarlyMouseMoves;
}

ContentPanningModule.prototype = {
  handleEvent: function handleEvent(aEvent) {
    // exit early for events outside displayed content area
    if (aEvent.target !== this._browserCanvas)
      return;

    switch (aEvent.type) {
      case "mousedown":
        this._onMouseDown(aEvent);
        break;
      case "mousemove":
        this._onMouseMove(aEvent);
        break;
      case "mouseout":
      case "mouseup":
        this._onMouseUp(aEvent);
        break;
    }
  },


  /* If someone else grabs events ahead of us, cancel any pending
   * timeouts we may have.
   */
  cancelPending: function cancelPending() {
    let dragData = this._dragData;
    // stop scrolling, pass last coordinate we used
    this._kineticData.endKinetic(dragData.sX, dragData.sY);
    this._owner.ungrab(this);
    dragData.reset();
  },

  _dragStart: function _dragStart(sX, sY) {
    let dragData = this._dragData;

    dragData.setDragStart(sX, sY);

    [sX, sY] = dragData.lockAxis(sX, sY);

    ws.dragStart(sX, sY);

    Browser.canvasBrowser.startPanning();
  },

  _dragStop: function _dragStop(sX, sY) {
    let dragData = this._dragData;

    this._owner.ungrab(this);

    [sX, sY] = dragData.lockMouseMove(sX, sY);

    // start kinetic scrolling here for canvas only
    if (!this._kineticData.startKinetic(sX, sY))
      this._kineticData.endKinetic(sX, sY);
    dragData.reset();
  },

  _dragBy: function _dragBy(dx, dy) {
    let panned = ws.dragBy(dx, dy);
    return panned;
  },

  _dragMove: function _dragMove(sX, sY) {
    let dragData = this._dragData;
    [sX, sY] = dragData.lockMouseMove(sX, sY);
    let panned = ws.dragMove(sX, sY);
    dragData.setDragPosition(sX, sY);
    return panned;
  },

  _onMouseDown: function _onMouseDown(aEvent) {
    let dragData = this._dragData;
    // if we're in the process of kineticly scrolling, stop and start over
    if (this._kineticData._kineticTimer != null) {
      this._kineticData.endKinetic(aEvent.screenX, aEvent.screenY);
      this._owner.ungrab(this);
      dragData.reset();
    }

    this._dragStart(aEvent.screenX, aEvent.screenY);
    this._onMouseMove(aEvent); // treat this as a mouse move too
  },

  _onMouseUp: function _onMouseUp(aEvent) {
    let dragData = this._dragData;

    if (dragData.dragging) {
      this._onMouseMove(aEvent); // treat this as a mouse move, incase our x/y are different
      this._dragStop(aEvent.screenX, aEvent.screenY);
    }

    dragData.reset(); // be sure to reset the timer
  },

  _onMouseMove: function _onMouseMove(aEvent) {
    // don't do anything if we're in the process of kineticly scrolling
    if (this._kineticData._kineticTimer != null)
      return;

    let dragData = this._dragData;

    // if we move enough, start a grab to prevent click from getting events
    if (dragData.isPointOutsideRadius(aEvent.screenX, aEvent.screenY))
      this._owner.grab(this);

    // if we never received a mouseDown, we need to go ahead and set this data
    if (!dragData.sX)
      dragData.setDragPosition(aEvent.screenX, aEvent.screenY);

    let [sX, sY] = dragData.lockMouseMove(aEvent.screenX, aEvent.screenY);

    // even if we haven't started dragging yet, we should queue up the
    // mousemoves in case we do start
    if (this._useEarlyMouseMoves || dragData.dragging)
      this._kineticData.addData(sX, sY);

    if (dragData.dragging)
      this._dragMove(sX, sY);
  },
};

/**
 * Mouse click handlers
 */

function ContentClickingModule(owner) {
  this._owner = owner;
  this._clickTimeout = -1;
  this._events = [];
  this._zoomedTo = null;
}

ContentClickingModule.prototype = {
  handleEvent: function handleEvent(aEvent) {
    // exit early for events outside displayed content area
    if (aEvent.target !== document.getElementById("browser-canvas"))
      return;

    switch (aEvent.type) {
      // UI panning events
      case "mousedown":
        this._events.push({event: aEvent, time: Date.now()});

        // we're waiting for a click
        if (this._clickTimeout != -1) {
          // go ahead and stop the timeout so no single click gets
          // sent, but don't clear clickTimeout here so that mouseUp
          // handler will treat this as a double click
          window.clearTimeout(this._clickTimeout);
        }
        break;
      case "mouseup":
        // keep an eye out for mouseups that didn't start with a mousedown
        if (!(this._events.length % 2)) {
          this._reset();
          break;
        }

        this._events.push({event: aEvent, time: Date.now()});

        if (this._clickTimeout == -1) {
          this._clickTimeout = window.setTimeout(function _clickTimeout(self) { self._sendSingleClick(); }, 400, this);
        }
        else {
          window.clearTimeout(this._clickTimeout);
          this._clickTimeout = -1;
          this._sendDoubleClick();
        }
        break;
    }
  },

  /* If someone else grabs events ahead of us, cancel any pending
   * timeouts we may have.
   */
  cancelPending: function cancelPending() {
    this._reset();
  },

  _reset: function _reset() {
    if (this._clickTimeout != -1)
      window.clearTimeout(this._clickTimeout);
    this._clickTimeout = -1;

    this._events = [];
  },

  _sendSingleClick: function _sendSingleClick() {
    this._owner.allowNextClick();

    this._owner.grab(this);
    this._dispatchContentMouseEvent(this._events[0].event);
    this._dispatchContentMouseEvent(this._events[1].event);
    this._owner.ungrab(this);

    this._reset();
  },

  _sendDoubleClick: function _sendDoubleClick() {
    this._owner.grab(this);

    function optimalElementForPoint(cX, cY) {
      var element = Browser.canvasBrowser.elementFromPoint(cX, cY);
      return element;
    }

    let firstEvent = this._events[0].event;
    let zoomElement = optimalElementForPoint(firstEvent.clientX, firstEvent.clientY);

    if (zoomElement) {
      if (zoomElement != this._zoomedTo) {
        this._zoomedTo = zoomElement;
        Browser.canvasBrowser.zoomToElement(zoomElement);
      } else {
        this._zoomedTo = null;
        Browser.canvasBrowser.zoomFromElement(zoomElement);
      }
    }

    this._owner.ungrab(this);

    this._reset();
  },


  _dispatchContentMouseEvent: function _dispatchContentMouseEvent(aEvent, aType) {
    if (!(aEvent instanceof MouseEvent)) {
      Cu.reportError("_dispatchContentMouseEvent called with a non-mouse event");
      return;
    }

    let cb = Browser.canvasBrowser;
    var [x, y] = cb._clientToContentCoords(aEvent.clientX, aEvent.clientY);
    var cwu = cb.contentDOMWindowUtils;

    // Redispatch the mouse event, ignoring the root scroll frame
    cwu.sendMouseEvent(aType || aEvent.type,
                       x, y,
                       aEvent.button || 0,
                       aEvent.detail || 1,
                       0, true);
  }
};

/**
 * Scrollwheel zooming handler
 */

function ScrollwheelModule(owner) {
  this._owner = owner;
}

ScrollwheelModule.prototype = {
  handleEvent: function handleEvent(aEvent) {
    switch (aEvent.type) {
      // UI panning events
      case "DOMMouseScroll":
        this._owner.grab(this);
        Browser.canvasBrowser.zoom(aEvent.detail);
        this._owner.ungrab(this);
        break;
    }
  },

  /* If someone else grabs events ahead of us, cancel any pending
   * timeouts we may have.
   */
  cancelPending: function cancelPending() {
  }
};