(function( $ ){
     
// dictionary from hash to private properties
var THIS = {};

/**
 *
 * The main point of entry into creating a zoomable image on the page.
 *
 * We have provided an idiomatic javascript constructor which takes
 * a single object, but still support the legacy positional arguments.
 *
 * The options below are given in order that they appeared in the constructor
 * as arguments and we translate a positional call into an idiomatic call.
 *
 * @class
 * @extends OpenSeadragon.EventHandler
 * @extends OpenSeadragon.ControlDock
 * @param {Object} options
 * @param {String} options.element Id of Element to attach to,
 * @param {String} options.xmlPath  Xpath ( TODO: not sure! ),
 * @param {String} options.prefixUrl  Url used to prepend to paths, eg button 
 *  images, etc.
 * @param {Seadragon.Controls[]} options.controls Array of Seadragon.Controls,
 * @param {Seadragon.Overlays[]} options.overlays Array of Seadragon.Overlays,
 * @param {Seadragon.Controls[]} options.overlayControls An Array of ( TODO: 
 *  not sure! )
 *
 **/    
$.Viewer = function( options ) {

    var args  = arguments,
        _this = this,
        i;


    //backward compatibility for positional args while prefering more 
    //idiomatic javascript options object as the only argument
    if( !$.isPlainObject( options ) ){
        options = {
            id:                 args[ 0 ],
            xmlPath:            args.length > 1 ? args[ 1 ] : undefined,
            prefixUrl:          args.length > 2 ? args[ 2 ] : undefined,
            controls:           args.length > 3 ? args[ 3 ] : undefined,
            overlays:           args.length > 4 ? args[ 4 ] : undefined,
            overlayControls:    args.length > 5 ? args[ 5 ] : undefined
        };
    }

    //options.config and the general config argument are deprecated
    //in favor of the more direct specification of optional settings
    //being pass directly on the options object
    if ( options.config ){
        $.extend( true, options, options.config );
        delete options.config;
    }
    
    //Allow the options object to override global defaults
    $.extend( true, this, { 

        id:                 options.id,
        hash:               options.id,
        overlays:           [],
        overlayControls:    [],

        //private state properties
        previousBody:       [],

        //This was originally initialized in the constructor and so could never
        //have anything in it.  now it can because we allow it to be specified
        //in the options and is only empty by default if not specified. Also
        //this array was returned from get_controls which I find confusing
        //since this object has a controls property which is treated in other
        //functions like clearControls.  I'm removing the accessors.
        customControls: [],

        //These are originally not part options but declared as members
        //in initialize.  Its still considered idiomatic to put them here
        source:         null,
        drawer:         null,
        viewport:       null,
        navigator:      null, 
        profiler:       null

    }, $.DEFAULT_SETTINGS, options );

    $.EventHandler.call( this );
    $.ControlDock.call( this, options );

    this.element        = this.element || document.getElementById( this.id );
    this.canvas         = $.makeNeutralElement( "div" );

    (function( canvas ){
        canvas.width    = "100%";
        canvas.height   = "100%";
        canvas.overflow = "hidden";
        canvas.position = "absolute";
        canvas.top      = "0px";
        canvas.left     = "0px";
    }(  this.canvas.style ));

    (function( container ){
        container.width     = "100%";
        container.height    = "100%";
        container.position  = "relative";
        container.left      = "0px";
        container.top       = "0px";
        container.textAlign = "left";  // needed to protect against
    }( this.container.style ));

    this.container.insertBefore( this.canvas, this.container.firstChild);
    this.element.appendChild( this.container );

    //Used for toggling between fullscreen and default container size
    //TODO: these can be closure private and shared across Viewer
    //      instances.
    this.bodyWidth      = document.body.style.width;
    this.bodyHeight     = document.body.style.height;
    this.bodyOverflow   = document.body.style.overflow;
    this.docOverflow    = document.documentElement.style.overflow;

    THIS[ this.hash ] = {
        "fsBoundsDelta":     new $.Point( 1, 1 ),
        "prevContainerSize": null,
        "lastOpenStartTime": 0,
        "lastOpenEndTime":   0,
        "animating":         false,
        "forceRedraw":       false,
        "mouseInside":       false
    };

    this.innerTracker = new $.MouseTracker({
        element:            this.canvas, 
        clickTimeThreshold: this.clickTimeThreshold, 
        clickDistThreshold: this.clickDistThreshold,
        clickHandler:       $.delegate( this, onCanvasClick ),
        dragHandler:        $.delegate( this, onCanvasDrag ),
        releaseHandler:     $.delegate( this, onCanvasRelease ),
        scrollHandler:      $.delegate( this, onCanvasScroll )
    }).setTracking( this.mouseNavEnabled ? true : false ); // default state

    this.outerTracker = new $.MouseTracker({
        element:            this.container, 
        clickTimeThreshold: this.clickTimeThreshold, 
        clickDistThreshold: this.clickDistThreshold,
        enterHandler:       $.delegate( this, onContainerEnter ),
        exitHandler:        $.delegate( this, onContainerExit ),
        releaseHandler:     $.delegate( this, onContainerRelease )
    }).setTracking( this.mouseNavEnabled ? true : false ); // always tracking


    //private state properties
    $.extend( THIS[ this.hash ], {
        "group":        null,
        // whether we should be continuously zooming
        "zooming":      false,
        // how much we should be continuously zooming by
        "zoomFactor":   null,  
        "lastZoomTime": null
    });

    //////////////////////////////////////////////////////////////////////////
    // Navigation Controls
    //////////////////////////////////////////////////////////////////////////
    var beginZoomingInHandler   = $.delegate( this, beginZoomingIn ),
        endZoomingHandler       = $.delegate( this, endZooming ),
        doSingleZoomInHandler   = $.delegate( this, doSingleZoomIn ),
        beginZoomingOutHandler  = $.delegate( this, beginZoomingOut ),
        doSingleZoomOutHandler  = $.delegate( this, doSingleZoomOut ),
        onHomeHandler           = $.delegate( this, onHome ),
        onFullPageHandler       = $.delegate( this, onFullPage ),
        onFocusHandler          = $.delegate( this, onFocus ),
        onBlurHandler           = $.delegate( this, onBlur ),
        navImages               = this.navImages;

    this.zoomInButton           = null;
    this.zoomOutButton          = null;
    this.goHomeButton           = null;
    this.fullPageButton         = null;

    if( this.showNavigationControl ){

         this.zoomInButton = new $.Button({ 
            clickTimeThreshold: this.clickTimeThreshold,
            clickDistThreshold: this.clickDistThreshold,
            tooltip:    $.getString( "Tooltips.ZoomIn" ), 
            srcRest:    resolveUrl( this.prefixUrl, navImages.zoomIn.REST ),
            srcGroup:   resolveUrl( this.prefixUrl, navImages.zoomIn.GROUP ),
            srcHover:   resolveUrl( this.prefixUrl, navImages.zoomIn.HOVER ),
            srcDown:    resolveUrl( this.prefixUrl, navImages.zoomIn.DOWN ),
            onPress:    beginZoomingInHandler,
            onRelease:  endZoomingHandler,
            onClick:    doSingleZoomInHandler,
            onEnter:    beginZoomingInHandler,
            onExit:     endZoomingHandler,
            onFocus:    onFocusHandler,
            onBlur:     onBlurHandler
        });

        this.zoomOutButton = new $.Button({ 
            clickTimeThreshold: this.clickTimeThreshold,
            clickDistThreshold: this.clickDistThreshold,
            tooltip:    $.getString( "Tooltips.ZoomOut" ), 
            srcRest:    resolveUrl( this.prefixUrl, navImages.zoomOut.REST ), 
            srcGroup:   resolveUrl( this.prefixUrl, navImages.zoomOut.GROUP ), 
            srcHover:   resolveUrl( this.prefixUrl, navImages.zoomOut.HOVER ), 
            srcDown:    resolveUrl( this.prefixUrl, navImages.zoomOut.DOWN ),
            onPress:    beginZoomingOutHandler, 
            onRelease:  endZoomingHandler, 
            onClick:    doSingleZoomOutHandler, 
            onEnter:    beginZoomingOutHandler, 
            onExit:     endZoomingHandler,
            onFocus:    onFocusHandler,
            onBlur:     onBlurHandler
        });

        this.goHomeButton = new $.Button({ 
            clickTimeThreshold: this.clickTimeThreshold,
            clickDistThreshold: this.clickDistThreshold,
            tooltip:    $.getString( "Tooltips.Home" ), 
            srcRest:    resolveUrl( this.prefixUrl, navImages.home.REST ), 
            srcGroup:   resolveUrl( this.prefixUrl, navImages.home.GROUP ), 
            srcHover:   resolveUrl( this.prefixUrl, navImages.home.HOVER ), 
            srcDown:    resolveUrl( this.prefixUrl, navImages.home.DOWN ),
            onRelease:  onHomeHandler,
            onFocus:    onFocusHandler,
            onBlur:     onBlurHandler
        });

        this.fullPageButton = new $.Button({ 
            clickTimeThreshold: this.clickTimeThreshold,
            clickDistThreshold: this.clickDistThreshold,
            tooltip:    $.getString( "Tooltips.FullPage" ),
            srcRest:    resolveUrl( this.prefixUrl, navImages.fullpage.REST ),
            srcGroup:   resolveUrl( this.prefixUrl, navImages.fullpage.GROUP ),
            srcHover:   resolveUrl( this.prefixUrl, navImages.fullpage.HOVER ),
            srcDown:    resolveUrl( this.prefixUrl, navImages.fullpage.DOWN ),
            onRelease:  onFullPageHandler,
            onFocus:    onFocusHandler,
            onBlur:     onBlurHandler
        });

        this.buttons = new $.ButtonGroup({ 
            clickTimeThreshold: this.clickTimeThreshold,
            clickDistThreshold: this.clickDistThreshold,
            buttons: [ 
                this.zoomInButton, 
                this.zoomOutButton, 
                this.goHomeButton, 
                this.fullPageButton 
            ] 
        });

        this.navControl  = this.buttons.element;
        this.navControl[ $.SIGNAL ] = true;   // hack to get our controls to fade
        this.addHandler( 'open', $.delegate( this, lightUp ) );
        
        if( this.toolbar ){
            this.toolbar = new $.ControlDock({ element: this.toolbar });
            this.toolbar.addControl( this.navControl, $.ControlAnchor.TOP_LEFT  );
        }else{
            this.addControl( this.navControl, $.ControlAnchor.BOTTOM_RIGHT );
        }
    }

    for ( i = 0; i < this.customControls.length; i++ ) {
        this.addControl(
            this.customControls[ i ].id, 
            this.customControls[ i ].anchor
        );
    }

    //Instantiate a navigator if configured
    if ( this.showNavigator ){
        this.navigator = new $.Navigator({
            id:          this.navigatorElement,
            position:    this.navigatorPosition,
            sizeRatio:   this.navigatorSizeRatio,
            height:      this.navigatorHeight,
            width:       this.navigatorWidth,
            tileSources: this.tileSources,
            prefixUrl:   this.prefixUrl,
            overlays:    this.overlays,
            viewer:      this
        });
    }

    window.setTimeout( function(){
        beginControlsAutoHide( _this );
    }, 1 );    // initial fade out

    var initialTileSource,
        customTileSource;

    if ( this.xmlPath  ){
        //Deprecated option.  Now it is preferred to use the tileSources option
        this.tileSources = [ this.xmlPath ];
    }

    if ( this.tileSources  ){
        //tileSource is a complex option...
        //It can be a string, object, function, or an array of any of these.
        //A string implies a DZI
        //An object implies a simple image
        //A function implies a custom tile source callback
        //An array implies a sequence of tile sources which can be any of the
        //above
        if( $.isArray( this.tileSources ) ){
            if( $.isPlainObject( this.tileSources[ 0 ] ) ){
                //This is a non-sequenced legacy tile source
                initialTileSource = this.tileSources;
            } else {
                //Sequenced tile source
                initialTileSource = this.tileSources[ 0 ];
            }
        } else {
            initialTileSource = this.tileSources
        }

        if ( $.type( initialTileSource ) == 'string') {
            //Standard DZI format
            this.openDzi( initialTileSource );
        } else if ( $.isArray( initialTileSource ) ){
            //Legacy image pyramid
            this.open( new $.LegacyTileSource( initialTileSource ) );
        } else if ( $.isPlainObject( initialTileSource ) && $.isFunction( initialTileSource.getTileUrl ) ){
            //Custom tile source
            customTileSource = new $.TileSource(
                initialTileSource.width,
                initialTileSource.height,
                initialTileSource.tileSize,
                initialTileSource.tileOverlap,
                initialTileSource.minLevel,
                initialTileSource.maxLevel
            );
            customTileSource.getTileUrl = initialTileSource.getTileUrl;
            this.open( customTileSource );
        }
    }
};

$.extend( $.Viewer.prototype, $.EventHandler.prototype, $.ControlDock.prototype, {


    /**
     * @function
     * @name OpenSeadragon.Viewer.prototype.isOpen
     * @return {Boolean}
     */
    isOpen: function () {
        return !!this.source;
    },

    /**
     * If the string is xml is simply parsed and opened, otherwise the string 
     * is treated as an URL and an xml document is requested via ajax, parsed 
     * and then opened in the viewer.
     * @function
     * @name OpenSeadragon.Viewer.prototype.openDzi
     * @param {String} dzi and xml string or the url to a DZI xml document.
     * @return {OpenSeadragon.Viewer} Chainable.
     */
    openDzi: function ( dzi ) {
        var _this = this;
        $.createFromDZI(
            dzi,
            function( source ){
               _this.open( source );
            }
        );
        return this;
    },

    /**
     * @function
     * @name OpenSeadragon.Viewer.prototype.openTileSource
     * @return {OpenSeadragon.Viewer} Chainable.
     */
    openTileSource: function ( tileSource ) {
        var _this = this;
        window.setTimeout( function () {
            _this.open( tileSource );
        }, 1 );
        return this;
    },

    /**
     * @function
     * @name OpenSeadragon.Viewer.prototype.open
     * @return {OpenSeadragon.Viewer} Chainable.
     */
    open: function( source ) {
        var _this = this,
            overlay,
            i;

        if ( this.source ) {
            this.close();
        }
        
        // to ignore earlier opens
        THIS[ this.hash ].lastOpenStartTime = +new Date();

        window.setTimeout( function () {
            if ( THIS[ _this.hash ].lastOpenStartTime > THIS[ _this.hash ].lastOpenEndTime ) {
                THIS[ _this.hash ].setMessage( $.getString( "Messages.Loading" ) );
            }
        }, 2000);

        THIS[ this.hash ].lastOpenEndTime = +new Date();
        this.canvas.innerHTML = "";
        THIS[ this.hash ].prevContainerSize = $.getElementSize( this.container );

        if( source ){
            this.source = source;
        }

        this.viewport = new $.Viewport({
            containerSize:      THIS[ this.hash ].prevContainerSize, 
            contentSize:        this.source.dimensions, 
            springStiffness:    this.springStiffness,
            animationTime:      this.animationTime,
            minZoomImageRatio:  this.minZoomImageRatio,
            maxZoomPixelRatio:  this.maxZoomPixelRatio,
            visibilityRatio:    this.visibilityRatio,
            wrapHorizontal:     this.wrapHorizontal,
            wrapVertical:       this.wrapVertical
        });

        this.drawer = new $.Drawer({
            source:             this.source, 
            viewport:           this.viewport, 
            element:            this.canvas,
            overlays:           this.overlays,
            maxImageCacheCount: this.maxImageCacheCount,
            imageLoaderLimit:   this.imageLoaderLimit,
            minZoomImageRatio:  this.minZoomImageRatio,
            wrapHorizontal:     this.wrapHorizontal,
            wrapVertical:       this.wrapVertical,
            immediateRender:    this.immediateRender,
            blendTime:          this.blendTime,
            alwaysBlend:        this.alwaysBlend,
            minPixelRatio:      this.minPixelRatio
        });

        //this.profiler = new $.Profiler();

        THIS[ this.hash ].animating = false;
        THIS[ this.hash ].forceRedraw = true;
        scheduleUpdate( this, updateMulti );

        //Assuming you had programatically created a bunch of overlays
        //and added them via configuration
        for ( i = 0; i < this.overlayControls.length; i++ ) {
            
            overlay = this.overlayControls[ i ];
            
            if ( overlay.point != null ) {
            
                this.drawer.addOverlay(
                    overlay.id, 
                    new $.Point( 
                        overlay.point.X, 
                        overlay.point.Y 
                    ), 
                    $.OverlayPlacement.TOP_LEFT
                );
            
            } else {
            
                this.drawer.addOverlay(
                    overlay.id, 
                    new $.Rect(
                        overlay.rect.Point.X, 
                        overlay.rect.Point.Y, 
                        overlay.rect.Width, 
                        overlay.rect.Height
                    ), 
                    overlay.placement
                );
            
            }
        }
        VIEWERS[ this.hash ] = this;
        this.raiseEvent( "open" );
        return this;
    },

    /**
     * @function
     * @name OpenSeadragon.Viewer.prototype.close
     * @return {OpenSeadragon.Viewer} Chainable.
     */
    close: function () {
        this.source     = null;
        this.viewport   = null;
        this.drawer     = null;
        //this.profiler   = null;
        this.canvas.innerHTML = "";

        VIEWERS[ this.hash ] = null;
        delete VIEWERS[ this.hash ];
        
        return this;
    },


    /**
     * @function
     * @name OpenSeadragon.Viewer.prototype.isMouseNavEnabled
     * @return {Boolean}
     */
    isMouseNavEnabled: function () {
        return this.innerTracker.isTracking();
    },

    /**
     * @function
     * @name OpenSeadragon.Viewer.prototype.setMouseNavEnabled
     * @return {OpenSeadragon.Viewer} Chainable.
     */
    setMouseNavEnabled: function( enabled ){
        this.innerTracker.setTracking( enabled );
        return this;
    },


    /**
     * @function
     * @name OpenSeadragon.Viewer.prototype.isDashboardEnabled
     * @return {Boolean}
     */
    areControlsEnabled: function () {
        return this.controls.length && this.controls[ i ].isVisibile();
    },


    /**
     * @function
     * @name OpenSeadragon.Viewer.prototype.setDashboardEnabled
     * @return {OpenSeadragon.Viewer} Chainable.
     */
    setControlsEnabled: function( enabled ) {
        if( enabled ){
            abortControlsAutoHide( this );
        } else {
            beginControlsAutoHide( this );
        };
    },

    
    /**
     * @function
     * @name OpenSeadragon.Viewer.prototype.isFullPage
     * @return {Boolean}
     */
    isFullPage: function () {
        return this.container.parentNode == document.body;
    },


    /**
     * Toggle full page mode.
     * @function
     * @name OpenSeadragon.Viewer.prototype.setFullPage
     * @param {Boolean} fullPage
     *      If true, enter full page mode.  If false, exit full page mode.
     * @return {OpenSeadragon.Viewer} Chainable.
     */
    setFullPage: function( fullPage ) {

        var body            = document.body,
            bodyStyle       = body.style,
            docStyle        = document.documentElement.style,
            containerStyle  = this.container.style,
            canvasStyle     = this.canvas.style,
            oldBounds,
            newBounds,
            viewer,
            hash,
            nodes,
            i;
        
        //dont bother modifying the DOM if we are already in full page mode.
        if ( fullPage == this.isFullPage() ) {
            return;
        }

        if ( fullPage ) {
            
            this.bodyOverflow   = bodyStyle.overflow;
            this.docOverflow    = docStyle.overflow;
            bodyStyle.overflow  = "hidden";
            docStyle.overflow   = "hidden";

            this.bodyWidth      = bodyStyle.width;
            this.bodyHeight     = bodyStyle.height;
            bodyStyle.width     = "100%";
            bodyStyle.height    = "100%";

            canvasStyle.backgroundColor = "black";
            canvasStyle.color           = "white";

            containerStyle.position = "fixed";

            //when entering full screen on the ipad it wasnt sufficient to leave
            //the body intact as only only the top half of the screen would 
            //respond to touch events on the canvas, while the bottom half treated
            //them as touch events on the document body.  Thus we remove and store
            //the bodies elements and replace them when we leave full screen.
            this.previousBody = [];
            nodes = body.childNodes.length;
            for ( i = 0; i < nodes; i ++ ){
                this.previousBody.push( body.childNodes[ 0 ] );
                body.removeChild( body.childNodes[ 0 ] );
            }
            
            //If we've got a toolbar, we need to enable the user to use css to
            //preserve it in fullpage mode
            if( this.toolbar && this.toolbar.element ){
                //save a reference to the parent so we can put it back
                //in the long run we need a better strategy
                this.toolbar.parentNode = this.toolbar.element.parentNode;
                this.toolbar.nextSibling = this.toolbar.element.nextSibling;
                body.appendChild( this.toolbar.element );

                //Make sure the user has some ability to style the toolbar based
                //on the mode
                this.toolbar.element.setAttribute( 
                    'class',
                    this.toolbar.element.className +" fullpage"
                );
                this.toolbar.element.style.position = 'fixed';

                this.container.style.top = $.getElementSize(
                    this.toolbar.element
                ).y + 'px';
            }
            body.appendChild( this.container );
            THIS[ this.hash ].prevContainerSize = $.getWindowSize();

            // mouse will be inside container now
            $.delegate( this, onContainerEnter )();    


        } else {
            
            bodyStyle.overflow  = this.bodyOverflow;
            docStyle.overflow   = this.docOverflow;

            bodyStyle.width     = this.bodyWidth;
            bodyStyle.height    = this.bodyHeight;

            canvasStyle.backgroundColor = "";
            canvasStyle.color           = "";

            containerStyle.position = "relative";
            containerStyle.zIndex   = "";

            //If we've got a toolbar, we need to enable the user to use css to
            //reset it to its original state 
            if( this.toolbar && this.toolbar.element ){
                body.removeChild( this.toolbar.element );

                //Make sure the user has some ability to style the toolbar based
                //on the mode
                this.toolbar.element.setAttribute( 
                    'class',
                    this.toolbar.element.className.replace('fullpage','')
                );
                this.toolbar.element.style.position = 'relative';
                this.toolbar.parentNode.insertBefore( 
                    this.toolbar.element,
                    this.toolbar.nextSibling
                );
                delete this.toolbar.parentNode;
                delete this.toolbar.nextSibling;

                this.container.style.top = 'auto';
            }

            body.removeChild( this.container );
            nodes = this.previousBody.length;
            for ( i = 0; i < nodes; i++ ){
                body.appendChild( this.previousBody.shift() );
            }
            this.element.appendChild( this.container );
            THIS[ this.hash ].prevContainerSize = $.getElementSize( this.element );
            
            // mouse will likely be outside now
            $.delegate( this, onContainerExit )();      

        }

        if ( this.viewport ) {
            oldBounds = this.viewport.getBounds();
            this.viewport.resize( THIS[ this.hash ].prevContainerSize );
            newBounds = this.viewport.getBounds();

            if ( fullPage ) {
                THIS[ this.hash ].fsBoundsDelta = new $.Point(
                    newBounds.width  / oldBounds.width,
                    newBounds.height / oldBounds.height
                );
            } else {
                this.viewport.update();
                this.viewport.zoomBy(
                    Math.max( 
                        THIS[ this.hash ].fsBoundsDelta.x, 
                        THIS[ this.hash ].fsBoundsDelta.y 
                    ),
                    null, 
                    true
                );
                //Ensures that if multiple viewers are on a page, the viewers that
                //were hidden during fullpage are 'reopened'
                for( hash in VIEWERS ){
                    viewer = VIEWERS[ hash ];
                    if( viewer !== this && viewer != this.navigator ){
                        viewer.open( viewer.source );
                    }
                }
            }

            THIS[ this.hash ].forceRedraw = true;
            this.raiseEvent( "resize", this );
            updateOnce( this );

        }
        return this;
    },

    
    /**
     * @function
     * @name OpenSeadragon.Viewer.prototype.isVisible
     * @return {Boolean}
     */
    isVisible: function () {
        return this.container.style.visibility != "hidden";
    },


    /**
     * @function
     * @name OpenSeadragon.Viewer.prototype.setVisible
     * @return {OpenSeadragon.Viewer} Chainable.
     */
    setVisible: function( visible ){
        this.container.style.visibility = visible ? "" : "hidden";
        return this;
    }

});

///////////////////////////////////////////////////////////////////////////////
// Schedulers provide the general engine for animation
///////////////////////////////////////////////////////////////////////////////

function scheduleUpdate( viewer, updateFunc, prevUpdateTime ){
    var currentTime,
        targetTime,
        deltaTime;

    if ( THIS[ viewer.hash ].animating ) {
        return window.setTimeout( function(){
            updateFunc( viewer );
        }, 1 );
    }

    currentTime     = +new Date();
    prevUpdateTime  = prevUpdateTime ? prevUpdateTime : currentTime;
    // 60 frames per second is ideal
    targetTime      = prevUpdateTime + 1000 / 60;
    deltaTime       = Math.max( 1, targetTime - currentTime );
    
    return window.setTimeout( function(){
        updateFunc( viewer );
    }, deltaTime );
};

//provides a sequence in the fade animation
function scheduleControlsFade( viewer ) {
    window.setTimeout( function(){
        updateControlsFade( viewer );
    }, 20);
};

//initiates an animation to hide the controls
function beginControlsAutoHide( viewer ) {
    if ( !viewer.autoHideControls ) {
        return;
    }
    viewer.controlsShouldFade = true;
    viewer.controlsFadeBeginTime = 
        +new Date() + 
        viewer.controlsFadeDelay;

    window.setTimeout( function(){
        scheduleControlsFade( viewer );
    }, viewer.controlsFadeDelay );
};


//determines if fade animation is done or continues the animation
function updateControlsFade( viewer ) {
    var currentTime,
        deltaTime,
        opacity,
        i;
    if ( viewer.controlsShouldFade ) {
        currentTime = new Date().getTime();
        deltaTime = currentTime - viewer.controlsFadeBeginTime;
        opacity = 1.0 - deltaTime / viewer.controlsFadeLength;

        opacity = Math.min( 1.0, opacity );
        opacity = Math.max( 0.0, opacity );

        for ( i = viewer.controls.length - 1; i >= 0; i--) {
            viewer.controls[ i ].setOpacity( opacity );
        }

        if ( opacity > 0 ) {
            // fade again
            scheduleControlsFade( viewer ); 
        }
    }
};

//stop the fade animation on the controls and show them
function abortControlsAutoHide( viewer ) {
    var i;
    viewer.controlsShouldFade = false;
    for ( i = viewer.controls.length - 1; i >= 0; i-- ) {
        viewer.controls[ i ].setOpacity( 1.0 );
    }
};


///////////////////////////////////////////////////////////////////////////////
// Default view event handlers.
///////////////////////////////////////////////////////////////////////////////
function onFocus(){
    abortControlsAutoHide( this );
};

function onBlur(){
    beginControlsAutoHide( this );
    
};

function onCanvasClick( tracker, position, quick, shift ) {
    var zoomPreClick,
        factor;
    if ( this.viewport && quick ) {    // ignore clicks where mouse moved         
        zoomPerClick = this.zoomPerClick;
        factor = shift ? 1.0 / zoomPerClick : zoomPerClick;
        this.viewport.zoomBy(
            factor, 
            this.viewport.pointFromPixel( position, true )
        );
        this.viewport.applyConstraints();
    }
};

function onCanvasDrag( tracker, position, delta, shift ) {
    if ( this.viewport ) {
        this.viewport.panBy( 
            this.viewport.deltaPointsFromPixels( 
                delta.negate() 
            ) 
        );
    }
};

function onCanvasRelease( tracker, position, insideElementPress, insideElementRelease ) {
    if ( insideElementPress && this.viewport ) {
        this.viewport.applyConstraints();
    }
};

function onCanvasScroll( tracker, position, scroll, shift ) {
    var factor;
    if ( this.viewport ) {
        factor = Math.pow( this.zoomPerScroll, scroll );
        this.viewport.zoomBy( 
            factor, 
            this.viewport.pointFromPixel( position, true ) 
        );
        this.viewport.applyConstraints();
    }
};

function onContainerExit( tracker, position, buttonDownElement, buttonDownAny ) {
    if ( !buttonDownElement ) {
        THIS[ this.hash ].mouseInside = false;
        if ( !THIS[ this.hash ].animating ) {
            beginControlsAutoHide( this );
        }
    }
};

function onContainerRelease( tracker, position, insideElementPress, insideElementRelease ) {
    if ( !insideElementRelease ) {
        THIS[ this.hash ].mouseInside = false;
        if ( !THIS[ this.hash ].animating ) {
            beginControlsAutoHide( this );
        }
    }
};

function onContainerEnter( tracker, position, buttonDownElement, buttonDownAny ) {
    THIS[ this.hash ].mouseInside = true;
    abortControlsAutoHide( this );
};


///////////////////////////////////////////////////////////////////////////////
// Page update routines ( aka Views - for future reference )
///////////////////////////////////////////////////////////////////////////////

function updateMulti( viewer ) {

    var beginTime;

    if ( !viewer.source ) {
        return;
    }

    beginTime = +new Date();
    updateOnce( viewer );
    scheduleUpdate( viewer, arguments.callee, beginTime );
};

function updateOnce( viewer ) {

    var containerSize,
        animated;

    if ( !viewer.source ) {
        return;
    }

    //viewer.profiler.beginUpdate();

    containerSize = $.getElementSize( viewer.container );
    if ( !containerSize.equals( THIS[ viewer.hash ].prevContainerSize ) ) {
        // maintain image position
        viewer.viewport.resize( containerSize, true ); 
        THIS[ viewer.hash ].prevContainerSize = containerSize;
        viewer.raiseEvent( "resize" );
    }

    animated = viewer.viewport.update();
    if ( !THIS[ viewer.hash ].animating && animated ) {
        viewer.raiseEvent( "animationstart" );
        abortControlsAutoHide( viewer );
    }

    if ( animated ) {
        viewer.drawer.update();
        if( viewer.navigator ){
            viewer.navigator.update( viewer.viewport );
        }
        viewer.raiseEvent( "animation" );
    } else if ( THIS[ viewer.hash ].forceRedraw || viewer.drawer.needsUpdate() ) {
        viewer.drawer.update();
        if( viewer.navigator ){
            viewer.navigator.update( viewer.viewport );
        }
        THIS[ viewer.hash ].forceRedraw = false;
    } 

    if ( THIS[ viewer.hash ].animating && !animated ) {
        viewer.raiseEvent( "animationfinish" );

        if ( !THIS[ viewer.hash ].mouseInside ) {
            beginControlsAutoHide( viewer );
        }
    }

    THIS[ viewer.hash ].animating = animated;

    //viewer.profiler.endUpdate();
};

///////////////////////////////////////////////////////////////////////////////
// Navigation Controls
///////////////////////////////////////////////////////////////////////////////

function resolveUrl( prefix, url ) {
    return prefix ? prefix + url : url;
};


function beginZoomingIn() {
    THIS[ this.hash ].lastZoomTime = +new Date();
    THIS[ this.hash ].zoomFactor = this.zoomPerSecond;
    THIS[ this.hash ].zooming = true;
    scheduleZoom( this );
}

function beginZoomingOut() {
    THIS[ this.hash ].lastZoomTime = +new Date();
    THIS[ this.hash ].zoomFactor = 1.0 / this.zoomPerSecond;
    THIS[ this.hash ].zooming = true;
    scheduleZoom( this );
}

function endZooming() {
    THIS[ this.hash ].zooming = false;
}

function scheduleZoom( viewer ) {
    window.setTimeout( $.delegate( viewer, doZoom ), 10 );
}

function doZoom() {
    var currentTime,
        deltaTime,
        adjustFactor;

    if ( THIS[ this.hash ].zooming && this.viewport) {
        currentTime     = +new Date();
        deltaTime       = currentTime - THIS[ this.hash ].lastZoomTime;
        adjustedFactor  = Math.pow( THIS[ this.hash ].zoomFactor, deltaTime / 1000 );

        this.viewport.zoomBy( adjustedFactor );
        this.viewport.applyConstraints();
        THIS[ this.hash ].lastZoomTime = currentTime;
        scheduleZoom( this );
    }
};

function doSingleZoomIn() {
    if ( this.viewport ) {
        THIS[ this.hash ].zooming = false;
        this.viewport.zoomBy( 
            this.zoomPerClick / 1.0 
        );
        this.viewport.applyConstraints();
    }
};

function doSingleZoomOut() {
    if ( this.viewport ) {
        THIS[ this.hash ].zooming = false;
        this.viewport.zoomBy(
            1.0 / this.zoomPerClick
        );
        this.viewport.applyConstraints();
    }
};

function lightUp() {
    this.buttons.emulateEnter();
    this.buttons.emulateExit();
};

function onHome() {
    if ( this.viewport ) {
        this.viewport.goHome();
    }
};

function onFullPage() {
    this.setFullPage( !this.isFullPage() );
    // correct for no mouseout event on change
    this.buttons.emulateExit();
    this.fullPageButton.element.focus();
    if ( this.viewport ) {
        this.viewport.applyConstraints();
    }
};

}( OpenSeadragon ));