/*!

* reveal.js
* http://lab.hakim.se/reveal-js
* MIT licensed
* Version 3.1.0
*
* Copyright (C) 2015 Hakim El Hattab, http://hakim.se
*/

(function( root, factory ) {

if( typeof define === 'function' && define.amd ) {
        // AMD. Register as an anonymous module.
        define( function() {
                root.Reveal = factory();
                return root.Reveal;
        } );
} else if( typeof exports === 'object' ) {
        // Node. Does not work with strict CommonJS.
        module.exports = factory();
} else {
        // Browser globals.
        root.Reveal = factory();
}

}( this, function() {

'use strict';

var Reveal;

var SLIDES_SELECTOR = '.slides section',
        HORIZONTAL_SLIDES_SELECTOR = '.slides>section',
        VERTICAL_SLIDES_SELECTOR = '.slides>section.present>section',
        HOME_SLIDE_SELECTOR = '.slides>section:first-of-type',

// Configuration defaults, can be overridden at initialization time
        config = {

                // The "normal" size of the presentation, aspect ratio will be preserved
                // when the presentation is scaled to fit different resolutions
                width: 960,
                height: 700,

                // Factor of the display size that should remain empty around the content
                margin: 0.1,

                // Bounds for smallest/largest possible scale to apply to content
                minScale: 0.2,
                maxScale: 1.5,

                // Display controls in the bottom right corner
                controls: true,

                // Display a presentation progress bar
                progress: true,

                // Display the page number of the current slide
                slideNumber: false,

                // Push each slide change to the browser history
                history: false,

                // Enable keyboard shortcuts for navigation
                keyboard: true,

                // Optional function that blocks keyboard events when retuning false
                keyboardCondition: null,

                // Enable the slide overview mode
                overview: true,

                // Vertical centering of slides
                center: true,

                // Enables touch navigation on devices with touch input
                touch: true,

                // Loop the presentation
                loop: false,

                // Change the presentation direction to be RTL
                rtl: false,

                // Turns fragments on and off globally
                fragments: true,

                // Flags if the presentation is running in an embedded mode,
                // i.e. contained within a limited portion of the screen
                embedded: false,

                // Flags if we should show a help overlay when the questionmark
                // key is pressed
                help: true,

                // Flags if it should be possible to pause the presentation (blackout)
                pause: true,

                // Number of milliseconds between automatically proceeding to the
                // next slide, disabled when set to 0, this value can be overwritten
                // by using a data-autoslide attribute on your slides
                autoSlide: 0,

                // Stop auto-sliding after user input
                autoSlideStoppable: true,

                // Enable slide navigation via mouse wheel
                mouseWheel: false,

                // Apply a 3D roll to links on hover
                rollingLinks: false,

                // Hides the address bar on mobile devices
                hideAddressBar: true,

                // Opens links in an iframe preview overlay
                previewLinks: false,

                // Exposes the reveal.js API through window.postMessage
                postMessage: true,

                // Dispatches all reveal.js events to the parent window through postMessage
                postMessageEvents: false,

                // Focuses body when page changes visiblity to ensure keyboard shortcuts work
                focusBodyOnPageVisibilityChange: true,

                // Transition style
                transition: 'slide', // none/fade/slide/convex/concave/zoom

                // Transition speed
                transitionSpeed: 'default', // default/fast/slow

                // Transition style for full page slide backgrounds
                backgroundTransition: 'fade', // none/fade/slide/convex/concave/zoom

                // Parallax background image
                parallaxBackgroundImage: '', // CSS syntax, e.g. "a.jpg"

                // Parallax background size
                parallaxBackgroundSize: '', // CSS syntax, e.g. "3000px 2000px"

                // Amount of pixels to move the parallax background per slide step
                parallaxBackgroundHorizontal: null,
                parallaxBackgroundVertical: null,

                // Number of slides away from the current that are visible
                viewDistance: 3,

                // Script dependencies to load
                dependencies: []

        },

// Flags if reveal.js is loaded (has dispatched the 'ready' event)
        loaded = false,

// Flags if the overview mode is currently active
        overview = false,

// The horizontal and vertical index of the currently active slide
        indexh,
        indexv,

// The previous and current slide HTML elements
        previousSlide,
        currentSlide,

        previousBackground,

// Slides may hold a data-state attribute which we pick up and apply
// as a class to the body. This list contains the combined state of
// all current slides.
        state = [],

// The current scale of the presentation (see width/height config)
        scale = 1,

// CSS transform that is currently applied to the slides container,
// split into two groups
        slidesTransform = { layout: '', overview: '' },

// Cached references to DOM elements
        dom = {},

// Features supported by the browser, see #checkCapabilities()
        features = {},

// Client is a mobile device, see #checkCapabilities()
        isMobileDevice,

// Throttles mouse wheel navigation
        lastMouseWheelStep = 0,

// Delays updates to the URL due to a Chrome thumbnailer bug
        writeURLTimeout = 0,

// Flags if the interaction event listeners are bound
        eventsAreBound = false,

// The current auto-slide duration
        autoSlide = 0,

// Auto slide properties
        autoSlidePlayer,
        autoSlideTimeout = 0,
        autoSlideStartTime = -1,
        autoSlidePaused = false,

// Holds information about the currently ongoing touch input
        touch = {
                startX: 0,
                startY: 0,
                startSpan: 0,
                startCount: 0,
                captured: false,
                threshold: 40
        },

// Holds information about the keyboard shortcuts
        keyboardShortcuts = {
                'N  ,  SPACE':                  'Next slide',
                'P':                                    'Previous slide',
                '←  ,  H':                'Navigate left',
                '→  ,  L':                'Navigate right',
                '↑  ,  K':                'Navigate up',
                '↓  ,  J':                'Navigate down',
                'Home':                                 'First slide',
                'End':                                  'Last slide',
                'B  ,  .':                              'Pause',
                'F':                                    'Fullscreen',
                'ESC, O':                               'Slide overview'
        };

/**
 * Starts up the presentation if the client is capable.
 */
function initialize( options ) {

        checkCapabilities();

        if( !features.transforms2d && !features.transforms3d ) {
                document.body.setAttribute( 'class', 'no-transforms' );

                // Since JS won't be running any further, we load all lazy
                // loading elements upfront
                var images = toArray( document.getElementsByTagName( 'img' ) ),
                        iframes = toArray( document.getElementsByTagName( 'iframe' ) );

                var lazyLoadable = images.concat( iframes );

                for( var i = 0, len = lazyLoadable.length; i < len; i++ ) {
                        var element = lazyLoadable[i];
                        if( element.getAttribute( 'data-src' ) ) {
                                element.setAttribute( 'src', element.getAttribute( 'data-src' ) );
                                element.removeAttribute( 'data-src' );
                        }
                }

                // If the browser doesn't support core features we won't be
                // using JavaScript to control the presentation
                return;
        }

        // Cache references to key DOM elements
        dom.wrapper = document.querySelector( '.reveal' );
        dom.slides = document.querySelector( '.reveal .slides' );

        // Force a layout when the whole page, incl fonts, has loaded
        window.addEventListener( 'load', layout, false );

        var query = Reveal.getQueryHash();

        // Do not accept new dependencies via query config to avoid
        // the potential of malicious script injection
        if( typeof query['dependencies'] !== 'undefined' ) delete query['dependencies'];

        // Copy options over to our config object
        extend( config, options );
        extend( config, query );

        // Hide the address bar in mobile browsers
        hideAddressBar();

        // Loads the dependencies and continues to #start() once done
        load();

}

/**
 * Inspect the client to see what it's capable of, this
 * should only happens once per runtime.
 */
function checkCapabilities() {

        features.transforms3d = 'WebkitPerspective' in document.body.style ||
                'MozPerspective' in document.body.style ||
                'msPerspective' in document.body.style ||
                'OPerspective' in document.body.style ||
                'perspective' in document.body.style;

        features.transforms2d = 'WebkitTransform' in document.body.style ||
                'MozTransform' in document.body.style ||
                'msTransform' in document.body.style ||
                'OTransform' in document.body.style ||
                'transform' in document.body.style;

        features.requestAnimationFrameMethod = window.requestAnimationFrame || window.webkitRequestAnimationFrame || window.mozRequestAnimationFrame;
        features.requestAnimationFrame = typeof features.requestAnimationFrameMethod === 'function';

        features.canvas = !!document.createElement( 'canvas' ).getContext;

        features.touch = !!( 'ontouchstart' in window );

        // Transitions in the overview are disabled in desktop and
        // mobile Safari due to lag
        features.overviewTransitions = !/Version\/[\d\.]+.*Safari/.test( navigator.userAgent );

        isMobileDevice = /(iphone|ipod|ipad|android)/gi.test( navigator.userAgent );

}

/**
 * Loads the dependencies of reveal.js. Dependencies are
 * defined via the configuration option 'dependencies'
 * and will be loaded prior to starting/binding reveal.js.
 * Some dependencies may have an 'async' flag, if so they
 * will load after reveal.js has been started up.
 */
function load() {

        var scripts = [],
                scriptsAsync = [],
                scriptsToPreload = 0;

        // Called once synchronous scripts finish loading
        function proceed() {
                if( scriptsAsync.length ) {
                        // Load asynchronous scripts
                        head.js.apply( null, scriptsAsync );
                }

                start();
        }

        function loadScript( s ) {
                head.ready( s.src.match( /([\w\d_\-]*)\.?js$|[^\\\/]*$/i )[0], function() {
                        // Extension may contain callback functions
                        if( typeof s.callback === 'function' ) {
                                s.callback.apply( this );
                        }

                        if( --scriptsToPreload === 0 ) {
                                proceed();
                        }
                });
        }

        for( var i = 0, len = config.dependencies.length; i < len; i++ ) {
                var s = config.dependencies[i];

                // Load if there's no condition or the condition is truthy
                if( !s.condition || s.condition() ) {
                        if( s.async ) {
                                scriptsAsync.push( s.src );
                        }
                        else {
                                scripts.push( s.src );
                        }

                        loadScript( s );
                }
        }

        if( scripts.length ) {
                scriptsToPreload = scripts.length;

                // Load synchronous scripts
                head.js.apply( null, scripts );
        }
        else {
                proceed();
        }

}

/**
 * Starts up reveal.js by binding input events and navigating
 * to the current URL deeplink if there is one.
 */
function start() {

        // Make sure we've got all the DOM elements we need
        setupDOM();

        // Listen to messages posted to this window
        setupPostMessage();

        // Prevent iframes from scrolling the slides out of view
        setupIframeScrollPrevention();

        // Resets all vertical slides so that only the first is visible
        resetVerticalSlides();

        // Updates the presentation to match the current configuration values
        configure();

        // Read the initial hash
        readURL();

        // Update all backgrounds
        updateBackground( true );

        // Notify listeners that the presentation is ready but use a 1ms
        // timeout to ensure it's not fired synchronously after #initialize()
        setTimeout( function() {
                // Enable transitions now that we're loaded
                dom.slides.classList.remove( 'no-transition' );

                loaded = true;

                dispatchEvent( 'ready', {
                        'indexh': indexh,
                        'indexv': indexv,
                        'currentSlide': currentSlide
                } );
        }, 1 );

        // Special setup and config is required when printing to PDF
        if( isPrintingPDF() ) {
                removeEventListeners();

                // The document needs to have loaded for the PDF layout
                // measurements to be accurate
                if( document.readyState === 'complete' ) {
                        setupPDF();
                }
                else {
                        window.addEventListener( 'load', setupPDF );
                }
        }

}

/**
 * Finds and stores references to DOM elements which are
 * required by the presentation. If a required element is
 * not found, it is created.
 */
function setupDOM() {

        // Prevent transitions while we're loading
        dom.slides.classList.add( 'no-transition' );

        // Background element
        dom.background = createSingletonNode( dom.wrapper, 'div', 'backgrounds', null );

        // Progress bar
        dom.progress = createSingletonNode( dom.wrapper, 'div', 'progress', '<span></span>' );
        dom.progressbar = dom.progress.querySelector( 'span' );

        // Arrow controls
        createSingletonNode( dom.wrapper, 'aside', 'controls',
                '<div class="navigate-left"></div>' +
                '<div class="navigate-right"></div>' +
                '<div class="navigate-up"></div>' +
                '<div class="navigate-down"></div>' );

        // Slide number
        dom.slideNumber = createSingletonNode( dom.wrapper, 'div', 'slide-number', '' );

        // Overlay graphic which is displayed during the paused mode
        createSingletonNode( dom.wrapper, 'div', 'pause-overlay', null );

        // Cache references to elements
        dom.controls = document.querySelector( '.reveal .controls' );
        dom.theme = document.querySelector( '#theme' );

        dom.wrapper.setAttribute( 'role', 'application' );

        // There can be multiple instances of controls throughout the page
        dom.controlsLeft = toArray( document.querySelectorAll( '.navigate-left' ) );
        dom.controlsRight = toArray( document.querySelectorAll( '.navigate-right' ) );
        dom.controlsUp = toArray( document.querySelectorAll( '.navigate-up' ) );
        dom.controlsDown = toArray( document.querySelectorAll( '.navigate-down' ) );
        dom.controlsPrev = toArray( document.querySelectorAll( '.navigate-prev' ) );
        dom.controlsNext = toArray( document.querySelectorAll( '.navigate-next' ) );

        dom.statusDiv = createStatusDiv();
}

/**
 * Creates a hidden div with role aria-live to announce the
 * current slide content. Hide the div off-screen to make it
 * available only to Assistive Technologies.
 */
function createStatusDiv() {

        var statusDiv = document.getElementById( 'aria-status-div' );
        if( !statusDiv ) {
                statusDiv = document.createElement( 'div' );
                statusDiv.style.position = 'absolute';
                statusDiv.style.height = '1px';
                statusDiv.style.width = '1px';
                statusDiv.style.overflow ='hidden';
                statusDiv.style.clip = 'rect( 1px, 1px, 1px, 1px )';
                statusDiv.setAttribute( 'id', 'aria-status-div' );
                statusDiv.setAttribute( 'aria-live', 'polite' );
                statusDiv.setAttribute( 'aria-atomic','true' );
                dom.wrapper.appendChild( statusDiv );
        }
        return statusDiv;

}

/**
 * Configures the presentation for printing to a static
 * PDF.
 */
function setupPDF() {

        var slideSize = getComputedSlideSize( window.innerWidth, window.innerHeight );

        // Dimensions of the PDF pages
        var pageWidth = Math.floor( slideSize.width * ( 1 + config.margin ) ),
                pageHeight = Math.floor( slideSize.height * ( 1 + config.margin  ) );

        // Dimensions of slides within the pages
        var slideWidth = slideSize.width,
                slideHeight = slideSize.height;

        // Let the browser know what page size we want to print
        injectStyleSheet( '@page{size:'+ pageWidth +'px '+ pageHeight +'px; margin: 0;}' );

        // Limit the size of certain elements to the dimensions of the slide
        injectStyleSheet( '.reveal section>img, .reveal section>video, .reveal section>iframe{max-width: '+ slideWidth +'px; max-height:'+ slideHeight +'px}' );

        document.body.classList.add( 'print-pdf' );
        document.body.style.width = pageWidth + 'px';
        document.body.style.height = pageHeight + 'px';

        // Slide and slide background layout
        toArray( dom.wrapper.querySelectorAll( SLIDES_SELECTOR ) ).forEach( function( slide ) {

                // Vertical stacks are not centred since their section
                // children will be
                if( slide.classList.contains( 'stack' ) === false ) {
                        // Center the slide inside of the page, giving the slide some margin
                        var left = ( pageWidth - slideWidth ) / 2,
                                top = ( pageHeight - slideHeight ) / 2;

                        var contentHeight = getAbsoluteHeight( slide );
                        var numberOfPages = Math.max( Math.ceil( contentHeight / pageHeight ), 1 );

                        // Center slides vertically
                        if( numberOfPages === 1 && config.center || slide.classList.contains( 'center' ) ) {
                                top = Math.max( ( pageHeight - contentHeight ) / 2, 0 );
                        }

                        // Position the slide inside of the page
                        slide.style.left = left + 'px';
                        slide.style.top = top + 'px';
                        slide.style.width = slideWidth + 'px';

                        // TODO Backgrounds need to be multiplied when the slide
                        // stretches over multiple pages
                        var background = slide.querySelector( '.slide-background' );
                        if( background ) {
                                background.style.width = pageWidth + 'px';
                                background.style.height = ( pageHeight * numberOfPages ) + 'px';
                                background.style.top = -top + 'px';
                                background.style.left = -left + 'px';
                        }
                }

        } );

        // Show all fragments
        toArray( dom.wrapper.querySelectorAll( SLIDES_SELECTOR + ' .fragment' ) ).forEach( function( fragment ) {
                fragment.classList.add( 'visible' );
        } );

}

/**
 * This is an unfortunate necessity. Iframes can trigger the
 * parent window to scroll, for example by focusing an input.
 * This scrolling can not be prevented by hiding overflow in
 * CSS so we have to resort to repeatedly checking if the
 * browser has decided to offset our slides :(
 */
function setupIframeScrollPrevention() {

        if( dom.slides.querySelector( 'iframe' ) ) {
                setInterval( function() {
                        if( dom.wrapper.scrollTop !== 0 || dom.wrapper.scrollLeft !== 0 ) {
                                dom.wrapper.scrollTop = 0;
                                dom.wrapper.scrollLeft = 0;
                        }
                }, 500 );
        }

}

/**
 * Creates an HTML element and returns a reference to it.
 * If the element already exists the existing instance will
 * be returned.
 */
function createSingletonNode( container, tagname, classname, innerHTML ) {

        // Find all nodes matching the description
        var nodes = container.querySelectorAll( '.' + classname );

        // Check all matches to find one which is a direct child of
        // the specified container
        for( var i = 0; i < nodes.length; i++ ) {
                var testNode = nodes[i];
                if( testNode.parentNode === container ) {
                        return testNode;
                }
        }

        // If no node was found, create it now
        var node = document.createElement( tagname );
        node.classList.add( classname );
        if( typeof innerHTML === 'string' ) {
                node.innerHTML = innerHTML;
        }
        container.appendChild( node );

        return node;

}

/**
 * Creates the slide background elements and appends them
 * to the background container. One element is created per
 * slide no matter if the given slide has visible background.
 */
function createBackgrounds() {

        var printMode = isPrintingPDF();

        // Clear prior backgrounds
        dom.background.innerHTML = '';
        dom.background.classList.add( 'no-transition' );

        // Iterate over all horizontal slides
        toArray( dom.wrapper.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR ) ).forEach( function( slideh ) {

                var backgroundStack;

                if( printMode ) {
                        backgroundStack = createBackground( slideh, slideh );
                }
                else {
                        backgroundStack = createBackground( slideh, dom.background );
                }

                // Iterate over all vertical slides
                toArray( slideh.querySelectorAll( 'section' ) ).forEach( function( slidev ) {

                        if( printMode ) {
                                createBackground( slidev, slidev );
                        }
                        else {
                                createBackground( slidev, backgroundStack );
                        }

                        backgroundStack.classList.add( 'stack' );

                } );

        } );

        // Add parallax background if specified
        if( config.parallaxBackgroundImage ) {

                dom.background.style.backgroundImage = 'url("' + config.parallaxBackgroundImage + '")';
                dom.background.style.backgroundSize = config.parallaxBackgroundSize;

                // Make sure the below properties are set on the element - these properties are
                // needed for proper transitions to be set on the element via CSS. To remove
                // annoying background slide-in effect when the presentation starts, apply
                // these properties after short time delay
                setTimeout( function() {
                        dom.wrapper.classList.add( 'has-parallax-background' );
                }, 1 );

        }
        else {

                dom.background.style.backgroundImage = '';
                dom.wrapper.classList.remove( 'has-parallax-background' );

        }

}

/**
 * Creates a background for the given slide.
 *
 * @param {HTMLElement} slide
 * @param {HTMLElement} container The element that the background
 * should be appended to
 */
function createBackground( slide, container ) {

        var data = {
                background: slide.getAttribute( 'data-background' ),
                backgroundSize: slide.getAttribute( 'data-background-size' ),
                backgroundImage: slide.getAttribute( 'data-background-image' ),
                backgroundVideo: slide.getAttribute( 'data-background-video' ),
                backgroundIframe: slide.getAttribute( 'data-background-iframe' ),
                backgroundColor: slide.getAttribute( 'data-background-color' ),
                backgroundRepeat: slide.getAttribute( 'data-background-repeat' ),
                backgroundPosition: slide.getAttribute( 'data-background-position' ),
                backgroundTransition: slide.getAttribute( 'data-background-transition' )
        };

        var element = document.createElement( 'div' );

        // Carry over custom classes from the slide to the background
        element.className = 'slide-background ' + slide.className.replace( /present|past|future/, '' );

        if( data.background ) {
                // Auto-wrap image urls in url(...)
                if( /^(http|file|\/\/)/gi.test( data.background ) || /\.(svg|png|jpg|jpeg|gif|bmp)$/gi.test( data.background ) ) {
                        slide.setAttribute( 'data-background-image', data.background );
                }
                else {
                        element.style.background = data.background;
                }
        }

        // Create a hash for this combination of background settings.
        // This is used to determine when two slide backgrounds are
        // the same.
        if( data.background || data.backgroundColor || data.backgroundImage || data.backgroundVideo || data.backgroundIframe ) {
                element.setAttribute( 'data-background-hash', data.background +
                        data.backgroundSize +
                        data.backgroundImage +
                        data.backgroundVideo +
                        data.backgroundIframe +
                        data.backgroundColor +
                        data.backgroundRepeat +
                        data.backgroundPosition +
                        data.backgroundTransition );
        }

        // Additional and optional background properties
        if( data.backgroundSize ) element.style.backgroundSize = data.backgroundSize;
        if( data.backgroundColor ) element.style.backgroundColor = data.backgroundColor;
        if( data.backgroundRepeat ) element.style.backgroundRepeat = data.backgroundRepeat;
        if( data.backgroundPosition ) element.style.backgroundPosition = data.backgroundPosition;
        if( data.backgroundTransition ) element.setAttribute( 'data-background-transition', data.backgroundTransition );

        container.appendChild( element );

        // If backgrounds are being recreated, clear old classes
        slide.classList.remove( 'has-dark-background' );
        slide.classList.remove( 'has-light-background' );

        // If this slide has a background color, add a class that
        // signals if it is light or dark. If the slide has no background
        // color, no class will be set
        var computedBackgroundColor = window.getComputedStyle( element ).backgroundColor;
        if( computedBackgroundColor ) {
                var rgb = colorToRgb( computedBackgroundColor );

                // Ignore fully transparent backgrounds. Some browsers return
                // rgba(0,0,0,0) when reading the computed background color of
                // an element with no background
                if( rgb && rgb.a !== 0 ) {
                        if( colorBrightness( computedBackgroundColor ) < 128 ) {
                                slide.classList.add( 'has-dark-background' );
                        }
                        else {
                                slide.classList.add( 'has-light-background' );
                        }
                }
        }

        return element;

}

/**
 * Registers a listener to postMessage events, this makes it
 * possible to call all reveal.js API methods from another
 * window. For example:
 *
 * revealWindow.postMessage( JSON.stringify({
 *   method: 'slide',
 *   args: [ 2 ]
 * }), '*' );
 */
function setupPostMessage() {

        if( config.postMessage ) {
                window.addEventListener( 'message', function ( event ) {
                        var data = event.data;

                        // Make sure we're dealing with JSON
                        if( typeof data === 'string' && data.charAt( 0 ) === '{' && data.charAt( data.length - 1 ) === '}' ) {
                                data = JSON.parse( data );

                                // Check if the requested method can be found
                                if( data.method && typeof Reveal[data.method] === 'function' ) {
                                        Reveal[data.method].apply( Reveal, data.args );
                                }
                        }
                }, false );
        }

}

/**
 * Applies the configuration settings from the config
 * object. May be called multiple times.
 */
function configure( options ) {

        var numberOfSlides = dom.wrapper.querySelectorAll( SLIDES_SELECTOR ).length;

        dom.wrapper.classList.remove( config.transition );

        // New config options may be passed when this method
        // is invoked through the API after initialization
        if( typeof options === 'object' ) extend( config, options );

        // Force linear transition based on browser capabilities
        if( features.transforms3d === false ) config.transition = 'linear';

        dom.wrapper.classList.add( config.transition );

        dom.wrapper.setAttribute( 'data-transition-speed', config.transitionSpeed );
        dom.wrapper.setAttribute( 'data-background-transition', config.backgroundTransition );

        dom.controls.style.display = config.controls ? 'block' : 'none';
        dom.progress.style.display = config.progress ? 'block' : 'none';

        if( config.rtl ) {
                dom.wrapper.classList.add( 'rtl' );
        }
        else {
                dom.wrapper.classList.remove( 'rtl' );
        }

        if( config.center ) {
                dom.wrapper.classList.add( 'center' );
        }
        else {
                dom.wrapper.classList.remove( 'center' );
        }

        // Exit the paused mode if it was configured off
        if( config.pause === false ) {
                resume();
        }

        if( config.mouseWheel ) {
                document.addEventListener( 'DOMMouseScroll', onDocumentMouseScroll, false ); // FF
                document.addEventListener( 'mousewheel', onDocumentMouseScroll, false );
        }
        else {
                document.removeEventListener( 'DOMMouseScroll', onDocumentMouseScroll, false ); // FF
                document.removeEventListener( 'mousewheel', onDocumentMouseScroll, false );
        }

        // Rolling 3D links
        if( config.rollingLinks ) {
                enableRollingLinks();
        }
        else {
                disableRollingLinks();
        }

        // Iframe link previews
        if( config.previewLinks ) {
                enablePreviewLinks();
        }
        else {
                disablePreviewLinks();
                enablePreviewLinks( '[data-preview-link]' );
        }

        // Remove existing auto-slide controls
        if( autoSlidePlayer ) {
                autoSlidePlayer.destroy();
                autoSlidePlayer = null;
        }

        // Generate auto-slide controls if needed
        if( numberOfSlides > 1 && config.autoSlide && config.autoSlideStoppable && features.canvas && features.requestAnimationFrame ) {
                autoSlidePlayer = new Playback( dom.wrapper, function() {
                        return Math.min( Math.max( ( Date.now() - autoSlideStartTime ) / autoSlide, 0 ), 1 );
                } );

                autoSlidePlayer.on( 'click', onAutoSlidePlayerClick );
                autoSlidePaused = false;
        }

        // When fragments are turned off they should be visible
        if( config.fragments === false ) {
                toArray( dom.slides.querySelectorAll( '.fragment' ) ).forEach( function( element ) {
                        element.classList.add( 'visible' );
                        element.classList.remove( 'current-fragment' );
                } );
        }

        sync();

}

/**
 * Binds all event listeners.
 */
function addEventListeners() {

        eventsAreBound = true;

        window.addEventListener( 'hashchange', onWindowHashChange, false );
        window.addEventListener( 'resize', onWindowResize, false );

        if( config.touch ) {
                dom.wrapper.addEventListener( 'touchstart', onTouchStart, false );
                dom.wrapper.addEventListener( 'touchmove', onTouchMove, false );
                dom.wrapper.addEventListener( 'touchend', onTouchEnd, false );

                // Support pointer-style touch interaction as well
                if( window.navigator.pointerEnabled ) {
                        // IE 11 uses un-prefixed version of pointer events
                        dom.wrapper.addEventListener( 'pointerdown', onPointerDown, false );
                        dom.wrapper.addEventListener( 'pointermove', onPointerMove, false );
                        dom.wrapper.addEventListener( 'pointerup', onPointerUp, false );
                }
                else if( window.navigator.msPointerEnabled ) {
                        // IE 10 uses prefixed version of pointer events
                        dom.wrapper.addEventListener( 'MSPointerDown', onPointerDown, false );
                        dom.wrapper.addEventListener( 'MSPointerMove', onPointerMove, false );
                        dom.wrapper.addEventListener( 'MSPointerUp', onPointerUp, false );
                }
        }

        if( config.keyboard ) {
                document.addEventListener( 'keydown', onDocumentKeyDown, false );
                document.addEventListener( 'keypress', onDocumentKeyPress, false );
        }

        if( config.progress && dom.progress ) {
                dom.progress.addEventListener( 'click', onProgressClicked, false );
        }

        if( config.focusBodyOnPageVisibilityChange ) {
                var visibilityChange;

                if( 'hidden' in document ) {
                        visibilityChange = 'visibilitychange';
                }
                else if( 'msHidden' in document ) {
                        visibilityChange = 'msvisibilitychange';
                }
                else if( 'webkitHidden' in document ) {
                        visibilityChange = 'webkitvisibilitychange';
                }

                if( visibilityChange ) {
                        document.addEventListener( visibilityChange, onPageVisibilityChange, false );
                }
        }

        // Listen to both touch and click events, in case the device
        // supports both
        var pointerEvents = [ 'touchstart', 'click' ];

        // Only support touch for Android, fixes double navigations in
        // stock browser
        if( navigator.userAgent.match( /android/gi ) ) {
                pointerEvents = [ 'touchstart' ];
        }

        pointerEvents.forEach( function( eventName ) {
                dom.controlsLeft.forEach( function( el ) { el.addEventListener( eventName, onNavigateLeftClicked, false ); } );
                dom.controlsRight.forEach( function( el ) { el.addEventListener( eventName, onNavigateRightClicked, false ); } );
                dom.controlsUp.forEach( function( el ) { el.addEventListener( eventName, onNavigateUpClicked, false ); } );
                dom.controlsDown.forEach( function( el ) { el.addEventListener( eventName, onNavigateDownClicked, false ); } );
                dom.controlsPrev.forEach( function( el ) { el.addEventListener( eventName, onNavigatePrevClicked, false ); } );
                dom.controlsNext.forEach( function( el ) { el.addEventListener( eventName, onNavigateNextClicked, false ); } );
        } );

}

/**
 * Unbinds all event listeners.
 */
function removeEventListeners() {

        eventsAreBound = false;

        document.removeEventListener( 'keydown', onDocumentKeyDown, false );
        document.removeEventListener( 'keypress', onDocumentKeyPress, false );
        window.removeEventListener( 'hashchange', onWindowHashChange, false );
        window.removeEventListener( 'resize', onWindowResize, false );

        dom.wrapper.removeEventListener( 'touchstart', onTouchStart, false );
        dom.wrapper.removeEventListener( 'touchmove', onTouchMove, false );
        dom.wrapper.removeEventListener( 'touchend', onTouchEnd, false );

        // IE11
        if( window.navigator.pointerEnabled ) {
                dom.wrapper.removeEventListener( 'pointerdown', onPointerDown, false );
                dom.wrapper.removeEventListener( 'pointermove', onPointerMove, false );
                dom.wrapper.removeEventListener( 'pointerup', onPointerUp, false );
        }
        // IE10
        else if( window.navigator.msPointerEnabled ) {
                dom.wrapper.removeEventListener( 'MSPointerDown', onPointerDown, false );
                dom.wrapper.removeEventListener( 'MSPointerMove', onPointerMove, false );
                dom.wrapper.removeEventListener( 'MSPointerUp', onPointerUp, false );
        }

        if ( config.progress && dom.progress ) {
                dom.progress.removeEventListener( 'click', onProgressClicked, false );
        }

        [ 'touchstart', 'click' ].forEach( function( eventName ) {
                dom.controlsLeft.forEach( function( el ) { el.removeEventListener( eventName, onNavigateLeftClicked, false ); } );
                dom.controlsRight.forEach( function( el ) { el.removeEventListener( eventName, onNavigateRightClicked, false ); } );
                dom.controlsUp.forEach( function( el ) { el.removeEventListener( eventName, onNavigateUpClicked, false ); } );
                dom.controlsDown.forEach( function( el ) { el.removeEventListener( eventName, onNavigateDownClicked, false ); } );
                dom.controlsPrev.forEach( function( el ) { el.removeEventListener( eventName, onNavigatePrevClicked, false ); } );
                dom.controlsNext.forEach( function( el ) { el.removeEventListener( eventName, onNavigateNextClicked, false ); } );
        } );

}

/**
 * Extend object a with the properties of object b.
 * If there's a conflict, object b takes precedence.
 */
function extend( a, b ) {

        for( var i in b ) {
                a[ i ] = b[ i ];
        }

}

/**
 * Converts the target object to an array.
 */
function toArray( o ) {

        return Array.prototype.slice.call( o );

}

/**
 * Utility for deserializing a value.
 */
function deserialize( value ) {

        if( typeof value === 'string' ) {
                if( value === 'null' ) return null;
                else if( value === 'true' ) return true;
                else if( value === 'false' ) return false;
                else if( value.match( /^\d+$/ ) ) return parseFloat( value );
        }

        return value;

}

/**
 * Measures the distance in pixels between point a
 * and point b.
 *
 * @param {Object} a point with x/y properties
 * @param {Object} b point with x/y properties
 */
function distanceBetween( a, b ) {

        var dx = a.x - b.x,
                dy = a.y - b.y;

        return Math.sqrt( dx*dx + dy*dy );

}

/**
 * Applies a CSS transform to the target element.
 */
function transformElement( element, transform ) {

        element.style.WebkitTransform = transform;
        element.style.MozTransform = transform;
        element.style.msTransform = transform;
        element.style.transform = transform;

}

/**
 * Applies CSS transforms to the slides container. The container
 * is transformed from two separate sources: layout and the overview
 * mode.
 */
function transformSlides( transforms ) {

        // Pick up new transforms from arguments
        if( typeof transforms.layout === 'string' ) slidesTransform.layout = transforms.layout;
        if( typeof transforms.overview === 'string' ) slidesTransform.overview = transforms.overview;

        // Apply the transforms to the slides container
        if( slidesTransform.layout ) {
                transformElement( dom.slides, slidesTransform.layout + ' ' + slidesTransform.overview );
        }
        else {
                transformElement( dom.slides, slidesTransform.overview );
        }

}

/**
 * Injects the given CSS styles into the DOM.
 */
function injectStyleSheet( value ) {

        var tag = document.createElement( 'style' );
        tag.type = 'text/css';
        if( tag.styleSheet ) {
                tag.styleSheet.cssText = value;
        }
        else {
                tag.appendChild( document.createTextNode( value ) );
        }
        document.getElementsByTagName( 'head' )[0].appendChild( tag );

}

/**
 * Converts various color input formats to an {r:0,g:0,b:0} object.
 *
 * @param {String} color The string representation of a color,
 * the following formats are supported:
 * - #000
 * - #000000
 * - rgb(0,0,0)
 */
function colorToRgb( color ) {

        var hex3 = color.match( /^#([0-9a-f]{3})$/i );
        if( hex3 && hex3[1] ) {
                hex3 = hex3[1];
                return {
                        r: parseInt( hex3.charAt( 0 ), 16 ) * 0x11,
                        g: parseInt( hex3.charAt( 1 ), 16 ) * 0x11,
                        b: parseInt( hex3.charAt( 2 ), 16 ) * 0x11
                };
        }

        var hex6 = color.match( /^#([0-9a-f]{6})$/i );
        if( hex6 && hex6[1] ) {
                hex6 = hex6[1];
                return {
                        r: parseInt( hex6.substr( 0, 2 ), 16 ),
                        g: parseInt( hex6.substr( 2, 2 ), 16 ),
                        b: parseInt( hex6.substr( 4, 2 ), 16 )
                };
        }

        var rgb = color.match( /^rgb\s*\(\s*(\d+)\s*,\s*(\d+)\s*,\s*(\d+)\s*\)$/i );
        if( rgb ) {
                return {
                        r: parseInt( rgb[1], 10 ),
                        g: parseInt( rgb[2], 10 ),
                        b: parseInt( rgb[3], 10 )
                };
        }

        var rgba = color.match( /^rgba\s*\(\s*(\d+)\s*,\s*(\d+)\s*,\s*(\d+)\s*\,\s*([\d]+|[\d]*.[\d]+)\s*\)$/i );
        if( rgba ) {
                return {
                        r: parseInt( rgba[1], 10 ),
                        g: parseInt( rgba[2], 10 ),
                        b: parseInt( rgba[3], 10 ),
                        a: parseFloat( rgba[4] )
                };
        }

        return null;

}

/**
 * Calculates brightness on a scale of 0-255.
 *
 * @param color See colorStringToRgb for supported formats.
 */
function colorBrightness( color ) {

        if( typeof color === 'string' ) color = colorToRgb( color );

        if( color ) {
                return ( color.r * 299 + color.g * 587 + color.b * 114 ) / 1000;
        }

        return null;

}

/**
 * Retrieves the height of the given element by looking
 * at the position and height of its immediate children.
 */
function getAbsoluteHeight( element ) {

        var height = 0;

        if( element ) {
                var absoluteChildren = 0;

                toArray( element.childNodes ).forEach( function( child ) {

                        if( typeof child.offsetTop === 'number' && child.style ) {
                                // Count # of abs children
                                if( window.getComputedStyle( child ).position === 'absolute' ) {
                                        absoluteChildren += 1;
                                }

                                height = Math.max( height, child.offsetTop + child.offsetHeight );
                        }

                } );

                // If there are no absolute children, use offsetHeight
                if( absoluteChildren === 0 ) {
                        height = element.offsetHeight;
                }

        }

        return height;

}

/**
 * Returns the remaining height within the parent of the
 * target element.
 *
 * remaining height = [ configured parent height ] - [ current parent height ]
 */
function getRemainingHeight( element, height ) {

        height = height || 0;

        if( element ) {
                var newHeight, oldHeight = element.style.height;

                // Change the .stretch element height to 0 in order find the height of all
                // the other elements
                element.style.height = '0px';
                newHeight = height - element.parentNode.offsetHeight;

                // Restore the old height, just in case
                element.style.height = oldHeight + 'px';

                return newHeight;
        }

        return height;

}

/**
 * Checks if this instance is being used to print a PDF.
 */
function isPrintingPDF() {

        return ( /print-pdf/gi ).test( window.location.search );

}

/**
 * Hides the address bar if we're on a mobile device.
 */
function hideAddressBar() {

        if( config.hideAddressBar && isMobileDevice ) {
                // Events that should trigger the address bar to hide
                window.addEventListener( 'load', removeAddressBar, false );
                window.addEventListener( 'orientationchange', removeAddressBar, false );
        }

}

/**
 * Causes the address bar to hide on mobile devices,
 * more vertical space ftw.
 */
function removeAddressBar() {

        setTimeout( function() {
                window.scrollTo( 0, 1 );
        }, 10 );

}

/**
 * Dispatches an event of the specified type from the
 * reveal DOM element.
 */
function dispatchEvent( type, args ) {

        var event = document.createEvent( 'HTMLEvents', 1, 2 );
        event.initEvent( type, true, true );
        extend( event, args );
        dom.wrapper.dispatchEvent( event );

        // If we're in an iframe, post each reveal.js event to the
        // parent window. Used by the notes plugin
        if( config.postMessageEvents && window.parent !== window.self ) {
                window.parent.postMessage( JSON.stringify({ namespace: 'reveal', eventName: type, state: getState() }), '*' );
        }

}

/**
 * Wrap all links in 3D goodness.
 */
function enableRollingLinks() {

        if( features.transforms3d && !( 'msPerspective' in document.body.style ) ) {
                var anchors = dom.wrapper.querySelectorAll( SLIDES_SELECTOR + ' a' );

                for( var i = 0, len = anchors.length; i < len; i++ ) {
                        var anchor = anchors[i];

                        if( anchor.textContent && !anchor.querySelector( '*' ) && ( !anchor.className || !anchor.classList.contains( anchor, 'roll' ) ) ) {
                                var span = document.createElement('span');
                                span.setAttribute('data-title', anchor.text);
                                span.innerHTML = anchor.innerHTML;

                                anchor.classList.add( 'roll' );
                                anchor.innerHTML = '';
                                anchor.appendChild(span);
                        }
                }
        }

}

/**
 * Unwrap all 3D links.
 */
function disableRollingLinks() {

        var anchors = dom.wrapper.querySelectorAll( SLIDES_SELECTOR + ' a.roll' );

        for( var i = 0, len = anchors.length; i < len; i++ ) {
                var anchor = anchors[i];
                var span = anchor.querySelector( 'span' );

                if( span ) {
                        anchor.classList.remove( 'roll' );
                        anchor.innerHTML = span.innerHTML;
                }
        }

}

/**
 * Bind preview frame links.
 */
function enablePreviewLinks( selector ) {

        var anchors = toArray( document.querySelectorAll( selector ? selector : 'a' ) );

        anchors.forEach( function( element ) {
                if( /^(http|www)/gi.test( element.getAttribute( 'href' ) ) ) {
                        element.addEventListener( 'click', onPreviewLinkClicked, false );
                }
        } );

}

/**
 * Unbind preview frame links.
 */
function disablePreviewLinks() {

        var anchors = toArray( document.querySelectorAll( 'a' ) );

        anchors.forEach( function( element ) {
                if( /^(http|www)/gi.test( element.getAttribute( 'href' ) ) ) {
                        element.removeEventListener( 'click', onPreviewLinkClicked, false );
                }
        } );

}

/**
 * Opens a preview window for the target URL.
 */
function showPreview( url ) {

        closeOverlay();

        dom.overlay = document.createElement( 'div' );
        dom.overlay.classList.add( 'overlay' );
        dom.overlay.classList.add( 'overlay-preview' );
        dom.wrapper.appendChild( dom.overlay );

        dom.overlay.innerHTML = [
                '<header>',
                '<a class="close" href="#"><span class="icon"></span></a>',
                '<a class="external" href="'+ url +'" target="_blank"><span class="icon"></span></a>',
                '</header>',
                '<div class="spinner"></div>',
                '<div class="viewport">',
                '<iframe src="'+ url +'"></iframe>',
                '</div>'
        ].join('');

        dom.overlay.querySelector( 'iframe' ).addEventListener( 'load', function( event ) {
                dom.overlay.classList.add( 'loaded' );
        }, false );

        dom.overlay.querySelector( '.close' ).addEventListener( 'click', function( event ) {
                closeOverlay();
                event.preventDefault();
        }, false );

        dom.overlay.querySelector( '.external' ).addEventListener( 'click', function( event ) {
                closeOverlay();
        }, false );

        setTimeout( function() {
                dom.overlay.classList.add( 'visible' );
        }, 1 );

}

/**
 * Opens a overlay window with help material.
 */
function showHelp() {

        if( config.help ) {

                closeOverlay();

                dom.overlay = document.createElement( 'div' );
                dom.overlay.classList.add( 'overlay' );
                dom.overlay.classList.add( 'overlay-help' );
                dom.wrapper.appendChild( dom.overlay );

                var html = '<p class="title">Keyboard Shortcuts</p><br/>';

                html += '<table><th>KEY</th><th>ACTION</th>';
                for( var key in keyboardShortcuts ) {
                        html += '<tr><td>' + key + '</td><td>' + keyboardShortcuts[ key ] + '</td></tr>';
                }

                html += '</table>';

                dom.overlay.innerHTML = [
                        '<header>',
                        '<a class="close" href="#"><span class="icon"></span></a>',
                        '</header>',
                        '<div class="viewport">',
                        '<div class="viewport-inner">'+ html +'</div>',
                        '</div>'
                ].join('');

                dom.overlay.querySelector( '.close' ).addEventListener( 'click', function( event ) {
                        closeOverlay();
                        event.preventDefault();
                }, false );

                setTimeout( function() {
                        dom.overlay.classList.add( 'visible' );
                }, 1 );

        }

}

/**
 * Closes any currently open overlay.
 */
function closeOverlay() {

        if( dom.overlay ) {
                dom.overlay.parentNode.removeChild( dom.overlay );
                dom.overlay = null;
        }

}

/**
 * Applies JavaScript-controlled layout rules to the
 * presentation.
 */
function layout() {

        if( dom.wrapper && !isPrintingPDF() ) {

                var size = getComputedSlideSize();

                var slidePadding = 20; // TODO Dig this out of DOM

                // Layout the contents of the slides
                layoutSlideContents( config.width, config.height, slidePadding );

                dom.slides.style.width = size.width + 'px';
                dom.slides.style.height = size.height + 'px';

                // Determine scale of content to fit within available space
                scale = Math.min( size.presentationWidth / size.width, size.presentationHeight / size.height );

                // Respect max/min scale settings
                scale = Math.max( scale, config.minScale );
                scale = Math.min( scale, config.maxScale );

                // Don't apply any scaling styles if scale is 1
                if( scale === 1 ) {
                        dom.slides.style.zoom = '';
                        dom.slides.style.left = '';
                        dom.slides.style.top = '';
                        dom.slides.style.bottom = '';
                        dom.slides.style.right = '';
                        transformSlides( { layout: '' } );
                }
                else {
                        // Prefer zooming in desktop Chrome so that content remains crisp
                        if( !isMobileDevice && /chrome/i.test( navigator.userAgent ) && typeof dom.slides.style.zoom !== 'undefined' ) {
                                dom.slides.style.zoom = scale;
                                transformSlides( { layout: '' } );
                        }
                        // Apply scale transform as a fallback
                        else {
                                dom.slides.style.left = '50%';
                                dom.slides.style.top = '50%';
                                dom.slides.style.bottom = 'auto';
                                dom.slides.style.right = 'auto';
                                transformSlides( { layout: 'translate(-50%, -50%) scale('+ scale +')' } );
                        }
                }

                // Select all slides, vertical and horizontal
                var slides = toArray( dom.wrapper.querySelectorAll( SLIDES_SELECTOR ) );

                for( var i = 0, len = slides.length; i < len; i++ ) {
                        var slide = slides[ i ];

                        // Don't bother updating invisible slides
                        if( slide.style.display === 'none' ) {
                                continue;
                        }

                        if( config.center || slide.classList.contains( 'center' ) ) {
                                // Vertical stacks are not centred since their section
                                // children will be
                                if( slide.classList.contains( 'stack' ) ) {
                                        slide.style.top = 0;
                                }
                                else {
                                        slide.style.top = Math.max( ( ( size.height - getAbsoluteHeight( slide ) ) / 2 ) - slidePadding, 0 ) + 'px';
                                }
                        }
                        else {
                                slide.style.top = '';
                        }

                }

                updateProgress();
                updateParallax();

        }

}

/**
 * Applies layout logic to the contents of all slides in
 * the presentation.
 */
function layoutSlideContents( width, height, padding ) {

        // Handle sizing of elements with the 'stretch' class
        toArray( dom.slides.querySelectorAll( 'section > .stretch' ) ).forEach( function( element ) {

                // Determine how much vertical space we can use
                var remainingHeight = getRemainingHeight( element, height );

                // Consider the aspect ratio of media elements
                if( /(img|video)/gi.test( element.nodeName ) ) {
                        var nw = element.naturalWidth || element.videoWidth,
                                nh = element.naturalHeight || element.videoHeight;

                        var es = Math.min( width / nw, remainingHeight / nh );

                        element.style.width = ( nw * es ) + 'px';
                        element.style.height = ( nh * es ) + 'px';

                }
                else {
                        element.style.width = width + 'px';
                        element.style.height = remainingHeight + 'px';
                }

        } );

}

/**
 * Calculates the computed pixel size of our slides. These
 * values are based on the width and height configuration
 * options.
 */
function getComputedSlideSize( presentationWidth, presentationHeight ) {

        var size = {
                // Slide size
                width: config.width,
                height: config.height,

                // Presentation size
                presentationWidth: presentationWidth || dom.wrapper.offsetWidth,
                presentationHeight: presentationHeight || dom.wrapper.offsetHeight
        };

        // Reduce available space by margin
        size.presentationWidth -= ( size.presentationWidth * config.margin );
        size.presentationHeight -= ( size.presentationHeight * config.margin );

        // Slide width may be a percentage of available width
        if( typeof size.width === 'string' && /%$/.test( size.width ) ) {
                size.width = parseInt( size.width, 10 ) / 100 * size.presentationWidth;
        }

        // Slide height may be a percentage of available height
        if( typeof size.height === 'string' && /%$/.test( size.height ) ) {
                size.height = parseInt( size.height, 10 ) / 100 * size.presentationHeight;
        }

        return size;

}

/**
 * Stores the vertical index of a stack so that the same
 * vertical slide can be selected when navigating to and
 * from the stack.
 *
 * @param {HTMLElement} stack The vertical stack element
 * @param {int} v Index to memorize
 */
function setPreviousVerticalIndex( stack, v ) {

        if( typeof stack === 'object' && typeof stack.setAttribute === 'function' ) {
                stack.setAttribute( 'data-previous-indexv', v || 0 );
        }

}

/**
 * Retrieves the vertical index which was stored using
 * #setPreviousVerticalIndex() or 0 if no previous index
 * exists.
 *
 * @param {HTMLElement} stack The vertical stack element
 */
function getPreviousVerticalIndex( stack ) {

        if( typeof stack === 'object' && typeof stack.setAttribute === 'function' && stack.classList.contains( 'stack' ) ) {
                // Prefer manually defined start-indexv
                var attributeName = stack.hasAttribute( 'data-start-indexv' ) ? 'data-start-indexv' : 'data-previous-indexv';

                return parseInt( stack.getAttribute( attributeName ) || 0, 10 );
        }

        return 0;

}

/**
 * Displays the overview of slides (quick nav) by scaling
 * down and arranging all slide elements.
 */
function activateOverview() {

        // Only proceed if enabled in config
        if( config.overview && !isOverview() ) {

                overview = true;

                dom.wrapper.classList.add( 'overview' );
                dom.wrapper.classList.remove( 'overview-deactivating' );

                if( features.overviewTransitions ) {
                        setTimeout( function() {
                                dom.wrapper.classList.add( 'overview-animated' );
                        }, 1 );
                }

                // Don't auto-slide while in overview mode
                cancelAutoSlide();

                // Move the backgrounds element into the slide container to
                // that the same scaling is applied
                dom.slides.appendChild( dom.background );

                // Clicking on an overview slide navigates to it
                toArray( dom.wrapper.querySelectorAll( SLIDES_SELECTOR ) ).forEach( function( slide ) {
                        if( !slide.classList.contains( 'stack' ) ) {
                                slide.addEventListener( 'click', onOverviewSlideClicked, true );
                        }
                } );

                updateSlidesVisibility();
                layoutOverview();
                updateOverview();

                layout();

                // Notify observers of the overview showing
                dispatchEvent( 'overviewshown', {
                        'indexh': indexh,
                        'indexv': indexv,
                        'currentSlide': currentSlide
                } );

        }

}

/**
 * Uses CSS transforms to position all slides in a grid for
 * display inside of the overview mode.
 */
function layoutOverview() {

        var margin = 70;
        var slideWidth = config.width + margin,
                slideHeight = config.height + margin;

        // Reverse in RTL mode
        if( config.rtl ) {
                slideWidth = -slideWidth;
        }

        // Layout slides
        toArray( dom.wrapper.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR ) ).forEach( function( hslide, h ) {
                hslide.setAttribute( 'data-index-h', h );
                transformElement( hslide, 'translate3d(' + ( h * slideWidth ) + 'px, 0, 0)' );

                if( hslide.classList.contains( 'stack' ) ) {

                        toArray( hslide.querySelectorAll( 'section' ) ).forEach( function( vslide, v ) {
                                vslide.setAttribute( 'data-index-h', h );
                                vslide.setAttribute( 'data-index-v', v );

                                transformElement( vslide, 'translate3d(0, ' + ( v * slideHeight ) + 'px, 0)' );
                        } );

                }
        } );

        // Layout slide backgrounds
        toArray( dom.background.childNodes ).forEach( function( hbackground, h ) {
                transformElement( hbackground, 'translate3d(' + ( h * slideWidth ) + 'px, 0, 0)' );

                toArray( hbackground.querySelectorAll( '.slide-background' ) ).forEach( function( vbackground, v ) {
                        transformElement( vbackground, 'translate3d(0, ' + ( v * slideHeight ) + 'px, 0)' );
                } );
        } );

}

/**
 * Moves the overview viewport to the current slides.
 * Called each time the current slide changes.
 */
function updateOverview() {

        var margin = 70;
        var slideWidth = config.width + margin,
                slideHeight = config.height + margin;

        // Reverse in RTL mode
        if( config.rtl ) {
                slideWidth = -slideWidth;
        }

        transformSlides( {
                overview: [
                        'translateX('+ ( -indexh * slideWidth ) +'px)',
                        'translateY('+ ( -indexv * slideHeight ) +'px)',
                        'translateZ('+ ( window.innerWidth < 400 ? -1000 : -2500 ) +'px)'
                ].join( ' ' )
        } );

}

/**
 * Exits the slide overview and enters the currently
 * active slide.
 */
function deactivateOverview() {

        // Only proceed if enabled in config
        if( config.overview ) {

                overview = false;

                dom.wrapper.classList.remove( 'overview' );
                dom.wrapper.classList.remove( 'overview-animated' );

                // Temporarily add a class so that transitions can do different things
                // depending on whether they are exiting/entering overview, or just
                // moving from slide to slide
                dom.wrapper.classList.add( 'overview-deactivating' );

                setTimeout( function () {
                        dom.wrapper.classList.remove( 'overview-deactivating' );
                }, 1 );

                // Move the background element back out
                dom.wrapper.appendChild( dom.background );

                // Clean up changes made to slides
                toArray( dom.wrapper.querySelectorAll( SLIDES_SELECTOR ) ).forEach( function( slide ) {
                        transformElement( slide, '' );

                        slide.removeEventListener( 'click', onOverviewSlideClicked, true );
                } );

                // Clean up changes made to backgrounds
                toArray( dom.background.querySelectorAll( '.slide-background' ) ).forEach( function( background ) {
                        transformElement( background, '' );
                } );

                transformSlides( { overview: '' } );

                slide( indexh, indexv );

                layout();

                cueAutoSlide();

                // Notify observers of the overview hiding
                dispatchEvent( 'overviewhidden', {
                        'indexh': indexh,
                        'indexv': indexv,
                        'currentSlide': currentSlide
                } );

        }
}

/**
 * Toggles the slide overview mode on and off.
 *
 * @param {Boolean} override Optional flag which overrides the
 * toggle logic and forcibly sets the desired state. True means
 * overview is open, false means it's closed.
 */
function toggleOverview( override ) {

        if( typeof override === 'boolean' ) {
                override ? activateOverview() : deactivateOverview();
        }
        else {
                isOverview() ? deactivateOverview() : activateOverview();
        }

}

/**
 * Checks if the overview is currently active.
 *
 * @return {Boolean} true if the overview is active,
 * false otherwise
 */
function isOverview() {

        return overview;

}

/**
 * Checks if the current or specified slide is vertical
 * (nested within another slide).
 *
 * @param {HTMLElement} slide [optional] The slide to check
 * orientation of
 */
function isVerticalSlide( slide ) {

        // Prefer slide argument, otherwise use current slide
        slide = slide ? slide : currentSlide;

        return slide && slide.parentNode && !!slide.parentNode.nodeName.match( /section/i );

}

/**
 * Handling the fullscreen functionality via the fullscreen API
 *
 * @see http://fullscreen.spec.whatwg.org/
 * @see https://developer.mozilla.org/en-US/docs/DOM/Using_fullscreen_mode
 */
function enterFullscreen() {

        var element = document.body;

        // Check which implementation is available
        var requestMethod = element.requestFullScreen ||
                element.webkitRequestFullscreen ||
                element.webkitRequestFullScreen ||
                element.mozRequestFullScreen ||
                element.msRequestFullscreen;

        if( requestMethod ) {
                requestMethod.apply( element );
        }

}

/**
 * Enters the paused mode which fades everything on screen to
 * black.
 */
function pause() {

        if( config.pause ) {
                var wasPaused = dom.wrapper.classList.contains( 'paused' );

                cancelAutoSlide();
                dom.wrapper.classList.add( 'paused' );

                if( wasPaused === false ) {
                        dispatchEvent( 'paused' );
                }
        }

}

/**
 * Exits from the paused mode.
 */
function resume() {

        var wasPaused = dom.wrapper.classList.contains( 'paused' );
        dom.wrapper.classList.remove( 'paused' );

        cueAutoSlide();

        if( wasPaused ) {
                dispatchEvent( 'resumed' );
        }

}

/**
 * Toggles the paused mode on and off.
 */
function togglePause( override ) {

        if( typeof override === 'boolean' ) {
                override ? pause() : resume();
        }
        else {
                isPaused() ? resume() : pause();
        }

}

/**
 * Checks if we are currently in the paused mode.
 */
function isPaused() {

        return dom.wrapper.classList.contains( 'paused' );

}

/**
 * Toggles the auto slide mode on and off.
 *
 * @param {Boolean} override Optional flag which sets the desired state.
 * True means autoplay starts, false means it stops.
 */

function toggleAutoSlide( override ) {

        if( typeof override === 'boolean' ) {
                override ? resumeAutoSlide() : pauseAutoSlide();
        }

        else {
                autoSlidePaused ? resumeAutoSlide() : pauseAutoSlide();
        }

}

/**
 * Checks if the auto slide mode is currently on.
 */
function isAutoSliding() {

        return !!( autoSlide && !autoSlidePaused );

}

/**
 * Steps from the current point in the presentation to the
 * slide which matches the specified horizontal and vertical
 * indices.
 *
 * @param {int} h Horizontal index of the target slide
 * @param {int} v Vertical index of the target slide
 * @param {int} f Optional index of a fragment within the
 * target slide to activate
 * @param {int} o Optional origin for use in multimaster environments
 */
function slide( h, v, f, o ) {

        // Remember where we were at before
        previousSlide = currentSlide;

        // Query all horizontal slides in the deck
        var horizontalSlides = dom.wrapper.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR );

        // If no vertical index is specified and the upcoming slide is a
        // stack, resume at its previous vertical index
        if( v === undefined && !isOverview() ) {
                v = getPreviousVerticalIndex( horizontalSlides[ h ] );
        }

        // If we were on a vertical stack, remember what vertical index
        // it was on so we can resume at the same position when returning
        if( previousSlide && previousSlide.parentNode && previousSlide.parentNode.classList.contains( 'stack' ) ) {
                setPreviousVerticalIndex( previousSlide.parentNode, indexv );
        }

        // Remember the state before this slide
        var stateBefore = state.concat();

        // Reset the state array
        state.length = 0;

        var indexhBefore = indexh || 0,
                indexvBefore = indexv || 0;

        // Activate and transition to the new slide
        indexh = updateSlides( HORIZONTAL_SLIDES_SELECTOR, h === undefined ? indexh : h );
        indexv = updateSlides( VERTICAL_SLIDES_SELECTOR, v === undefined ? indexv : v );

        // Update the visibility of slides now that the indices have changed
        updateSlidesVisibility();

        layout();

        // Apply the new state
        stateLoop: for( var i = 0, len = state.length; i < len; i++ ) {
                // Check if this state existed on the previous slide. If it
                // did, we will avoid adding it repeatedly
                for( var j = 0; j < stateBefore.length; j++ ) {
                        if( stateBefore[j] === state[i] ) {
                                stateBefore.splice( j, 1 );
                                continue stateLoop;
                        }
                }

                document.documentElement.classList.add( state[i] );

                // Dispatch custom event matching the state's name
                dispatchEvent( state[i] );
        }

        // Clean up the remains of the previous state
        while( stateBefore.length ) {
                document.documentElement.classList.remove( stateBefore.pop() );
        }

        // Update the overview if it's currently active
        if( isOverview() ) {
                updateOverview();
        }

        // Find the current horizontal slide and any possible vertical slides
        // within it
        var currentHorizontalSlide = horizontalSlides[ indexh ],
                currentVerticalSlides = currentHorizontalSlide.querySelectorAll( 'section' );

        // Store references to the previous and current slides
        currentSlide = currentVerticalSlides[ indexv ] || currentHorizontalSlide;

        // Show fragment, if specified
        if( typeof f !== 'undefined' ) {
                navigateFragment( f );
        }

        // Dispatch an event if the slide changed
        var slideChanged = ( indexh !== indexhBefore || indexv !== indexvBefore );
        if( slideChanged ) {
                dispatchEvent( 'slidechanged', {
                        'indexh': indexh,
                        'indexv': indexv,
                        'previousSlide': previousSlide,
                        'currentSlide': currentSlide,
                        'origin': o
                } );
        }
        else {
                // Ensure that the previous slide is never the same as the current
                previousSlide = null;
        }

        // Solves an edge case where the previous slide maintains the
        // 'present' class when navigating between adjacent vertical
        // stacks
        if( previousSlide ) {
                previousSlide.classList.remove( 'present' );
                previousSlide.setAttribute( 'aria-hidden', 'true' );

                // Reset all slides upon navigate to home
                // Issue: #285
                if ( dom.wrapper.querySelector( HOME_SLIDE_SELECTOR ).classList.contains( 'present' ) ) {
                        // Launch async task
                        setTimeout( function () {
                                var slides = toArray( dom.wrapper.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR + '.stack') ), i;
                                for( i in slides ) {
                                        if( slides[i] ) {
                                                // Reset stack
                                                setPreviousVerticalIndex( slides[i], 0 );
                                        }
                                }
                        }, 0 );
                }
        }

        // Handle embedded content
        if( slideChanged || !previousSlide ) {
                stopEmbeddedContent( previousSlide );
                startEmbeddedContent( currentSlide );
        }

        // Announce the current slide contents, for screen readers
        dom.statusDiv.textContent = currentSlide.textContent;

        updateControls();
        updateProgress();
        updateBackground();
        updateParallax();
        updateSlideNumber();

        // Update the URL hash
        writeURL();

        cueAutoSlide();

}

/**
 * Syncs the presentation with the current DOM. Useful
 * when new slides or control elements are added or when
 * the configuration has changed.
 */
function sync() {

        // Subscribe to input
        removeEventListeners();
        addEventListeners();

        // Force a layout to make sure the current config is accounted for
        layout();

        // Reflect the current autoSlide value
        autoSlide = config.autoSlide;

        // Start auto-sliding if it's enabled
        cueAutoSlide();

        // Re-create the slide backgrounds
        createBackgrounds();

        // Write the current hash to the URL
        writeURL();

        sortAllFragments();

        updateControls();
        updateProgress();
        updateBackground( true );
        updateSlideNumber();
        updateSlidesVisibility();

        formatEmbeddedContent();
        startEmbeddedContent( currentSlide );

        if( isOverview() ) {
                layoutOverview();
        }

}

/**
 * Resets all vertical slides so that only the first
 * is visible.
 */
function resetVerticalSlides() {

        var horizontalSlides = toArray( dom.wrapper.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR ) );
        horizontalSlides.forEach( function( horizontalSlide ) {

                var verticalSlides = toArray( horizontalSlide.querySelectorAll( 'section' ) );
                verticalSlides.forEach( function( verticalSlide, y ) {

                        if( y > 0 ) {
                                verticalSlide.classList.remove( 'present' );
                                verticalSlide.classList.remove( 'past' );
                                verticalSlide.classList.add( 'future' );
                                verticalSlide.setAttribute( 'aria-hidden', 'true' );
                        }

                } );

        } );

}

/**
 * Sorts and formats all of fragments in the
 * presentation.
 */
function sortAllFragments() {

        var horizontalSlides = toArray( dom.wrapper.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR ) );
        horizontalSlides.forEach( function( horizontalSlide ) {

                var verticalSlides = toArray( horizontalSlide.querySelectorAll( 'section' ) );
                verticalSlides.forEach( function( verticalSlide, y ) {

                        sortFragments( verticalSlide.querySelectorAll( '.fragment' ) );

                } );

                if( verticalSlides.length === 0 ) sortFragments( horizontalSlide.querySelectorAll( '.fragment' ) );

        } );

}

/**
 * Updates one dimension of slides by showing the slide
 * with the specified index.
 *
 * @param {String} selector A CSS selector that will fetch
 * the group of slides we are working with
 * @param {Number} index The index of the slide that should be
 * shown
 *
 * @return {Number} The index of the slide that is now shown,
 * might differ from the passed in index if it was out of
 * bounds.
 */
function updateSlides( selector, index ) {

        // Select all slides and convert the NodeList result to
        // an array
        var slides = toArray( dom.wrapper.querySelectorAll( selector ) ),
                slidesLength = slides.length;

        var printMode = isPrintingPDF();

        if( slidesLength ) {

                // Should the index loop?
                if( config.loop ) {
                        index %= slidesLength;

                        if( index < 0 ) {
                                index = slidesLength + index;
                        }
                }

                // Enforce max and minimum index bounds
                index = Math.max( Math.min( index, slidesLength - 1 ), 0 );

                for( var i = 0; i < slidesLength; i++ ) {
                        var element = slides[i];

                        var reverse = config.rtl && !isVerticalSlide( element );

                        element.classList.remove( 'past' );
                        element.classList.remove( 'present' );
                        element.classList.remove( 'future' );

                        // http://www.w3.org/html/wg/drafts/html/master/editing.html#the-hidden-attribute
                        element.setAttribute( 'hidden', '' );
                        element.setAttribute( 'aria-hidden', 'true' );

                        // If this element contains vertical slides
                        if( element.querySelector( 'section' ) ) {
                                element.classList.add( 'stack' );
                        }

                        // If we're printing static slides, all slides are "present"
                        if( printMode ) {
                                element.classList.add( 'present' );
                                continue;
                        }

                        if( i < index ) {
                                // Any element previous to index is given the 'past' class
                                element.classList.add( reverse ? 'future' : 'past' );

                                if( config.fragments ) {
                                        var pastFragments = toArray( element.querySelectorAll( '.fragment' ) );

                                        // Show all fragments on prior slides
                                        while( pastFragments.length ) {
                                                var pastFragment = pastFragments.pop();
                                                pastFragment.classList.add( 'visible' );
                                                pastFragment.classList.remove( 'current-fragment' );
                                        }
                                }
                        }
                        else if( i > index ) {
                                // Any element subsequent to index is given the 'future' class
                                element.classList.add( reverse ? 'past' : 'future' );

                                if( config.fragments ) {
                                        var futureFragments = toArray( element.querySelectorAll( '.fragment.visible' ) );

                                        // No fragments in future slides should be visible ahead of time
                                        while( futureFragments.length ) {
                                                var futureFragment = futureFragments.pop();
                                                futureFragment.classList.remove( 'visible' );
                                                futureFragment.classList.remove( 'current-fragment' );
                                        }
                                }
                        }
                }

                // Mark the current slide as present
                slides[index].classList.add( 'present' );
                slides[index].removeAttribute( 'hidden' );
                slides[index].removeAttribute( 'aria-hidden' );

                // If this slide has a state associated with it, add it
                // onto the current state of the deck
                var slideState = slides[index].getAttribute( 'data-state' );
                if( slideState ) {
                        state = state.concat( slideState.split( ' ' ) );
                }

        }
        else {
                // Since there are no slides we can't be anywhere beyond the
                // zeroth index
                index = 0;
        }

        return index;

}

/**
 * Optimization method; hide all slides that are far away
 * from the present slide.
 */
function updateSlidesVisibility() {

        // Select all slides and convert the NodeList result to
        // an array
        var horizontalSlides = toArray( dom.wrapper.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR ) ),
                horizontalSlidesLength = horizontalSlides.length,
                distanceX,
                distanceY;

        if( horizontalSlidesLength && typeof indexh !== 'undefined' ) {

                // The number of steps away from the present slide that will
                // be visible
                var viewDistance = isOverview() ? 10 : config.viewDistance;

                // Limit view distance on weaker devices
                if( isMobileDevice ) {
                        viewDistance = isOverview() ? 6 : 2;
                }

                // All slides need to be visible when exporting to PDF
                if( isPrintingPDF() ) {
                        viewDistance = Number.MAX_VALUE;
                }

                for( var x = 0; x < horizontalSlidesLength; x++ ) {
                        var horizontalSlide = horizontalSlides[x];

                        var verticalSlides = toArray( horizontalSlide.querySelectorAll( 'section' ) ),
                                verticalSlidesLength = verticalSlides.length;

                        // Determine how far away this slide is from the present
                        distanceX = Math.abs( ( indexh || 0 ) - x ) || 0;

                        // If the presentation is looped, distance should measure
                        // 1 between the first and last slides
                        if( config.loop ) {
                                distanceX = Math.abs( ( ( indexh || 0 ) - x ) % ( horizontalSlidesLength - viewDistance ) ) || 0;
                        }

                        // Show the horizontal slide if it's within the view distance
                        if( distanceX < viewDistance ) {
                                showSlide( horizontalSlide );
                        }
                        else {
                                hideSlide( horizontalSlide );
                        }

                        if( verticalSlidesLength ) {

                                var oy = getPreviousVerticalIndex( horizontalSlide );

                                for( var y = 0; y < verticalSlidesLength; y++ ) {
                                        var verticalSlide = verticalSlides[y];

                                        distanceY = x === ( indexh || 0 ) ? Math.abs( ( indexv || 0 ) - y ) : Math.abs( y - oy );

                                        if( distanceX + distanceY < viewDistance ) {
                                                showSlide( verticalSlide );
                                        }
                                        else {
                                                hideSlide( verticalSlide );
                                        }
                                }

                        }
                }

        }

}

/**
 * Updates the progress bar to reflect the current slide.
 */
function updateProgress() {

        // Update progress if enabled
        if( config.progress && dom.progressbar ) {

                dom.progressbar.style.width = getProgress() * dom.wrapper.offsetWidth + 'px';

        }

}

/**
 * Updates the slide number div to reflect the current slide.
 *
 * Slide number format can be defined as a string using the
 * following variables:
 *  h: current slide's horizontal index
 *  v: current slide's vertical index
 *  c: current slide index (flattened)
 *  t: total number of slides (flattened)
 */
function updateSlideNumber() {

        // Update slide number if enabled
        if( config.slideNumber && dom.slideNumber) {

                // Default to only showing the current slide number
                var format = 'c';

                // Check if a custom slide number format is available
                if( typeof config.slideNumber === 'string' ) {
                        format = config.slideNumber;
                }

                dom.slideNumber.innerHTML = format.replace( /h/g, indexh )
                        .replace( /v/g, indexv )
                        .replace( /c/g, getSlidePastCount() + 1 )
                        .replace( /t/g, getTotalSlides() );
        }

}

/**
 * Updates the state of all control/navigation arrows.
 */
function updateControls() {

        var routes = availableRoutes();
        var fragments = availableFragments();

        // Remove the 'enabled' class from all directions
        dom.controlsLeft.concat( dom.controlsRight )
                .concat( dom.controlsUp )
                .concat( dom.controlsDown )
                .concat( dom.controlsPrev )
                .concat( dom.controlsNext ).forEach( function( node ) {
                        node.classList.remove( 'enabled' );
                        node.classList.remove( 'fragmented' );
                } );

        // Add the 'enabled' class to the available routes
        if( routes.left ) dom.controlsLeft.forEach( function( el ) { el.classList.add( 'enabled' );     } );
        if( routes.right ) dom.controlsRight.forEach( function( el ) { el.classList.add( 'enabled' ); } );
        if( routes.up ) dom.controlsUp.forEach( function( el ) { el.classList.add( 'enabled' ); } );
        if( routes.down ) dom.controlsDown.forEach( function( el ) { el.classList.add( 'enabled' ); } );

        // Prev/next buttons
        if( routes.left || routes.up ) dom.controlsPrev.forEach( function( el ) { el.classList.add( 'enabled' ); } );
        if( routes.right || routes.down ) dom.controlsNext.forEach( function( el ) { el.classList.add( 'enabled' ); } );

        // Highlight fragment directions
        if( currentSlide ) {

                // Always apply fragment decorator to prev/next buttons
                if( fragments.prev ) dom.controlsPrev.forEach( function( el ) { el.classList.add( 'fragmented', 'enabled' ); } );
                if( fragments.next ) dom.controlsNext.forEach( function( el ) { el.classList.add( 'fragmented', 'enabled' ); } );

                // Apply fragment decorators to directional buttons based on
                // what slide axis they are in
                if( isVerticalSlide( currentSlide ) ) {
                        if( fragments.prev ) dom.controlsUp.forEach( function( el ) { el.classList.add( 'fragmented', 'enabled' ); } );
                        if( fragments.next ) dom.controlsDown.forEach( function( el ) { el.classList.add( 'fragmented', 'enabled' ); } );
                }
                else {
                        if( fragments.prev ) dom.controlsLeft.forEach( function( el ) { el.classList.add( 'fragmented', 'enabled' ); } );
                        if( fragments.next ) dom.controlsRight.forEach( function( el ) { el.classList.add( 'fragmented', 'enabled' ); } );
                }

        }

}

/**
 * Updates the background elements to reflect the current
 * slide.
 *
 * @param {Boolean} includeAll If true, the backgrounds of
 * all vertical slides (not just the present) will be updated.
 */
function updateBackground( includeAll ) {

        var currentBackground = null;

        // Reverse past/future classes when in RTL mode
        var horizontalPast = config.rtl ? 'future' : 'past',
                horizontalFuture = config.rtl ? 'past' : 'future';

        // Update the classes of all backgrounds to match the
        // states of their slides (past/present/future)
        toArray( dom.background.childNodes ).forEach( function( backgroundh, h ) {

                backgroundh.classList.remove( 'past' );
                backgroundh.classList.remove( 'present' );
                backgroundh.classList.remove( 'future' );

                if( h < indexh ) {
                        backgroundh.classList.add( horizontalPast );
                }
                else if ( h > indexh ) {
                        backgroundh.classList.add( horizontalFuture );
                }
                else {
                        backgroundh.classList.add( 'present' );

                        // Store a reference to the current background element
                        currentBackground = backgroundh;
                }

                if( includeAll || h === indexh ) {
                        toArray( backgroundh.querySelectorAll( '.slide-background' ) ).forEach( function( backgroundv, v ) {

                                backgroundv.classList.remove( 'past' );
                                backgroundv.classList.remove( 'present' );
                                backgroundv.classList.remove( 'future' );

                                if( v < indexv ) {
                                        backgroundv.classList.add( 'past' );
                                }
                                else if ( v > indexv ) {
                                        backgroundv.classList.add( 'future' );
                                }
                                else {
                                        backgroundv.classList.add( 'present' );

                                        // Only if this is the present horizontal and vertical slide
                                        if( h === indexh ) currentBackground = backgroundv;
                                }

                        } );
                }

        } );

        // Stop any currently playing video background
        if( previousBackground ) {

                var previousVideo = previousBackground.querySelector( 'video' );
                if( previousVideo ) previousVideo.pause();

        }

        if( currentBackground ) {

                // Start video playback
                var currentVideo = currentBackground.querySelector( 'video' );
                if( currentVideo ) {
                        currentVideo.currentTime = 0;
                        currentVideo.play();
                }

                var backgroundImageURL = currentBackground.style.backgroundImage || '';

                // Restart GIFs (doesn't work in Firefox)
                if( /\.gif/i.test( backgroundImageURL ) ) {
                        currentBackground.style.backgroundImage = '';
                        window.getComputedStyle( currentBackground ).opacity;
                        currentBackground.style.backgroundImage = backgroundImageURL;
                }

                // Don't transition between identical backgrounds. This
                // prevents unwanted flicker.
                var previousBackgroundHash = previousBackground ? previousBackground.getAttribute( 'data-background-hash' ) : null;
                var currentBackgroundHash = currentBackground.getAttribute( 'data-background-hash' );
                if( currentBackgroundHash && currentBackgroundHash === previousBackgroundHash && currentBackground !== previousBackground ) {
                        dom.background.classList.add( 'no-transition' );
                }

                previousBackground = currentBackground;

        }

        // If there's a background brightness flag for this slide,
        // bubble it to the .reveal container
        if( currentSlide ) {
                [ 'has-light-background', 'has-dark-background' ].forEach( function( classToBubble ) {
                        if( currentSlide.classList.contains( classToBubble ) ) {
                                dom.wrapper.classList.add( classToBubble );
                        }
                        else {
                                dom.wrapper.classList.remove( classToBubble );
                        }
                } );
        }

        // Allow the first background to apply without transition
        setTimeout( function() {
                dom.background.classList.remove( 'no-transition' );
        }, 1 );

}

/**
 * Updates the position of the parallax background based
 * on the current slide index.
 */
function updateParallax() {

        if( config.parallaxBackgroundImage ) {

                var horizontalSlides = dom.wrapper.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR ),
                        verticalSlides = dom.wrapper.querySelectorAll( VERTICAL_SLIDES_SELECTOR );

                var backgroundSize = dom.background.style.backgroundSize.split( ' ' ),
                        backgroundWidth, backgroundHeight;

                if( backgroundSize.length === 1 ) {
                        backgroundWidth = backgroundHeight = parseInt( backgroundSize[0], 10 );
                }
                else {
                        backgroundWidth = parseInt( backgroundSize[0], 10 );
                        backgroundHeight = parseInt( backgroundSize[1], 10 );
                }

                var slideWidth = dom.background.offsetWidth,
                        horizontalSlideCount = horizontalSlides.length,
                        horizontalOffsetMultiplier,
                        horizontalOffset;

                if( typeof config.parallaxBackgroundHorizontal === 'number' ) {
                        horizontalOffsetMultiplier = config.parallaxBackgroundHorizontal;
                }
                else {
                        horizontalOffsetMultiplier = ( backgroundWidth - slideWidth ) / ( horizontalSlideCount-1 );
                }

                horizontalOffset = horizontalOffsetMultiplier * indexh * -1;

                var slideHeight = dom.background.offsetHeight,
                        verticalSlideCount = verticalSlides.length,
                        verticalOffsetMultiplier,
                        verticalOffset;

                if( typeof config.parallaxBackgroundVertical === 'number' ) {
                        verticalOffsetMultiplier = config.parallaxBackgroundVertical;
                }
                else {
                        verticalOffsetMultiplier = ( backgroundHeight - slideHeight ) / ( verticalSlideCount-1 );
                }

                verticalOffset = verticalSlideCount > 0 ?  verticalOffsetMultiplier * indexv * 1 : 0;

                dom.background.style.backgroundPosition = horizontalOffset + 'px ' + -verticalOffset + 'px';

        }

}

/**
 * Called when the given slide is within the configured view
 * distance. Shows the slide element and loads any content
 * that is set to load lazily (data-src).
 */
function showSlide( slide ) {

        // Show the slide element
        slide.style.display = 'block';

        // Media elements with data-src attributes
        toArray( slide.querySelectorAll( 'img[data-src], video[data-src], audio[data-src]' ) ).forEach( function( element ) {
                element.setAttribute( 'src', element.getAttribute( 'data-src' ) );
                element.removeAttribute( 'data-src' );
        } );

        // Media elements with <source> children
        toArray( slide.querySelectorAll( 'video, audio' ) ).forEach( function( media ) {
                var sources = 0;

                toArray( media.querySelectorAll( 'source[data-src]' ) ).forEach( function( source ) {
                        source.setAttribute( 'src', source.getAttribute( 'data-src' ) );
                        source.removeAttribute( 'data-src' );
                        sources += 1;
                } );

                // If we rewrote sources for this video/audio element, we need
                // to manually tell it to load from its new origin
                if( sources > 0 ) {
                        media.load();
                }
        } );

        // Show the corresponding background element
        var indices = getIndices( slide );
        var background = getSlideBackground( indices.h, indices.v );
        if( background ) {
                background.style.display = 'block';

                // If the background contains media, load it
                if( background.hasAttribute( 'data-loaded' ) === false ) {
                        background.setAttribute( 'data-loaded', 'true' );

                        var backgroundImage = slide.getAttribute( 'data-background-image' ),
                                backgroundVideo = slide.getAttribute( 'data-background-video' ),
                                backgroundVideoLoop = slide.hasAttribute( 'data-background-video-loop' ),
                                backgroundIframe = slide.getAttribute( 'data-background-iframe' );

                        // Images
                        if( backgroundImage ) {
                                background.style.backgroundImage = 'url('+ backgroundImage +')';
                        }
                        // Videos
                        else if ( backgroundVideo && !isSpeakerNotes() ) {
                                var video = document.createElement( 'video' );

                                if( backgroundVideoLoop ) {
                                        video.setAttribute( 'loop', '' );
                                }

                                // Support comma separated lists of video sources
                                backgroundVideo.split( ',' ).forEach( function( source ) {
                                        video.innerHTML += '<source src="'+ source +'">';
                                } );

                                background.appendChild( video );
                        }
                        // Iframes
                        else if( backgroundIframe ) {
                                var iframe = document.createElement( 'iframe' );
                                iframe.setAttribute( 'src', backgroundIframe );
                                iframe.style.width  = '100%';
                                iframe.style.height = '100%';
                                iframe.style.maxHeight = '100%';
                                iframe.style.maxWidth = '100%';

                                background.appendChild( iframe );
                        }
                }
        }

}

/**
 * Called when the given slide is moved outside of the
 * configured view distance.
 */
function hideSlide( slide ) {

        // Hide the slide element
        slide.style.display = 'none';

        // Hide the corresponding background element
        var indices = getIndices( slide );
        var background = getSlideBackground( indices.h, indices.v );
        if( background ) {
                background.style.display = 'none';
        }

}

/**
 * Determine what available routes there are for navigation.
 *
 * @return {Object} containing four booleans: left/right/up/down
 */
function availableRoutes() {

        var horizontalSlides = dom.wrapper.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR ),
                verticalSlides = dom.wrapper.querySelectorAll( VERTICAL_SLIDES_SELECTOR );

        var routes = {
                left: indexh > 0 || config.loop,
                right: indexh < horizontalSlides.length - 1 || config.loop,
                up: indexv > 0,
                down: indexv < verticalSlides.length - 1
        };

        // reverse horizontal controls for rtl
        if( config.rtl ) {
                var left = routes.left;
                routes.left = routes.right;
                routes.right = left;
        }

        return routes;

}

/**
 * Returns an object describing the available fragment
 * directions.
 *
 * @return {Object} two boolean properties: prev/next
 */
function availableFragments() {

        if( currentSlide && config.fragments ) {
                var fragments = currentSlide.querySelectorAll( '.fragment' );
                var hiddenFragments = currentSlide.querySelectorAll( '.fragment:not(.visible)' );

                return {
                        prev: fragments.length - hiddenFragments.length > 0,
                        next: !!hiddenFragments.length
                };
        }
        else {
                return { prev: false, next: false };
        }

}

/**
 * Enforces origin-specific format rules for embedded media.
 */
function formatEmbeddedContent() {

        var _appendParamToIframeSource = function( sourceAttribute, sourceURL, param ) {
                toArray( dom.slides.querySelectorAll( 'iframe['+ sourceAttribute +'*="'+ sourceURL +'"]' ) ).forEach( function( el ) {
                        var src = el.getAttribute( sourceAttribute );
                        if( src && src.indexOf( param ) === -1 ) {
                                el.setAttribute( sourceAttribute, src + ( !/\?/.test( src ) ? '?' : '&' ) + param );
                        }
                });
        };

        // YouTube frames must include "?enablejsapi=1"
        _appendParamToIframeSource( 'src', 'youtube.com/embed/', 'enablejsapi=1' );
        _appendParamToIframeSource( 'data-src', 'youtube.com/embed/', 'enablejsapi=1' );

        // Vimeo frames must include "?api=1"
        _appendParamToIframeSource( 'src', 'player.vimeo.com/', 'api=1' );
        _appendParamToIframeSource( 'data-src', 'player.vimeo.com/', 'api=1' );

}

/**
 * Start playback of any embedded content inside of
 * the targeted slide.
 */
function startEmbeddedContent( slide ) {

        if( slide && !isSpeakerNotes() ) {
                // Restart GIFs
                toArray( slide.querySelectorAll( 'img[src$=".gif"]' ) ).forEach( function( el ) {
                        // Setting the same unchanged source like this was confirmed
                        // to work in Chrome, FF & Safari
                        el.setAttribute( 'src', el.getAttribute( 'src' ) );
                } );

                // HTML5 media elements
                toArray( slide.querySelectorAll( 'video, audio' ) ).forEach( function( el ) {
                        if( el.hasAttribute( 'data-autoplay' ) && typeof el.play === 'function' ) {
                                el.play();
                        }
                } );

                // Normal iframes
                toArray( slide.querySelectorAll( 'iframe[src]' ) ).forEach( function( el ) {
                        startEmbeddedIframe( { target: el } );
                } );

                // Lazy loading iframes
                toArray( slide.querySelectorAll( 'iframe[data-src]' ) ).forEach( function( el ) {
                        if( el.getAttribute( 'src' ) !== el.getAttribute( 'data-src' ) ) {
                                el.removeEventListener( 'load', startEmbeddedIframe ); // remove first to avoid dupes
                                el.addEventListener( 'load', startEmbeddedIframe );
                                el.setAttribute( 'src', el.getAttribute( 'data-src' ) );
                        }
                } );
        }

}

/**
 * "Starts" the content of an embedded iframe using the
 * postmessage API.
 */
function startEmbeddedIframe( event ) {

        var iframe = event.target;

        // YouTube postMessage API
        if( /youtube\.com\/embed\//.test( iframe.getAttribute( 'src' ) ) && iframe.hasAttribute( 'data-autoplay' ) ) {
                iframe.contentWindow.postMessage( '{"event":"command","func":"playVideo","args":""}', '*' );
        }
        // Vimeo postMessage API
        else if( /player\.vimeo\.com\//.test( iframe.getAttribute( 'src' ) ) && iframe.hasAttribute( 'data-autoplay' ) ) {
                iframe.contentWindow.postMessage( '{"method":"play"}', '*' );
        }
        // Generic postMessage API
        else {
                iframe.contentWindow.postMessage( 'slide:start', '*' );
        }

}

/**
 * Stop playback of any embedded content inside of
 * the targeted slide.
 */
function stopEmbeddedContent( slide ) {

        if( slide && slide.parentNode ) {
                // HTML5 media elements
                toArray( slide.querySelectorAll( 'video, audio' ) ).forEach( function( el ) {
                        if( !el.hasAttribute( 'data-ignore' ) && typeof el.pause === 'function' ) {
                                el.pause();
                        }
                } );

                // Generic postMessage API for non-lazy loaded iframes
                toArray( slide.querySelectorAll( 'iframe' ) ).forEach( function( el ) {
                        el.contentWindow.postMessage( 'slide:stop', '*' );
                        el.removeEventListener( 'load', startEmbeddedIframe );
                });

                // YouTube postMessage API
                toArray( slide.querySelectorAll( 'iframe[src*="youtube.com/embed/"]' ) ).forEach( function( el ) {
                        if( !el.hasAttribute( 'data-ignore' ) && typeof el.contentWindow.postMessage === 'function' ) {
                                el.contentWindow.postMessage( '{"event":"command","func":"pauseVideo","args":""}', '*' );
                        }
                });

                // Vimeo postMessage API
                toArray( slide.querySelectorAll( 'iframe[src*="player.vimeo.com/"]' ) ).forEach( function( el ) {
                        if( !el.hasAttribute( 'data-ignore' ) && typeof el.contentWindow.postMessage === 'function' ) {
                                el.contentWindow.postMessage( '{"method":"pause"}', '*' );
                        }
                });

                // Lazy loading iframes
                toArray( slide.querySelectorAll( 'iframe[data-src]' ) ).forEach( function( el ) {
                        // Only removing the src doesn't actually unload the frame
                        // in all browsers (Firefox) so we set it to blank first
                        el.setAttribute( 'src', 'about:blank' );
                        el.removeAttribute( 'src' );
                } );
        }

}

/**
 * Returns the number of past slides. This can be used as a global
 * flattened index for slides.
 */
function getSlidePastCount() {

        var horizontalSlides = toArray( dom.wrapper.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR ) );

        // The number of past slides
        var pastCount = 0;

        // Step through all slides and count the past ones
        mainLoop: for( var i = 0; i < horizontalSlides.length; i++ ) {

                var horizontalSlide = horizontalSlides[i];
                var verticalSlides = toArray( horizontalSlide.querySelectorAll( 'section' ) );

                for( var j = 0; j < verticalSlides.length; j++ ) {

                        // Stop as soon as we arrive at the present
                        if( verticalSlides[j].classList.contains( 'present' ) ) {
                                break mainLoop;
                        }

                        pastCount++;

                }

                // Stop as soon as we arrive at the present
                if( horizontalSlide.classList.contains( 'present' ) ) {
                        break;
                }

                // Don't count the wrapping section for vertical slides
                if( horizontalSlide.classList.contains( 'stack' ) === false ) {
                        pastCount++;
                }

        }

        return pastCount;

}

/**
 * Returns a value ranging from 0-1 that represents
 * how far into the presentation we have navigated.
 */
function getProgress() {

        // The number of past and total slides
        var totalCount = getTotalSlides();
        var pastCount = getSlidePastCount();

        if( currentSlide ) {

                var allFragments = currentSlide.querySelectorAll( '.fragment' );

                // If there are fragments in the current slide those should be
                // accounted for in the progress.
                if( allFragments.length > 0 ) {
                        var visibleFragments = currentSlide.querySelectorAll( '.fragment.visible' );

                        // This value represents how big a portion of the slide progress
                        // that is made up by its fragments (0-1)
                        var fragmentWeight = 0.9;

                        // Add fragment progress to the past slide count
                        pastCount += ( visibleFragments.length / allFragments.length ) * fragmentWeight;
                }

        }

        return pastCount / ( totalCount - 1 );

}

/**
 * Checks if this presentation is running inside of the
 * speaker notes window.
 */
function isSpeakerNotes() {

        return !!window.location.search.match( /receiver/gi );

}

/**
 * Reads the current URL (hash) and navigates accordingly.
 */
function readURL() {

        var hash = window.location.hash;

        // Attempt to parse the hash as either an index or name
        var bits = hash.slice( 2 ).split( '/' ),
                name = hash.replace( /#|\//gi, '' );

        // If the first bit is invalid and there is a name we can
        // assume that this is a named link
        if( isNaN( parseInt( bits[0], 10 ) ) && name.length ) {
                var element;

                // Ensure the named link is a valid HTML ID attribute
                if( /^[a-zA-Z][\w:.-]*$/.test( name ) ) {
                        // Find the slide with the specified ID
                        element = document.getElementById( name );
                }

                if( element ) {
                        // Find the position of the named slide and navigate to it
                        var indices = Reveal.getIndices( element );
                        slide( indices.h, indices.v );
                }
                // If the slide doesn't exist, navigate to the current slide
                else {
                        slide( indexh || 0, indexv || 0 );
                }
        }
        else {
                // Read the index components of the hash
                var h = parseInt( bits[0], 10 ) || 0,
                        v = parseInt( bits[1], 10 ) || 0;

                if( h !== indexh || v !== indexv ) {
                        slide( h, v );
                }
        }

}

/**
 * Updates the page URL (hash) to reflect the current
 * state.
 *
 * @param {Number} delay The time in ms to wait before
 * writing the hash
 */
function writeURL( delay ) {

        if( config.history ) {

                // Make sure there's never more than one timeout running
                clearTimeout( writeURLTimeout );

                // If a delay is specified, timeout this call
                if( typeof delay === 'number' ) {
                        writeURLTimeout = setTimeout( writeURL, delay );
                }
                else if( currentSlide ) {
                        var url = '/';

                        // Attempt to create a named link based on the slide's ID
                        var id = currentSlide.getAttribute( 'id' );
                        if( id ) {
                                id = id.toLowerCase();
                                id = id.replace( /[^a-zA-Z0-9\-\_\:\.]/g, '' );
                        }

                        // If the current slide has an ID, use that as a named link
                        if( typeof id === 'string' && id.length ) {
                                url = '/' + id;
                        }
                        // Otherwise use the /h/v index
                        else {
                                if( indexh > 0 || indexv > 0 ) url += indexh;
                                if( indexv > 0 ) url += '/' + indexv;
                        }

                        window.location.hash = url;
                }
        }

}

/**
 * Retrieves the h/v location of the current, or specified,
 * slide.
 *
 * @param {HTMLElement} slide If specified, the returned
 * index will be for this slide rather than the currently
 * active one
 *
 * @return {Object} { h: <int>, v: <int>, f: <int> }
 */
function getIndices( slide ) {

        // By default, return the current indices
        var h = indexh,
                v = indexv,
                f;

        // If a slide is specified, return the indices of that slide
        if( slide ) {
                var isVertical = isVerticalSlide( slide );
                var slideh = isVertical ? slide.parentNode : slide;

                // Select all horizontal slides
                var horizontalSlides = toArray( dom.wrapper.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR ) );

                // Now that we know which the horizontal slide is, get its index
                h = Math.max( horizontalSlides.indexOf( slideh ), 0 );

                // Assume we're not vertical
                v = undefined;

                // If this is a vertical slide, grab the vertical index
                if( isVertical ) {
                        v = Math.max( toArray( slide.parentNode.querySelectorAll( 'section' ) ).indexOf( slide ), 0 );
                }
        }

        if( !slide && currentSlide ) {
                var hasFragments = currentSlide.querySelectorAll( '.fragment' ).length > 0;
                if( hasFragments ) {
                        var currentFragment = currentSlide.querySelector( '.current-fragment' );
                        if( currentFragment && currentFragment.hasAttribute( 'data-fragment-index' ) ) {
                                f = parseInt( currentFragment.getAttribute( 'data-fragment-index' ), 10 );
                        }
                        else {
                                f = currentSlide.querySelectorAll( '.fragment.visible' ).length - 1;
                        }
                }
        }

        return { h: h, v: v, f: f };

}

/**
 * Retrieves the total number of slides in this presentation.
 */
function getTotalSlides() {

        return dom.wrapper.querySelectorAll( SLIDES_SELECTOR + ':not(.stack)' ).length;

}

/**
 * Returns the slide element matching the specified index.
 */
function getSlide( x, y ) {

        var horizontalSlide = dom.wrapper.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR )[ x ];
        var verticalSlides = horizontalSlide && horizontalSlide.querySelectorAll( 'section' );

        if( verticalSlides && verticalSlides.length && typeof y === 'number' ) {
                return verticalSlides ? verticalSlides[ y ] : undefined;
        }

        return horizontalSlide;

}

/**
 * Returns the background element for the given slide.
 * All slides, even the ones with no background properties
 * defined, have a background element so as long as the
 * index is valid an element will be returned.
 */
function getSlideBackground( x, y ) {

        // When printing to PDF the slide backgrounds are nested
        // inside of the slides
        if( isPrintingPDF() ) {
                var slide = getSlide( x, y );
                if( slide ) {
                        var background = slide.querySelector( '.slide-background' );
                        if( background && background.parentNode === slide ) {
                                return background;
                        }
                }

                return undefined;
        }

        var horizontalBackground = dom.wrapper.querySelectorAll( '.backgrounds>.slide-background' )[ x ];
        var verticalBackgrounds = horizontalBackground && horizontalBackground.querySelectorAll( '.slide-background' );

        if( verticalBackgrounds && verticalBackgrounds.length && typeof y === 'number' ) {
                return verticalBackgrounds ? verticalBackgrounds[ y ] : undefined;
        }

        return horizontalBackground;

}

/**
 * Retrieves the current state of the presentation as
 * an object. This state can then be restored at any
 * time.
 */
function getState() {

        var indices = getIndices();

        return {
                indexh: indices.h,
                indexv: indices.v,
                indexf: indices.f,
                paused: isPaused(),
                overview: isOverview()
        };

}

/**
 * Restores the presentation to the given state.
 *
 * @param {Object} state As generated by getState()
 */
function setState( state ) {

        if( typeof state === 'object' ) {
                slide( deserialize( state.indexh ), deserialize( state.indexv ), deserialize( state.indexf ) );

                var pausedFlag = deserialize( state.paused ),
                        overviewFlag = deserialize( state.overview );

                if( typeof pausedFlag === 'boolean' && pausedFlag !== isPaused() ) {
                        togglePause( pausedFlag );
                }

                if( typeof overviewFlag === 'boolean' && overviewFlag !== isOverview() ) {
                        toggleOverview( overviewFlag );
                }
        }

}

/**
 * Return a sorted fragments list, ordered by an increasing
 * "data-fragment-index" attribute.
 *
 * Fragments will be revealed in the order that they are returned by
 * this function, so you can use the index attributes to control the
 * order of fragment appearance.
 *
 * To maintain a sensible default fragment order, fragments are presumed
 * to be passed in document order. This function adds a "fragment-index"
 * attribute to each node if such an attribute is not already present,
 * and sets that attribute to an integer value which is the position of
 * the fragment within the fragments list.
 */
function sortFragments( fragments ) {

        fragments = toArray( fragments );

        var ordered = [],
                unordered = [],
                sorted = [];

        // Group ordered and unordered elements
        fragments.forEach( function( fragment, i ) {
                if( fragment.hasAttribute( 'data-fragment-index' ) ) {
                        var index = parseInt( fragment.getAttribute( 'data-fragment-index' ), 10 );

                        if( !ordered[index] ) {
                                ordered[index] = [];
                        }

                        ordered[index].push( fragment );
                }
                else {
                        unordered.push( [ fragment ] );
                }
        } );

        // Append fragments without explicit indices in their
        // DOM order
        ordered = ordered.concat( unordered );

        // Manually count the index up per group to ensure there
        // are no gaps
        var index = 0;

        // Push all fragments in their sorted order to an array,
        // this flattens the groups
        ordered.forEach( function( group ) {
                group.forEach( function( fragment ) {
                        sorted.push( fragment );
                        fragment.setAttribute( 'data-fragment-index', index );
                } );

                index ++;
        } );

        return sorted;

}

/**
 * Navigate to the specified slide fragment.
 *
 * @param {Number} index The index of the fragment that
 * should be shown, -1 means all are invisible
 * @param {Number} offset Integer offset to apply to the
 * fragment index
 *
 * @return {Boolean} true if a change was made in any
 * fragments visibility as part of this call
 */
function navigateFragment( index, offset ) {

        if( currentSlide && config.fragments ) {

                var fragments = sortFragments( currentSlide.querySelectorAll( '.fragment' ) );
                if( fragments.length ) {

                        // If no index is specified, find the current
                        if( typeof index !== 'number' ) {
                                var lastVisibleFragment = sortFragments( currentSlide.querySelectorAll( '.fragment.visible' ) ).pop();

                                if( lastVisibleFragment ) {
                                        index = parseInt( lastVisibleFragment.getAttribute( 'data-fragment-index' ) || 0, 10 );
                                }
                                else {
                                        index = -1;
                                }
                        }

                        // If an offset is specified, apply it to the index
                        if( typeof offset === 'number' ) {
                                index += offset;
                        }

                        var fragmentsShown = [],
                                fragmentsHidden = [];

                        toArray( fragments ).forEach( function( element, i ) {

                                if( element.hasAttribute( 'data-fragment-index' ) ) {
                                        i = parseInt( element.getAttribute( 'data-fragment-index' ), 10 );
                                }

                                // Visible fragments
                                if( i <= index ) {
                                        if( !element.classList.contains( 'visible' ) ) fragmentsShown.push( element );
                                        element.classList.add( 'visible' );
                                        element.classList.remove( 'current-fragment' );

                                        // Announce the fragments one by one to the Screen Reader
                                        dom.statusDiv.textContent = element.textContent;

                                        if( i === index ) {
                                                element.classList.add( 'current-fragment' );
                                        }
                                }
                                // Hidden fragments
                                else {
                                        if( element.classList.contains( 'visible' ) ) fragmentsHidden.push( element );
                                        element.classList.remove( 'visible' );
                                        element.classList.remove( 'current-fragment' );
                                }

                        } );

                        if( fragmentsHidden.length ) {
                                dispatchEvent( 'fragmenthidden', { fragment: fragmentsHidden[0], fragments: fragmentsHidden } );
                        }

                        if( fragmentsShown.length ) {
                                dispatchEvent( 'fragmentshown', { fragment: fragmentsShown[0], fragments: fragmentsShown } );
                        }

                        updateControls();
                        updateProgress();

                        return !!( fragmentsShown.length || fragmentsHidden.length );

                }

        }

        return false;

}

/**
 * Navigate to the next slide fragment.
 *
 * @return {Boolean} true if there was a next fragment,
 * false otherwise
 */
function nextFragment() {

        return navigateFragment( null, 1 );

}

/**
 * Navigate to the previous slide fragment.
 *
 * @return {Boolean} true if there was a previous fragment,
 * false otherwise
 */
function previousFragment() {

        return navigateFragment( null, -1 );

}

/**
 * Cues a new automated slide if enabled in the config.
 */
function cueAutoSlide() {

        cancelAutoSlide();

        if( currentSlide ) {

                var currentFragment = currentSlide.querySelector( '.current-fragment' );

                var fragmentAutoSlide = currentFragment ? currentFragment.getAttribute( 'data-autoslide' ) : null;
                var parentAutoSlide = currentSlide.parentNode ? currentSlide.parentNode.getAttribute( 'data-autoslide' ) : null;
                var slideAutoSlide = currentSlide.getAttribute( 'data-autoslide' );

                // Pick value in the following priority order:
                // 1. Current fragment's data-autoslide
                // 2. Current slide's data-autoslide
                // 3. Parent slide's data-autoslide
                // 4. Global autoSlide setting
                if( fragmentAutoSlide ) {
                        autoSlide = parseInt( fragmentAutoSlide, 10 );
                }
                else if( slideAutoSlide ) {
                        autoSlide = parseInt( slideAutoSlide, 10 );
                }
                else if( parentAutoSlide ) {
                        autoSlide = parseInt( parentAutoSlide, 10 );
                }
                else {
                        autoSlide = config.autoSlide;
                }

                // If there are media elements with data-autoplay,
                // automatically set the autoSlide duration to the
                // length of that media. Not applicable if the slide
                // is divided up into fragments.
                if( currentSlide.querySelectorAll( '.fragment' ).length === 0 ) {
                        toArray( currentSlide.querySelectorAll( 'video, audio' ) ).forEach( function( el ) {
                                if( el.hasAttribute( 'data-autoplay' ) ) {
                                        if( autoSlide && el.duration * 1000 > autoSlide ) {
                                                autoSlide = ( el.duration * 1000 ) + 1000;
                                        }
                                }
                        } );
                }

                // Cue the next auto-slide if:
                // - There is an autoSlide value
                // - Auto-sliding isn't paused by the user
                // - The presentation isn't paused
                // - The overview isn't active
                // - The presentation isn't over
                if( autoSlide && !autoSlidePaused && !isPaused() && !isOverview() && ( !Reveal.isLastSlide() || availableFragments().next || config.loop === true ) ) {
                        autoSlideTimeout = setTimeout( navigateNext, autoSlide );
                        autoSlideStartTime = Date.now();
                }

                if( autoSlidePlayer ) {
                        autoSlidePlayer.setPlaying( autoSlideTimeout !== -1 );
                }

        }

}

/**
 * Cancels any ongoing request to auto-slide.
 */
function cancelAutoSlide() {

        clearTimeout( autoSlideTimeout );
        autoSlideTimeout = -1;

}

function pauseAutoSlide() {

        if( autoSlide && !autoSlidePaused ) {
                autoSlidePaused = true;
                dispatchEvent( 'autoslidepaused' );
                clearTimeout( autoSlideTimeout );

                if( autoSlidePlayer ) {
                        autoSlidePlayer.setPlaying( false );
                }
        }

}

function resumeAutoSlide() {

        if( autoSlide && autoSlidePaused ) {
                autoSlidePaused = false;
                dispatchEvent( 'autoslideresumed' );
                cueAutoSlide();
        }

}

function navigateLeft() {

        // Reverse for RTL
        if( config.rtl ) {
                if( ( isOverview() || nextFragment() === false ) && availableRoutes().left ) {
                        slide( indexh + 1 );
                }
        }
        // Normal navigation
        else if( ( isOverview() || previousFragment() === false ) && availableRoutes().left ) {
                slide( indexh - 1 );
        }

}

function navigateRight() {

        // Reverse for RTL
        if( config.rtl ) {
                if( ( isOverview() || previousFragment() === false ) && availableRoutes().right ) {
                        slide( indexh - 1 );
                }
        }
        // Normal navigation
        else if( ( isOverview() || nextFragment() === false ) && availableRoutes().right ) {
                slide( indexh + 1 );
        }

}

function navigateUp() {

        // Prioritize hiding fragments
        if( ( isOverview() || previousFragment() === false ) && availableRoutes().up ) {
                slide( indexh, indexv - 1 );
        }

}

function navigateDown() {

        // Prioritize revealing fragments
        if( ( isOverview() || nextFragment() === false ) && availableRoutes().down ) {
                slide( indexh, indexv + 1 );
        }

}

/**
 * Navigates backwards, prioritized in the following order:
 * 1) Previous fragment
 * 2) Previous vertical slide
 * 3) Previous horizontal slide
 */
function navigatePrev() {

        // Prioritize revealing fragments
        if( previousFragment() === false ) {
                if( availableRoutes().up ) {
                        navigateUp();
                }
                else {
                        // Fetch the previous horizontal slide, if there is one
                        var previousSlide;

                        if( config.rtl ) {
                                previousSlide = toArray( dom.wrapper.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR + '.future' ) ).pop();
                        }
                        else {
                                previousSlide = toArray( dom.wrapper.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR + '.past' ) ).pop();
                        }

                        if( previousSlide ) {
                                var v = ( previousSlide.querySelectorAll( 'section' ).length - 1 ) || undefined;
                                var h = indexh - 1;
                                slide( h, v );
                        }
                }
        }

}

/**
 * The reverse of #navigatePrev().
 */
function navigateNext() {

        // Prioritize revealing fragments
        if( nextFragment() === false ) {
                if( availableRoutes().down ) {
                        navigateDown();
                }
                else if( config.rtl ) {
                        navigateLeft();
                }
                else {
                        navigateRight();
                }
        }

        // If auto-sliding is enabled we need to cue up
        // another timeout
        cueAutoSlide();

}

// --------------------------------------------------------------------//
// ----------------------------- EVENTS -------------------------------//
// --------------------------------------------------------------------//

/**
 * Called by all event handlers that are based on user
 * input.
 */
function onUserInput( event ) {

        if( config.autoSlideStoppable ) {
                pauseAutoSlide();
        }

}

/**
 * Handler for the document level 'keypress' event.
 */
function onDocumentKeyPress( event ) {

        // Check if the pressed key is question mark
        if( event.shiftKey && event.charCode === 63 ) {
                if( dom.overlay ) {
                        closeOverlay();
                }
                else {
                        showHelp( true );
                }
        }

}

/**
 * Handler for the document level 'keydown' event.
 */
function onDocumentKeyDown( event ) {

        // If there's a condition specified and it returns false,
        // ignore this event
        if( typeof config.keyboardCondition === 'function' && config.keyboardCondition() === false ) {
                return true;
        }

        // Remember if auto-sliding was paused so we can toggle it
        var autoSlideWasPaused = autoSlidePaused;

        onUserInput( event );

        // Check if there's a focused element that could be using
        // the keyboard
        var activeElementIsCE = document.activeElement && document.activeElement.contentEditable !== 'inherit';
        var activeElementIsInput = document.activeElement && document.activeElement.tagName && /input|textarea/i.test( document.activeElement.tagName );

        // Disregard the event if there's a focused element or a
        // keyboard modifier key is present
        if( activeElementIsCE || activeElementIsInput || (event.shiftKey && event.keyCode !== 32) || event.altKey || event.ctrlKey || event.metaKey ) return;

        // While paused only allow "unpausing" keyboard events (b and .)
        if( isPaused() && [66,190,191].indexOf( event.keyCode ) === -1 ) {
                return false;
        }

        var triggered = false;

        // 1. User defined key bindings
        if( typeof config.keyboard === 'object' ) {

                for( var key in config.keyboard ) {

                        // Check if this binding matches the pressed key
                        if( parseInt( key, 10 ) === event.keyCode ) {

                                var value = config.keyboard[ key ];

                                // Callback function
                                if( typeof value === 'function' ) {
                                        value.apply( null, [ event ] );
                                }
                                // String shortcuts to reveal.js API
                                else if( typeof value === 'string' && typeof Reveal[ value ] === 'function' ) {
                                        Reveal[ value ].call();
                                }

                                triggered = true;

                        }

                }

        }

        // 2. System defined key bindings
        if( triggered === false ) {

                // Assume true and try to prove false
                triggered = true;

                switch( event.keyCode ) {
                        // p, page up
                        case 80: case 33: navigatePrev(); break;
                        // n, page down
                        case 78: case 34: navigateNext(); break;
                        // h, left
                        case 72: case 37: navigateLeft(); break;
                        // l, right
                        case 76: case 39: navigateRight(); break;
                        // k, up
                        case 75: case 38: navigateUp(); break;
                        // j, down
                        case 74: case 40: navigateDown(); break;
                        // home
                        case 36: slide( 0 ); break;
                        // end
                        case 35: slide( Number.MAX_VALUE ); break;
                        // space
                        case 32: isOverview() ? deactivateOverview() : event.shiftKey ? navigatePrev() : navigateNext(); break;
                        // return
                        case 13: isOverview() ? deactivateOverview() : triggered = false; break;
                        // two-spot, semicolon, b, period, Logitech presenter tools "black screen" button
                        case 58: case 59: case 66: case 190: case 191: togglePause(); break;
                        // f
                        case 70: enterFullscreen(); break;
                        // a
                        case 65: if ( config.autoSlideStoppable ) toggleAutoSlide( autoSlideWasPaused ); break;
                        default:
                                triggered = false;
                }

        }

        // If the input resulted in a triggered action we should prevent
        // the browsers default behavior
        if( triggered ) {
                event.preventDefault && event.preventDefault();
        }
        // ESC or O key
        else if ( ( event.keyCode === 27 || event.keyCode === 79 ) && features.transforms3d ) {
                if( dom.overlay ) {
                        closeOverlay();
                }
                else {
                        toggleOverview();
                }

                event.preventDefault && event.preventDefault();
        }

        // If auto-sliding is enabled we need to cue up
        // another timeout
        cueAutoSlide();

}

/**
 * Handler for the 'touchstart' event, enables support for
 * swipe and pinch gestures.
 */
function onTouchStart( event ) {

        touch.startX = event.touches[0].clientX;
        touch.startY = event.touches[0].clientY;
        touch.startCount = event.touches.length;

        // If there's two touches we need to memorize the distance
        // between those two points to detect pinching
        if( event.touches.length === 2 && config.overview ) {
                touch.startSpan = distanceBetween( {
                        x: event.touches[1].clientX,
                        y: event.touches[1].clientY
                }, {
                        x: touch.startX,
                        y: touch.startY
                } );
        }

}

/**
 * Handler for the 'touchmove' event.
 */
function onTouchMove( event ) {

        // Each touch should only trigger one action
        if( !touch.captured ) {
                onUserInput( event );

                var currentX = event.touches[0].clientX;
                var currentY = event.touches[0].clientY;

                // If the touch started with two points and still has
                // two active touches; test for the pinch gesture
                if( event.touches.length === 2 && touch.startCount === 2 && config.overview ) {

                        // The current distance in pixels between the two touch points
                        var currentSpan = distanceBetween( {
                                x: event.touches[1].clientX,
                                y: event.touches[1].clientY
                        }, {
                                x: touch.startX,
                                y: touch.startY
                        } );

                        // If the span is larger than the desire amount we've got
                        // ourselves a pinch
                        if( Math.abs( touch.startSpan - currentSpan ) > touch.threshold ) {
                                touch.captured = true;

                                if( currentSpan < touch.startSpan ) {
                                        activateOverview();
                                }
                                else {
                                        deactivateOverview();
                                }
                        }

                        event.preventDefault();

                }
                // There was only one touch point, look for a swipe
                else if( event.touches.length === 1 && touch.startCount !== 2 ) {

                        var deltaX = currentX - touch.startX,
                                deltaY = currentY - touch.startY;

                        if( deltaX > touch.threshold && Math.abs( deltaX ) > Math.abs( deltaY ) ) {
                                touch.captured = true;
                                navigateLeft();
                        }
                        else if( deltaX < -touch.threshold && Math.abs( deltaX ) > Math.abs( deltaY ) ) {
                                touch.captured = true;
                                navigateRight();
                        }
                        else if( deltaY > touch.threshold ) {
                                touch.captured = true;
                                navigateUp();
                        }
                        else if( deltaY < -touch.threshold ) {
                                touch.captured = true;
                                navigateDown();
                        }

                        // If we're embedded, only block touch events if they have
                        // triggered an action
                        if( config.embedded ) {
                                if( touch.captured || isVerticalSlide( currentSlide ) ) {
                                        event.preventDefault();
                                }
                        }
                        // Not embedded? Block them all to avoid needless tossing
                        // around of the viewport in iOS
                        else {
                                event.preventDefault();
                        }

                }
        }
        // There's a bug with swiping on some Android devices unless
        // the default action is always prevented
        else if( navigator.userAgent.match( /android/gi ) ) {
                event.preventDefault();
        }

}

/**
 * Handler for the 'touchend' event.
 */
function onTouchEnd( event ) {

        touch.captured = false;

}

/**
 * Convert pointer down to touch start.
 */
function onPointerDown( event ) {

        if( event.pointerType === event.MSPOINTER_TYPE_TOUCH || event.pointerType === "touch" ) {
                event.touches = [{ clientX: event.clientX, clientY: event.clientY }];
                onTouchStart( event );
        }

}

/**
 * Convert pointer move to touch move.
 */
function onPointerMove( event ) {

        if( event.pointerType === event.MSPOINTER_TYPE_TOUCH || event.pointerType === "touch" )  {
                event.touches = [{ clientX: event.clientX, clientY: event.clientY }];
                onTouchMove( event );
        }

}

/**
 * Convert pointer up to touch end.
 */
function onPointerUp( event ) {

        if( event.pointerType === event.MSPOINTER_TYPE_TOUCH || event.pointerType === "touch" )  {
                event.touches = [{ clientX: event.clientX, clientY: event.clientY }];
                onTouchEnd( event );
        }

}

/**
 * Handles mouse wheel scrolling, throttled to avoid skipping
 * multiple slides.
 */
function onDocumentMouseScroll( event ) {

        if( Date.now() - lastMouseWheelStep > 600 ) {

                lastMouseWheelStep = Date.now();

                var delta = event.detail || -event.wheelDelta;
                if( delta > 0 ) {
                        navigateNext();
                }
                else {
                        navigatePrev();
                }

        }

}

/**
 * Clicking on the progress bar results in a navigation to the
 * closest approximate horizontal slide using this equation:
 *
 * ( clickX / presentationWidth ) * numberOfSlides
 */
function onProgressClicked( event ) {

        onUserInput( event );

        event.preventDefault();

        var slidesTotal = toArray( dom.wrapper.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR ) ).length;
        var slideIndex = Math.floor( ( event.clientX / dom.wrapper.offsetWidth ) * slidesTotal );

        if( config.rtl ) {
                slideIndex = slidesTotal - slideIndex;
        }

        slide( slideIndex );

}

/**
 * Event handler for navigation control buttons.
 */
function onNavigateLeftClicked( event ) { event.preventDefault(); onUserInput(); navigateLeft(); }
function onNavigateRightClicked( event ) { event.preventDefault(); onUserInput(); navigateRight(); }
function onNavigateUpClicked( event ) { event.preventDefault(); onUserInput(); navigateUp(); }
function onNavigateDownClicked( event ) { event.preventDefault(); onUserInput(); navigateDown(); }
function onNavigatePrevClicked( event ) { event.preventDefault(); onUserInput(); navigatePrev(); }
function onNavigateNextClicked( event ) { event.preventDefault(); onUserInput(); navigateNext(); }

/**
 * Handler for the window level 'hashchange' event.
 */
function onWindowHashChange( event ) {

        readURL();

}

/**
 * Handler for the window level 'resize' event.
 */
function onWindowResize( event ) {

        layout();

}

/**
 * Handle for the window level 'visibilitychange' event.
 */
function onPageVisibilityChange( event ) {

        var isHidden =  document.webkitHidden ||
                document.msHidden ||
                document.hidden;

        // If, after clicking a link or similar and we're coming back,
        // focus the document.body to ensure we can use keyboard shortcuts
        if( isHidden === false && document.activeElement !== document.body ) {
                // Not all elements support .blur() - SVGs among them.
                if( typeof document.activeElement.blur === 'function' ) {
                        document.activeElement.blur();
                }
                document.body.focus();
        }

}

/**
 * Invoked when a slide is and we're in the overview.
 */
function onOverviewSlideClicked( event ) {

        // TODO There's a bug here where the event listeners are not
        // removed after deactivating the overview.
        if( eventsAreBound && isOverview() ) {
                event.preventDefault();

                var element = event.target;

                while( element && !element.nodeName.match( /section/gi ) ) {
                        element = element.parentNode;
                }

                if( element && !element.classList.contains( 'disabled' ) ) {

                        deactivateOverview();

                        if( element.nodeName.match( /section/gi ) ) {
                                var h = parseInt( element.getAttribute( 'data-index-h' ), 10 ),
                                        v = parseInt( element.getAttribute( 'data-index-v' ), 10 );

                                slide( h, v );
                        }

                }
        }

}

/**
 * Handles clicks on links that are set to preview in the
 * iframe overlay.
 */
function onPreviewLinkClicked( event ) {

        if( event.currentTarget && event.currentTarget.hasAttribute( 'href' ) ) {
                var url = event.currentTarget.getAttribute( 'href' );
                if( url ) {
                        showPreview( url );
                        event.preventDefault();
                }
        }

}

/**
 * Handles click on the auto-sliding controls element.
 */
function onAutoSlidePlayerClick( event ) {

        // Replay
        if( Reveal.isLastSlide() && config.loop === false ) {
                slide( 0, 0 );
                resumeAutoSlide();
        }
        // Resume
        else if( autoSlidePaused ) {
                resumeAutoSlide();
        }
        // Pause
        else {
                pauseAutoSlide();
        }

}

// --------------------------------------------------------------------//
// ------------------------ PLAYBACK COMPONENT ------------------------//
// --------------------------------------------------------------------//

/**
 * Constructor for the playback component, which displays
 * play/pause/progress controls.
 *
 * @param {HTMLElement} container The component will append
 * itself to this
 * @param {Function} progressCheck A method which will be
 * called frequently to get the current progress on a range
 * of 0-1
 */
function Playback( container, progressCheck ) {

        // Cosmetics
        this.diameter = 50;
        this.thickness = 3;

        // Flags if we are currently playing
        this.playing = false;

        // Current progress on a 0-1 range
        this.progress = 0;

        // Used to loop the animation smoothly
        this.progressOffset = 1;

        this.container = container;
        this.progressCheck = progressCheck;

        this.canvas = document.createElement( 'canvas' );
        this.canvas.className = 'playback';
        this.canvas.width = this.diameter;
        this.canvas.height = this.diameter;
        this.context = this.canvas.getContext( '2d' );

        this.container.appendChild( this.canvas );

        this.render();

}

Playback.prototype.setPlaying = function( value ) {

        var wasPlaying = this.playing;

        this.playing = value;

        // Start repainting if we weren't already
        if( !wasPlaying && this.playing ) {
                this.animate();
        }
        else {
                this.render();
        }

};

Playback.prototype.animate = function() {

        var progressBefore = this.progress;

        this.progress = this.progressCheck();

        // When we loop, offset the progress so that it eases
        // smoothly rather than immediately resetting
        if( progressBefore > 0.8 && this.progress < 0.2 ) {
                this.progressOffset = this.progress;
        }

        this.render();

        if( this.playing ) {
                features.requestAnimationFrameMethod.call( window, this.animate.bind( this ) );
        }

};

/**
 * Renders the current progress and playback state.
 */
Playback.prototype.render = function() {

        var progress = this.playing ? this.progress : 0,
                radius = ( this.diameter / 2 ) - this.thickness,
                x = this.diameter / 2,
                y = this.diameter / 2,
                iconSize = 14;

        // Ease towards 1
        this.progressOffset += ( 1 - this.progressOffset ) * 0.1;

        var endAngle = ( - Math.PI / 2 ) + ( progress * ( Math.PI * 2 ) );
        var startAngle = ( - Math.PI / 2 ) + ( this.progressOffset * ( Math.PI * 2 ) );

        this.context.save();
        this.context.clearRect( 0, 0, this.diameter, this.diameter );

        // Solid background color
        this.context.beginPath();
        this.context.arc( x, y, radius + 2, 0, Math.PI * 2, false );
        this.context.fillStyle = 'rgba( 0, 0, 0, 0.4 )';
        this.context.fill();

        // Draw progress track
        this.context.beginPath();
        this.context.arc( x, y, radius, 0, Math.PI * 2, false );
        this.context.lineWidth = this.thickness;
        this.context.strokeStyle = '#666';
        this.context.stroke();

        if( this.playing ) {
                // Draw progress on top of track
                this.context.beginPath();
                this.context.arc( x, y, radius, startAngle, endAngle, false );
                this.context.lineWidth = this.thickness;
                this.context.strokeStyle = '#fff';
                this.context.stroke();
        }

        this.context.translate( x - ( iconSize / 2 ), y - ( iconSize / 2 ) );

        // Draw play/pause icons
        if( this.playing ) {
                this.context.fillStyle = '#fff';
                this.context.fillRect( 0, 0, iconSize / 2 - 2, iconSize );
                this.context.fillRect( iconSize / 2 + 2, 0, iconSize / 2 - 2, iconSize );
        }
        else {
                this.context.beginPath();
                this.context.translate( 2, 0 );
                this.context.moveTo( 0, 0 );
                this.context.lineTo( iconSize - 2, iconSize / 2 );
                this.context.lineTo( 0, iconSize );
                this.context.fillStyle = '#fff';
                this.context.fill();
        }

        this.context.restore();

};

Playback.prototype.on = function( type, listener ) {
        this.canvas.addEventListener( type, listener, false );
};

Playback.prototype.off = function( type, listener ) {
        this.canvas.removeEventListener( type, listener, false );
};

Playback.prototype.destroy = function() {

        this.playing = false;

        if( this.canvas.parentNode ) {
                this.container.removeChild( this.canvas );
        }

};

// --------------------------------------------------------------------//
// ------------------------------- API --------------------------------//
// --------------------------------------------------------------------//

Reveal = {
        initialize: initialize,
        configure: configure,
        sync: sync,

        // Navigation methods
        slide: slide,
        left: navigateLeft,
        right: navigateRight,
        up: navigateUp,
        down: navigateDown,
        prev: navigatePrev,
        next: navigateNext,

        // Fragment methods
        navigateFragment: navigateFragment,
        prevFragment: previousFragment,
        nextFragment: nextFragment,

        // Deprecated aliases
        navigateTo: slide,
        navigateLeft: navigateLeft,
        navigateRight: navigateRight,
        navigateUp: navigateUp,
        navigateDown: navigateDown,
        navigatePrev: navigatePrev,
        navigateNext: navigateNext,

        // Forces an update in slide layout
        layout: layout,

        // Returns an object with the available routes as booleans (left/right/top/bottom)
        availableRoutes: availableRoutes,

        // Returns an object with the available fragments as booleans (prev/next)
        availableFragments: availableFragments,

        // Toggles the overview mode on/off
        toggleOverview: toggleOverview,

        // Toggles the "black screen" mode on/off
        togglePause: togglePause,

        // Toggles the auto slide mode on/off
        toggleAutoSlide: toggleAutoSlide,

        // State checks
        isOverview: isOverview,
        isPaused: isPaused,
        isAutoSliding: isAutoSliding,

        // Adds or removes all internal event listeners (such as keyboard)
        addEventListeners: addEventListeners,
        removeEventListeners: removeEventListeners,

        // Facility for persisting and restoring the presentation state
        getState: getState,
        setState: setState,

        // Presentation progress on range of 0-1
        getProgress: getProgress,

        // Returns the indices of the current, or specified, slide
        getIndices: getIndices,

        getTotalSlides: getTotalSlides,

        // Returns the slide element at the specified index
        getSlide: getSlide,

        // Returns the slide background element at the specified index
        getSlideBackground: getSlideBackground,

        // Returns the previous slide element, may be null
        getPreviousSlide: function() {
                return previousSlide;
        },

        // Returns the current slide element
        getCurrentSlide: function() {
                return currentSlide;
        },

        // Returns the current scale of the presentation content
        getScale: function() {
                return scale;
        },

        // Returns the current configuration object
        getConfig: function() {
                return config;
        },

        // Helper method, retrieves query string as a key/value hash
        getQueryHash: function() {
                var query = {};

                location.search.replace( /[A-Z0-9]+?=([\w\.%-]*)/gi, function(a) {
                        query[ a.split( '=' ).shift() ] = a.split( '=' ).pop();
                } );

                // Basic deserialization
                for( var i in query ) {
                        var value = query[ i ];

                        query[ i ] = deserialize( unescape( value ) );
                }

                return query;
        },

        // Returns true if we're currently on the first slide
        isFirstSlide: function() {
                return ( indexh === 0 && indexv === 0 );
        },

        // Returns true if we're currently on the last slide
        isLastSlide: function() {
                if( currentSlide ) {
                        // Does this slide has next a sibling?
                        if( currentSlide.nextElementSibling ) return false;

                        // If it's vertical, does its parent have a next sibling?
                        if( isVerticalSlide( currentSlide ) && currentSlide.parentNode.nextElementSibling ) return false;

                        return true;
                }

                return false;
        },

        // Checks if reveal.js has been loaded and is ready for use
        isReady: function() {
                return loaded;
        },

        // Forward event binding to the reveal DOM element
        addEventListener: function( type, listener, useCapture ) {
                if( 'addEventListener' in window ) {
                        ( dom.wrapper || document.querySelector( '.reveal' ) ).addEventListener( type, listener, useCapture );
                }
        },
        removeEventListener: function( type, listener, useCapture ) {
                if( 'addEventListener' in window ) {
                        ( dom.wrapper || document.querySelector( '.reveal' ) ).removeEventListener( type, listener, useCapture );
                }
        },

        // Programatically triggers a keyboard event
        triggerKey: function( keyCode ) {
                onDocumentKeyDown( { keyCode: keyCode } );
        }
};

return Reveal;

}));