reveal.js

/*!
 * reveal.js
 * http://lab.hakim.se/reveal-js
 * MIT licensed
 *
 * Copyright (C) 2013 Hakim El Hattab, http://hakim.se
 */
var Reveal = (function(){

	'use strict';

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

		// Configurations 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: 1.0,

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

			// Display a presentation progress bar
			progress: true,

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

			// Enable keyboard shortcuts for navigation
			keyboard: true,

			// Enable the slide overview mode
			overview: true,

			// Vertical centring 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,

			// 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,

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

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

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

			// Theme (see /css/theme)
			theme: null,

			// Transition style
			transition: 'default', // default/cube/page/concave/zoom/linear/fade/none

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

			// Transition style for full page slide backgrounds
			backgroundTransition: 'default', // default/linear/none

			// Script dependencies to load
			dependencies: []
		},

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

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

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

		// 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,

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

		// Client support for CSS 3D transforms, see #checkCapabilities()
		supports3DTransforms,

		// Client support for CSS 2D transforms, see #checkCapabilities()
		supports2DTransforms,

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

		// Throttles mouse wheel navigation
		lastMouseWheelStep = 0,

		// An interval used to automatically move on to the next slide
		autoSlideTimeout = 0,

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

		// A delay used to activate the overview mode
		activateOverviewTimeout = 0,

		// A delay used to deactivate the overview mode
		deactivateOverviewTimeout = 0,

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

		// Holds information about the currently ongoing touch input
		touch = {
			startX: 0,
			startY: 0,
			startSpan: 0,
			startCount: 0,
			handled: false,
			threshold: 80
		};

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

		checkCapabilities();

		if( !supports2DTransforms && !supports3DTransforms ) {
			document.body.setAttribute( 'class', 'no-transforms' );

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

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

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

		// 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() {

		supports3DTransforms =  '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;

		supports2DTransforms =  '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;

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

	}

	/**
	 * 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() {

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

		// Background element
		if( !document.querySelector( '.reveal .backgrounds' ) ) {
			dom.background = document.createElement( 'div' );
			dom.background.classList.add( 'backgrounds' );
			dom.wrapper.appendChild( dom.background );
		}

		// Progress bar
		if( !dom.wrapper.querySelector( '.progress' ) ) {
			var progressElement = document.createElement( 'div' );
			progressElement.classList.add( 'progress' );
			progressElement.innerHTML = '<span></span>';
			dom.wrapper.appendChild( progressElement );
		}

		// Arrow controls
		if( !dom.wrapper.querySelector( '.controls' ) ) {
			var controlsElement = document.createElement( 'aside' );
			controlsElement.classList.add( 'controls' );
			controlsElement.innerHTML = '<div class="navigate-left"></div>' +
										'<div class="navigate-right"></div>' +
										'<div class="navigate-up"></div>' +
										'<div class="navigate-down"></div>';
			dom.wrapper.appendChild( controlsElement );
		}

		// State background element [DEPRECATED]
		if( !dom.wrapper.querySelector( '.state-background' ) ) {
			var stateBackgroundElement = document.createElement( 'div' );
			stateBackgroundElement.classList.add( 'state-background' );
			dom.wrapper.appendChild( stateBackgroundElement );
		}

		// Overlay graphic which is displayed during the paused mode
		if( !dom.wrapper.querySelector( '.pause-overlay' ) ) {
			var pausedElement = document.createElement( 'div' );
			pausedElement.classList.add( 'pause-overlay' );
			dom.wrapper.appendChild( pausedElement );
		}

		// Cache references to elements
		dom.progress = document.querySelector( '.reveal .progress' );
		dom.progressbar = document.querySelector( '.reveal .progress span' );

		if ( config.controls ) {
			dom.controls = document.querySelector( '.reveal .controls' );

			// 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' ) );
		}

	}

	/**
	 * 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() {

		if( isPrintingPDF() ) {
			document.body.classList.add( 'print-pdf' );
		}

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

		// Helper method for creating a background element for the
		// given slide
		function _createBackground( slide, container ) {

			var data = {
				background: slide.getAttribute( 'data-background' ),
				backgroundSize: slide.getAttribute( 'data-background-size' ),
				backgroundImage: slide.getAttribute( 'data-background-image' ),
				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' );
			element.className = 'slide-background';

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

			// Additional and optional background properties
			if( data.backgroundSize ) element.style.backgroundSize = data.backgroundSize;
			if( data.backgroundImage ) element.style.backgroundImage = 'url("' + data.backgroundImage + '")';
			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 );

			return element;

		}

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

			var backgroundStack;

			if( isPrintingPDF() ) {
				backgroundStack = _createBackground( slideh, slideh );
			}
			else {
				backgroundStack = _createBackground( slideh, dom.background );
			}

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

				if( isPrintingPDF() ) {
					_createBackground( slidev, slidev );
				}
				else {
					_createBackground( slidev, backgroundStack );
				}

			} );

		} );

	}

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

		if( /iphone|ipod|android/gi.test( navigator.userAgent ) && !/crios/gi.test( navigator.userAgent ) ) {
			// Events that should trigger the address bar to hide
			window.addEventListener( 'load', removeAddressBar, false );
			window.addEventListener( 'orientationchange', removeAddressBar, false );
		}

	}

	/**
	 * 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 = [];

		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 );
				}

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

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

			start();
		}

		if( scripts.length ) {
			head.ready( proceed );

			// 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();

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

		// Read the initial hash
		readURL();

		// Notify listeners that the presentation is ready but use a 1ms
		// timeout to ensure it's not fired synchronously after #initialize()
		setTimeout( function() {
			dispatchEvent( 'ready', {
				'indexh': indexh,
				'indexv': indexv,
				'currentSlide': currentSlide
			} );
		}, 1 );

	}

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

		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( supports3DTransforms === 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 );

		if( dom.controls ) {
			dom.controls.style.display = ( config.controls && dom.controls ) ? 'block' : 'none';
		}

		if( dom.progress ) {
			dom.progress.style.display = ( config.progress && dom.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' );
		}

		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]' );
		}

		// Load the theme in the config, if it's not already loaded
		if( config.theme && dom.theme ) {
			var themeURL = dom.theme.getAttribute( 'href' );
			var themeFinder = /[^\/]*?(?=\.css)/;
			var themeName = themeURL.match(themeFinder)[0];

			if(  config.theme !== themeName ) {
				themeURL = themeURL.replace(themeFinder, config.theme);
				dom.theme.setAttribute( 'href', themeURL );
			}
		}

		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.msPointerEnabled ) {
				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 );
		}

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

		if ( config.controls && dom.controls ) {
			[ 'touchstart', 'click' ].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 );
		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 );

		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 );
		}

		if ( config.controls && dom.controls ) {
			[ '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 );

	}

	/**
	 * 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 );

	}

	/**
	 * 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( child.style.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;

	}

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

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

	}

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

		if( window.orientation === 0 ) {
			document.documentElement.style.overflow = 'scroll';
			document.body.style.height = '120%';
		}
		else {
			document.documentElement.style.overflow = '';
			document.body.style.height = '100%';
		}

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

	}

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

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

	}

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

		if( supports3DTransforms && !( 'msPerspective' in document.body.style ) ) {
			var anchors = document.querySelectorAll( SLIDES_SELECTOR + ' a:not(.image)' );

			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 = document.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 openPreview( url ) {

		closePreview();

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

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

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

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

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

	}

	/**
	 * Closes the iframe preview window.
	 */
	function closePreview() {

		if( dom.preview ) {
			dom.preview.setAttribute( 'src', '' );
			dom.preview.parentNode.removeChild( dom.preview );
			dom.preview = null;
		}

	}

	/**
	 * 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 ) {

		var a = toArray( fragments );

		a.forEach( function( el, idx ) {
			if( !el.hasAttribute( 'data-fragment-index' ) ) {
				el.setAttribute( 'data-fragment-index', idx );
			}
		} );

		a.sort( function( l, r ) {
			return l.getAttribute( 'data-fragment-index' ) - r.getAttribute( 'data-fragment-index');
		} );

		return a;

	}

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

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

			// Available space to scale within
			var availableWidth = dom.wrapper.offsetWidth,
				availableHeight = dom.wrapper.offsetHeight;

			// Reduce available space by margin
			availableWidth -= ( availableHeight * config.margin );
			availableHeight -= ( availableHeight * config.margin );

			// Dimensions of the content
			var slideWidth = config.width,
				slideHeight = config.height;

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

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

			dom.slides.style.width = slideWidth + 'px';
			dom.slides.style.height = slideHeight + 'px';

			// Determine scale of content to fit within available space
			scale = Math.min( availableWidth / slideWidth, availableHeight / slideHeight );

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

			// Prefer applying scale via zoom since Chrome blurs scaled content
			// with nested transforms
			if( typeof dom.slides.style.zoom !== 'undefined' && !navigator.userAgent.match( /(iphone|ipod|ipad|android)/gi ) ) {
				dom.slides.style.zoom = scale;
			}
			// Apply scale transform as a fallback
			else {
				var transform = 'translate(-50%, -50%) scale('+ scale +') translate(50%, 50%)';

				dom.slides.style.WebkitTransform = transform;
				dom.slides.style.MozTransform = transform;
				dom.slides.style.msTransform = transform;
				dom.slides.style.OTransform = transform;
				dom.slides.style.transform = transform;
			}

			// Select all slides, vertical and horizontal
			var slides = toArray( document.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 ) {
					// 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( - ( getAbsoluteHeight( slide ) / 2 ) - 20, -slideHeight / 2 ) + 'px';
					}
				}
				else {
					slide.style.top = '';
				}

			}

			updateProgress();

		}

	}

	/**
	 * 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