reveal.js

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

		return index;

	}

	/**
	 * Updates the progress bar to reflect the current slide.
	 */
	function updateProgress() {
		// Update progress if enabled
		if( config.progress && dom.progress ) {

			var horizontalSlides = toArray( document.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR ) );

			// The number of past and total slides
			var totalCount = document.querySelectorAll( SLIDES_SELECTOR + ':not(.stack)' ).length;
			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++;
				}

			}

			dom.progressbar.style.width = ( pastCount / ( totalCount - 1 ) ) * window.innerWidth + 'px';

		}
	}

	/**
	 * Updates the state of all control/navigation arrows.
	 */
	function updateControls() {
		if ( config.controls && dom.controls ) {

			var routes = availableRoutes();

			// 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' );
			} );

			// 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' ); } );

		}
	}

	/**
	 * Determine what available routes there are for navigation.
	 *
	 * @return {Object} containing four booleans: left/right/up/down
	 */
	function availableRoutes() {
		var horizontalSlides = document.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR ),
			verticalSlides = document.querySelectorAll( VERTICAL_SLIDES_SELECTOR );

		return {
			left: indexh > 0,
			right: indexh < horizontalSlides.length - 1,
			up: indexv > 0,
			down: indexv < verticalSlides.length - 1
		};
	}

	/**
	 * 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 ) {
			// Find the slide with the specified name
			var element = document.querySelector( '#' + 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, indexv );
			}
		}
		else {
			// Read the index components of the hash
			var h = parseInt( bits[0], 10 ) || 0,
				v = parseInt( bits[1], 10 ) || 0;

			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 {
				var url = '/';

				// If the current slide has an ID, use that as a named link
				if( currentSlide && typeof currentSlide.getAttribute( 'id' ) === 'string' ) {
					url = '/' + currentSlide.getAttribute( '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> }
	 */
	function getIndices( slide ) {
		// By default, return the current indices
		var h = indexh,
			v = indexv;

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

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

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

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

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

	/**
	 * Navigate to the next slide fragment.
	 *
	 * @return {Boolean} true if there was a next fragment,
	 * false otherwise
	 */
	function nextFragment() {
		// Vertical slides:
		if( document.querySelector( VERTICAL_SLIDES_SELECTOR + '.present' ) ) {
			var verticalFragments = document.querySelectorAll( VERTICAL_SLIDES_SELECTOR + '.present .fragment:not(.visible)' );
			if( verticalFragments.length ) {
				verticalFragments[0].classList.add( 'visible' );

				// Notify subscribers of the change
				dispatchEvent( 'fragmentshown', { fragment: verticalFragments[0] } );
				return true;
			}
		}
		// Horizontal slides:
		else {
			var horizontalFragments = document.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR + '.present .fragment:not(.visible)' );
			if( horizontalFragments.length ) {
				horizontalFragments[0].classList.add( 'visible' );

				// Notify subscribers of the change
				dispatchEvent( 'fragmentshown', { fragment: horizontalFragments[0] } );
				return true;
			}
		}

		return false;
	}

	/**
	 * Navigate to the previous slide fragment.
	 *
	 * @return {Boolean} true if there was a previous fragment,
	 * false otherwise
	 */
	function previousFragment() {
		// Vertical slides:
		if( document.querySelector( VERTICAL_SLIDES_SELECTOR + '.present' ) ) {
			var verticalFragments = document.querySelectorAll( VERTICAL_SLIDES_SELECTOR + '.present .fragment.visible' );
			if( verticalFragments.length ) {
				verticalFragments[ verticalFragments.length - 1 ].classList.remove( 'visible' );

				// Notify subscribers of the change
				dispatchEvent( 'fragmenthidden', { fragment: verticalFragments[ verticalFragments.length - 1 ] } );
				return true;
			}
		}
		// Horizontal slides:
		else {
			var horizontalFragments = document.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR + '.present .fragment.visible' );
			if( horizontalFragments.length ) {
				horizontalFragments[ horizontalFragments.length - 1 ].classList.remove( 'visible' );

				// Notify subscribers of the change
				dispatchEvent( 'fragmenthidden', { fragment: horizontalFragments[ horizontalFragments.length - 1 ] } );
				return true;
			}
		}

		return false;
	}

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

		// Cue the next auto-slide if enabled
		if( autoSlide ) {
			autoSlideTimeout = setTimeout( navigateNext, autoSlide );
		}
	}

	function navigateLeft() {
		// Prioritize hiding fragments
		if( availableRoutes().left && isOverviewActive() || previousFragment() === false ) {
			slide( indexh - 1 );
		}
	}

	function navigateRight() {
		// Prioritize revealing fragments
		if( availableRoutes().right && isOverviewActive() || nextFragment() === false ) {
			slide( indexh + 1 );
		}
	}

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

	function navigateDown() {
		// Prioritize revealing fragments
		if( availableRoutes().down && isOverviewActive() || nextFragment() === false ) {
			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 = document.querySelector( HORIZONTAL_SLIDES_SELECTOR + '.past:nth-child(' + indexh + ')' );

				if( previousSlide ) {
					indexv = ( previousSlide.querySelectorAll( 'section' ).length + 1 ) || undefined;
					indexh --;
					slide();
				}
			}
		}
	}

	/**
	 * Same as #navigatePrev() but navigates forwards.
	 */
	function navigateNext() {
		// Prioritize revealing fragments
		if( nextFragment() === false ) {
			availableRoutes().down ? navigateDown() : navigateRight();
		}

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


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


	/**
	 * Handler for the document level 'keydown' event.
	 *
	 * @param {Object} event
	 */
	function onDocumentKeyDown( event ) {
		// Check if there's a focused element that could be using 
		// the keyboard
		var activeElement = document.activeElement;
		var hasFocus = !!( document.activeElement && ( document.activeElement.type || document.activeElement.href || document.activeElement.contentEditable !== 'inherit' ) );

		// Disregard the event if there's a focused element or a 
		// keyboard modifier key is present
		if ( hasFocus || event.shiftKey || event.altKey || event.ctrlKey || event.metaKey ) return;

		var 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: isOverviewActive() ? deactivateOverview() : navigateNext(); break;
			// return
			case 13: isOverviewActive() ? deactivateOverview() : triggered = false; break;
			// b, period, Logitech presenter tools "black screen" button
			case 66: case 190: case 191: togglePause(); break;
			// f
			case 70: enterFullscreen(); break;
			default:
				triggered = false;
		}

		// If the input resulted in a triggered action we should prevent
		// the browsers default behavior
		if( triggered ) {
			event.preventDefault();
		}
		else if ( event.keyCode === 27 && supports3DTransforms ) {
			toggleOverview();

			event.preventDefault();
		}

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

	}

	/**
	 * Handler for the document level 'touchstart' event,
	 * enables support for swipe and pinch gestures.
	 */
	function onDocumentTouchStart( 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 document level 'touchmove' event.
	 */
	function onDocumentTouchMove( event ) {
		// Each touch should only trigger one action
		if( !touch.handled ) {
			var currentX = event.touches[0].clientX;
			var currentY = event.touches[0].clientY;

			// If the touch started off 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.handled = 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.handled = true;
					navigateLeft();
				}
				else if( deltaX < -touch.threshold && Math.abs( deltaX ) > Math.abs( deltaY ) ) {
					touch.handled = true;
					navigateRight();
				}
				else if( deltaY > touch.threshold ) {
					touch.handled = true;
					navigateUp();
				}
				else if( deltaY < -touch.threshold ) {
					touch.handled = true;
					navigateDown();
				}

				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 document level 'touchend' event.
	 */
	function onDocumentTouchEnd( event ) {
		touch.handled = false;
	}

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

		mouseWheelTimeout = setTimeout( function() {
			var delta = event.detail || -event.wheelDelta;
			if( delta > 0 ) {
				navigateNext();
			}
			else {
				navigatePrev();
			}
		}, 100 );
	}

	/**
	 * Clicking on the progress bar results in a navigation to the
	 * closest approximate horizontal slide using this equation:
	 *
	 * ( clickX / presentationWidth ) * numberOfSlides
	 */
	function onProgressClick( event ) {
		var slidesTotal = toArray( document.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR ) ).length;
		var slideIndex = Math.floor( ( event.clientX / dom.wrapper.offsetWidth ) * slidesTotal );

		slide( slideIndex );
	}

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

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

	/**
	 * 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( isOverviewActive() ) {
			event.preventDefault();

			deactivateOverview();

			var element = event.target;

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

			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 );
			}
		}
	}


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


	return {
		initialize: initialize,

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

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

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

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

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

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

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

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

		// 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();
			} );

			return query;
		},

		// 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 );
			}
		}
	};

})();