reveal.js

		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;

}));