break autoanimate and loading of slide content into separate controllers

js/controllers/autoanimate.js

@@ -0,0 +1,544 @@
+import { extend, toArray, createStyleSheet } from '../utils/util.js'
+
+export default class AutoAnimate {
+
+	constructor( Reveal ) {
+
+		this.Reveal = Reveal;
+
+		// Counter used to generate unique IDs for auto-animated elements
+		this.autoAnimateCounter = 0;
+
+	}
+
+	/**
+	 * Runs an auto-animation between the given slides.
+	 *
+	 * @param  {HTMLElement} fromSlide
+	 * @param  {HTMLElement} toSlide
+	 */
+	run( fromSlide, toSlide ) {
+
+		// Clean up after prior animations
+		this.reset();
+
+		// Ensure that both slides are auto-animate targets
+		if( fromSlide.hasAttribute( 'data-auto-animate' ) && toSlide.hasAttribute( 'data-auto-animate' ) ) {
+
+			// Create a new auto-animate sheet
+			this.autoAnimateStyleSheet = this.autoAnimateStyleSheet || createStyleSheet();
+
+			let animationOptions = this.getAutoAnimateOptions( toSlide );
+
+			// Set our starting state
+			fromSlide.dataset.autoAnimate = 'pending';
+			toSlide.dataset.autoAnimate = 'pending';
+
+			// Inject our auto-animate styles for this transition
+			let css = this.getAutoAnimatableElements( fromSlide, toSlide ).map( elements => {
+				return this.getAutoAnimateCSS( elements.from, elements.to, elements.options || {}, animationOptions, this.autoAnimateCounter++ );
+			} );
+
+			// Animate unmatched elements, if enabled
+			if( toSlide.dataset.autoAnimateUnmatched !== 'false' && this.Reveal.getConfig().autoAnimateUnmatched === true ) {
+				this.getUnmatchedAutoAnimateElements( toSlide ).forEach( unmatchedElement => {
+					unmatchedElement.dataset.autoAnimateTarget = 'unmatched';
+				} );
+
+				css.push( `[data-auto-animate="running"] [data-auto-animate-target="unmatched"] { transition: opacity ${animationOptions.duration*0.8}s ease ${animationOptions.duration*0.2}s; }` );
+			}
+
+			// Setting the whole chunk of CSS at once is the most
+			// efficient way to do this. Using sheet.insertRule
+			// is multiple factors slower.
+			this.autoAnimateStyleSheet.innerHTML = css.join( '' );
+
+			// Start the animation next cycle
+			requestAnimationFrame( () => {
+				if( this.autoAnimateStyleSheet ) {
+					// This forces our newly injected styles to be applied in Firefox
+					getComputedStyle( this.autoAnimateStyleSheet ).fontWeight;
+
+					toSlide.dataset.autoAnimate = 'running';
+				}
+			} );
+
+			this.Reveal.dispatchEvent( 'autoanimate', { fromSlide: fromSlide, toSlide: toSlide, sheet: this.autoAnimateStyleSheet } );
+
+		}
+
+	}
+
+	/**
+	 * Rolls back all changes that we've made to the DOM so
+	 * that as part of animating.
+	 */
+	reset() {
+
+		// Reset slides
+		toArray( this.Reveal.getRevealElement().querySelectorAll( '[data-auto-animate]:not([data-auto-animate=""])' ) ).forEach( element => {
+			element.dataset.autoAnimate = '';
+		} );
+
+		// Reset elements
+		toArray( this.Reveal.getRevealElement().querySelectorAll( '[data-auto-animate-target]' ) ).forEach( element => {
+			delete element.dataset.autoAnimateTarget;
+		} );
+
+		// Remove the animation sheet
+		if( this.autoAnimateStyleSheet && this.autoAnimateStyleSheet.parentNode ) {
+			this.autoAnimateStyleSheet.parentNode.removeChild( this.autoAnimateStyleSheet );
+			this.autoAnimateStyleSheet = null;
+		}
+
+	}
+
+	/**
+	 * Auto-animates the properties of an element from their original
+	 * values to their new state.
+	 *
+	 * @param {HTMLElement} from
+	 * @param {HTMLElement} to
+	 * @param {Object} elementOptions Options for this element pair
+	 * @param {Object} animationOptions Options set at the slide level
+	 * @param {String} id Unique ID that we can use to identify this
+	 * auto-animate element in the DOM
+	 */
+	getAutoAnimateCSS( from, to, elementOptions, animationOptions, id ) {
+
+		// 'from' elements are given a data-auto-animate-target with no value,
+		// 'to' elements are are given a data-auto-animate-target with an ID
+		from.dataset.autoAnimateTarget = '';
+		to.dataset.autoAnimateTarget = id;
+
+		// Each element may override any of the auto-animate options
+		// like transition easing, duration and delay via data-attributes
+		let options = this.getAutoAnimateOptions( to, animationOptions );
+
+		// If we're using a custom element matcher the element options
+		// may contain additional transition overrides
+		if( typeof elementOptions.delay !== 'undefined' ) options.delay = elementOptions.delay;
+		if( typeof elementOptions.duration !== 'undefined' ) options.duration = elementOptions.duration;
+		if( typeof elementOptions.easing !== 'undefined' ) options.easing = elementOptions.easing;
+
+		let fromProps = this.getAutoAnimatableProperties( 'from', from, elementOptions ),
+			toProps = this.getAutoAnimatableProperties( 'to', to, elementOptions );
+
+		// If translation and/or scaling are enabled, css transform
+		// the 'to' element so that it matches the position and size
+		// of the 'from' element
+		if( elementOptions.translate !== false || elementOptions.scale !== false ) {
+
+			let presentationScale = this.Reveal.getScale();
+
+			let delta = {
+				x: ( fromProps.x - toProps.x ) / presentationScale,
+				y: ( fromProps.y - toProps.y ) / presentationScale,
+				scaleX: fromProps.width / toProps.width,
+				scaleY: fromProps.height / toProps.height
+			};
+
+			// Limit decimal points to avoid 0.0001px blur and stutter
+			delta.x = Math.round( delta.x * 1000 ) / 1000;
+			delta.y = Math.round( delta.y * 1000 ) / 1000;
+			delta.scaleX = Math.round( delta.scaleX * 1000 ) / 1000;
+			delta.scaleX = Math.round( delta.scaleX * 1000 ) / 1000;
+
+			let translate = elementOptions.translate !== false && ( delta.x !== 0 || delta.y !== 0 ),
+				scale = elementOptions.scale !== false && ( delta.scaleX !== 0 || delta.scaleY !== 0 );
+
+			// No need to transform if nothing's changed
+			if( translate || scale ) {
+
+				let transform = [];
+
+				if( translate ) transform.push( `translate(${delta.x}px, ${delta.y}px)` );
+				if( scale ) transform.push( `scale(${delta.scaleX}, ${delta.scaleY})` );
+
+				fromProps.styles['transform'] = transform.join( ' ' );
+				fromProps.styles['transform-origin'] = 'top left';
+
+				toProps.styles['transform'] = 'none';
+
+			}
+
+		}
+
+		// Delete all unchanged 'to' styles
+		for( let propertyName in toProps.styles ) {
+			const toValue = toProps.styles[propertyName];
+			const fromValue = fromProps.styles[propertyName];
+
+			if( toValue === fromValue ) {
+				delete toProps.styles[propertyName];
+			}
+			else {
+				// If these property values were set via a custom matcher providing
+				// an explicit 'from' and/or 'to' value, we always inject those values.
+				if( toValue.explicitValue === true ) {
+					toProps.styles[propertyName] = toValue.value;
+				}
+
+				if( fromValue.explicitValue === true ) {
+					fromProps.styles[propertyName] = fromValue.value;
+				}
+			}
+		}
+
+		let css = '';
+
+		let toStyleProperties = Object.keys( toProps.styles );
+
+		// Only create animate this element IF at least one style
+		// property has changed
+		if( toStyleProperties.length > 0 ) {
+
+			// Instantly move to the 'from' state
+			fromProps.styles['transition'] = 'none';
+
+			// Animate towards the 'to' state
+			toProps.styles['transition'] = `all ${options.duration}s ${options.easing} ${options.delay}s`;
+			toProps.styles['transition-property'] = toStyleProperties.join( ', ' );
+			toProps.styles['will-change'] = toStyleProperties.join( ', ' );
+
+			// Build up our custom CSS. We need to override inline styles
+			// so we need to make our styles vErY IMPORTANT!1!!
+			let fromCSS = Object.keys( fromProps.styles ).map( propertyName => {
+				return propertyName + ': ' + fromProps.styles[propertyName] + ' !important;';
+			} ).join( '' );
+
+			let toCSS = Object.keys( toProps.styles ).map( propertyName => {
+				return propertyName + ': ' + toProps.styles[propertyName] + ' !important;';
+			} ).join( '' );
+
+			css = 	'[data-auto-animate-target="'+ id +'"] {'+ fromCSS +'}' +
+					'[data-auto-animate="running"] [data-auto-animate-target="'+ id +'"] {'+ toCSS +'}';
+
+		}
+
+		return css;
+
+	}
+
+	/**
+	 * Returns the auto-animate options for the given element.
+	 *
+	 * @param {HTMLElement} element Element to pick up options
+	 * from, either a slide or an animation target
+	 * @param {Object} [inheritedOptions] Optional set of existing
+	 * options
+	 */
+	getAutoAnimateOptions( element, inheritedOptions ) {
+
+		let options = {
+			easing: this.Reveal.getConfig().autoAnimateEasing,
+			duration: this.Reveal.getConfig().autoAnimateDuration,
+			delay: 0
+		};
+
+		options = extend( options, inheritedOptions );
+
+		// Inherit options from parent elements
+		if( element.closest && element.parentNode ) {
+			let autoAnimatedParent = element.parentNode.closest( '[data-auto-animate-target]' );
+			if( autoAnimatedParent ) {
+				options = this.getAutoAnimateOptions( autoAnimatedParent, options );
+			}
+		}
+
+		if( element.dataset.autoAnimateEasing ) {
+			options.easing = element.dataset.autoAnimateEasing;
+		}
+
+		if( element.dataset.autoAnimateDuration ) {
+			options.duration = parseFloat( element.dataset.autoAnimateDuration );
+		}
+
+		if( element.dataset.autoAnimateDelay ) {
+			options.delay = parseFloat( element.dataset.autoAnimateDelay );
+		}
+
+		return options;
+
+	}
+
+	/**
+	 * Returns an object containing all of the properties
+	 * that can be auto-animated for the given element and
+	 * their current computed values.
+	 *
+	 * @param {String} direction 'from' or 'to'
+	 */
+	getAutoAnimatableProperties( direction, element, elementOptions ) {
+
+		let properties = { styles: [] };
+
+		// Position and size
+		if( elementOptions.translate !== false || elementOptions.scale !== false ) {
+			let bounds;
+
+			// Custom auto-animate may optionally return a custom tailored
+			// measurement function
+			if( typeof elementOptions.measure === 'function' ) {
+				bounds = elementOptions.measure( element );
+			}
+			else {
+				bounds = element.getBoundingClientRect();
+			}
+
+			properties.x = bounds.x;
+			properties.y = bounds.y;
+			properties.width = bounds.width;
+			properties.height = bounds.height;
+		}
+
+		const computedStyles = getComputedStyle( element );
+
+		// CSS styles
+		( elementOptions.styles || this.Reveal.getConfig().autoAnimateStyles ).forEach( style => {
+			let value;
+
+			// `style` is either the property name directly, or an object
+			// definition of a style property
+			if( typeof style === 'string' ) style = { property: style };
+
+			if( typeof style.from !== 'undefined' && direction === 'from' ) {
+				value = { value: style.from, explicitValue: true };
+			}
+			else if( typeof style.to !== 'undefined' && direction === 'to' ) {
+				value = { value: style.to, explicitValue: true };
+			}
+			else {
+				value = computedStyles[style.property];
+			}
+
+			if( value !== '' ) {
+				properties.styles[style.property] = value;
+			}
+		} );
+
+		return properties;
+
+	}
+
+	/**
+	 * Get a list of all element pairs that we can animate
+	 * between the given slides.
+	 *
+	 * @param {HTMLElement} fromSlide
+	 * @param {HTMLElement} toSlide
+	 *
+	 * @return {Array} Each value is an array where [0] is
+	 * the element we're animating from and [1] is the
+	 * element we're animating to
+	 */
+	getAutoAnimatableElements( fromSlide, toSlide ) {
+
+		let matcher = typeof this.Reveal.getConfig().autoAnimateMatcher === 'function' ? this.Reveal.getConfig().autoAnimateMatcher : this.getAutoAnimatePairs;
+
+		let pairs = matcher.call( this, fromSlide, toSlide );
+
+		let reserved = [];
+
+		// Remove duplicate pairs
+		return pairs.filter( ( pair, index ) => {
+			if( reserved.indexOf( pair.to ) === -1 ) {
+				reserved.push( pair.to );
+				return true;
+			}
+		} );
+
+	}
+
+	/**
+	 * Identifies matching elements between slides.
+	 *
+	 * You can specify a custom matcher function by using
+	 * the `autoAnimateMatcher` config option.
+	 */
+	getAutoAnimatePairs( fromSlide, toSlide ) {
+
+		let pairs = [];
+
+		const codeNodes = 'pre';
+		const textNodes = 'h1, h2, h3, h4, h5, h6, p, li';
+		const mediaNodes = 'img, video, iframe';
+
+		// Eplicit matches via data-id
+		this.findAutoAnimateMatches( pairs, fromSlide, toSlide, '[data-id]', node => {
+			return node.nodeName + ':::' + node.getAttribute( 'data-id' );
+		} );
+
+		// Text
+		this.findAutoAnimateMatches( pairs, fromSlide, toSlide, textNodes, node => {
+			return node.nodeName + ':::' + node.innerText;
+		} );
+
+		// Media
+		this.findAutoAnimateMatches( pairs, fromSlide, toSlide, mediaNodes, node => {
+			return node.nodeName + ':::' + ( node.getAttribute( 'src' ) || node.getAttribute( 'data-src' ) );
+		} );
+
+		// Code
+		this.findAutoAnimateMatches( pairs, fromSlide, toSlide, codeNodes, node => {
+			return node.nodeName + ':::' + node.innerText;
+		} );
+
+		pairs.forEach( pair => {
+
+			// Disable scale transformations on text nodes, we transiition
+			// each individual text property instead
+			if( pair.from.matches( textNodes ) ) {
+				pair.options = { scale: false };
+			}
+			// Animate individual lines of code
+			else if( pair.from.matches( codeNodes ) ) {
+
+				// Transition the code block's width and height instead of scaling
+				// to prevent its content from being squished
+				pair.options = { scale: false, styles: [ 'width', 'height' ] };
+
+				// Lines of code
+				this.findAutoAnimateMatches( pairs, pair.from, pair.to, '.hljs .hljs-ln-code', node => {
+					return node.textContent;
+				}, {
+					scale: false,
+					styles: [],
+					measure: this.getLocalBoundingBox.bind( this )
+				} );
+
+				// Line numbers
+				this.findAutoAnimateMatches( pairs, pair.from, pair.to, '.hljs .hljs-ln-line[data-line-number]', node => {
+					return node.getAttribute( 'data-line-number' );
+				}, {
+					scale: false,
+					styles: [ 'width' ],
+					measure: this.getLocalBoundingBox.bind( this )
+				} );
+
+			}
+
+		}, this );
+
+		return pairs;
+
+	}
+
+	/**
+	 * Helper method which returns a bounding box based on
+	 * the given elements offset coordinates.
+	 *
+	 * @param {HTMLElement} element
+	 * @return {Object} x, y, width, height
+	 */
+	getLocalBoundingBox( element ) {
+
+		const presentationScale = this.Reveal.getScale();
+
+		return {
+			x: Math.round( ( element.offsetLeft * presentationScale ) * 100 ) / 100,
+			y: Math.round( ( element.offsetTop * presentationScale ) * 100 ) / 100,
+			width: Math.round( ( element.offsetWidth * presentationScale ) * 100 ) / 100,
+			height: Math.round( ( element.offsetHeight * presentationScale ) * 100 ) / 100
+		};
+
+	}
+
+	/**
+	 * Finds matching elements between two slides.
+	 *
+	 * @param {Array} pairs            	List of pairs to push matches to
+	 * @param {HTMLElement} fromScope   Scope within the from element exists
+	 * @param {HTMLElement} toScope     Scope within the to element exists
+	 * @param {String} selector         CSS selector of the element to match
+	 * @param {Function} serializer     A function that accepts an element and returns
+	 *                                  a stringified ID based on its contents
+	 * @param {Object} animationOptions Optional config options for this pair
+	 */
+	findAutoAnimateMatches( pairs, fromScope, toScope, selector, serializer, animationOptions ) {
+
+		let fromMatches = {};
+		let toMatches = {};
+
+		[].slice.call( fromScope.querySelectorAll( selector ) ).forEach( ( element, i ) => {
+			const key = serializer( element );
+			if( typeof key === 'string' && key.length ) {
+				fromMatches[key] = fromMatches[key] || [];
+				fromMatches[key].push( element );
+			}
+		} );
+
+		[].slice.call( toScope.querySelectorAll( selector ) ).forEach( ( element, i ) => {
+			const key = serializer( element );
+			toMatches[key] = toMatches[key] || [];
+			toMatches[key].push( element );
+
+			let fromElement;
+
+			// Retrieve the 'from' element
+			if( fromMatches[key] ) {
+				const pimaryIndex = toMatches[key].length - 1;
+				const secondaryIndex = fromMatches[key].length - 1;
+
+				// If there are multiple identical from elements, retrieve
+				// the one at the same index as our to-element.
+				if( fromMatches[key][ pimaryIndex ] ) {
+					fromElement = fromMatches[key][ pimaryIndex ];
+					fromMatches[key][ pimaryIndex ] = null;
+				}
+				// If there are no matching from-elements at the same index,
+				// use the last one.
+				else if( fromMatches[key][ secondaryIndex ] ) {
+					fromElement = fromMatches[key][ secondaryIndex ];
+					fromMatches[key][ secondaryIndex ] = null;
+				}
+			}
+
+			// If we've got a matching pair, push it to the list of pairs
+			if( fromElement ) {
+				pairs.push({
+					from: fromElement,
+					to: element,
+					options: animationOptions
+				});
+			}
+		} );
+
+	}
+
+	/**
+	 * Returns a all elements within the given scope that should
+	 * be considered unmatched in an auto-animate transition. If
+	 * fading of unmatched elements is turned on, these elements
+	 * will fade when going between auto-animate slides.
+	 *
+	 * Note that parents of auto-animate targets are NOT considerd
+	 * unmatched since fading them would break the auto-animation.
+	 *
+	 * @param {HTMLElement} rootElement
+	 * @return {Array}
+	 */
+	getUnmatchedAutoAnimateElements( rootElement ) {
+
+		return [].slice.call( rootElement.children ).reduce( ( result, element ) => {
+
+			const containsAnimatedElements = element.querySelector( '[data-auto-animate-target]' );
+
+			// The element is unmatched if
+			// - It is not an auto-animate target
+			// - It does not contain any auto-animate targets
+			if( !element.hasAttribute( 'data-auto-animate-target' ) && !containsAnimatedElements ) {
+				result.push( element );
+			}
+
+			if( element.querySelector( '[data-auto-animate-target]' ) ) {
+				result = result.concat( this.getUnmatchedAutoAnimateElements( element ) );
+			}
+
+			return result;
+
+		}, [] );
+
+	}
+
+}

js/controllers/plugins.js

@@ -7,8 +7,8 @@ export default class Plugins {
 
 	constructor() {
 
-		// Flags our current state (pending -> loading -> loaded)
-		this.state = 'pending';
+		// Flags our current state (idle -> loading -> loaded)
+		this.state = 'idle';
 
 		// An id:instance map of currently registed plugins
 		this.registeredPlugins = {};

js/controllers/slidecontent.js

@@ -0,0 +1,408 @@
+import { HORIZONTAL_SLIDES_SELECTOR, VERTICAL_SLIDES_SELECTOR } from '../utils/constants.js'
+import { extend, toArray, closestParent } from '../utils/util.js'
+
+export default class SlideContent {
+
+	constructor( Reveal ) {
+
+		this.Reveal = Reveal;
+
+	}
+
+	/**
+	 * 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).
+	 *
+	 * @param {HTMLElement} slide Slide to show
+	 */
+	load( slide, options = {} ) {
+
+		// Show the slide element
+		slide.style.display = this.Reveal.getConfig().display;
+
+		// Media elements with data-src attributes
+		toArray( slide.querySelectorAll( 'img[data-src], video[data-src], audio[data-src], iframe[data-src]' ) ).forEach( element => {
+			if( element.tagName !== 'IFRAME' || shouldPreload( element ) ) {
+				element.setAttribute( 'src', element.getAttribute( 'data-src' ) );
+				element.setAttribute( 'data-lazy-loaded', '' );
+				element.removeAttribute( 'data-src' );
+			}
+		} );
+
+		// Media elements with <source> children
+		toArray( slide.querySelectorAll( 'video, audio' ) ).forEach( media => {
+			let sources = 0;
+
+			toArray( media.querySelectorAll( 'source[data-src]' ) ).forEach( source => {
+				source.setAttribute( 'src', source.getAttribute( 'data-src' ) );
+				source.removeAttribute( 'data-src' );
+				source.setAttribute( 'data-lazy-loaded', '' );
+				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
+		let background = slide.slideBackgroundElement;
+		if( background ) {
+			background.style.display = 'block';
+
+			let backgroundContent = slide.slideBackgroundContentElement;
+			let backgroundIframe = slide.getAttribute( 'data-background-iframe' );
+
+			// If the background contains media, load it
+			if( background.hasAttribute( 'data-loaded' ) === false ) {
+				background.setAttribute( 'data-loaded', 'true' );
+
+				let backgroundImage = slide.getAttribute( 'data-background-image' ),
+					backgroundVideo = slide.getAttribute( 'data-background-video' ),
+					backgroundVideoLoop = slide.hasAttribute( 'data-background-video-loop' ),
+					backgroundVideoMuted = slide.hasAttribute( 'data-background-video-muted' );
+
+				// Images
+				if( backgroundImage ) {
+					backgroundContent.style.backgroundImage = 'url('+ encodeURI( backgroundImage ) +')';
+				}
+				// Videos
+				else if ( backgroundVideo && !this.Reveal.isSpeakerNotes() ) {
+					let video = document.createElement( 'video' );
+
+					if( backgroundVideoLoop ) {
+						video.setAttribute( 'loop', '' );
+					}
+
+					if( backgroundVideoMuted ) {
+						video.muted = true;
+					}
+
+					// Inline video playback works (at least in Mobile Safari) as
+					// long as the video is muted and the `playsinline` attribute is
+					// present
+					if( isMobileDevice ) {
+						video.muted = true;
+						video.autoplay = true;
+						video.setAttribute( 'playsinline', '' );
+					}
+
+					// Support comma separated lists of video sources
+					backgroundVideo.split( ',' ).forEach( source => {
+						video.innerHTML += '<source src="'+ source +'">';
+					} );
+
+					backgroundContent.appendChild( video );
+				}
+				// Iframes
+				else if( backgroundIframe && options.excludeIframes !== true ) {
+					let iframe = document.createElement( 'iframe' );
+					iframe.setAttribute( 'allowfullscreen', '' );
+					iframe.setAttribute( 'mozallowfullscreen', '' );
+					iframe.setAttribute( 'webkitallowfullscreen', '' );
+					iframe.setAttribute( 'allow', 'autoplay' );
+
+					iframe.setAttribute( 'data-src', backgroundIframe );
+
+					iframe.style.width  = '100%';
+					iframe.style.height = '100%';
+					iframe.style.maxHeight = '100%';
+					iframe.style.maxWidth = '100%';
+
+					backgroundContent.appendChild( iframe );
+				}
+			}
+
+			// Start loading preloadable iframes
+			let backgroundIframeElement = backgroundContent.querySelector( 'iframe[data-src]' );
+			if( backgroundIframeElement ) {
+
+				// Check if this iframe is eligible to be preloaded
+				if( shouldPreload( background ) && !/autoplay=(1|true|yes)/gi.test( backgroundIframe ) ) {
+					if( backgroundIframeElement.getAttribute( 'src' ) !== backgroundIframe ) {
+						backgroundIframeElement.setAttribute( 'src', backgroundIframe );
+					}
+				}
+
+			}
+
+		}
+
+	}
+
+	/**
+	 * Unloads and hides the given slide. This is called when the
+	 * slide is moved outside of the configured view distance.
+	 *
+	 * @param {HTMLElement} slide
+	 */
+	unload( slide ) {
+
+		// Hide the slide element
+		slide.style.display = 'none';
+
+		// Hide the corresponding background element
+		let background = this.Reveal.getSlideBackground( slide );
+		if( background ) {
+			background.style.display = 'none';
+
+			// Unload any background iframes
+			toArray( background.querySelectorAll( 'iframe[src]' ) ).forEach( element => {
+				element.removeAttribute( 'src' );
+			} );
+		}
+
+		// Reset lazy-loaded media elements with src attributes
+		toArray( slide.querySelectorAll( 'video[data-lazy-loaded][src], audio[data-lazy-loaded][src], iframe[data-lazy-loaded][src]' ) ).forEach( element => {
+			element.setAttribute( 'data-src', element.getAttribute( 'src' ) );
+			element.removeAttribute( 'src' );
+		} );
+
+		// Reset lazy-loaded media elements with <source> children
+		toArray( slide.querySelectorAll( 'video[data-lazy-loaded] source[src], audio source[src]' ) ).forEach( source => {
+			source.setAttribute( 'data-src', source.getAttribute( 'src' ) );
+			source.removeAttribute( 'src' );
+		} );
+
+	}
+
+	/**
+	 * Enforces origin-specific format rules for embedded media.
+	 */
+	formatEmbeddedContent() {
+
+		let _appendParamToIframeSource = ( sourceAttribute, sourceURL, param ) => {
+			toArray( this.Reveal.getSlidesElement().querySelectorAll( 'iframe['+ sourceAttribute +'*="'+ sourceURL +'"]' ) ).forEach( el => {
+				let 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 given element.
+	 *
+	 * @param {HTMLElement} element
+	 */
+	startEmbeddedContent( element ) {
+
+		if( element && !this.Reveal.isSpeakerNotes() ) {
+
+			// Restart GIFs
+			toArray( element.querySelectorAll( 'img[src$=".gif"]' ) ).forEach( 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( element.querySelectorAll( 'video, audio' ) ).forEach( el => {
+				if( closestParent( el, '.fragment' ) && !closestParent( el, '.fragment.visible' ) ) {
+					return;
+				}
+
+				// Prefer an explicit global autoplay setting
+				let autoplay = config.autoPlayMedia;
+
+				// If no global setting is available, fall back on the element's
+				// own autoplay setting
+				if( typeof autoplay !== 'boolean' ) {
+					autoplay = el.hasAttribute( 'data-autoplay' ) || !!closestParent( el, '.slide-background' );
+				}
+
+				if( autoplay && typeof el.play === 'function' ) {
+
+					// If the media is ready, start playback
+					if( el.readyState > 1 ) {
+						this.startEmbeddedMedia( { target: el } );
+					}
+					// Mobile devices never fire a loaded event so instead
+					// of waiting, we initiate playback
+					else if( isMobileDevice ) {
+						let promise = el.play();
+
+						// If autoplay does not work, ensure that the controls are visible so
+						// that the viewer can start the media on their own
+						if( promise && typeof promise.catch === 'function' && el.controls === false ) {
+							promise.catch( () => {
+								el.controls = true;
+
+								// Once the video does start playing, hide the controls again
+								el.addEventListener( 'play', () => {
+									el.controls = false;
+								} );
+							} );
+						}
+					}
+					// If the media isn't loaded, wait before playing
+					else {
+						el.removeEventListener( 'loadeddata', this.startEmbeddedMedia ); // remove first to avoid dupes
+						el.addEventListener( 'loadeddata', this.startEmbeddedMedia );
+					}
+
+				}
+			} );
+
+			// Normal iframes
+			toArray( element.querySelectorAll( 'iframe[src]' ) ).forEach( el => {
+				if( closestParent( el, '.fragment' ) && !closestParent( el, '.fragment.visible' ) ) {
+					return;
+				}
+
+				this.startEmbeddedIframe( { target: el } );
+			} );
+
+			// Lazy loading iframes
+			toArray( element.querySelectorAll( 'iframe[data-src]' ) ).forEach( el => {
+				if( closestParent( el, '.fragment' ) && !closestParent( el, '.fragment.visible' ) ) {
+					return;
+				}
+
+				if( el.getAttribute( 'src' ) !== el.getAttribute( 'data-src' ) ) {
+					el.removeEventListener( 'load', this.startEmbeddedIframe ); // remove first to avoid dupes
+					el.addEventListener( 'load', this.startEmbeddedIframe );
+					el.setAttribute( 'src', el.getAttribute( 'data-src' ) );
+				}
+			} );
+
+		}
+
+	}
+
+	/**
+	 * Starts playing an embedded video/audio element after
+	 * it has finished loading.
+	 *
+	 * @param {object} event
+	 */
+	startEmbeddedMedia( event ) {
+
+		let isAttachedToDOM = !!closestParent( event.target, 'html' ),
+			isVisible  		= !!closestParent( event.target, '.present' );
+
+		if( isAttachedToDOM && isVisible ) {
+			event.target.currentTime = 0;
+			event.target.play();
+		}
+
+		event.target.removeEventListener( 'loadeddata', this.startEmbeddedMedia );
+
+	}
+
+	/**
+	 * "Starts" the content of an embedded iframe using the
+	 * postMessage API.
+	 *
+	 * @param {object} event
+	 */
+	startEmbeddedIframe( event ) {
+
+		let iframe = event.target;
+
+		if( iframe && iframe.contentWindow ) {
+
+			let isAttachedToDOM = !!closestParent( event.target, 'html' ),
+				isVisible  		= !!closestParent( event.target, '.present' );
+
+			if( isAttachedToDOM && isVisible ) {
+
+				// Prefer an explicit global autoplay setting
+				let autoplay = config.autoPlayMedia;
+
+				// If no global setting is available, fall back on the element's
+				// own autoplay setting
+				if( typeof autoplay !== 'boolean' ) {
+					autoplay = iframe.hasAttribute( 'data-autoplay' ) || !!closestParent( iframe, '.slide-background' );
+				}
+
+				// YouTube postMessage API
+				if( /youtube\.com\/embed\//.test( iframe.getAttribute( 'src' ) ) && autoplay ) {
+					iframe.contentWindow.postMessage( '{"event":"command","func":"playVideo","args":""}', '*' );
+				}
+				// Vimeo postMessage API
+				else if( /player\.vimeo\.com\//.test( iframe.getAttribute( 'src' ) ) && 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.
+	 *
+	 * @param {HTMLElement} element
+	 */
+	stopEmbeddedContent( element, options = {} ) {
+
+		options = extend( {
+			// Defaults
+			unloadIframes: true
+		}, options );
+
+		if( element && element.parentNode ) {
+			// HTML5 media elements
+			toArray( element.querySelectorAll( 'video, audio' ) ).forEach( el => {
+				if( !el.hasAttribute( 'data-ignore' ) && typeof el.pause === 'function' ) {
+					el.setAttribute('data-paused-by-reveal', '');
+					el.pause();
+				}
+			} );
+
+			// Generic postMessage API for non-lazy loaded iframes
+			toArray( element.querySelectorAll( 'iframe' ) ).forEach( el => {
+				if( el.contentWindow ) el.contentWindow.postMessage( 'slide:stop', '*' );
+				el.removeEventListener( 'load', this.startEmbeddedIframe );
+			});
+
+			// YouTube postMessage API
+			toArray( element.querySelectorAll( 'iframe[src*="youtube.com/embed/"]' ) ).forEach( el => {
+				if( !el.hasAttribute( 'data-ignore' ) && el.contentWindow && typeof el.contentWindow.postMessage === 'function' ) {
+					el.contentWindow.postMessage( '{"event":"command","func":"pauseVideo","args":""}', '*' );
+				}
+			});
+
+			// Vimeo postMessage API
+			toArray( element.querySelectorAll( 'iframe[src*="player.vimeo.com/"]' ) ).forEach( el => {
+				if( !el.hasAttribute( 'data-ignore' ) && el.contentWindow && typeof el.contentWindow.postMessage === 'function' ) {
+					el.contentWindow.postMessage( '{"method":"pause"}', '*' );
+				}
+			});
+
+			if( options.unloadIframes === true ) {
+				// Unload lazy-loaded iframes
+				toArray( element.querySelectorAll( 'iframe[data-src]' ) ).forEach( 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' );
+				} );
+			}
+		}
+
+	}
+
+}

js/utils/util.js

@@ -140,16 +140,22 @@ export const enterFullscreen = () => {
  *
  * @param {string} value
  */
-export const injectStyleSheet = ( value ) => {
+export const createStyleSheet = ( value ) => {
 
 	let tag = document.createElement( 'style' );
 	tag.type = 'text/css';
-	if( tag.styleSheet ) {
-		tag.styleSheet.cssText = value;
-	}
-	else {
-		tag.appendChild( document.createTextNode( value ) );
+
+	if( value && value.length > 0 ) {
+		if( tag.styleSheet ) {
+			tag.styleSheet.cssText = value;
+		}
+		else {
+			tag.appendChild( document.createTextNode( value ) );
+		}
 	}
-	document.getElementsByTagName( 'head' )[0].appendChild( tag );
+
+	document.head.appendChild( tag );
+
+	return tag;
 
 }