update()

in js/controllers/backgrounds.js [231:340]
69 lines of code
21 McCabe index (conditional complexity)

	update( includeAll = false ) {

		let currentSlide = this.Reveal.getCurrentSlide();
		let indices = this.Reveal.getIndices();

		let currentBackground = null;

		// Reverse past/future classes when in RTL mode
		let horizontalPast = this.Reveal.getConfig().rtl ? 'future' : 'past',
			horizontalFuture = this.Reveal.getConfig().rtl ? 'past' : 'future';

		// Update the classes of all backgrounds to match the
		// states of their slides (past/present/future)
		Array.from( this.element.childNodes ).forEach( ( backgroundh, h ) => {

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

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

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

			if( includeAll || h === indices.h ) {
				queryAll( backgroundh, '.slide-background' ).forEach( ( backgroundv, v ) => {

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

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

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

				} );
			}

		} );

		// Stop content inside of previous backgrounds
		if( this.previousBackground ) {

			this.Reveal.slideContent.stopEmbeddedContent( this.previousBackground, { unloadIframes: !this.Reveal.slideContent.shouldPreload( this.previousBackground ) } );

		}

		// Start content in the current background
		if( currentBackground ) {

			this.Reveal.slideContent.startEmbeddedContent( currentBackground );

			let currentBackgroundContent = currentBackground.querySelector( '.slide-background-content' );
			if( currentBackgroundContent ) {

				let backgroundImageURL = currentBackgroundContent.style.backgroundImage || '';

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

			}

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

			this.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( classToBubble => {
				if( currentSlide.classList.contains( classToBubble ) ) {
					this.Reveal.getRevealElement().classList.add( classToBubble );
				}
				else {
					this.Reveal.getRevealElement().classList.remove( classToBubble );
				}
			}, this );
		}

		// Allow the first background to apply without transition
		setTimeout( () => {
			this.element.classList.remove( 'no-transition' );
		}, 1 );

	}