function syncBackground()

in js/reveal.js [1153:1255]
74 lines of code
23 McCabe index (conditional complexity)

	function syncBackground( slide ) {

		var element = slide.slideBackgroundElement,
			contentElement = slide.slideBackgroundContentElement;

		// Reset the prior background state in case this is not the
		// initial sync
		slide.classList.remove( 'has-dark-background' );
		slide.classList.remove( 'has-light-background' );

		element.removeAttribute( 'data-loaded' );
		element.removeAttribute( 'data-background-hash' );
		element.removeAttribute( 'data-background-size' );
		element.removeAttribute( 'data-background-transition' );
		element.style.backgroundColor = '';

		contentElement.style.backgroundSize = '';
		contentElement.style.backgroundRepeat = '';
		contentElement.style.backgroundPosition = '';
		contentElement.style.backgroundImage = '';
		contentElement.style.opacity = '';
		contentElement.innerHTML = '';

		var data = {
			background: slide.getAttribute( 'data-background' ),
			backgroundSize: slide.getAttribute( 'data-background-size' ),
			backgroundImage: slide.getAttribute( 'data-background-image' ),
			backgroundVideo: slide.getAttribute( 'data-background-video' ),
			backgroundIframe: slide.getAttribute( 'data-background-iframe' ),
			backgroundColor: slide.getAttribute( 'data-background-color' ),
			backgroundRepeat: slide.getAttribute( 'data-background-repeat' ),
			backgroundPosition: slide.getAttribute( 'data-background-position' ),
			backgroundTransition: slide.getAttribute( 'data-background-transition' ),
			backgroundOpacity: slide.getAttribute( 'data-background-opacity' )
		};

		if( data.background ) {
			// Auto-wrap image urls in url(...)
			if( /^(http|file|\/\/)/gi.test( data.background ) || /\.(svg|png|jpg|jpeg|gif|bmp)([?#\s]|$)/gi.test( data.background ) ) {
				slide.setAttribute( 'data-background-image', data.background );
			}
			else {
				element.style.background = data.background;
			}
		}

		// Create a hash for this combination of background settings.
		// This is used to determine when two slide backgrounds are
		// the same.
		if( data.background || data.backgroundColor || data.backgroundImage || data.backgroundVideo || data.backgroundIframe ) {
			element.setAttribute( 'data-background-hash', data.background +
															data.backgroundSize +
															data.backgroundImage +
															data.backgroundVideo +
															data.backgroundIframe +
															data.backgroundColor +
															data.backgroundRepeat +
															data.backgroundPosition +
															data.backgroundTransition +
															data.backgroundOpacity );
		}

		// Additional and optional background properties
		if( data.backgroundSize ) element.setAttribute( 'data-background-size', data.backgroundSize );
		if( data.backgroundColor ) element.style.backgroundColor = data.backgroundColor;
		if( data.backgroundTransition ) element.setAttribute( 'data-background-transition', data.backgroundTransition );

		// Background image options are set on the content wrapper
		if( data.backgroundSize ) contentElement.style.backgroundSize = data.backgroundSize;
		if( data.backgroundRepeat ) contentElement.style.backgroundRepeat = data.backgroundRepeat;
		if( data.backgroundPosition ) contentElement.style.backgroundPosition = data.backgroundPosition;
		if( data.backgroundOpacity ) contentElement.style.opacity = data.backgroundOpacity;

		// If this slide has a background color, we add a class that
		// signals if it is light or dark. If the slide has no background
		// color, no class will be added
		var contrastColor = data.backgroundColor;

		// If no bg color was found, check the computed background
		if( !contrastColor ) {
			var computedBackgroundStyle = window.getComputedStyle( element );
			if( computedBackgroundStyle && computedBackgroundStyle.backgroundColor ) {
				contrastColor = computedBackgroundStyle.backgroundColor;
			}
		}

		if( contrastColor ) {
			var rgb = colorToRgb( contrastColor );

			// Ignore fully transparent backgrounds. Some browsers return
			// rgba(0,0,0,0) when reading the computed background color of
			// an element with no background
			if( rgb && rgb.a !== 0 ) {
				if( colorBrightness( contrastColor ) < 128 ) {
					slide.classList.add( 'has-dark-background' );
				}
				else {
					slide.classList.add( 'has-light-background' );
				}
			}
		}

	}