add support for overriding the default layout (#2121)

* add support for overriding the default layout
New `overrideLayout` option (if true) will prevent h/w calcs.

* fix error if options are empty

* Implement requested changes
Rename overrideLayout to disableLayout and remove code to unset display

js/reveal.js

@@ -84,6 +84,10 @@
 			// Enable the slide overview mode
 			overview: true,
 
+			// Enable/disable user specified layouts (like css-grid)
+			// (basically prevents all the display & height/width calculations)
+			disableLayout: false,
+
 			// Vertical centering of slides
 			center: true,
 
@@ -1853,76 +1857,80 @@
 
 		if( dom.wrapper && !isPrintingPDF() ) {
 
-			var size = getComputedSlideSize();
+			if( !config.disableLayout ) {
 
-			// Layout the contents of the slides
-			layoutSlideContents( config.width, config.height );
+				var size = getComputedSlideSize();
 
-			dom.slides.style.width = size.width + 'px';
-			dom.slides.style.height = size.height + 'px';
+				// Layout the contents of the slides
+				layoutSlideContents( config.width, config.height );
 
-			// Determine scale of content to fit within available space
-			scale = Math.min( size.presentationWidth / size.width, size.presentationHeight / size.height );
+				dom.slides.style.width = size.width + 'px';
+				dom.slides.style.height = size.height + 'px';
 
-			// Respect max/min scale settings
-			scale = Math.max( scale, config.minScale );
-			scale = Math.min( scale, config.maxScale );
+				// Determine scale of content to fit within available space
+				scale = Math.min( size.presentationWidth / size.width, size.presentationHeight / size.height );
 
-			// Don't apply any scaling styles if scale is 1
-			if( scale === 1 ) {
-				dom.slides.style.zoom = '';
-				dom.slides.style.left = '';
-				dom.slides.style.top = '';
-				dom.slides.style.bottom = '';
-				dom.slides.style.right = '';
-				transformSlides( { layout: '' } );
-			}
-			else {
-				// Prefer zoom for scaling up so that content remains crisp.
-				// Don't use zoom to scale down since that can lead to shifts
-				// in text layout/line breaks.
-				if( scale > 1 && features.zoom ) {
-					dom.slides.style.zoom = scale;
+				// Respect max/min scale settings
+				scale = Math.max( scale, config.minScale );
+				scale = Math.min( scale, config.maxScale );
+
+				// Don't apply any scaling styles if scale is 1
+				if( scale === 1 ) {
+					dom.slides.style.zoom = '';
 					dom.slides.style.left = '';
 					dom.slides.style.top = '';
 					dom.slides.style.bottom = '';
 					dom.slides.style.right = '';
 					transformSlides( { layout: '' } );
 				}
-				// Apply scale transform as a fallback
 				else {
-					dom.slides.style.zoom = '';
-					dom.slides.style.left = '50%';
-					dom.slides.style.top = '50%';
-					dom.slides.style.bottom = 'auto';
-					dom.slides.style.right = 'auto';
-					transformSlides( { layout: 'translate(-50%, -50%) scale('+ scale +')' } );
+					// Prefer zoom for scaling up so that content remains crisp.
+					// Don't use zoom to scale down since that can lead to shifts
+					// in text layout/line breaks.
+					if( scale > 1 && features.zoom ) {
+						dom.slides.style.zoom = scale;
+						dom.slides.style.left = '';
+						dom.slides.style.top = '';
+						dom.slides.style.bottom = '';
+						dom.slides.style.right = '';
+						transformSlides( { layout: '' } );
+					}
+					// Apply scale transform as a fallback
+					else {
+						dom.slides.style.zoom = '';
+						dom.slides.style.left = '50%';
+						dom.slides.style.top = '50%';
+						dom.slides.style.bottom = 'auto';
+						dom.slides.style.right = 'auto';
+						transformSlides( { layout: 'translate(-50%, -50%) scale('+ scale +')' } );
+					}
 				}
-			}
 
-			// Select all slides, vertical and horizontal
-			var slides = toArray( dom.wrapper.querySelectorAll( SLIDES_SELECTOR ) );
+				// Select all slides, vertical and horizontal
+				var slides = toArray( dom.wrapper.querySelectorAll( SLIDES_SELECTOR ) );
 
-			for( var i = 0, len = slides.length; i < len; i++ ) {
-				var slide = slides[ i ];
+				for( var i = 0, len = slides.length; i < len; i++ ) {
+					var slide = slides[ i ];
 
-				// Don't bother updating invisible slides
-				if( slide.style.display === 'none' ) {
-					continue;
-				}
+					// Don't bother updating invisible slides
+					if( slide.style.display === 'none' ) {
+						continue;
+					}
 
-				if( config.center || slide.classList.contains( 'center' ) ) {
-					// Vertical stacks are not centred since their section
-					// children will be
-					if( slide.classList.contains( 'stack' ) ) {
-						slide.style.top = 0;
+					if( config.center || slide.classList.contains( 'center' ) ) {
+						// Vertical stacks are not centred since their section
+						// children will be
+						if( slide.classList.contains( 'stack' ) ) {
+							slide.style.top = 0;
+						}
+						else {
+							slide.style.top = Math.max( ( size.height - slide.scrollHeight ) / 2, 0 ) + 'px';
+						}
 					}
 					else {
-						slide.style.top = Math.max( ( size.height - slide.scrollHeight ) / 2, 0 ) + 'px';
+						slide.style.top = '';
 					}
-				}
-				else {
-					slide.style.top = '';
+
 				}
 
 			}