1 files changed, 33 insertions, 10 deletions

diff --git a/js/reveal.js b/js/reveal.js
index c9f3b3b..afbc35a 100644
--- a/js/reveal.js
+++ b/js/reveal.js
@@ -107,6 +107,20 @@
 			// Change the presentation direction to be RTL
 			rtl: false,
 
+			// When this is enabled, stepping left/right from a vertical stack
+			// to an adjacent vertical stack will land you at the same vertical
+			// index.
+			//
+			// Consider a deck with six slides ordered in two stacks like this:
+			// 1.1    2.1
+			// 1.2    2.2
+			// 1.3    2.3
+			//
+			// If you're on slide 1.3 and navigate right, you will normally move
+			// from 1.3 -> 2.1. With "gridNavigation" enabled the same navigation
+			// takes you from 1.3 -> 2.3.
+			gridNavigation: false,
+
 			// Randomizes the order of slides each time the presentation loads
 			shuffle: false,
 
@@ -1134,18 +1148,27 @@
 		if( data.backgroundPosition ) contentElement.style.backgroundPosition = data.backgroundPosition;
 		if( data.backgroundOpacity ) contentElement.style.opacity = data.backgroundOpacity;
 
-		// If this slide has a background color, add a class that
+		// 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 set
-		var computedBackgroundStyle = window.getComputedStyle( element );
-		if( computedBackgroundStyle && computedBackgroundStyle.backgroundColor ) {
-			var rgb = colorToRgb( computedBackgroundStyle.backgroundColor );
+		// 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( computedBackgroundStyle.backgroundColor ) < 128 ) {
+				if( colorBrightness( contrastColor ) < 128 ) {
 					slide.classList.add( 'has-dark-background' );
 				}
 				else {
@@ -4674,12 +4697,12 @@
 		// Reverse for RTL
 		if( config.rtl ) {
 			if( ( isOverview() || nextFragment() === false ) && availableRoutes().left ) {
-				slide( indexh + 1 );
+				slide( indexh + 1, config.gridNavigation ? indexv : undefined );
 			}
 		}
 		// Normal navigation
 		else if( ( isOverview() || previousFragment() === false ) && availableRoutes().left ) {
-			slide( indexh - 1 );
+			slide( indexh - 1, config.gridNavigation ? indexv : undefined );
 		}
 
 	}
@@ -4691,12 +4714,12 @@
 		// Reverse for RTL
 		if( config.rtl ) {
 			if( ( isOverview() || previousFragment() === false ) && availableRoutes().right ) {
-				slide( indexh - 1 );
+				slide( indexh - 1, config.gridNavigation ? indexv : undefined );
 			}
 		}
 		// Normal navigation
 		else if( ( isOverview() || nextFragment() === false ) && availableRoutes().right ) {
-			slide( indexh + 1 );
+			slide( indexh + 1, config.gridNavigation ? indexv : undefined );
 		}
 
 	}