fix missing backgrounds when scroll view is actived responsively (fixes

#3554)

js/reveal.js

@@ -1016,20 +1016,10 @@ export default function( revealElement, options ) {
 						}
 					});
 				}
-
-				// Responsively turn on the scroll mode if there is an activation
-				// width configured. Ignore if we're configured to always be in
-				// scroll mode.
-				if( typeof config.scrollActivationWidth === 'number' && config.view !== 'scroll' ) {
-					if( size.presentationWidth > 0 && size.presentationWidth <= config.scrollActivationWidth ) {
-						if( !scrollView.isActive() ) scrollView.activate();
-					}
-					else {
-						if( scrollView.isActive() ) scrollView.deactivate();
-					}
-				}
 			}
 
+			checkResponsiveScrollView();
+
 			dom.viewport.style.setProperty( '--slide-scale', scale );
 			dom.viewport.style.setProperty( '--viewport-width', viewportWidth + 'px' );
 			dom.viewport.style.setProperty( '--viewport-height', viewportHeight + 'px' );
@@ -1081,6 +1071,40 @@ export default function( revealElement, options ) {
 
 	}
 
+	/**
+	 * Responsively activates the scroll mode when we reach the configured
+	 * activation width.
+	 */
+	function checkResponsiveScrollView() {
+
+		// Only proceed if...
+		// 1. The DOM is ready
+		// 2. Layouts aren't disabled via config
+		// 3. We're not currently printing
+		// 4. There is a scrollActivationWidth set
+		// 5. The deck isn't configured to always use the scroll view
+		if(
+			dom.wrapper &&
+			!config.disableLayout &&
+			!printView.isActive() &&
+			typeof config.scrollActivationWidth === 'number' &&
+			config.view !== 'scroll'
+		) {
+			const size = getComputedSlideSize();
+
+			if( size.presentationWidth > 0 && size.presentationWidth <= config.scrollActivationWidth ) {
+				if( !scrollView.isActive() ) {
+					backgrounds.create();
+					scrollView.activate()
+				};
+			}
+			else {
+				if( scrollView.isActive() ) scrollView.deactivate();
+			}
+		}
+
+	}
+
 	/**
 	 * Calculates the computed pixel size of our slides. These
 	 * values are based on the width and height configuration
@@ -2700,7 +2724,6 @@ export default function( revealElement, options ) {
 	function onWindowResize( event ) {
 
 		layout();
-
 	}
 
 	/**

package.json

@@ -1,6 +1,6 @@
 {
   "name": "reveal.js",
-  "version": "5.0.3",
+  "version": "5.0.4",
   "description": "The HTML Presentation Framework",
   "homepage": "https://revealjs.com",
   "subdomain": "revealjs",