Better method.

Author: fredcw

js/ui/layout.js

@@ -775,6 +775,12 @@ Chrome.prototype = {
     },
 
     _updateVisibility: function() {
+        const monitorsInFullscreen = [];
+        this._monitors.forEach( monitor => {
+            const topWindow = this.getTopWindowOnMonitor(monitor.index)
+            monitorsInFullscreen[monitor.index] = topWindow && topWindow.is_fullscreen();
+        });
+
         this._trackedActors.forEach( actorData => {
             const monitor = this.findMonitorForActor(actorData.actor);
             let visible = false;
@@ -795,14 +801,7 @@ Chrome.prototype = {
             } else if (this._inOverview)
                 visible = true;
             else {
-                const focusedWindow = global.display.get_focus_window();
-                if (!actorData.visibleInFullscreen && focusedWindow && focusedWindow.is_fullscreen()
-                    && focusedWindow.get_monitor() === monitor.index) {
-                    visible = false;
-                } else if (!actorData.visibleInFullscreen && monitor.inFullscreen
-                    && focusedWindow && focusedWindow.get_monitor() != monitor.index) {
-                    visible = false;
-                } else {
+                if (actorData.visibleInFullscreen || !monitorsInFullscreen[monitor.index]) {
                     visible = true;
                 }
             }
@@ -812,6 +811,23 @@ Chrome.prototype = {
         this._queueUpdateRegions();
     },
 
+    getTopWindowOnMonitor: function(monitorIndex) {
+        let topWindow = null, topWindowTime = 0;
+        global.get_window_actors().forEach(actor=> {
+            const window = actor.meta_window;
+            if (!window || window.get_monitor() !== monitorIndex ||
+                window.minimized || !window.showing_on_its_workspace() ||
+                window.get_workspace() !== global.workspace_manager.get_active_workspace())
+                return;
+            if (window.get_user_time() > topWindowTime) {
+                topWindowTime = window.get_user_time();
+                topWindow = window;
+            }
+        });
+        
+        return topWindow;
+    },
+
     _overviewShowing: function() {
         this._inOverview = true;
         this._updateVisibility();

js/ui/panel.js

@@ -1293,7 +1293,7 @@ PanelDummy.prototype = {
 
         this.actor = new Cinnamon.GenericContainer({style_class: "panel-dummy", reactive: true, track_hover: true, important: true});
 
-        Main.layoutManager.addChrome(this.actor, { addToWindowgroup: false });
+        Main.layoutManager.addChrome(this.actor, { addToWindowgroup: false, visibleInFullscreen: true });
         //
         // layouts set to be full width horizontal panels, and vertical panels set to use as much available space as is left
         //