Center menu on monitor if applet in center zone of horizontal panel

Author: fredcw

files/usr/share/cinnamon/applets/[email protected]/applet.js

@@ -1243,6 +1243,7 @@ class CinnamonMenuApplet extends Applet.TextIconApplet {
     constructor(orientation, panel_height, instance_id) {
         super(orientation, panel_height, instance_id);
 
+        this.orientation = orientation;
         this.setAllowedLayout(Applet.AllowedLayout.BOTH);
 
         this.set_applet_tooltip(_("Menu"));
@@ -1507,6 +1508,7 @@ class CinnamonMenuApplet extends Applet.TextIconApplet {
     }
 
     on_orientation_changed (orientation) {
+        this.orientation = orientation;
         this._updateIconAndLabel();
         this._size_dirty = true;
     }
@@ -1551,6 +1553,16 @@ class CinnamonMenuApplet extends Applet.TextIconApplet {
             }
             this._allAppsCategoryButton.actor.style_class = "appmenu-category-button-selected";
 
+            // Center menu if applet in center zone of top or bottom panel.
+            const appletDefinition = Main.AppletManager.getAppletDefinition({applet_id: this.instance_id});
+            if ((this.orientation === St.Side.BOTTOM || this.orientation === St.Side.TOP) &&
+                appletDefinition.location_label === 'center') {
+                const monitor = Main.layoutManager.findMonitorForActor(this.menu.actor);
+                this.menu.shiftToPosition(Math.floor(monitor.width / 2) + monitor.x);
+            } else {
+                this.menu.shiftToPosition(-1);
+            }
+
             Mainloop.idle_add(() => {
                 if(this.lastSelectedCategory !== null) //if a category is already selected
                     return;