tell desktop about preference changes

interface/resources/qml/hifi/Desktop.qml

@@ -51,19 +51,24 @@ OriginalDesktop.Desktop {
     Toolbar {
         id: sysToolbar;
         objectName: "com.highfidelity.interface.toolbar.system";
-        anchors.horizontalCenter: settings.systemToolbarHorizontalConstraint ? desktop.horizontalCenter : undefined;
+        anchors.horizontalCenter: settings.constrainToolbarToCenterX ? desktop.horizontalCenter : undefined;
         // Literal 50 is overwritten by settings from previous session, and sysToolbar.x comes from settings when not constrained.
         x: sysToolbar.x
         y: 50
     }
+    Settings {
+        id: settings;
+        category: "toolbar";
+        property bool constrainToolbarToCenterX: true;
+    }
+    function setConstrainToolbarToCenterX(constrain) { // Learn about c++ preference change.
+        settings.constrainToolbarToCenterX = constrain;
+    }
     property var toolbars: (function (map) { // answer dictionary preloaded with sysToolbar
         map[sysToolbar.objectName] = sysToolbar;
         return map; })({});
 
-    Settings {
+
-        id: settings
-        property bool systemToolbarHorizontalConstraint: true
-    }
     Component.onCompleted: {
         WebEngine.settings.javascriptCanOpenWindows = true;
         WebEngine.settings.javascriptCanAccessClipboard = false;

interface/src/Application.cpp

@@ -2153,6 +2153,7 @@ void Application::setFieldOfView(float fov) {
 
 void Application::setSettingConstrainToolbarPosition(bool setting) {
     _constrainToolbarPosition.set(setting);
+    DependencyManager::get<OffscreenUi>()->setConstrainToolbarToCenterX(setting);
 }
 
 void Application::aboutApp() {

libraries/ui/src/OffscreenUi.cpp

@@ -371,6 +371,13 @@ void OffscreenUi::setPinned(bool pinned) {
     }
 }
 
+void OffscreenUi::setConstrainToolbarToCenterX(bool constrained) {
+    bool invokeResult = QMetaObject::invokeMethod(_desktop, "setConstrainToolbarToCenterX", Q_ARG(QVariant, constrained));
+    if (!invokeResult) {
+        qWarning() << "Failed to set toolbar constraint";
+    }
+}
+
 void OffscreenUi::addMenuInitializer(std::function<void(VrMenu*)> f) {
     if (!_vrMenu) {
         _queuedMenuInitializers.push_back(f);

libraries/ui/src/OffscreenUi.h

@@ -52,6 +52,7 @@ public:
     void setPinned(bool pinned = true);
 
     void togglePinned();
+    void setConstrainToolbarToCenterX(bool constrained);
 
     bool eventFilter(QObject* originalDestination, QEvent* event) override;
     void addMenuInitializer(std::function<void(VrMenu*)> f);