Ensure SnapToGrid only appears when GridSnapping is enabled LYN-2302 (#1362)

* updates to better support showing/hiding viewport ui when grid snapping is enabled/disabled

* connect up editor settings callbacks

* minor polish changes

* api rename

* updates following review feedback

Code/Sandbox/Editor/EditorViewportSettings.cpp

@@ -14,6 +14,7 @@
 
 #include <AzCore/Casting/numeric_cast.h>
 #include <AzCore/Settings/SettingsRegistry.h>
+#include <AzCore/Settings/SettingsRegistryMergeUtils.h>
 #include <AzCore/std/string/string_view.h>
 
 namespace SandboxEditor
@@ -56,6 +57,39 @@ namespace SandboxEditor
         return value;
     }
 
+    struct EditorViewportSettingsCallbacksImpl : public EditorViewportSettingsCallbacks
+    {
+        EditorViewportSettingsCallbacksImpl()
+        {
+            if (auto* registry = AZ::SettingsRegistry::Get())
+            {
+                using AZ::SettingsRegistryMergeUtils::IsPathAncestorDescendantOrEqual;
+
+                m_notifyEventHandler = registry->RegisterNotifier(
+                    [this](const AZStd::string_view path, [[maybe_unused]] const AZ::SettingsRegistryInterface::Type type)
+                    {
+                        if (IsPathAncestorDescendantOrEqual(GridSnappingSetting, path))
+                        {
+                            m_gridSnappingChanged.Signal(GridSnappingEnabled());
+                        }
+                    });
+            }
+        }
+
+        void SetGridSnappingChangedEvent(GridSnappingChangedEvent::Handler& handler) override
+        {
+            handler.Connect(m_gridSnappingChanged);
+        }
+
+        GridSnappingChangedEvent m_gridSnappingChanged;
+        AZ::SettingsRegistryInterface::NotifyEventHandler m_notifyEventHandler;
+    };
+
+    AZStd::unique_ptr<EditorViewportSettingsCallbacks> CreateEditorViewportSettingsCallbacks()
+    {
+        return AZStd::make_unique<EditorViewportSettingsCallbacksImpl>();
+    }
+
     bool GridSnappingEnabled()
     {
         return GetRegistry(GridSnappingSetting, false);

Code/Sandbox/Editor/EditorViewportSettings.h

@@ -14,8 +14,27 @@
 
 #include <SandboxAPI.h>
 
+#include <AzCore/Settings/SettingsRegistry.h>
+#include <AzCore/std/smart_ptr/unique_ptr.h>
+
 namespace SandboxEditor
 {
+    using GridSnappingChangedEvent = AZ::Event<bool>;
+
+    //! Set callbacks to listen for editor settings change events.
+    class EditorViewportSettingsCallbacks
+    {
+    public:
+        virtual ~EditorViewportSettingsCallbacks() = default;
+
+        virtual void SetGridSnappingChangedEvent(GridSnappingChangedEvent::Handler& handler) = 0;
+    };
+
+    //! Create an instance of EditorViewportSettingsCallbacks
+    //! Note: EditorViewportSettingsCallbacks is implemented in EditorViewportSettings.cpp - a change
+    //! event will fire when a value in the settings registry (editorpreferences.setreg) is modified.
+    SANDBOX_API AZStd::unique_ptr<EditorViewportSettingsCallbacks> CreateEditorViewportSettingsCallbacks();
+
     SANDBOX_API bool GridSnappingEnabled();
     SANDBOX_API void SetGridSnapping(bool enabled);
 

Code/Sandbox/Editor/EditorViewportWidget.cpp

@@ -76,7 +76,6 @@
 #include "EditorPreferencesPageGeneral.h"
 #include "ViewportManipulatorController.h"
 #include "LegacyViewportCameraController.h"
-#include "EditorViewportSettings.h"
 
 #include "ViewPane.h"
 #include "CustomResolutionDlg.h"
@@ -1450,6 +1449,17 @@ void EditorViewportWidget::SetViewportId(int id)
     {
         SetAsActiveViewport();
     }
+
+    m_editorViewportSettingsCallbacks = SandboxEditor::CreateEditorViewportSettingsCallbacks();
+
+    m_gridSnappingHandler = SandboxEditor::GridSnappingChangedEvent::Handler(
+        [id](const bool snapping)
+        {
+            AzToolsFramework::ViewportInteraction::ViewportSettingsNotificationBus::Event(
+                id, &AzToolsFramework::ViewportInteraction::ViewportSettingsNotificationBus::Events::OnGridSnappingChanged, snapping);
+        });
+
+    m_editorViewportSettingsCallbacks->SetGridSnappingChangedEvent(m_gridSnappingHandler);
 }
 
 void EditorViewportWidget::ConnectViewportInteractionRequestBus()

Code/Sandbox/Editor/EditorViewportWidget.h

@@ -24,6 +24,7 @@
 #include "Objects/DisplayContext.h"
 #include "Undo/Undo.h"
 #include "Util/PredefinedAspectRatios.h"
+#include "EditorViewportSettings.h"
 
 #include <AzCore/Component/EntityId.h>
 #include <AzCore/std/optional.h>
@@ -571,6 +572,9 @@ private:
 
     AzFramework::EntityVisibilityQuery m_entityVisibilityQuery;
 
+    SandboxEditor::GridSnappingChangedEvent::Handler m_gridSnappingHandler;
+    AZStd::unique_ptr<SandboxEditor::EditorViewportSettingsCallbacks> m_editorViewportSettingsCallbacks;
+
     QSet<int> m_keyDown;
 
     bool m_freezeViewportInput = false;