Merge pull request o3de#17634 from aws-lumberyard-dev/daimini/Prefabs/StopStoringNonFocusedInstanceDomInMemory

Prefabs | Reduce memory consumption on big, deeply nested levels.

Author: AMZN-daimini

Code/Framework/AzToolsFramework/AzToolsFramework/Prefab/Instance/Instance.cpp

@@ -18,6 +18,8 @@
 #include <AzToolsFramework/Prefab/Instance/InstanceEntityMapperInterface.h>
 #include <AzToolsFramework/Prefab/Instance/TemplateInstanceMapperInterface.h>
 
+#include <AzToolsFramework/Prefab/PrefabFocusInterface.h>
+
 namespace AzToolsFramework
 {
     namespace Prefab
@@ -85,6 +87,8 @@ namespace AzToolsFramework
                 "It is a requirement for the Prefab Instance class. "
                 "Check that it is being correctly initialized.");
 
+            m_isDomCachingEnabled = s_DomCachingEnabledDefault;
+
             if (parent)
             {
                 AliasPath absoluteInstancePath = m_parent->GetAbsoluteInstanceAliasPath();
@@ -947,8 +951,21 @@ namespace AzToolsFramework
 
         void Instance::SetCachedInstanceDom(PrefabDomValueConstReference instanceDom)
         {
-            m_cachedInstanceDom = PrefabDom(); // force a flush of memory by clearing first.
-            m_cachedInstanceDom.CopyFrom(instanceDom->get(), m_cachedInstanceDom.GetAllocator());
+            // force a flush of memory by clearing first if cache isn't empty.
+            if (!m_cachedInstanceDom.IsNull())
+            {
+                m_cachedInstanceDom = PrefabDom(); 
+            }
+
+            if (m_isDomCachingEnabled)
+            {
+                m_cachedInstanceDom.CopyFrom(instanceDom->get(), m_cachedInstanceDom.GetAllocator());
+            }
+        }
+
+        void Instance::EnableDomCaching(bool enableDomCaching)
+        {
+            m_isDomCachingEnabled = enableDomCaching;
         }
     }
 } // namespace AzToolsFramework

Code/Framework/AzToolsFramework/AzToolsFramework/Prefab/Instance/Instance.h

@@ -98,6 +98,10 @@ namespace AzToolsFramework
             //! @param context reflection context.
             static void Reflect(AZ::ReflectContext* context);
 
+            //! Whether caching the instance's dom should be enabled by default.
+            //! Setting can be changed for individual instances using EnableDomCaching.
+            inline static bool s_DomCachingEnabledDefault = false;
+
             //! Gets template id.
             //! @return Template id of the instance.
             TemplateId GetTemplateId() const;
@@ -315,10 +319,12 @@ namespace AzToolsFramework
             //! @}
 
             //! Getter and setter for cached instance DOM.
+            //! Note that caching the DOM is disabled by default and needs to be enabled per instance.
             //! @{
             PrefabDomConstReference GetCachedInstanceDom() const;
             PrefabDomReference GetCachedInstanceDom();
             void SetCachedInstanceDom(PrefabDomValueConstReference instanceDom);
+            void EnableDomCaching(bool enableDomCaching);
             //! @}
 
         private:
@@ -408,6 +414,10 @@ namespace AzToolsFramework
 
             // Defines entity id and instance relationship. The default relationship is one-to-one.
             EntityIdInstanceRelationship m_entityIdInstanceRelationship = DefaultEntityIdInstanceRelationship;
+
+            // Whether the instance should store a cache of its DOM or not.
+            // Default value is set by s_DomCachingEnabledDefault in the constructor.
+            bool m_isDomCachingEnabled = false;
         };
     } // namespace Prefab
 } // namespace AzToolsFramework

Code/Framework/AzToolsFramework/AzToolsFramework/Prefab/PrefabFocusHandler.cpp

@@ -287,6 +287,13 @@ namespace AzToolsFramework::Prefab
         m_rootAliasFocusPath = focusedInstance->get().GetAbsoluteInstanceAliasPath();
         m_rootAliasFocusPathLength = aznumeric_cast<int>(AZStd::distance(m_rootAliasFocusPath.begin(), m_rootAliasFocusPath.end()));
 
+        // Unset the DOM caching for previous focus and enabled it in new focus to optimize editing.
+        if (previousFocusedInstance.has_value())
+        {
+            previousFocusedInstance->get().EnableDomCaching(false);
+        }
+        focusedInstance->get().EnableDomCaching(true);
+
         // Focus on the container entity in the Editor, if the interface is initialized.
         if (m_focusModeInterface)
         {

Code/Framework/AzToolsFramework/Tests/Prefab/PrefabTestFixture.cpp

@@ -61,6 +61,9 @@ namespace UnitTest
         m_settingsRegistryInterface = AZ::SettingsRegistry::Get();
         EXPECT_TRUE(m_settingsRegistryInterface);
 
+        // Have all instances cache their DOM for testing purposes.
+        Instance::s_DomCachingEnabledDefault = true;
+
         // This is for calling CreateEditorRepresentation that adds required editor components.
         AzToolsFramework::EditorRequestBus::Handler::BusConnect();