Unreal Engine 4.27 (UE4.27) has a similar modular structure to UE5, but there are key differences, such as the use of PhysX for physics instead of Chaos, different rendering systems, and a slightly different folder structure. Below is the UE4.27 Layer-Module-Source Code Mapping Table to help you navigate and modify the source code efficiently.

📌 UE4.27 Layers, Modules, and Source Code Folder Mapping

Layer Module UE4.27 Source Code Location Key Files to Look At
Game Layer Game Code (C++, Blueprints) 📁 YourGame/Source/YourGame/ YourGameGameMode.cpp, YourGameCharacter.cpp
  Asset Management (Pak, Virtual Texturing) 📁 Engine/Source/Runtime/Engine/ TextureStreamingManager.cpp, AssetManager.cpp
Framework Layer Gameplay Framework (Actors, GameMode, Pawns) 📁 Engine/Source/Runtime/Engine/ GameModeBase.cpp, AActor.cpp, UWorld.cpp
  AI System (NavMesh, Behavior Trees) 📁 Engine/Source/Runtime/AIModule/ NavigationSystem.cpp, BehaviorTreeComponent.cpp
  Input System (Legacy Input, Touch Input) 📁 Engine/Source/Runtime/InputCore/ InputComponent.cpp, TouchInterface.cpp
  UI System (Slate, UMG) 📁 Engine/Source/Runtime/Slate/
📁 Engine/Source/Runtime/UMG/		 SlateApplication.cpp, UserWidget.cpp
Engine Layer Engine (World, Actors, Input, Events) 📁 Engine/Source/Runtime/Engine/ GameInstance.cpp, LevelStreaming.cpp
  RenderCore (Rendering Pipeline) 📁 Engine/Source/Runtime/RenderCore/ Renderer.cpp, RenderGraph.cpp
  RHI (Render Hardware Interface) 📁 Engine/Source/Runtime/RHI/ RHI.cpp, DynamicRHI.cpp
  PhysicsCore (PhysX Physics Engine) 📁 Engine/Source/Runtime/PhysicsCore/ PhysicsEngine.cpp, PhysXSupport.cpp
  Audio (SoundCore, AudioMixer) 📁 Engine/Source/Runtime/AudioMixer/ AudioMixer.cpp, DSP.cpp
  Networking (NetDriver, Replication) 📁 Engine/Source/Runtime/Online/ NetDriver.cpp, ReplicationGraph.cpp
Core Layer Core (Memory, Logging, Math, Threading) 📁 Engine/Source/Runtime/Core/ Core.cpp, ThreadManager.cpp
  CoreUObject (Serialization, GC) 📁 Engine/Source/Runtime/CoreUObject/ UObjectBase.cpp, GarbageCollection.cpp

🔍 Key Differences Between UE4.27 and UE5

| Feature | UE4.27 | UE5 | |——————-|———————————|——————————–| | Physics Engine | PhysX (Nvidia) for rigid body physics | Chaos Physics Engine (default) | | Rendering | Uses Deferred & Forward Renderers | Introduces Nanite & Lumen | | UI System | Slate & UMG | Same (but improved in performance) | | AI System | NavMesh, Behavior Trees | Same (but with minor optimizations) | | Networking | NetDriver, OnlineSubsystem | Same (but better replication performance) |

🔎 How to Find & Modify Modules in UE4.27 Source Code

  1. Locate the Module Folder
    • Go to Engine/Source/Runtime/ for engine modules.
    • Go to YourGame/Source/ for game-specific modules.
    • Use Visual Studio’s Solution Explorer to browse files.
  2. Find the Build Script (.Build.cs)
    • Every module has a ModuleName.Build.cs file.
    • This file defines dependencies and compilation settings.
  3. Modify the Relevant .cpp and .h Files
    • Gameplay: Modify AActor.cpp, GameModeBase.cpp, or AIController.cpp.
    • Rendering: Edit RenderCore.cpp or RHI.cpp.
    • Physics: Adjust PhysXSupport.cpp instead of ChaosSolver.cpp.
    • Networking: Optimize replication settings in NetDriver.cpp.
  4. Recompile & Test
    • Run GenerateProjectFiles.bat (Windows) or GenerateProjectFiles.sh (Mac/Linux).
    • Open Visual Studio and build the engine/game.
    • Use Unreal Insights to measure performance after changes.

🚀 Best Practices for Mobile Porting in UE4.27

✔ Disable Unused Modules

  • Modify YourGame.Target.cs to remove unnecessary desktop features.
    ✔ Optimize Rendering (RenderCore, RHI)
  • Switch to Forward Rendering for mobile.
  • Use low-overhead shaders and reduce dynamic lighting.
    ✔ Reduce Physics Overhead (PhysicsCore)
  • Use simple collision meshes and disable complex physics calculations.
    ✔ Improve AI Efficiency (AIModule)
  • Lower AI tick rate and simplify pathfinding logic.

📌 Final Takeaway

  • UE4.27 uses PhysX instead of Chaos, meaning different physics-related files.
  • UE5’s rendering is more advanced, but UE4.27 still supports Mobile Forward Rendering.
  • Networking, UI, and AI systems are similar, so porting strategies remain largely the same.

This should help you navigate UE4.27’s source code efficiently and make the right porting optimizations. Need help with a specific module? Let me know! 🚀