Understanding MVC, MVP, and MVVM Patterns in Unreal Engine: Key Differences and Practical Implementation

In game development, choosing the right architectural pattern for your project is crucial to ensure scalability, maintainability, and smooth performance. While Unity developers often discuss design patterns like MVC (Model-View-Controller), MVP (Model-View-Presenter), and MVVM (Model-View-ViewModel), Unreal Engine developers tend to overlook these patterns. However, understanding and applying these patterns can significantly improve the structure of your Unreal Engine projects.

Why are MVC, MVP, and MVVM Important in Game Development?

These architectural patterns provide clear guidelines for separating concerns within your game code, leading to better code organization, reusability, and testability. Here’s why understanding these patterns is essential for Unreal Engine developers:

• Scalability: With well-structured code, you can easily add new features without rewriting large portions of your game logic.
• Maintainability: Clear separation of concerns makes it easier to modify or debug specific parts of your game without affecting other components.
• Team Collaboration: Multiple developers can work on different aspects of the game (e.g., UI, game logic) without stepping on each other’s toes, thanks to the separation that these patterns enforce.

What Are MVC, MVP, and MVVM?

Before jumping into how these patterns differ, let’s define each one.

• MVC (Model-View-Controller):
  • Model: Represents the game’s data and business logic.
  • View: Displays the UI elements and visualizes the model.
  • Controller: Handles user input and updates the model and view.
• MVP (Model-View-Presenter):
  • Model: Same as MVC, it holds the data.
  • View: Handles UI but delegates user input to the presenter.
  • Presenter: Acts as a middleman between the view and the model. It manipulates the model based on user input and updates the view accordingly.
• MVVM (Model-View-ViewModel):
  • Model: Same as the previous patterns, it holds the data.
  • View: The UI components that are bound to properties of the ViewModel.
  • ViewModel: An abstraction of the view that communicates with the model and holds all the logic for what the view should display.

Key Differences Between MVC, MVP, and MVVM

Now that we’ve defined these patterns, let’s break down their key differences and explore how each pattern would be used in an Unreal Engine context.

1. MVC in Unreal Engine:
   • In Unreal, the Controller could be the Game Mode or Player Controller, which is responsible for handling player input and controlling the flow of the game.
   • The View is typically represented by UI Widgets or HUDs, which visually present the data to the player.
   • The Model would consist of game data classes (e.g., health, inventory).
   Use Case: MVC works well for simple projects where there’s minimal user interaction, and the game logic is straightforward.
2. MVP in Unreal Engine:
   • The Presenter in Unreal Engine would be a Manager Class or UI Controller that takes care of manipulating the game data based on player interactions and updates the UI.
   • The View remains the UI Widget or HUD, but the Presenter would control how the UI is updated based on events such as button presses.
   • The Model would again be the data representing in-game objects or game state.
   Use Case: MVP is better suited for projects with more complex UIs or where user input needs to be processed in a more flexible manner.
3. MVVM in Unreal Engine:
   • The ViewModel would act as a bridge between the View (UI) and Model (game data), but unlike MVC or MVP, it holds the logic for what’s displayed on the UI. For example, the ViewModel could manage a character’s status and dynamically adjust what is shown in the UI without needing to access the Model directly.
   • Unreal Engine’s UMG (Unreal Motion Graphics) system could be used to bind ViewModel properties to the UI elements, allowing a more declarative style of UI development.
   Use Case: MVVM shines in complex applications where the UI’s state depends on multiple game data sources. It is particularly useful for dynamic UIs in games, such as RPGs, where multiple elements must be updated in real time based on the game’s internal state.

Practical Example Code

Let’s dive into some simple examples of each pattern using Unreal Engine’s Blueprints and C++.

Example 1: MVC in Unreal Engine

Model:

class FPlayerModel {
public:
    int Health;
    FPlayerModel() : Health(100) {}
};

Controller:

class APlayerController : public APlayerController {
public:
    void TakeDamage(int Damage) {
        PlayerModel.Health -= Damage;
    }
};

View (HUD Widget):

class UGameHUD : public UUserWidget {
public:
    UPROPERTY(meta = (BindWidget))
    UTextBlock* HealthText;

    void UpdateHealth(int Health) {
        HealthText->SetText(FText::AsNumber(Health));
    }
};

Example 2: MVP in Unreal Engine

Presenter:

class UGamePresenter {
private:
    UGameHUD* View;
    FPlayerModel* Model;

public:
    void SetView(UGameHUD* InView) {
        View = InView;
    }

    void SetModel(FPlayerModel* InModel) {
        Model = InModel;
    }

    void TakeDamage(int Damage) {
        Model->Health -= Damage;
        View->UpdateHealth(Model->Health);
    }
};

Example 3: MVVM in Unreal Engine

ViewModel:

class UPlayerViewModel : public UObject {
public:
    UPROPERTY(BlueprintReadOnly)
    int Health;

    UFUNCTION(BlueprintCallable)
    void TakeDamage(int Damage) {
        Health -= Damage;
        OnHealthChanged.Broadcast(Health);
    }

    DECLARE_DYNAMIC_MULTICAST_DELEGATE_OneParam(FHealthChanged, int, Health);
    FHealthChanged OnHealthChanged;
};

Advantages and Disadvantages

• MVC:
  • Advantages: Simple to implement, good for small projects with minimal user interactions.
  • Disadvantages: Can become cumbersome as the complexity of the game increases.
• MVP:
  • Advantages: More flexibility than MVC, better for projects with dynamic UIs.
  • Disadvantages: Introduces more code complexity, harder to maintain with very large projects.
• MVVM:
  • Advantages: Perfect for data-binding and complex UIs, increases testability and separation of concerns.
  • Disadvantages: Can be overkill for simple games, difficult to implement without experience.

Conclusion

Choosing between MVC, MVP, and MVVM depends on your game’s complexity, UI needs, and the size of your project. Unreal Engine developers often overlook these patterns, but applying the right one can lead to better project organization and more efficient development. With these patterns in mind, your Unreal Engine projects can achieve greater maintainability, scalability, and a more dynamic user experience.