The Open-Close Principle in Unreal Engine 5

?? Disclaimer: The examples provided in the article are simplified for clarity and understanding. They might not be the most optimal implementation for every use case, but they serve as a solid foundation for learning and applying OCP in your projects.

1. Introduction

In the fast-evolving world of game development, maintaining a codebase that is both flexible and robust is crucial. This is where the Open/Closed Principle (OCP), one of the foundational SOLID principles, comes into play. The essence of OCP is simple yet powerful: software entities (like classes, modules, or functions) should be open for extension but closed for modification. In other words, we should be able to add new functionality to our systems without altering existing code.

Why is this principle so vital in the context of Unreal Engine 5? Game development is inherently iterative, with features being added, removed, or modified throughout the development cycle. OCP enables developers to extend existing systems seamlessly, reducing the risk of introducing bugs when the inevitable changes occur. This is particularly relevant in Unreal Engine 5, where complex systems and rapid prototyping often push the boundaries of a project’s architecture.

In this article, we will explore the Open/Closed Principle in depth, discussing its importance, challenges, and benefits in the context of Unreal Engine 5. We'll also delve into practical strategies for applying OCP, with examples in both C++ and Blueprints to ensure that this principle can be effectively utilized regardless of your preferred development approach.

By the end of this article, you’ll have a solid understanding of how to apply OCP in your Unreal Engine 5 projects, making your codebase more maintainable, scalable, and resilient to change.

2. Understanding the Open-Close Principle

The Open/Closed Principle (OCP) is one of the key tenets of object-oriented design, and it serves as a cornerstone for building scalable and maintainable software. Originally coined by Bertrand Meyer, OCP states that software entities like classes, modules, and functions should be open for extension but closed for modification. This might sound abstract at first, but it boils down to a simple and powerful idea: you should be able to add new functionality to your system without altering existing code.

Why is this important? When you modify existing code to add new features or fix issues, you risk introducing new bugs or breaking existing functionality. OCP aims to minimize this risk by encouraging developers to write code in a way that allows for growth and change without direct modification of existing code structures. By adhering to this principle, you can create a more stable and flexible codebase, which is especially valuable in complex and evolving projects like game development.

2.1. The Concept in Practice

Let’s break it down with a simple analogy. Imagine you're building a game, and you have a base class Weapon that defines common behaviors like Attack(). According to OCP, rather than modifying the Weapon class directly every time you need a new weapon type (say, a Sword or a Bow), you should instead extend the class. This could be done by creating subclasses that inherit from Weapon, each implementing its specific behavior.

Here’s a simple C++ example to illustrate this:

class Weapon {
public:
    virtual void Attack() = 0;  // Pure virtual function, making Weapon an abstract class
};

class Sword : public Weapon {
public:
    void Attack() override {
        // Implementation for sword attack

        std::cout << "Swinging sword!" << std::endl;
    }
};

class Bow : public Weapon {
public:
    void Attack() override {
        // Implementation for bow attack
        std::cout << "Shooting arrow!" << std::endl;
    }
};        

In this example, the Weapon class is closed for modification (we don't change it when adding new weapon types), but it’s open for extension through inheritance. This adheres to OCP by allowing new weapons to be added without altering the existing code in Weapon, thereby minimizing the risk of introducing errors into the codebase.

2.2. The Power of Abstraction

At the heart of OCP is the idea of abstraction. By abstracting general behaviors into interfaces or base classes, you create a flexible framework that can be easily extended. This abstraction layer acts as a contract that guarantees certain behaviors while allowing the specifics to be defined in subclasses or modules.

In Unreal Engine 5, abstraction often takes the form of interfaces or abstract base classes. These tools allow developers to define general behaviors that can be shared across multiple objects or systems, making it easier to extend functionality without needing to modify existing code directly.

2.3. OCP and Maintenance

One of the most significant advantages of adhering to OCP is improved maintainability. When your codebase is structured to follow this principle, adding new features becomes a matter of extending existing classes or modules rather than diving into the guts of existing code. This reduces the likelihood of introducing new bugs and makes the code easier to understand and modify for other developers.

In game development, where teams often need to iterate rapidly and build on top of existing systems, this level of maintainability is crucial. It allows for a more agile development process and enables teams to respond to changes in design or scope without the fear of destabilizing the project.

3. Challenges of Applying OCP in Game Development

While the Open/Closed Principle (OCP) is a powerful guideline for creating maintainable and scalable code, applying it in the fast-paced and ever-evolving world of game development can present unique challenges. Game development often requires balancing the need for flexibility with the realities of performance constraints, tight deadlines, and the necessity of rapidly iterating on features. These challenges can make adhering to OCP more difficult in practice.

3.1. Performance Concerns

One of the primary challenges of applying OCP in game development is performance. The abstraction required to achieve OCP can sometimes introduce overhead, particularly in performance-critical sections of the game such as rendering, physics calculations, or AI processing. For instance, virtual function calls in C++ (used to achieve polymorphism) are generally slightly slower than direct function calls because they involve an extra level of indirection.

Consider a game where different types of enemies have varied movement behaviors. If we design this system following OCP, we might create a base EnemyMovement class with a virtual Move() method and then extend it with subclasses like FlyingMovement, WalkingMovement, and SwimmingMovement.

class EnemyMovement {
public:
    virtual void Move() = 0;
};

class FlyingMovement : public EnemyMovement {
public:
    void Move() override {
        // Implementation for flying
    }
};

class WalkingMovement : public EnemyMovement {
public:
    void Move() override {
        // Implementation for walking
    }
};        

While this approach follows OCP, in a game with hundreds of enemies being updated every frame, the cost of virtual function calls can add up, potentially leading to performance issues. In such cases, the abstraction might need to be reconsidered or optimized, possibly through techniques like avoiding virtual functions in hot paths or using more direct approaches in performance-critical areas.

3.2. Over-Engineering

Another challenge is the risk of over-engineering. In an attempt to make the codebase more extensible, developers might create overly complex abstractions or hierarchies that complicate the system more than necessary. This can lead to a codebase that is difficult to understand, maintain, and extend, ironically defeating the purpose of OCP.

Imagine you’re developing a game where characters can equip different types of gear. To follow OCP, you might create an extensive hierarchy of classes to represent various types of equipment (e.g., Weapon, Armor, Accessory, each with multiple subclasses). While this design is flexible, it might also be overkill if the game’s scope is small or if these classes end up being too rigid for future changes.

class Equipment {
public:
    virtual void Equip() = 0;
};

class Weapon : public Equipment {
public:
    void Equip() override {
        // Equip weapon
    }
};

class Armor : public Equipment {
public:
    void Equip() override {
        // Equip armor
    }
};        

If the requirements of the game change, such as needing to handle new equipment types that don't fit neatly into this hierarchy, the design might become a burden rather than a benefit. Sometimes, a simpler approach, like using data-driven design with configuration files or simpler structures, might be more appropriate.

3.3. Difficulty in Predicting Future Requirements

OCP is most effective when the future extensions of a system can be reasonably anticipated. However, game development is notoriously unpredictable, with frequent design changes based on playtesting feedback, shifts in creative direction, or new technological requirements. This unpredictability can make it difficult to design a system that is both closed for modification and open for all potential future extensions.

Suppose you’re developing a game with a Weapon system where weapons are designed following OCP. You’ve created subclasses for different weapon types, such as MeleeWeapon and RangedWeapon. Initially, this design works well, covering the current needs of the game.

class Weapon {
public:
    virtual void Attack() = 0;
};

 

class MeleeWeapon : public Weapon {
public:
    void Attack() override {
        // Melee attack implementation
    }
};

class RangedWeapon : public Weapon {
public:
    void Attack() override {
        // Ranged attack implementation
    }
};        

Later in development, the game design evolves, and the team decides to introduce a new category of weapons: ExplosiveWeapon, which operates differently from the existing MeleeWeapon and RangedWeapon. The new weapon type requires additional methods or attributes that don't fit neatly into the existing Weapon hierarchy.

class ExplosiveWeapon : public Weapon {
public:
    void Attack() override {
        // Explosive attack implementation
    }

    void Detonate() {
        // Specific method for explosive weapons
    }
};        

In this case, your original Weapon design may no longer be ideal because it didn’t account for these specific needs. Adhering strictly to OCP would require modifying the base Weapon class or creating awkward workarounds to accommodate the new ExplosiveWeapon type. This situation illustrates the difficulty in predicting future requirements and the potential need for refactoring when those requirements change.

The challenge here is that while OCP encourages extending rather than modifying existing code, the reality of game development often involves significant design changes that can render initial abstractions less effective. A more flexible initial design or a willingness to refactor may sometimes be necessary to balance extensibility with the evolving needs of the project.

4. Benefits of Adhering to OCP in Unreal Engine 5

Applying the Open-Closed Principle (OCP) in Unreal Engine 5 can bring substantial advantages to game development, especially in a complex and rapidly evolving environment like a game studio. By designing systems that are open to extension but closed to modification, developers can create more robust, maintainable, and scalable codebases. Here are some key benefits of adhering to OCP in the context of Unreal Engine 5:

4.1. Enhanced Code Maintainability

When your code is designed to accommodate future extensions without requiring modifications to existing classes, it becomes easier to maintain. In Unreal Engine 5, this means that you can introduce new features, mechanics, or content without the risk of breaking existing functionality.

Imagine a gameplay system where different types of AI characters need to exhibit unique behaviors. By using OCP, you can define a base AICharacter class and extend it with specific behaviors for different enemy types. As your game evolves, you can add new enemy types without altering the existing AICharacter class, ensuring that previously implemented AI behaviors remain intact.

4.2. Improved Collaboration and Parallel Development

In a collaborative environment like a game development studio, multiple developers often work on different parts of the project simultaneously. OCP can significantly enhance collaboration by minimizing the need for developers to modify the same classes or assets.

In Unreal Engine 5, when using Blueprints, adhering to OCP allows different team members to extend gameplay functionality by creating new Blueprint classes that inherit from existing ones. This reduces the risk of merge conflicts, especially given that Blueprints are binary files and can’t be easily merged like text-based code files. For instance, if two developers are working on new types of weapon, both can extend the base class independently without stepping on each other's toes.

4.3. Facilitated Testing and Debugging

When a system is open to extension but closed to modification, testing and debugging become more straightforward. Since you’re not constantly altering the base class, you reduce the chances of introducing bugs into previously working code.

In Unreal Engine 5, this could apply to gameplay mechanics, such as adding new abilities to a character. If each ability is an extension of a base Ability class, you can test each new ability in isolation, confident that it won’t interfere with the functionality of existing abilities. This compartmentalization of features makes it easier to pinpoint issues and ensures that adding new content doesn’t inadvertently break existing mechanics.

4.4. Scalability and Future-Proofing

OCP helps future-proof your code by making it easier to scale your game as new features, content, or mechanics are required. This is particularly important in Game Development, where games often grow in scope and complexity over time.

Consider a modular inventory system where you need to handle various item types (e.g., weapons, consumables, and quest items). By adhering to OCP, you can introduce new item types or modify existing ones by extending the base item class without altering the core inventory system. As a result, your game can expand with new content, such as DLC or updates, without requiring significant rewrites of the underlying systems.

4.5. Reduced Risk of Regression Bugs

By extending rather than modifying existing code, you reduce the risk of regression bugs—issues that arise when changes to the codebase inadvertently break existing functionality.

In Unreal Engine 5, imagine you have a character movement system that’s been thoroughly tested and is stable. If you want to add new movement types, like wall-running or gliding, adhering to OCP would mean creating new movement components or classes that extend the base movement system. This approach minimizes the chances of introducing bugs into the established movement system, preserving the stability of the core gameplay.

5. Practical Strategies for Applying OCP in Unreal Engine 5

When it comes to implementing the Open-Closed Principle (OCP) in Unreal Engine 5, there are specific strategies that can help you design systems and architecture that are extensible and resilient to change. These strategies focus on structuring your code and Blueprints in a way that allows for easy extension without the need for modifying existing functionality. Below are some key strategies to apply OCP effectively in your Unreal Engine 5 projects.

5.1. Embrace Inheritance and Composition

One of the most straightforward ways to apply OCP is through the use of inheritance and composition.

  • Inheritance: Design your base classes or Blueprints to be generic enough to handle common functionality, then create derived classes that add or override specific behaviors. This way, you can introduce new features by simply creating new subclasses, rather than modifying existing ones.
  • Composition: Instead of building monolithic classes with all functionalities, use composition to create modular components. This allows you to mix and match components to build new features. For example, in Unreal Engine, you can create reusable components like health systems, movement systems, or inventory systems, and then combine them in different ways to create new gameplay elements.

5.2. Leverage Interfaces for Extensibility

Interfaces are a powerful tool for achieving OCP. By defining interfaces for different behaviors or functionalities, you can ensure that new classes can implement these interfaces without modifying existing code.

  • Use Case: In Unreal Engine, you can create C++ interfaces or Blueprint interfaces to define contracts for specific functionality, such as a Damageable interface for any object that can take damage. Different objects like enemies, destructible environments, or even vehicles can implement this interface, making it easy to add new damageable entities to your game without changing existing classes.

5.3. Utilize Unreal’s Event-Driven Architecture

Unreal Engine 5 is heavily event-driven, which provides a natural way to apply OCP. By relying on events and delegates, you can decouple different parts of your code, allowing new functionality to be added without altering existing code.

  • Custom Events and Delegates: Create custom events or delegates that other parts of your code can subscribe to. When you need to extend functionality, you can simply bind new functions or methods to these events, keeping the original system unchanged.
  • Blueprints: Use Blueprint Event Dispatchers to create events that other Blueprints can listen to and respond to. This is particularly useful in UI systems or gameplay mechanics, where different elements need to react to the same event but in different ways.

5.4. Modularize Blueprints

Modular Blueprints are a key strategy for applying OCP in Unreal Engine 5. By breaking down complex Blueprints into smaller, reusable modules, you can extend functionality by creating new modules rather than altering existing ones.

  • Blueprint Functions and Macros: Use Blueprint functions and macros to encapsulate common functionality that can be reused across multiple Blueprints. When you need to add new functionality, you can do so by creating new functions or macros, rather than editing the existing ones.
  • Sub-Blueprints: Consider using Blueprint subclasses or child Blueprints to extend the functionality of a parent Blueprint. This allows you to create variations of a Blueprint that add new features without modifying the parent, keeping your Blueprints clean and maintainable.

5.5. Apply Design Patterns

Design patterns provide a structured approach to solving common software design problems and can be instrumental in applying OCP.

  • Strategy Pattern: Use the Strategy pattern to define a family of algorithms, encapsulate each one, and make them interchangeable. This pattern is especially useful in AI systems or gameplay mechanics where different behaviors or strategies need to be swapped without altering the existing code.
  • Decorator Pattern: The Decorator pattern allows you to dynamically add behavior to objects without modifying their code. This can be particularly useful in cases where you need to extend the functionality of UI elements or gameplay objects.

5.6. Use Plugins and Modules

Unreal Engine’s plugin and module system is a powerful way to apply OCP at a larger scale. By creating plugins or modules, you can encapsulate specific features or systems, making them easily extendable and reusable across different projects.

  • Create Plugins: When you have a system or feature that could be reused or extended in the future, consider developing it as a plugin. This allows you to package the functionality separately from your main project, making it easy to extend or replace without touching the core codebase.
  • Create Modules: Leverage Unreal Engine’s support for modular systems by breaking your game’s functionality into different modules. This makes it easier to extend specific areas of your game (like combat, UI, or inventory) without affecting other areas.

5.7. Abstract Asset Management

Asset management is a critical part of game development, and applying OCP to how assets are managed can significantly improve your workflow.

  • Data-Driven Design: Store game data (e.g., character stats, item properties) in external data tables or configuration files, allowing you to add new assets or modify existing ones without altering your code. This approach makes it easier to introduce new content or balance changes later in development.
  • Asset Variants: Use Unreal Engine’s asset inheritance or duplication features to create new asset variants based on existing ones. This allows you to introduce new content while reusing and extending existing assets, without the need for modification.

5.8. Maintain Clear Documentation and Guidelines

Finally, to ensure that OCP is consistently applied across your project, it’s essential to maintain clear documentation and coding guidelines.

  • Documentation: Provide detailed documentation on how your systems are designed to be extended. This helps other developers understand how to add new features without modifying existing code.
  • Coding Standards: Establish coding standards that emphasize the importance of OCP, encouraging developers to always think about extensibility when writing new code or creating new Blueprints.

6. C++ Example in Unreal Engine 5

?In this section, we’ll implement a progression system in Unreal Engine 5 using C++. This system will demonstrate how to apply the Open-Closed Principle (OCP) in a practical context. Specifically, we'll create a progression system that can handle a series of progression steps, each with its own set of requirements and rewards. The idea is to have a flexible system where new types of requirements and rewards can be added without modifying the existing code. This system can be extended to support quests, leveling, skill upgrades, and other systems with similar progression with requirements and rewards.

6.1. Designing the Progression System

The core concept of the progression system involves:

  • Progress Steps: Each step has a set of requirements (e.g., XP, items) that must be met to unlock the next step.
  • Requirements: Conditions that need to be fulfilled to progress.
  • Rewards: Actions that are executed when a step is completed, such as awarding loot or increasing stats.

We'll start by defining interfaces for the requirements and rewards, which will allow us to extend the system easily by adding new types of requirements and rewards without changing the existing code.

6.2. Implementing the Interfaces

Let's begin by creating interfaces for the requirements and rewards.

// IRequirement.h
#pragma once

#include "CoreMinimal.h"
#include "IRequirement.generated.h"

UINTERFACE(MinimalAPI)
class URequirement : public UInterface
{
    GENERATED_BODY()
};

class IRequirement
{
    GENERATED_BODY()

public:
    // Check if the requirement is met
    virtual bool IsMet(class APlayerController* Player) const = 0;
};


// IReward.h
#pragma once

#include "CoreMinimal.h"
#include "IReward.generated.h"

UINTERFACE(MinimalAPI)
class UReward : public UInterface
{
    GENERATED_BODY()
};

class IReward
{
    GENERATED_BODY()

public:
    // Execute the reward for the player
    virtual void ExecuteReward(class APlayerController* Player) = 0;
};        

These interfaces define the basic structure for any requirement or reward that can be part of our progression system. By using these interfaces, we ensure that new requirements or rewards can be introduced by simply implementing the interfaces in new classes.

6.3. Creating Concrete Implementations

Now, let's implement some concrete classes for requirements and rewards.

// XPRequirement.h
#pragma once

#include "CoreMinimal.h"
#include "IRequirement.h"
#include "XPRequirement.generated.h"

UCLASS()
class YOURGAME_API UXPRequirement : public UObject, public IRequirement
{
    GENERATED_BODY()

public:
    UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "Requirement")
    int32 RequiredXP;

    virtual bool IsMet(APlayerController* Player) const override;
};


// XPRequirement.cpp

#include "XPRequirement.h"
#include "YourGamePlayerController.h"

bool UXPRequirement::IsMet(APlayerController* Player) const
{
    AYourGamePlayerController* GamePlayer = Cast<AYourGamePlayerController>(Player);
    if (GamePlayer)
    {
        return GamePlayer->GetPlayerXP() >= RequiredXP;
    }

    return false;
}        

In this example, UXPRequirement checks whether the player has enough XP to meet the requirement. We can easily create other requirements (e.g., UItemRequirement) by following the same pattern.

For rewards, let's implement a class that grants the player an item:

// ItemReward.h
#pragma once

#include "CoreMinimal.h"
#include "IReward.h"
#include "ItemReward.generated.h"

UCLASS()
class YOURGAME_API UItemReward : public UObject, public IReward
{
    GENERATED_BODY()

public:
    UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "Reward")
    TSubclassOf<class AYourGameItem> ItemClass;

    virtual void ExecuteReward(APlayerController* Player) override;
};


// ItemReward.cpp
#include "ItemReward.h"
#include "YourGamePlayerController.h"
#include "YourGameItem.h"

void UItemReward::ExecuteReward(APlayerController* Player)
{
    AYourGamePlayerController* GamePlayer = Cast<AYourGamePlayerController>(Player);
    if (GamePlayer && ItemClass)
    {
        // Grant the player the item
        GamePlayer->AddItemToInventory(ItemClass);
    }
}        

UItemReward grants a specific item to the player when the reward is executed.

6.4. ?Defining the Progress Step

Next, let's create the class that defines each progress step:

// ProgressStep.h
#pragma once

#include "CoreMinimal.h"
#include "UObject/NoExportTypes.h"
#include "ProgressStep.generated.h"

UCLASS()
class YOURGAME_API UProgressStep : public UObject
{
    GENERATED_BODY()

public:
    // List of requirements for this step
    UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "Progression")
    TArray<TScriptInterface<IRequirement>> Requirements;

    // List of rewards for this step
    UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "Progression")
    TArray<TScriptInterface<IReward>> Rewards;

    // Check if all requirements are met
    bool AreRequirementsMet(APlayerController* Player) const;

    // Grant all rewards
    void GrantRewards(APlayerController* Player) const;
};


// ProgressStep.cpp
#include "ProgressStep.h"

bool UProgressStep::AreRequirementsMet(APlayerController* Player) const
{
    for (const auto& Requirement : Requirements)
    {
        if (!Requirement->IsMet(Player))
        {
            return false;
        }
    }
    return true;
}

void UProgressStep::GrantRewards(APlayerController* Player) const
{
    for (const auto& Reward : Rewards)
    {
        Reward->ExecuteReward(Player);
    }
}        

The UProgressStep class aggregates a set of requirements and rewards. It checks if all requirements are met and grants the associated rewards when a step is completed.

6.5. Integrating the Progression System

Finally, we need to integrate this progression system into the game. This could be done by a manager class or directly within your game’s player or progression component.

// ProgressionManager.h
#pragma once

#include "CoreMinimal.h"
#include "GameFramework/Actor.h"
#include "ProgressionManager.generated.h"

UCLASS()
class YOURGAME_API AProgressionManager : public AActor
{
    GENERATED_BODY()

public:
    // List of progression steps
    UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "Progression")
    TArray<UProgressStep*> ProgressionSteps;

    void AdvanceProgression(APlayerController* Player);
};


// ProgressionManager.cpp
#include "ProgressionManager.h"

void AProgressionManager::AdvanceProgression(APlayerController* Player)
{
    for (UProgressStep* Step : ProgressionSteps)
    {
        if (Step->AreRequirementsMet(Player))
        {
            Step->GrantRewards(Player);
            // Move to the next step, handle progression logic...
            break;
        }
    }
}        

The AProgressionManager class manages the progression steps and handles the logic for advancing through them.

6.6. ?Summary

This C++ implementation of the progression system illustrates how the Open-Closed Principle can be applied in a game development context. By using interfaces for requirements and rewards, we ensure that the system can be easily extended with new types of progression steps, requirements, and rewards without altering existing code. This design not only adheres to OCP but also makes the system more maintainable and scalable, allowing for the smooth addition of new features as your game evolves.

In the next section, we’ll explore how to extend and interact with this progression system using Unreal Engine 5’s Blueprints, continuing to adhere to the Open-Closed Principle in a visual scripting context.

7. Blueprint Example in Unreal Engine

In this section, we will extend the C++ progression system using Unreal Engine 5's Blueprint system. This approach will illustrate how to apply the Open-Closed Principle (OCP) in a visual scripting environment, enabling game designers to customize and extend the progression system without modifying the underlying C++ code.

While the example provided effectively illustrates the Open-Closed Principle, it's important to note that a data-driven approach might be more appropriate for a progression system like this in a real-world scenario. Specifically, the current setup has limitations, such as the inability to dynamically replace the RequiredXP variable from the BP_XPRequirement and the ItemClass variable from the BP_ItemReward directly in BP_ProgressStep's details panel. A data-driven system would allow for more flexibility and ease of modification, particularly when scaling or adjusting the system without requiring changes to the Blueprint instances.

7.1. Setting Up Blueprint Classes

First, we need to create Blueprint classes based on our C++ interfaces and base classes. This setup will allow us to define new requirements and rewards directly in Blueprints.

  1. Creating Blueprint Classes: Requirement Blueprint: Create a new Blueprint class based on the IRequirement interface. Name it BP_XPRequirement. Add na Integer Variable named RequiredXP. Reward Blueprint: Create a new Blueprint class based on the IReward interface. Name it BP_ItemReward. Create na Object Class Variable names ItemClass Progress Step Blueprint: Create a new Blueprint class based on the UProgressStep class. Name it BP_ProgressStep.

These Blueprint classes will allow us to define specific requirements and rewards using the visual scripting tools provided by Unreal Engine 5.

7.2. Implementing a New Requirement in Blueprint

Let's implement a new requirement type in Blueprint that checks if the player has collected a specific item.

  1. Adding the Requirement Logic: Open BP_XPRequirement and implement the IsMet function.
  2. Inside the function, add the following logic:

7.3. Implementing a New Reward in Blueprint

Next, let's create a reward that increases the player's health when a progress step is completed.

  1. Adding the Reward Logic: Open BP_ItemReward and implement the ExecuteReward function.
  2. Inside the function, add the following logic:

7.4. Assembling the Progression Step in Blueprint

Now, let's bring everything together by creating a progression step that requires the player to have a specific item and rewards them with increased health.

  1. Configuring the Progress Step: Open BP_ProgressStep.
  2. In the details panel, add the BP_XPRequirement and BP_ItemReward instances as elements in the Requirements and Rewards arrays, respectively.

7.5. Summary

In this section, we have illustrated how to extend the C++ progression system using Blueprints in Unreal Engine 5. By creating Blueprint-based implementations of the requirement and reward interfaces, we can easily define new behaviors and integrate them into the progression system without altering the underlying C++ code. This approach adheres to the Open-Closed Principle, allowing game designers to customize and expand the system in a flexible and maintainable way.

8. Trade-offs and When to Bend the Rules

While the Open-Closed Principle (OCP) offers significant benefits, particularly in maintaining clean, scalable, and flexible code, there are situations where adhering to it strictly may not be the most practical or efficient approach. In game development, especially within Unreal Engine 5 (UE5), there are trade-offs to consider that might warrant bending the rules.

8.1. Performance Considerations

One of the primary trade-offs when implementing OCP is performance. In UE5, creating highly modular and extensible systems can introduce additional layers of abstraction. For instance, extensive use of interfaces and inheritance can lead to a higher number of virtual function calls, which may slightly impact performance, particularly in performance-critical areas like AI systems or rendering pipelines. While the impact might be minimal in many cases, in highly optimized game code, it’s worth considering whether the flexibility provided by OCP justifies the potential performance overhead.

8.2. Complexity vs. Simplicity

Another trade-off is the balance between complexity and simplicity. Implementing OCP often requires breaking down systems into smaller, more focused classes or Blueprints, which can lead to an increase in the number of files and the overall complexity of the project. While this modularity is beneficial for larger projects, in smaller or less complex systems, it might be overkill. In such cases, the simplicity of a less modular approach could outweigh the benefits of OCP. For example, a small indie game with a tight development schedule might benefit more from straightforward, less abstracted code than from a system that is fully open for extension.

8.3. Blueprint Limitations

In UE5, while Blueprints offer a highly flexible and visual approach to implementing game logic, they come with certain limitations that can make adhering to OCP challenging. For instance, as discussed in the C++ and Blueprint examples, replacing variables or modifying behavior in a data-driven way can be difficult within Blueprints due to their nature as binary assets. This can limit the flexibility of extending functionality without modifying existing Blueprints directly.

In such cases, bending the rules of OCP might involve making small adjustments directly within Blueprints rather than creating entirely new classes or interfaces. This approach can be more pragmatic, especially when working with a team of designers and developers who need to iterate quickly without getting bogged down in excessive complexity.

8.4. Team Dynamics and Project Scale

The size of the development team and the scale of the project are also important factors in deciding when to adhere strictly to OCP. In large teams or long-term projects, the benefits of OCP are more pronounced, as multiple developers working on the same codebase can introduce changes with less risk of causing regressions. However, in smaller teams or short-term projects, the overhead of implementing OCP might not be justified. In such scenarios, it might be more effective to opt for a simpler, more direct implementation that serves the immediate needs of the project, even if it means some parts of the code are not as open for extension.

8.5. When to Bend the Rules

There are situations in game development where bending or even breaking OCP is acceptable, such as:

  • Rapid Prototyping: During the early stages of development or while prototyping, when the focus is on speed and experimentation, it might make sense to forgo strict adherence to OCP in favor of quicker development.
  • Tightly Coupled Systems: In systems where the components are inherently tightly coupled, such as a specific character controller closely tied to its animations, it may not be practical or necessary to fully implement OCP.
  • Single-Use Cases: For features or systems that are unlikely to change or be reused elsewhere in the project, adhering to OCP might introduce unnecessary complexity. In these cases, a more straightforward approach can be more efficient.

9. Additional Resources

Clean Architecture: A Craftsman's Guide to Software Structure and Design by Robert C. Martin: This book, written by "Uncle Bob," explores principles like OCP in-depth, providing a broader context for their application in software development.

Game Programming Patterns by Robert Nystrom: This book offers an excellent collection of patterns used in game development, including tips on how to apply principles like OCP in practical game development scenarios.

OCP code-walk by Christopher Okhravi is an excellent video on the topic. I enjoy his way of addressing it and how he makes good points during his lectures.

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Shahdin Salman????

Experienced Freelance Frontend Developer | Enhancing Digital Presence | Proficient in TypeScript and Tailwind CSS | Specializing in Next.js | Turning Concepts into Impactful Websites

3 个月

Congratulations, Rafael, on your latest article about the Open-Closed Principle in Unreal Engine 5! Your dedication to sharing practical strategies for applying OCP in game development is truly inspiring. Your insightful breakdown of real-world challenges and hands-on examples will undoubtedly help fellow developers create more maintainable and flexible codebases. Your commitment to continuous learning and improvement shines through in your work. Thank you for sharing your knowledge with the community.

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