unreal-systems

Core Philosophy

Modern Unreal Engine 5 development is anchored by three technological pillars: Nanite (virtualized micropolygon geometry), Lumen (real-time dynamic global illumination and reflections), and the Gameplay Ability System (GAS). Building scalable Unreal systems requires navigating the C++ vs Blueprint continuum: architecting core performance-critical mechanics and foundational types in clean C++, while exposing flexible tuning parameters, abilities, and cosmetic triggers to designers in Blueprints.

4-Step Unreal Engine 5 Systems Architecture

Step 1: The C++ vs Blueprint Continuum

1. The Golden Rule:
   • C++: Math, algorithmic logic, data structures, multiplayer networking, file I/O, base actor classes, Gameplay Ability tasks.
   • Blueprints: Visual assembly, animation state machine hooks, cosmetic audio/particle binding, rapid iteration tuning.
2. No Pure Blueprint Actors:
   • Every production Blueprint actor must derive from a custom C++ base class (AMyGameCharacter -> BP_MyGameCharacter). Never derive directly from native engine classes in Blueprint.

Step 2: Gameplay Ability System (GAS) Architecture

1. The Core Components of GAS:
   • UAbilitySystemComponent (ASC): The brain component attached to any character that can use abilities.
   • UAttributeSet: Manages numerical attributes (Health, Stamina, Armor) with clamping and modification hooks:
     • PreAttributeChange() and PostGameplayEffectExecute().
   • Gameplay Tags (FGameplayTag): Hierarchical string-like identifiers for state and categorization (e.g. State.Debuff.Stunned, Ability.Melee.HeavyAttack).
   • Gameplay Effects (GE): Data-driven modifications to attributes (Instant damage, Duration buffs, Periodic poison).
   • Gameplay Abilities (GA): Scripted actions executed via Ability Tasks (e.g. PlayMontageAndWait).

Step 3: Nanite Virtualized Geometry Rules

1. Nanite Asset Standards:
   • Import high-poly ZBrush sculpts (1M - 10M triangles) directly without manual LOD generation.
   • Nanite Constraints:
     • Nanite does NOT support non-rigid deforming skeletal meshes (characters) in earlier UE5 versions; reserve for static meshes and rigid foliage.
     • Avoid complex masked/translucent materials on Nanite geometry (forces software rasterizer fallback).

Step 4: Lumen Global Illumination Optimization

1. Software vs Hardware Ray Tracing:
   • Software Ray Tracing (Default): Uses Mesh Distance Fields and Global Distance Fields. Highly performant across consoles.
   • Hardware Ray Tracing (HWRT): Requires DX12 and dedicated ray-tracing GPU hardware.
2. Mesh Distance Field Hygiene:
   • Ensure all static meshes have manifold, two-sided geometry without open backfaces to prevent light leaking through walls.

Deliverable Format: Production GAS Attribute Set (C++)

// AttributeSetBase.h
#pragma once
#include "CoreMinimal.h"
#include "AttributeSet.h"
#include "AbilitySystemComponent.h"
#include "AttributeSetBase.generated.h"

#define ATTRIBUTE_ACCESSORS(ClassName, PropertyName) \
    GAMEPLAYATTRIBUTE_PROPERTY_GETTER(ClassName, PropertyName) \
    GAMEPLAYATTRIBUTE_VALUE_GETTER(PropertyName) \
    GAMEPLAYATTRIBUTE_VALUE_SETTER(PropertyName) \
    GAMEPLAYATTRIBUTE_VALUE_INITTER(PropertyName)

UCLASS()
class UAttributeSetBase : public UAttributeSet {
    GENERATED_BODY()

public:
    UAttributeSetBase();

    UPROPERTY(BlueprintReadOnly, Category = "Attributes")
    FGameplayAttributeData Health;
    ATTRIBUTE_ACCESSORS(UAttributeSetBase, Health)

    UPROPERTY(BlueprintReadOnly, Category = "Attributes")
    FGameplayAttributeData MaxHealth;
    ATTRIBUTE_ACCESSORS(UAttributeSetBase, MaxHealth)

    virtual void PreAttributeChange(const FGameplayAttribute& Attribute, float& NewValue) override;
    virtual void PostGameplayEffectExecute(const FGameplayEffectModCallbackData& Data) override;
};

Worked Example: Eliminating 14ms Hitching via C++ GAS Migration

• Problem: In a 4-player cooperative action RPG, casting a meteor storm ability caused a severe 14ms frame drop on all clients.
• Diagnosis: Profiling in Unreal Insights revealed that the meteor ability was authored entirely in Blueprint, spawning 80 individual Blueprint actors, each executing tick functions and heavy cast operations (Cast<ABP_Enemy>).
• Optimization:
  1. Migrated the meteor storm into a C++ UGameplayAbility using an asynchronous UAbilityTask.
  2. Replaced Actor spawning with batched Gameplay Effects targeting enemy ASCs directly via Gameplay Tags.
• Outcome: Ability activation frame time dropped from 14ms to 0.18ms with zero hitching.

Verification Checklist

• All gameplay classes inherit from custom C++ base classes, not raw engine types.
• Attributes use the ATTRIBUTE_ACCESSORS macro and clamp values safely.
• State transitions orchestrated via hierarchical GameplayTags.
• Nanite enabled on high-poly static environment meshes.
• Mesh Distance Fields generate cleanly without light bleed in Lumen visualization views.

Anti-Patterns

• Casting in High-Frequency Blueprint Ticks: Using Cast To BP_Character inside Event Tick, destroying CPU cache locality.
• Hard Object References in Blueprints: Directly referencing heavy textures or audio in Blueprints, causing the entire asset tree to load into RAM upon opening the level.
• Overriding Health via Setters Instead of Gameplay Effects: Directly setting character health values without routing through the Ability System Component, bypassing buffs, shields, and damage mitigation rules.