GAS Overview¶

Summary: Project Eternal uses the Gameplay Ability System (GAS) as the foundation for all character actions, abilities, status effects, and attributes. This document explains the architectural decisions, component relationships, and data flow patterns.

Why GAS?¶

GAS provides a production-ready framework for: - Predictive Networking: Client-side prediction with server authority - Attribute Replication: Automatic sync of stats across clients - Effect Stacking: Complex buff/debuff interactions out of the box - Tag-Based Filtering: Abilities blocked/allowed by gameplay tags

Project Eternal extends GAS with custom input binding, Blueprint delegates for UI, and a consolidated attribute set.

Architecture¶

ASC Ownership Model¶

+---------------------------+
|   AEternalPlayerState     |  <-- Owner Actor (persists across respawn)
|   (Owner)                 |
+---------------------------+
           |
           | owns
           v
+---------------------------+
| UEternalAbilitySystemComponent |
|   - Manages abilities     |
|   - Tag-based input       |
|   - UI delegates          |
+---------------------------+
           |
           | contains
           v
+---------------------------+
|   UEternalAttributeSet    |
|   - All character stats   |
|   - Replicated values     |
+---------------------------+

Why PlayerState? - Survives pawn death/respawn - Proper multiplayer replication - Consistent ability state across character swaps

Input Flow¶

Enhanced Input Action
        |
        v
UEternalInputSubsystem
        |
        | Converts to GameplayTag
        v
AbilityInputTagHeld(Tag)
        |
        | Finds abilities with matching DynamicAbilityTags
        v
TryActivateAbility(Handle)

Component API¶

UEternalAbilitySystemComponent¶

Method	Purpose
`AddCharacterAbilities(TArray<TSubclassOf<UGameplayAbility>>)`	Grants startup abilities with input tags
`AbilityInputTagHeld(FGameplayTag)`	Activates abilities matching the input tag
`AbilityInputTagReleased(FGameplayTag)`	Notifies abilities of input release
`GetSpecByHandle(FGameplayAbilitySpecHandle)`	Retrieves ability spec for UI display

Delegates¶

Delegate	Fires When	Use Case
`OnAbilityGranted`	Any ability is given	Skillbar updates
`OnAbilityRemoved`	Any ability is removed	Skillbar cleanup
`EffectAssetTags`	GE with asset tags applied	UI notifications

Attribute Categories¶

Organization¶

+------------------+     +------------------+     +------------------+
|  Hard Attributes |     |  Vital Attributes|     | Recovery Rates   |
|  (Primary Stats) |     |  (Resources)     |     |                  |
+------------------+     +------------------+     +------------------+
| Ferocity         |     | Health/MaxHealth |     | HealthRecoveryRate    |
| Grace            |     | Stamina/MaxStamina|    | StaminaRecoveryRate   |
| Insight          |     | Resonance/MaxRes |     | ResonanceRecoveryRate |
| Clarity          |     | MaxAdrenaline    |     |                       |
| Feral            |     +------------------+     +------------------+
| Dread            |
+------------------+

+------------------+     +------------------+     +------------------+
| Soft Attributes  |     | Combat Attributes|     | Armor/Resistance |
| (Secondary)      |     |                  |     |                  |
+------------------+     +------------------+     +------------------+
| Resolve          |     | MovementSpeed    |     | Armor            |
| Presence         |     | Poise/MaxPoise   |     | ArmorPenetration |
+------------------+     | PoiseRecoveryRate|     | ResistanceFire   |
                         | BaseDamage       |     | ResistanceCorruption |
                         +------------------+     | ResistanceElectric |
                                                  +------------------+

+------------------+     +------------------+     +------------------+
| Critical Strike  |     | Area Modifiers   |     | Cost Modifiers   |
|                  |     |                  |     |                  |
+------------------+     +------------------+     +------------------+
| CritStrikeChance |     | DamageDealtMult  |     | StaminaCostMult  |
| CritStrikeDamage |     | DamageTakenMult  |     | ResonanceCostMult|
+------------------+     +------------------+     +------------------+

+----------------------------+     +-----------------------------+
| Increased Damage Buckets   |     | Conditional Damage vs Status|
| (additive %, base 0)       |     | (additive %, base 0)        |
+----------------------------+     +-----------------------------+
| IncreasedPhysicalDamage    |     | ConditionalDamageVsBleeding |
| IncreasedFireDamage        |     | ConditionalDamageVsIgnited  |
| IncreasedCorruptionDamage  |     | ConditionalDamageVsPoisoned |
| IncreasedElectricDamage    |     | ConditionalDamageVsShocked  |
| IncreasedDamageOverTime    |     +-----------------------------+
| IncreasedStatusDuration    |
+----------------------------+

Attribute Purposes¶

Category	Attributes	Role in Gameplay
Hard	Ferocity, Grace, Insight, Clarity, Feral, Dread	Core stats from character build
Vital	Health, Stamina, Resonance	Consumable resources
Recovery	*RecoveryRate variants	Passive regen speeds
Combat	MovementSpeed, Poise, BaseDamage	Combat pacing, NPC damage scaling (no AttackSpeed attribute — attack speed is weapon-local: weapon base rate + combo ramp)
Critical Strike	CriticalStrikeChance, CriticalStrikeDamage	Crit chance (%) and bonus damage multiplier
Defense	Armor, Resistances (Fire, Corruption, Electric)	Damage reduction
Area Modifiers	DamageDealtMultiplier, DamageTakenMultiplier	Dungeon area modifiers (base 1.0)
Cost Modifiers	StaminaCostMultiplier, ResonanceCostMultiplier	Ability cost scaling (base 1.0)
Increased Damage	IncreasedPhysical/Fire/Corruption/Electric, IncreasedDamageOverTime, IncreasedStatusDuration	Additive-summed % buckets folded into the per-type damage line — see Damage Execution
Conditional vs Status	ConditionalDamageVsBleeding/Ignited/Poisoned/Shocked	Flat % that joins the matching per-type Increased line only when the target carries the matching `Status.*` tag — see Conditional Modifiers
Meta	IncomingDamage, IncomingCritical	Damage pipeline (not replicated)

Note — IncreasedStatusDuration is not a damage bucket. Although it lives in the same Stats.Offensive.Increased.* family, the damage ExecCalc never reads it. It is consumed source-side by UOnHitAbility (via DurationMultiplierAttribute) to extend the duration of status effects the wearer inflicts — distinct from the per-type Increased buckets the ExecCalc folds into the damage line. See Damage Execution.

Replication¶

All gameplay-relevant attributes use REPNOTIFY_Always to ensure UI updates even when the value is unchanged (e.g., clamped at max).

Tag-to-Attribute Mapping¶

The AttributeSet maintains a runtime map for dynamic lookups:

FGameplayTag                              -> FGameplayAttribute Getter
--------------------------------------------|--------------------------
Stats.Attributes.Hard.Ferocity             -> GetFerocityAttribute
Stats.Attributes.Hard.Grace                -> GetGraceAttribute
Stats.Resources.Health                     -> GetHealthAttribute
Stats.Resources.Stamina                    -> GetStaminaAttribute
Stats.Offensive.Increased.Fire             -> GetIncreasedFireDamageAttribute
Stats.Offensive.ConditionalDamage.VsBleeding -> GetConditionalDamageVsBleedingAttribute
...

Why? Allows GameplayEffects to target attributes by tag rather than hardcoded references, enabling data-driven stat modifications. The Increased and Conditional buckets are resolved the same dynamic way — a rolled Stats.Offensive.* modifier never names a C++ attribute; the TagsToAttributes map turns its tag into the matching getter at apply time.

Character Class Configuration¶

Class Defaults¶

Class	Description	Starting Focus
Acolyte	Religious scholar	Insight, Clarity
Artist	Creative combatant	Grace, Presence
Commoner	Everyman survivor	Balanced stats
Weaver	Magical artisan	Insight, Feral

Each class defines: - Primary attribute GE (base stats) - Secondary attribute GE (derived stats) - Starter Ability Kit (StartupKit) - Starting item manifests

Ability granting is kit-based. The legacy flat "startup abilities array" was replaced by an Ability Kit (UEternalAbilitySet) referenced from the class row's StartupKit, granted server-side at possession. Abilities reach an ASC from three layers in order — class starter kit, preset kits, then item abilities — with input-slot collisions resolving last-granted-wins. See Ability Kits for the data model, the server-authority grant path, and the possession-race latch that grants each kit exactly once per session.

Dynamic GameplayEffect Pattern¶

Equipment, dungeon modifiers, and glyphs all apply stat modifications via runtime-created UGameplayEffect objects rather than Blueprint GE classes. This allows data-driven modifier definitions to target any attribute by tag without requiring a separate Blueprint asset per modifier.

How It Works¶

Modifier Source (Equipment, Dungeon, Glyph)
    │
    ├─ Resolve FGameplayTag → FGameplayAttribute via TagsToAttributes map
    ├─ Create UGameplayEffect at runtime (NewObject on ASC)
    ├─ Set DurationPolicy = Infinite
    ├─ Add FGameplayModifierInfo with:
    │   ├─ EModifierOperation::Flat → EGameplayModOp::Additive
    │   └─ EModifierOperation::Increased → EGameplayModOp::Multiplicative (bias 1.0)
    └─ ApplyGameplayEffectToSelf → ActiveEffectHandle for cleanup

Why Dynamic GEs?¶

Concern	Blueprint GEs	Dynamic GEs
New modifier type	New Blueprint asset	New data row only
Attribute targeting	Hardcoded per asset	Resolved by tag at runtime
Magnitude	Fixed or SetByCaller	Set directly from rolled value
Asset count	One per modifier family	Zero — all created at runtime

Systems Using This Pattern¶

System	Component	Applies When
Equipment	`FEquipmentFragment`	Item equipped
Dungeon	`UDungeonModifierComponent`	Player enters dungeon
Glyph	`UPlayerGlyphComponent`	Glyph socketed

Helper: UEternalAbilitySystemLibrary::ApplyDynamicModifierEffect()

Data Flow Examples¶

Ability Activation¶

1. Player presses attack button
2. InputSubsystem -> AbilityInputTagHeld("InputTag.Attack.Primary")
3. ASC iterates ActivatableAbilities
4. Finds ability with matching DynamicAbilityTags
5. Calls AbilitySpecInputPressed + TryActivateAbility
6. Ability activates, plays montage, waits for events

Attribute Modification¶

1. GameplayEffect applies to target
2. Modifier evaluated (base value + modifiers)
3. PreAttributeChange() - validation/clamping
4. Value updated on AttributeSet
5. PostGameplayEffectExecute() - side effects
6. OnRep_* fires on clients for UI update

Source Reference¶

Component	Location
EternalAbilitySystemComponent	`Source/ProjectEternal/Public/AbilitySystem/EternalAbilitySystemComponent.h`
EternalAttributeSet	`Source/ProjectEternal/Public/AbilitySystem/EternalAttributeSet.h`
CharacterClassInfo	`Source/ProjectEternal/Public/AbilitySystem/Data/CharacterClassInfo.h`
Tag-to-Attribute Map	`EternalAttributeSet.cpp:Constructor`
Dynamic GE Helper	`Source/ProjectEternal/Public/Utils/EternalAbilitySystemLibrary.h`
Modifier Operations	`Source/ProjectEternal/Public/Inventory/Modifiers/ModifierDefinitions.h` → `EModifierOperation`

Ability Classes - Ability hierarchy and types
Ability Kits - Kit composition, grant order, and the possession-race latch
Damage Execution - Damage calculation pipeline
Resource Recovery - Health/Stamina/Resonance regeneration
Character Framework - ASC ownership

Refactoring Considerations¶

Issue	Current State	Recommendation
Large AttributeSet	30+ attributes in one class	Split into focused sets (Vital, Combat, Poise, Resistance)
`EffectAssetTags` delegate	`FEffectAssetTags` (non-dynamic multicast), limited Blueprint use	Convert to a `BlueprintAssignable` dynamic multicast delegate
Input tag iteration	Scans all abilities per input	Cache `TMap<FGameplayTag, TArray<FGameplayAbilitySpecHandle>>`

Recent Changes¶

Date	Change	Impact
2026-06-17	Theorycraft attribute wave	Added Increased Damage buckets (Physical/Fire/Corruption/Electric, DamageOverTime, StatusDuration) and Conditional Damage vs Status (Bleeding/Ignited/Poisoned/Shocked); all resolved via `TagsToAttributes` from `Stats.Offensive.Increased.` / `Stats.Offensive.ConditionalDamage.Vs`
2026-02	Dynamic GE pattern	Runtime-created GEs replace Blueprint GEs for equipment, dungeon, glyph modifiers
2026-02	EModifierOperation enum	Flat (GAS Additive) and Increased (GAS Multiplicative with bias 1.0)
2026-02	Critical strike attributes	CriticalStrikeChance, CriticalStrikeDamage, IncomingCritical meta attribute
2026-02	Area modifier attributes	DamageDealtMultiplier, DamageTakenMultiplier (base 1.0, used by dungeon modifiers)
2026-02	Cost modifier attributes	StaminaCostMultiplier, ResonanceCostMultiplier (base 1.0)
2026-02	Added BaseDamage attribute	NPC damage scaling via Balance System
2025-Q1	Trimmed to 3 resistances	Fire, Corruption, Electric
2024-Q4	Added Poise attribute system	New MaxPoise, PoiseRecoveryRate attributes
2024-Q4	Blueprint delegates for UI	OnAbilityGranted/Removed now BlueprintAssignable
2024-Q3	Tag-based input binding	Replaced enum-based InputID system