GAS (Gameplay Ability System)

This chapter introduces the core components of GAS and the rationale behind using it. It then uses the dodge system as a complete case study, tracing the full data flow from player input to ability termination.

1.1 Core GAS Components

Component	Responsibility	Example
GameplayAbility (GA)	A container for gameplay logic. It activates when trigger conditions are met, such as a Tag or input binding, and executes Blueprint logic.	GA_Dodge, GA_LightAttack
GameplayCue (GC)	Presentation-only feedback such as VFX, SFX, and camera shake, triggered by Tags.	dodge trail VFX, hit blood splash
GameplayEffect (GE)	Attribute and state layer. It modifies Attributes, grants or removes Tags, and configures Cost / Cooldown behavior.	GE_Cost_Dodge, GE_Damage_Melee

GAS-related plugins: GameplayAbilities (built-in engine module), ComboGraph, GAS Companion

1.2 Why Use GAS?

Core Value

The main value of GAS is that it fully decouples logic (GA), attributes (GE/Attribute), and presentation (GC). This avoids the spaghetti architecture that often appears in traditional Blueprint workflows, where gameplay logic, numeric values, and audiovisual feedback are tightly mixed together.

• Modularity and decoupling: GA is responsible only for logic flow and state machines, GE only for numeric changes and constraints such as Cost / Cooldown, GC only for presentation, and Attribute Sets only for base character attributes.
• Tag-based state management: replaces “Bool variable hell” with a scalable way to manage triggering, blocking, and state relationships.
• Complex attribute calculation through Attribute Sets: GEs can add, multiply, or override base attributes at any time, avoiding the need to restructure gameplay algorithms when formulas evolve.
• Networking and prediction: in multiplayer games, GAS provides strong support for client-side prediction and synchronization of GameplayAbility activation, Attribute values such as Health and Mana, and GameplayEffect state.

This separation also becomes the foundation for later systems such as ComboGraph, Hit Reaction, and enemy AI hit states to share the same event chain.

1.3 Dodge as a GAS Implementation Example

Complete Dodge Data Flow

Player input → GSC_InputBinding → GA_Dodge → GE_Cost + GE_Cooldown → GameplayCue → Tag management → GA end

1.3.1 Defining Base Character Attributes — GAS Attributes

Dodge consumes stamina, which is one of the character’s base attributes. The Attribute Set stores player and enemy base data such as Health, Stamina, and Mana in a DataTable. This makes the system easy to maintain and extend. For example, if poise or stagger resistance needs to be added later, it can be configured centrally in the same data layer.

1.3.2 Taking Over Player Input — GSC_InputBinding

Player input is migrated into GSC_InputBinding, which provides high-level input management and assigns a corresponding Gameplay Tag to each character state.

When the player presses Shift (IA_Dodge), the logic inside GA_Dodge runs. In this project, all gameplay action inputs, such as attack, dodge, and skill activation, trigger a corresponding Gameplay Ability. The GA then owns the concrete logic implementation and state validation.

1.3.3 Executing the Dodge Logic in GA_Dodge

After the ability activates, it first checks whether the player currently has directional input. If the XY length of the input vector is ≤ 0 and the character is not falling, the system treats the character as standing still. If directional input exists, the system calculates the last input direction, which determines the dodge direction.

Directional input → forward dodge: the player Actor is instantly rotated toward the previous frame’s input vector, ensuring that the dodge follows the player’s intended direction. The forward dodge montage is played, the position at the moment of input is captured for the Gameplay Cue, and the Apply Root Motion Constant Force node takes over the CharacterMovementComponent to apply a forward force for the configured duration.

Standing still → backward dodge: the backward dodge montage is played directly. The input position is captured for the Gameplay Cue, and Apply Root Motion Constant Force takes over the CharacterMovementComponent to apply a backward force for the configured duration. The backward dodge has a shorter displacement than the forward dodge, which is exactly why this node is useful: it allows the displacement profile to be tuned per case.

1.3.4 Playing Dodge VFX Through Gameplay Cue

Gameplay Cue owns all presentation-related logic and is triggered by GameplayCue Tags.

Why Use GC Instead of Playing VFX Directly in Blueprint?

The server only needs to send a lightweight Tag, GameplayCue.Character.Dodge.PrefectDodge (the actual in-project name; semantically it corresponds to Perfect Dodge). The client then knows what to play and where to play it, which significantly reduces network bandwidth in a networked context.

Gameplay Cues have two main forms: GameplayCueNotify_Static, used for one-shot effects such as muzzle flashes, and GameplayCueNotify_Actor, used for persistent effects that require ticking, such as trails.

The dodge VFX Gameplay Cue obtains the GameplayCue location data and the instigator position, spawns a Niagara VFX with Spawn System Attached at the player position, and continuously follows the Actor position to create the trail effect.

1.3.5 Tag Management During GA_Dodge Execution

When GA_Dodge activates, the player receives the Ability.Character.Dodge Tag. The Tag is automatically removed when the GA ends.

BlockAbilitiesWithTag defines which Tags, and therefore which GAs, are blocked while this GA is active:

Blocked ability	Effect
All Ability.*	Attacks, including melee and ranged attacks, cannot be triggered during dodge.
Event.Character.Jump	Jump cannot be triggered during dodge.

1.3.6 Adding Stamina Cost and Cooldown Through GameplayEffect

At the same time, activating the ability triggers two Gameplay Effects: GE_Cost_Dodge and GE_Cooldown_Dodge.

1.3.7 Configuration of the Two GameplayEffects

• GE_Cost_Dodge: automatically triggered when the ability starts. It subtracts 5 from the Stamina Attribute defined in the first step.
• GE_Cooldown_Dodge: applied during the Ability activation/Commit phase. It grants the player the Cooldown.Dodge Tag for 1 second. During this duration, GAs governed by the same Cooldown constraint cannot be triggered again.

1.3.8 Ability End

When the dodge montage finishes, blends out, is interrupted, or is cancelled, the GA ends. State Tags granted for the active duration of this Ability are removed. The cooldown has already been applied by GE_Cooldown_Dodge during the Ability activation/Commit phase and continues to block reactivation through the Cooldown.Dodge Tag.