Gameplay Ability

The Gameplay Abilities is a plugin to handle gameplay mechanics in C++ or Blueprints. It also handles the replication.

Setup

• • To use the Gameplay Ability System attach the AbilitySystemComponent to any actor that implements the IAbilitySystemInterface.

  • Easy way is to CreateDefaultSubObject<UAbilitySystemComponent>(TEXT("AbilitySystem"));

  • The Component will activate abilities, store attributes, update effects, and handle interactions between actors.

  • GiveAbility

  • For pawns after possession call AbilitySystem->InitAbilityActorInfo().

    • Owner - The actor responsible for the abilitysystem.

    • Avatar- The actor through witch the ability system use abilities from.

    • RefreshAbilityActorInfo, BindAbilityActivationToInputComponent

AttributeSet

• • The float values of an actors game state.

  • Each FGameplayAttribue is described with UPROPERTY.

  • Functions to supervise any attemts to modify them, they are modified using GameplayEffects.

    • PreAttributeBaseChange / PreAttributeChange - Use to clamp values.

    • PreGameplayEffectExecute - Use to trigger actions from attribute change.

    • PostGameplayEffectExecute - Use to modify or discard the values passed into an effect execution.

  • AttributeSet needs to register with the ability system component. Set it as a subobject of the component owning actor or use the components GetOrCreateAttributeSubobject.

  • Use AbilitySystem::InitStats to init with a datatable.

GameplayTags

• • The 'bool' flags of a actors game state.

  • RegisterGamePlayTagEvent

GameplayEffects (GE_)

• • Implemented as data-only Blueprints (of base class UGameplayEffect).

  • Gameplay Effects are designed to be configured purely through variables.

  • 'Buffs' / 'Debuffs'.

  • ApplyGamePlayEffectToTarget, ApplyGameplayEffectoToOwner

  • Have tags

  • Modify attributes.

  • Add/remove tags.

  • Blocked by tags on owner or target.

  • Handle stacking of effects and overflow the stack

  • Trigger events

  • Can be instant, duration or infinite.

    • Instant: Direct changes to the Attribute's base value, like taking away health points from an Actor that has received damage.

    • Infinite: Persistent changes that are applied over time, like regenerating a certain amount of magic points per second over a period of several seconds (or indefinitely).

    • Had Duration: Temporary changes, like granting a boost to movement speed for a few seconds.

GameplayEffectSpecs

GameplayCues (GC_)

Gameplay Abilities (GA_)

• • C++ or Blueprint children of something with GameplayAbility as a ancestor.

    • GameplayAbility - Basic ability.

    • GameplayAbility_Montage - Ability that play a montage.

  • WaitTargetData node at the beginning to allow the player to visualize aiming.

  • Cooldown and cost will be applied when CommitAbility is used.

  • Before an Actor can use an Ability, its Ability System Component must be granted that Ability.

    • GiveAbility

    • GiveAbilityAndActivateOnce

  • Revoke access to an Ability from an Ability System Component,

    • ClearAbility

    • SetRemoveAbilityOnEnd

    • ClearAllAbilities

  • Other

    • CanActivateAbility

  • Use ability

    • CallActivateAbility

    • TryActivateAbility

  • Other 2

    • CommitAbility

    • ActivateAbility

  • Stop Ability

    • CancelAbility

    • CanBeCanceled

    • EndAbility - All path must lead to Endability to clean up.

Tags

This section can use tags to cancel abilities, block abilities, set tags and require/block the ability based on the activating, source or target actor/component (*).

• • Cancel Abilities With Tag Abilities with these tags are canceled when this ability is executed.

  • Block Abilities With Tag Abilities with these tags are blocked while this ability is activated.

  • Activation Owned Tags Tags to apply to activating owner while this ability is activated.

  • * Required Tags Ability can only be activated if the * actor/component has all of these tags.

  • * Blocked Tags The activation is blocked if the * actor/component has any of these tags.

Instancing Policy

• • Non-Instanced

  • Instanced per Actor

  • Instanced per Execution

Replication

• • Local Predicted - Most players

  • Local Only:

  • Server Initiated

  • Server Only

Other

• • Triggers: Makes it possible to execute the ability when a event is received, when a tag is added or activated/deactivated when a tag is added/removed.

  • Cost gameplay effect class: When the ability is commited this can be used to drain the (mana, stamine, etc) cost of the ability.

  • Colldown gameplay effect class: Applied when the ability is commited. The ability can not be used again until this has expired.

FGameplayAbilitySpec

FGameplayAbilitySpecHandle

Ability Tasks

• • They perform asynchronous work during a Gameplay Ability's execution, and have the capability to affect execution flow by calling Delegates (in native C++ code) or moving through one or more output execution pins (in Blueprints)

  • Ability Tasks can self-terminate by calling the EndTask function, or it can wait to be terminated automatically when the Gameplay Ability that ran it ends.

Gameplay Events

References

• UE4 Docs - Gameplay Ability System

• Gameplay Abilities in Action RPG

• GameplayAbilities and You

• GASDocumentation

• Hero AI - Gameplay Abilities Meet Behavior Trees

  • GASShooterUsing the Gameplay Ability System - 2019

  • Intro to the Unreal Engine Gameplay Abilities Module - 2018

  • Intro to Gameplay Abilities in Unreal Engine 4 - 2018

  • Gameplay Ability System Tutorial with C++ & Blueprint - 2018

Unreal Engine 5 - The truth of the Gameplay Ability System