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Melee Abilities In ARPG

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There are two main types of abilities in Action RPG (ARPG), Melee and Skills. While both abilities are similar, they do have some differences. For example, Melee abilities activate when the character’s weapon overlaps an enemy, while Skill abilities use skill-specific line trace checks. The following image shows the Blueprint graph for GA_MeleeBase which is the base for all the Melee abilities:

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ActivateAbility is called when an ability starts, and CommitAbility is used to commit the Cost (Mana for ARPG generally) and Cooldown for an ability. EndAbility is called to tell the system that the ability is done executing. The other two nodes are specific to ARPG, and it is expected that each game will add new functions and nodes as needed.

PlayMontageandWaitForEvent is an AbilityTask node, and corresponds to URPGAbilityTask_PlayMontageAndWaitForEvent. AbilityTasks are special objects that define a set of static functions to create the task (PlayMontageAndWaitForEvent in this case), variables and functions used to execute the task. There is also a set of dynamic/Blueprint delegates that are activated from the task. Each output execution pin (besides the top, which always activates immediately) corresponds to one of these delegates, and the output data pins match the signature of the delegate. This specific task is a combination of UAbilityTask_PlayMontageAndWait and UAbilityTask_WaitGameplayEvent, with some game-specific tweaks and comments. Your game will likely need to implement several new gameplay tasks, so this task is an excellent example of how to set this up.

The way these tasks work is by first playing a Montage and then listening for a Gameplay Event to be emitted from the AbilitySystemComponent. If an emitted Gameplay Event matches the passed in EventTags it will activate the EventReceived execution pin with a tag and a payload that will then call the ApplyEffectContainer function. When the Montage blends out, is interrupted, or canceled, the ability ends. The actual gameplay events are emitted from the WeaponActor Blueprint, using the following logic:

ARPG_Melee_Abilities_02.png

This is triggered when the weapon actor overlaps a character. When it does, it constructs a GameplayEventData payload and passes in a Target Actor + Instigator. It then sends a gameplay event using a tag set by an Anim Notify state placed in a Montage. So when that event is triggered, the ability graph will then activate the EventReceived execution pin. The ApplyEffectContainer node corresponds to URPGGameplayAbility::ApplyEffectContainer, which applies a set of gameplay effects. Each URPGGameplayAbility has a map of tags to FRPGGameplayEffectContainer structures, which contain target information and a list of Gameplay Effects to apply. Here is an example of that map from GA_PlayerAxeMelee:

ARPG_Melee_Abilities_03.png

When the AM_Attack_Axe montage is executed, it indicates that when the Event.Montage.Shared.WeaponHit GameplayEvent is emitted it will execute the GE_PlayerAxeMelee effect, using the targeting class RPGTargetType_UseEventData. That target type is implemented in native C++ in the RPGTargetType.cpp file and extracts the target Actors and the hit results from the passed in EventData. The second element in that map executes the BurstPound** special attack, which is a skill that will be described later.

The ApplyEffectContainer does two things: First, it looks for a FRPGGameplayEffectContainer inside this map that matches the passed in tag. If it finds one, it creates a FRPGGameplayEffectContainerSpec containing TargetData and a list of EffectSpecs. Then, it applies that ContainerSpec, which will do the actual damage to the target. Target data is a FGameplayAbilityTargetDataHandle that points to an array of polymorphic target structures that contain hit results, Actors, or something else that is game specific. EffectSpecs is an array of FGameplayEffectSpecHandle that point to an effect to apply plus a list of captured attribute values. Once the effects and target data has been captured, it can then be passed around, modified, and executed at a later point. But, in the case of melee, it is executed immediately after being captured. Each game using the Ability System will probably want to implement a system similar to ApplyEffectContainer, because it makes it easy to put Blueprint logic in a parent ability while placing the list of effects to execute in child Blueprints. However, each game will be slightly different, and if your game includes client prediction targeting it will be much more complicated than the version used in ARPG.