GameplayAbilitySystem

從這篇文章開始，我們將目光轉(zhuǎn)向Gameplay Ability System。
推薦最新的關(guān)于GAS的視頻，你也能下載到ppt：
unreal-fest-europe-2019/using-the-gameplay-ability-system
借用其中Concept部分，可以從整體上認(rèn)知GAS中各個(gè)組件的作用。

AbilitySystemComponent

我們回到AbilitySystemComponent上。從上面的說明我們已經(jīng)可以猜測(cè)到AbilitySystemComponent是一個(gè)龐大的類，"in charge of managing everything GAS related inside the actor"。事實(shí)上，的確如此。AbilitySystemComponent.h有1586行代碼?？纯垂俜浇o出對(duì)于AbilitySystemComponent的說明：

/** 
 *  UAbilitySystemComponent 
 *
 *  A component to easily interface with the 3 aspects of the AbilitySystem:
 *  
 *  GameplayAbilities:
 *      -Provides a way to give/assign abilities that can be used (by a player or AI for example)
 *      -Provides management of instanced abilities (something must hold onto them)
 *      -Provides replication functionality
 *          -Ability state must always be replicated on the UGameplayAbility itself, but UAbilitySystemComponent provides RPC replication
 *          for the actual activation of abilities
 *          
 *  GameplayEffects:
 *      -Provides an FActiveGameplayEffectsContainer for holding active GameplayEffects
 *      -Provides methods for applying GameplayEffects to a target or to self
 *      -Provides wrappers for querying information in FActiveGameplayEffectsContainers (duration, magnitude, etc)
 *      -Provides methods for clearing/remove GameplayEffects
 *      
 *  GameplayAttributes
 *      -Provides methods for allocating and initializing attribute sets
 *      -Provides methods for getting AttributeSets
 *  
 */

AbilitySystemComponent提供了豐富的“method”來(lái)與Ability、Effect、Attribute交互，隨著我們深入GAS，會(huì)接觸到。

URPGGameAbilitySystemComponent.h

// Copyright 1998-2019 Epic Games, Inc. All Rights Reserved.

#pragma once

#include "ActionRPG.h"
#include "AbilitySystemComponent.h"
#include "Abilities/RPGAbilityTypes.h"
#include "RPGAbilitySystemComponent.generated.h"

class URPGGameplayAbility;

/**
 * Subclass of ability system component with game-specific data
 * Most games will need to make a game-specific subclass to provide utility functions
 */
UCLASS()
class ACTIONRPG_API URPGAbilitySystemComponent : public UAbilitySystemComponent
{
    GENERATED_BODY()

public:
    // Constructors and overrides
    URPGAbilitySystemComponent();

    /** Returns a list of currently active ability instances that match the tags */
       /**   返回匹配tag的所有激活的ability實(shí)例**/
    void GetActiveAbilitiesWithTags(const FGameplayTagContainer& GameplayTagContainer, TArray<URPGGameplayAbility*>& ActiveAbilities);

    /** Returns the default level used for ability activations, derived from the character */
      /** 獲得當(dāng)前釋放技能的默認(rèn)等級(jí)，從人物角色上獲得(這個(gè)游戲設(shè)定，應(yīng)該是人物等級(jí)==技能等級(jí)) */
    int32 GetDefaultAbilityLevel() const;

    /** Version of function in AbilitySystemGlobals that returns correct type */
       /** 使用 AbilitySystemGlobals 類的方法，返回特定actor實(shí)例上的abilitysystemcomponent實(shí)例 */
    static URPGAbilitySystemComponent* GetAbilitySystemComponentFromActor(const AActor* Actor, bool LookForComponent = false);

};

拓展了三個(gè)方法，具體作用看注釋。

URPGGameAbilitySystemComponent.cpp

// Copyright 1998-2019 Epic Games, Inc. All Rights Reserved.

#include "Abilities/RPGAbilitySystemComponent.h"
#include "RPGCharacterBase.h"
#include "Abilities/RPGGameplayAbility.h"
#include "AbilitySystemGlobals.h"

URPGAbilitySystemComponent::URPGAbilitySystemComponent() {}

void URPGAbilitySystemComponent::GetActiveAbilitiesWithTags(const FGameplayTagContainer& GameplayTagContainer, TArray<URPGGameplayAbility*>& ActiveAbilities)
{
      /** FGameplayAbilitySpec是對(duì)gameplay ability的包裝，還包含了ability運(yùn)行時(shí)必要的信息 */
    TArray<FGameplayAbilitySpec*> AbilitiesToActivate;

          /** UAbilitySystemComponent的方法，獲得所有可激活的ability specification*/
    GetActivatableGameplayAbilitySpecsByAllMatchingTags(GameplayTagContainer, AbilitiesToActivate, false);

    // Iterate the list of all ability specs
    for (FGameplayAbilitySpec* Spec : AbilitiesToActivate)
    {
        // Iterate all instances on this ability spec
        TArray<UGameplayAbility*> AbilityInstances = Spec->GetAbilityInstances();

        for (UGameplayAbility* ActiveAbility : AbilityInstances)
        {
            ActiveAbilities.Add(Cast<URPGGameplayAbility>(ActiveAbility));
        }
    }
}

int32 URPGAbilitySystemComponent::GetDefaultAbilityLevel() const
{
    ARPGCharacterBase* OwningCharacter = Cast<ARPGCharacterBase>(OwnerActor);

    if (OwningCharacter)
    {
          /** 獲得人物等級(jí) */
        return OwningCharacter->GetCharacterLevel();
    }
    return 1;
}

URPGAbilitySystemComponent* URPGAbilitySystemComponent::GetAbilitySystemComponentFromActor(const AActor* Actor, bool LookForComponent)
{
      /** 使用UAbilitySystemGlobals的方法，對(duì)結(jié)果進(jìn)行cast */
    return Cast<URPGAbilitySystemComponent>(UAbilitySystemGlobals::GetAbilitySystemComponentFromActor(Actor, LookForComponent));
}

現(xiàn)在，我們回顧一下。發(fā)現(xiàn)三個(gè)新添加的get方法都是跟actor有關(guān)：

• GetActiveAbilitiesWithTags： 獲得actor（owner）所有與tag匹配的ability實(shí)例
• GetDefaultAbilityLevel：獲得character（owner）的等級(jí)
• GetAbilitySystemComponentFromActor： 獲得任意Actor實(shí)例掛載的AbilitySystemComponent實(shí)例