148 lines
9.9 KiB
Markdown
148 lines
9.9 KiB
Markdown
## UGameplayAbility
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UGameplayAbility在GameplayAbility框架中代表一个技能（也可以认为是能力，它可以事件主动或者被动技能），我们可以通过继承UGameplayAbility来编写新技能。
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UGameplayAbility主要提供以下功能：
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- 使用特性：技能cd、技能消耗等
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- 网络同步支持
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- 实例支持：non-instance（只在本地运行）、Instanced per owner、Instanced per execution (默认)
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其中GameplayAbility_Montage就是non-instanced ability的案例，non-instanced在网络同步中有若干限制，具体的参考源代码。
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### 使用方式
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在ActivateAbility事件中编写相关技能逻辑（角色动作、粒子效果、角色数值变动），最后根据具体情况（技能是否施展成功）调用CommitAbility()或EndAbility()。
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如果有特殊可以在对应的事件中编写代码，例如你需要技能释放结束后播放粒子特效：那么就需要在onEndAbility事件中编写代码。
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在c++中，你需要重写ActivateAbility()函数。这里建议直接复制ActivateAbility的代码并且在它的基础上编写逻辑，因为他兼顾了蓝图子类。
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编写了Ability之后就需要将它注册到AbilityComponent中。但首先你需要创建正式用于编写角色逻辑的角色类，ActionRPG案例中将基础的GameplayAbility逻辑都写在URPGCharacterBase类中，所以现在你需要通过继承URPGCharacterBase来编写正式的角色逻辑（包括各种输入、摄像机等等）
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此时你只需要在新建的子类的构造函数中手动添加GameplayAbilities数组即可：
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```
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GameplayAbilities.Push(UGA_SkillBase::StaticClass());
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```
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### 在ActionRPG案例中的做法
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在ActionRPG案例中，定义了URPGGameplayAbility（继承于UGameplayAbility）作为项目中所有GameplayAbility的基类。它实现了实现了以下方法：
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```
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/** Gameplay标签与GameplayEffect Map */
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UPROPERTY(EditDefaultsOnly, BlueprintReadOnly, Category = GameplayEffects)
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TMap<FGameplayTag, FRPGGameplayEffectContainer> EffectContainerMap;
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/** 读取指定的FRPGGameplayEffectContainer来生成FRPGGameplayEffectContainerSpec */
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UFUNCTION(BlueprintCallable, Category = Ability, meta = (AutoCreateRefTerm = "EventData"))
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virtual FRPGGameplayEffectContainerSpec MakeEffectContainerSpecFromContainer(const FRPGGameplayEffectContainer& Container, const FGameplayEventData& EventData, int32 OverrideGameplayLevel = -1);
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/** 通过GameplayTag来搜索EffectContainerMap，并且生成FRPGGameplayEffectContainerSpec */
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UFUNCTION(BlueprintCallable, Category = Ability, meta = (AutoCreateRefTerm = "EventData"))
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virtual FRPGGameplayEffectContainerSpec MakeEffectContainerSpec(FGameplayTag ContainerTag, const FGameplayEventData& EventData, int32 OverrideGameplayLevel = -1);
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/** 让FRPGGameplayEffectContainerSpec中的effect对指定目标生效 */
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UFUNCTION(BlueprintCallable, Category = Ability)
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virtual TArray<FActiveGameplayEffectHandle> ApplyEffectContainerSpec(const FRPGGameplayEffectContainerSpec& ContainerSpec);
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/** 调用MakeEffectContainerSpec生成FRPGGameplayEffectContainerSpec，再让Effect对目标生效 */
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UFUNCTION(BlueprintCallable, Category = Ability, meta = (AutoCreateRefTerm = "EventData"))
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virtual TArray<FActiveGameplayEffectHandle> ApplyEffectContainer(FGameplayTag ContainerTag, const FGameplayEventData& EventData, int32 OverrideGameplayLevel = -1);
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```
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代码很简单，大致可以归纳为：
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1. 维护一个GameplayTag与RPGGameplayEffectContainer的映射表EffectContainerMap。
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2. 创建FRPGGameplayEffectContainerSpec。(可以通过GameplayTag查找EffectContainerMap或者通过指定的RPGGameplayEffectContainer)。
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3. 通过FRPGGameplayEffectContainerSpec，让内部所有effect对目标生效。
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### URPGTargetType
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父类是UObject，只有一个GetTargets事件。之后通过各种的子类来实现各种的目标效果。
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该类用于实现获取Ability所作用的目标，换句话说是获取目标数据的逻辑（目标Actor数组）。用以实现例如：单体目标，范围目标等等
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### FRPGGameplayEffectContainer
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结构体，存储了URPGTargetType对象与UGameplayEffect容器数组对象。
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### FRPGGameplayEffectContainerSpec
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RPGGameplayEffectContainer的处理后版本。
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在URPGGameplayAbility中会调用MakeEffectContainerSpecFromContainer()生成。
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如果FRPGGameplayEffectContainer存在TargetType对象，就会调用它的GetTargets函数来获取HitResult数组与Actor数组。最后调用AddTargets函数来填充FRPGGameplayEffectContainerSpec中的Target信息。
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填充FRPGGameplayEffectContainerSpec的FGameplayEffectSpecHandle数组（FGameplayEffectSpecHandle中包含了FGameplayEffectSpec的智能指针）
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说了那么多，其实就是将Effect应用到所有TargetActor上。
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### 重要函数
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从头文件中复制的注释：
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```
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CanActivateAbility() - const function to see if ability is activatable. Callable by UI etc
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TryActivateAbility() - Attempts to activate the ability. Calls CanActivateAbility(). Input events can call this directly.
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- Also handles instancing-per-execution logic and replication/prediction calls.
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CallActivateAbility() - Protected, non virtual function. Does some boilerplate 'pre activate' stuff, then calls ActivateAbility()
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ActivateAbility() - What the abilities *does*. This is what child classes want to override.
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CommitAbility() - Commits reources/cooldowns etc. ActivateAbility() must call this!
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CancelAbility() - Interrupts the ability (from an outside source).
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EndAbility() - The ability has ended. This is intended to be called by the ability to end itself.
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```
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## 关于BindAbilityActivationToInputComponent
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~~这个东西我查了Github、AnswerHUB以及轮廓，没有任何资料（除了作者的Wiki）。看了源代码也看不出所以然，而且ActionRPG里也没有使用这个函数，可以看得出即使不用这个函数也不会影响该框架别的功能（可能会对联机游戏产生影响）。~~
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经过@键盘侠·伍德 的指导，我才知道用法：
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1. 声明一个用于映射输入的枚举类
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```
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UENUM(BlueprintType)
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enum class AbilityInput : uint8
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{
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UseAbility1 UMETA(DisplayName = "Use Spell 1"), //This maps the first ability(input ID should be 0 in int) to the action mapping(which you define in the project settings) by the name of "UseAbility1". "Use Spell 1" is the blueprint name of the element.
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UseAbility2 UMETA(DisplayName = "Use Spell 2"), //Maps ability 2(input ID 1) to action mapping UseAbility2. "Use Spell 2" is mostly used for when the enum is a blueprint variable.
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UseAbility3 UMETA(DisplayName = "Use Spell 3"),
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UseAbility4 UMETA(DisplayName = "Use Spell 4"),
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WeaponAbility UMETA(DisplayName = "Use Weapon"), //This finally maps the fifth ability(here designated to be your weaponability, or auto-attack, or whatever) to action mapping "WeaponAbility".
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//You may also do something like define an enum element name that is not actually mapped to an input, for example if you have a passive ability that isn't supposed to have an input. This isn't usually necessary though as you usually grant abilities via input ID,
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//which can be negative while enums cannot. In fact, a constant called "INDEX_NONE" exists for the exact purpose of rendering an input as unavailable, and it's simply defined as -1.
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//Because abilities are granted by input ID, which is an int, you may use enum elements to describe the ID anyway however, because enums are fancily dressed up ints.
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};
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```
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2. 在SetupPlayerInputComponent函数中调用BindAbilityActivationToInputComponent函数
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例如：
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```
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void ARPGCharacter::SetupPlayerInputComponent(class UInputComponent* PlayerInputComponent)
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{
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// Set up gameplay key bindings
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check(PlayerInputComponent);
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PlayerInputComponent->BindAction("Jump", IE_Pressed, this, &ACharacter::Jump);
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PlayerInputComponent->BindAction("Jump", IE_Released, this, &ACharacter::StopJumping);
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PlayerInputComponent->BindAxis("MoveForward", this, &ARPGCharacter::MoveForward);
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PlayerInputComponent->BindAxis("MoveRight", this, &ARPGCharacter::MoveRight);
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// We have 2 versions of the rotation bindings to handle different kinds of devices differently
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// "turn" handles devices that provide an absolute delta, such as a mouse.
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// "turnrate" is for devices that we choose to treat as a rate of change, such as an analog joystick
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PlayerInputComponent->BindAxis("Turn", this, &APawn::AddControllerYawInput);
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PlayerInputComponent->BindAxis("TurnRate", this, &ARPGCharacter::TurnAtRate);
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PlayerInputComponent->BindAxis("LookUp", this, &APawn::AddControllerPitchInput);
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PlayerInputComponent->BindAxis("LookUpRate", this, &ARPGCharacter::LookUpAtRate);
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//PlayerInputComponent->BindAction("CastBaseSkill", IE_Pressed, this, &ARPGCharacter::CastBaseSkill);
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AbilitySystemComponent->BindAbilityActivationToInputComponent(PlayerInputComponent, FGameplayAbilityInputBinds("ConfirmInput", "CancelInput", "AbilityInput"));
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}
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```
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3. 在执行GiveAbility函数（注册能力）时，设置输入id。输入id为枚举类中对应的枚举值。（例如本案例中UseAbility1为0，UseAbility2为1，UseAbility3为2）
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```
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FGameplayAbilitySpec(TSubclassOf<UGameplayAbility> InAbilityClass, int32 InLevel, int32 InInputID, UObject* InSourceObject)
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```
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4. 在项目设置——输入中，按照所设置的输入id所对应的枚举，添加ActionMapping。例如：UseAbility1、UseAbility2、UseAbility3。
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这样做可以达到对Control解耦的目的。因为你调用GiveAbility或者ClearAbility时会自动绑定输入。而不需要手动去角色类或者控制类中手动设置。
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### 有关InputPressed与InputReleased
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执行了上述输入绑定措施，你就可以通过重写InputPressed与InputReleased，来执行对应的逻辑。
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调用这两个虚函数的逻辑在UAbilitySystemComponent中的AbilitySpecInputPressed与AbilitySpecInputReleased。
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个人认为这些逻辑还会有可能会在蓝图中编写，所以新继承的类可以创建新的BlueprintNativeEvent，这样对工程开发会更加友好。
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