虚幻四Gameplay Ability System入门(10)-地爆天星！TargetActor Tick

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既然神罗天征都做了，那索性把地爆天星也给做了吧。

这里做几个小改动，首先就是将TargetActor的启动方式从Instant改为User Confirm。流程就变为1.start targeting 2.玩家confirm 3.结束targeting并传输数据

第二是给Actor加上tick，因为目标追踪本身是一个Actor，那么它自然可以拥有心跳（tick）。我们期望在玩家确认前可以随时调整技能的释放位置。

其它就是一些技能特效和逻辑的小改动。

先看看最终的效果吧（图片太大了放不进去）

TargetActor

首先还是创建TargetActor派生类，命名为AbilityChibakuTenseiTargetActor。

头文件中和之前做了些改动，需要重写Tick函数。新增了两个Actor对象，一个是用来显示技能释放的位置，这个位置会在Tick当中更新；一个用来作为技能效果，也就是视频中中心的那个球。还多了一个函数，用来获取角色的视线与地面碰撞的位置。

UCLASS()
class GAS_LEARN_API AAbilityChibakuTenseiTargetActor : public AGameplayAbilityTargetActor
{GENERATED_BODY()public:AAbilityChibakuTenseiTargetActor();virtual void StartTargeting(UGameplayAbility* Ability) override;virtual void ConfirmTargetingAndContinue() override;virtual void Tick(float DeltaSeconds) override;UPROPERTY(EditAnywhere, BlueprintReadWrite, Category="Ability Settings", meta=(ExposeOnSpawn = true))float Radius;UPROPERTY(EditAnywhere, BlueprintReadOnly, Category="Ability Settings", meta=(ExposeOnSpawn = true))TSubclassOf<AActor> ConePointClass;UPROPERTY(EditAnywhere, BlueprintReadOnly, Category="Ability Settings", meta=(ExposeOnSpawn = true))TSubclassOf<AActor> MeteorClass;// Get Player Looking Point VectorUFUNCTION(BlueprintCallable, Category="Chikabu Tensei")bool GetPlayerLookingPoint(FVector& LookingPoint);protected:UPROPERTY()AActor* ConePoint;UPROPERTY()AActor* Meteor;
};

构造函数中需要让Actor拥有心跳，所以需要让bCanEverTick=true

AAbilityChibakuTenseiTargetActor::AAbilityChibakuTenseiTargetActor()
{PrimaryActorTick.bCanEverTick = true;}

在开始追踪目标后，创建Actor ConePoint用来表示技能的释放位置。

void AAbilityChibakuTenseiTargetActor::StartTargeting(UGameplayAbility* Ability)
{OwningAbility = Ability;MasterPC = Cast<APlayerController>(Ability->GetOwningActorFromActorInfo()->GetInstigatorController());SourceActor = Ability->GetOwningActorFromActorInfo();ConePoint = GetWorld()->SpawnActor<AActor>(ConePointClass, FVector::ZeroVector, FRotator::ZeroRotator);
}

GetPlayerLookingPoint用来获取视线与地面的碰撞点：

通过PlayerController→GetPlayerViewPoint(ViewVector, ViewRotation)可以获取角色的视线方向和位置。当然，这里可以通过获取Character的Camera的位置和方向来替代这个函数。
然后通过GetWorld()->LineTraceSingleByChannel从角色视线方向发射一道射线，检测碰撞位置。
发生碰撞后，LookingPoint = HitResult.ImpactPoint就可以得到视线位置。

bool AAbilityChibakuTenseiTargetActor::GetPlayerLookingPoint(FVector& LookingPoint)
{// Get Player View Vector and View RotationFVector ViewVector;FRotator ViewRotation;if(MasterPC)MasterPC->GetPlayerViewPoint(ViewVector, ViewRotation);FCollisionQueryParams QueryParams;QueryParams.bTraceComplex = false;if(SourceActor){QueryParams.AddIgnoredActor(SourceActor->GetUniqueID());}FHitResult HitResult;bool TryTrace = GetWorld()->LineTraceSingleByChannel(HitResult,ViewVector,ViewVector + ViewRotation.Vector()*10000.0f,ECollisionChannel::ECC_Visibility,QueryParams);if(TryTrace){LookingPoint = HitResult.ImpactPoint;}else{LookingPoint = FVector::ZeroVector;}return TryTrace;
}

在Tick函数中，首先获取LookLocation，然后更新ConePoint的位置为视线看向的位置。

void AAbilityChibakuTenseiTargetActor::Tick(float DeltaSeconds)
{Super::Tick(DeltaSeconds);FVector LookLocation;GetPlayerLookingPoint(LookLocation);ConePoint->SetActorLocation(LookLocation);
}

ConfirmTargetingAndContinue函数基本和上一篇文章里的一样。

唯一的区别就是碰撞检测完成后生成一个代表技能效果的火球Actor，然后也将球放入TargetData中。

void AAbilityChibakuTenseiTargetActor::ConfirmTargetingAndContinue()
{// ViewLocation是生成碰撞检测的位置FVector ViewLocation;GetPlayerLookingPoint(ViewLocation);TArray<FOverlapResult> OverlapResults;TArray<TWeakObjectPtr<AActor>> OverlapActors;FCollisionQueryParams QueryParams;QueryParams.bTraceComplex = false;QueryParams.bReturnPhysicalMaterial = false;if(SourceActor){QueryParams.AddIgnoredActor(SourceActor->GetUniqueID());}bool TryOverlap = GetWorld()->OverlapMultiByObjectType(OverlapResults,ViewLocation,FQuat::Identity,FCollisionObjectQueryParams(ECC_Pawn),FCollisionShape::MakeSphere(Radius),QueryParams);if(TryOverlap){for(FOverlapResult& OverlapResult: OverlapResults){APawn* PawnOverlapped = Cast<APawn>(OverlapResult.Actor);if(PawnOverlapped){OverlapActors.AddUnique(PawnOverlapped);}}}FVector MeteorSpawnLocation = ConePoint->GetActorLocation();MeteorSpawnLocation += ConePoint->GetActorUpVector() * 100.0f;Meteor = GetWorld()->SpawnActor<AActor>(MeteorClass, MeteorSpawnLocation, ConePoint->GetActorRotation());ConePoint->Destroy();OverlapActors.Add(Meteor);FGameplayAbilityTargetDataHandle TargetData =  StartLocation.MakeTargetDataHandleFromActors(OverlapActors);TargetDataReadyDelegate.Broadcast(TargetData);}