说明

AI Service / AIDecorator

BTService

添加到行为树节点的特殊类. 自带Tick函数, 在其中实现游戏逻辑.

在给定条件, 可以修改黑板中的变量值.

本节将通过服务重写定位敌人逻辑, 当敌人出现在NPC的捕捉范围内, 计算得到敌人附近一点, 使NPC跑去该位置.

可以添加到行为树的任意节点

添加黑板变量

BB_STUCharacter

添加类型为Object的变量, 命名为EnemyActor; 存放选中敌人

创建行为树服务类

-
	AI/Services
基类	BTService
	Public
名称	STUFindEnemyService

每秒搜索距离NPC最近的敌人

修改头文件搜索路径

ShootThemUp: ShootThemUp.Build.cs

Copy 1PublicIncludePaths.AddRange(new string[]
 2{
 3    "ShootThemUp/Public/Player",
 4    "ShootThemUp/Public/Components",
 5    "ShootThemUp/Public/Dev",
 6    "ShootThemUp/Public/Weapon",
 7    "ShootThemUp/Public/UI",
 8    "ShootThemUp/Public/Animations",
 9    "ShootThemUp/Public/Pickups",
10    "ShootThemUp/Public/Weapon/Components",
11    "ShootThemUp/Public/AI",
12    "ShootThemUp/Public/AI/Tasks",
13    "ShootThemUp/Public/AI/Services"            
14});

添加构造函数

public

ShootThemUp: AI/Services/STUFindEnemyService.h

Copy1USTUFindEnemyService();

设置服务名称

ShootThemUp: AI/Services/STUFindEnemyService.cpp

Copy1USTUFindEnemyService::USTUFindEnemyService()
2{
3    NodeName = "Find Enemy";
4}

添加属性: 存放黑板变量信息

protected

ShootThemUp: AI/Services/STUFindEnemyService.h

Copy1UPROPERTY(EditAnywhere, BlueprintReadWrite)
2FBlackboardKeySelector EnemyActorKey;

添加TickNode函数

可以设置调用频率; 在此定位敌人

protected

ShootThemUp: AI/Services/STUFindEnemyService.h

Copy1virtual void TickNode(UBehaviorTreeComponent &OwnerComp, uint8 *NodeMemory, float DeltaSeconds) override;

ShootThemUp: AI/Services/STUFindEnemyService.cpp

Copy 1#include "BehaviorTree/BlackboardComponent.h"
 2#include "AIController.h"
 3#include "STUUtils.h"
 4#include "Components/STUAIPerceptionComponent.h"
 5
 6void USTUFindEnemyService::TickNode(UBehaviorTreeComponent &OwnerComp, uint8 *NodeMemory, float DeltaSeconds)
 7{
 8    const auto Blackboard = OwnerComp.GetBlackboardComponent();
 9    if (Blackboard)
10    {
11        const auto Controller = OwnerComp.GetAIOwner();
12        const auto PerceptionComponent = STUUtils::GetSTUPlayerComponent<USTUAIPerceptionComponent>(Controller);
13        if (PerceptionComponent)
14        {
15            Blackboard->SetValueAsObject(EnemyActorKey.SelectedKeyName, PerceptionComponent->GetClosestEnemy());
16        }
17    }
18    Super::TickNode(OwnerComp, NodeMemory, DeltaSeconds);
19}

SetValueAsObject函数

第一个参数: 变量名

第二个参数: 给出指向敌人的UObject指针

在AIController中使用服务

添加属性: 存放变量名

无法使用选择器, Controller不涉及黑板变量逻辑

ShootThemUp: AI/STUAIController.h

Copy1UPROPERTY(EditAnywhere, BlueprintReadWrite)
2FName FocusOnKeyName = "EnemyActor";

添加接口: 返回敌人对象

private

ShootThemUp: AI/STUAIController.h

Copy1AActor *GetFocusOnActor() const;

ShootThemUp: AI/STUAIController.cpp

Copy1#include "BehaviorTree/BlackboardComponent.h"
2
3AActor *ASTUAIController::GetFocusOnActor() const
4{
5    if (!GetBlackboardComponent()) return nullptr;
6    return Cast<AActor>(GetBlackboardComponent()->GetValueAsObject(FocusOnKeyName));
7}

在Tick函数中使用服务

不直接使用感知组件接口

ShootThemUp: AI/STUAIController.cpp

Copy1// Tick
2const auto AimActor = GetFocusOnActor();

NPC行为树

BT_STUCharacter

NPC有两个职责:

• 在地图上巡逻
  
  将序列命名为Random roam
  
• 攻击
  
  添加节点: Sequence, 命名为Attack
  

添加节点: Selector

从左到右运行子树. 若排行较前的子树返回Fail, 则执行下一子树

为Selector添加服务: 一直查找敌人

右键 Selector , Add Service > STUFindEnemyService

设置STUFindEnemyService

-		说明
EnemyActorKey	EnemyActor
Service > Interval		Tick调用频率上限F
Service > RandomDeviation		Tick调用频率活动范围FR

Tick实际调用频率在F-FR ~ F+FR之间

为Attack添加任务: MoveTo

Blackboard Key无法选择EnemyActor

设置黑板变量EnemyActor

BB_STUCharacter > Enemy Actor > Blackboard Details > Key Type > Base Class , 设置为Actor : UObject对象在世界中不具有变化属性

设置MoveTo目的地为EnemyActor; 勾选 Observe Blackboard Value

变量值发生改变时, 新目的地立即生效

查看

UE4.27: 当Find Enemy不为空, 且无法找到AimLocation时, 才会执行Attack序列

UE5.1: 定时执行Find Enemy, 从左到右执行Attack和Rand roam; Enemy Actor不为空, 靠近选中敌人, 为空, 去到随机生成的位置

使用Decorator

Decorator包含逻辑判断, 类似switch, 可以中断整棵子树

根据EnemyActor的设置情况, 决定执行哪个序列

为Attack添加Decorator: Blackboard

Blackboard会检查黑板变量的值

• 选中 Blackboard Based Condition

Details > Description > Node Name 命名为 Has Enemy
  

  Details > Blackboard > Blackboard Key , 选中EnemyActor
  

  Details > Blackboard > Key Query , 选择IsSet分支
  

  Details > Flow Control > Observer aborts , 选择Self
  

  

  
  

• 若EnemyActor有值, 执行Attack, 否则中止序列
  

为Random roam添加Decorator

• 命名为No Enemy
  

  Details > Blackboard > Blackboard Key , 选中EnemyActor
  

  Details > Blackboard > Key Query , 选择IsNotSet分支
  

  Details > Flow Control > Observer aborts , 选择Self
  

  

  
  

• 若EnemyActor没有值, 执行Random roam, 否则中止序列
  

使NPC移动到敌人附近

• 添加标志位: 以自身为圆心寻找随机点 巡逻 ; 以敌人为圆心寻找随机点 攻击

protected

ShootThemUp: AI/Tasks/STUNextLocationTask.h
  

  Copy1UPROPERTY(EditAnywhere, BlueprintReadWrite)
  2bool SelfCenter = true;

• 添加属性: 如果以敌人为圆心寻找随机点, 保存敌人信息
  
  protected

ShootThemUp: AI/Tasks/STUNextLocationTask.h
  

  Copy1UPROPERTY(EditAnywhere, BlueprintReadWrite, meta = (EditCondition = "!SelfCenter"))
  2FBlackboardKeySelector CenterActorKey;

• 设置随机位置中心点
  
  ShootThemUp: AI/Tasks/STUNextLocationTask.cpp
  

  Copy 1// ExecuteTask
   2
   3auto Location = Pawn->GetActorLocation();
   4if (!SelfCenter)
   5{
   6    auto CenterActor = Cast<AActor>(Blackboard->GetValueAsObject(CenterActorKey.SelectedKeyName));
   7    if (!CenterActor) return EBTNodeResult::Failed;
   8    Location = CenterActor->GetActorLocation();
   9}
  10
  11const auto Found = NavSys->GetRandomReachablePointInRadius(Location, Radius, NavLocation);

设置Attack序列

• 添加任务: STUNextLocationTask
  
  进行如下设置
  

  

  
  

• 设置MoveTo目的地