用UE4制作一个简单的AI小游戏

UnrealEngine是一个非常强大的引擎，UE4基于DirectX11，拥有新的材料流水线、蓝图视觉化脚本、直观蓝图调试、内容浏览器、人物动画、Matinee影院级工具集、后期处理效果、热重载、模拟与沉浸式视角、实时游戏预览、AI人工智能、音频、中间件集成等一系列全新特性。
下面是用C++结合蓝图实现一个简单的AI功能。效果如下图

• 首先创建一个C++的第三人称工程，UE4的工程有很多类型，我们可以根据自己的需要选择。

• 然后新建需要的C++文件，包括AIPatrol、AIPatrolController、AI巡逻的目标点AITargetPoint，类型分别为Character、Controller、TargetPoint。

• 将上述三个文件扩展成蓝图，这样C++和蓝图可以结合起来，比较方便的实现一些功能。

• 新建BehaviorTree、Blackboard。行为树用来实现AI的逻辑。
  ![T98AAKVRE6]OVK5(AWG0A.png](http://upload-images.jianshu.io/upload_images/1765742-312a11011d4cc53f.png?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240)

• 在AIPatrol上加BehaviorTree：

      UPROPERTY(EditAnywhere,Category=AI)//add behavior to character
      class UBehaviorTree* BehaviorTree;

• 配置character的参数

characer.png

![($$_]V}CV$-GAEQ5IIO7MOE.png](http://upload-images.jianshu.io/upload_images/1765742-ad8ce6fb1d799c49.png?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240)

• AIPatrolController
  .h文件：

             /*behavior tree component*/
            UBehaviorTreeComponent* BehaviorComp;

             /*Our blackboard component*/
             UBlackboardComponent* BlackboardComp;

             /*Blackboard keys*/
             UPROPERTY(EditDefaultsOnly, Category = AI)
                    FName LocationToGoKey;

             UPROPERTY(EditDefaultsOnly, Category = AI)
                    FName PlayerKey;

             //store all TargetPoints
             TArray PatrolPoints;

             virtual void Possess(APawn* Pawn) override;
public:
      AAIPatrolController();

      void SetPlayerCaught(APawn* Pawn);//caught:捕捉

      /*Inline getter functions*/
      FORCEINLINE UBlackboardComponent* GetBlackboardComp() const { return BlackboardComp; }
      FORCEINLINE TArray GetPatrolPoints() const { return PatrolPoints; }

.cpp文件：

AAIPatrolController::AAIPatrolController()
{
       /*initialize blackboard and behavior tree*/
       BehaviorComp = CreateDefaultSubobject(TEXT("BehaviorComp"));
       BlackboardComp = CreateDefaultSubobject(TEXT("BlackboardComp"));

       /*Initialize blackboard keys*/
       PlayerKey = "Target";
       LocationToGoKey = "LocationToGo";
}

void AAIPatrolController::SetPlayerCaught(APawn* MyPawn)
{
       if (BlackboardComp)
       {
              BlackboardComp->SetValueAsObject(PlayerKey, MyPawn);
       }
}

void AAIPatrolController::Possess(APawn* MyPawn)
{
       Super::Possess(MyPawn);

       /*Get reference to the character*/
       AAIPatrol* AICharacter = Cast(MyPawn);
       if (AICharacter)
       {
              if (AICharacter->BehaviorTree->BlackboardAsset)
              {
                     BlackboardComp->InitializeBlackboard(*(AICharacter->BehaviorTree->BlackboardAsset));
              }

              /*Populate patrol point array*/
              UGameplayStatics::GetAllActorsOfClass(GetWorld(), AAIpPatrolPoint::StaticClass(), PatrolPoints);

              BehaviorComp->StartTree(*AICharacter->BehaviorTree);

       }
}

• 玩家被抓住的方法：
  AIPatrolController：

void AAIPatrolController::SetPlayerCaught(APawn* MyPawn)//玩家被抓住
{
       if (BlackboardComp)
       {
              BlackboardComp->SetValueAsObject(PlayerKey, MyPawn);//给玩家添加key值
       }
}

AIPatrol：

AAIPatrol::AAIPatrol()
{
       //Initialize senses
       /**UPawnSensingComponent :
       * SensingComponent encapsulates(封装) sensory(感知) (ie sight and hearing) settings and functionality for an Actor,
       * allowing the actor to see/hear Pawns in the world. It does nothing on network clients.
       */
       PawnSensingComp = CreateDefaultSubobject(TEXT("PawnSensingComp"));
       PawnSensingComp->SetPeripheralVisionAngle(90.0f);

}

// Called when the game starts or when spawned
void AAIPatrol::BeginPlay()
{
       Super::BeginPlay();

       if (PawnSensingComp)
       {
              /** OnSeePawn : Delegate to execute when we see a Pawn. */
              PawnSensingComp->OnSeePawn.AddDynamic(this, &AAIPatrol::OnplayerCaught);
       }
}

void AAIPatrol::OnplayerCaught(APawn* Pawn)
{
       /*Get a reference to the palyer controller*/
       AAIPatrolController* AIController = Cast(GetController());
       if (AIController)
       {
              GEngine->AddOnScreenDebugMessage(-1, 5.0f, FColor::Red, TEXT("You having been caught!"));
              AIController->SetPlayerCaught(Pawn);
       }
}

*　创建BTTask的C++文件，命名为BTSelectPatrolPoint。注意，这时要在Source文件夹中找到ProjectName.Build.cs文件，添加GameplayTasks到PublicDependencyModuleName中。.build.cs文件是编译文件，位于游戏性模块的根目录中，它定义了UnrealBuildTool编译该模块时要使用的一些信息。

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BTTask：

EBTNodeResult::Type UBTSelectPatrolPoint::ExecuteTask(UBehaviorTreeComponent & OwnerComp, uint8 * NodeMemory)
{

       //get AIPatrolController
       AAIPatrolController* AICon = Cast(OwnerComp.GetAIOwner());

       // check the get is successful
       if (AICon)
       {
              //Get Blackboard Component
              UBlackboardComponent* BlackboardComp = AICon->GetBlackboardComp();

              // get patrolPoint
              AAIpPatrolPoint* CurrentPoint = Cast(BlackboardComp->GetValueAsObject("LocationToGo"));

              TArray AvailablePatrolPoints = AICon->GetPatrolPoints();
              AAIpPatrolPoint* NextPatrolPoint = nullptr;

              // set NextPatrolPoint
              if (AICon->CurrentPatrolPoint != AvailablePatrolPoints.Num() - 1)
              {
                     NextPatrolPoint = Cast(AvailablePatrolPoints[++AICon->CurrentPatrolPoint]);
              }
              else
              {
                     NextPatrolPoint = Cast(AvailablePatrolPoints[0]);
                     AICon->CurrentPatrolPoint = 0;
              }

              // set blackboard keyValue
              BlackboardComp->SetValueAsObject("LocationToGo", NextPatrolPoint);
              return EBTNodeResult::Succeeded;
       }
       return EBTNodeResult::Failed;

}

• 将BP_AIPatrol放入场景，摆放好BP_AIPatrolPoints，即AI 要走的路径，编辑BehaviorTree。

374539dd-5422-4ed9-b45d-5673aabe9863.png

BehaviorTree的思路是首先执行BTSelectPatrolPoint，如果没有找到目标，就move to key值为LocationToGo的点，如果找到了Target，就移动到Target处，然后在target处停留1秒。

• 最后，添加自动寻路组件NavMeshBoundsVolume，这样AI在寻路过程中就会自动绕开障碍物。