Hi, I’m making AI attack Player right now. But here’s where I got the problem. I was trying to make AI look at the Player. But it didn’t work.
There seemed to be nothing wrong with the code, so I deleted Intermediate, Binaries, and started it again. But when I suddenly played it, the AI didn’t move at all. I checked the Behavior tree while playing, and it stopped at Root and didn’t intend to go down to the lower node.
What should I check?
Hey @sehwa!
Let’s start out by showing us your code. 
That way we can go piece by piece over what the problem could be- the only things you CAN’T delete to refresh are Config, Content, Plugins, and Source.
Get us some pics and let’s get to work!
Thank you for your answer! First, I’ll show you my service code and tasks. First of all, please understand that the content may be long…! Sorry!!
First of all, I re-created the action tree today. With BT_Attack. BT_Attack ran. But I want to know why the existing BT_NPC doesn’t work…!
This picture is a weird thing to stop at the root when you play it.
void UBTService_SeePlayer::TickNode(UBehaviorTreeComponent& OwnerComp, uint8* NodeMemory, float DeltaSeconds)
{
Super::TickNode(OwnerComp, NodeMemory, DeltaSeconds);
APawn* Player = UGameplayStatics::GetPlayerPawn(GetWorld(), 0); // 플레이어 폰 가져오기
AAIController* AIController = OwnerComp.GetAIOwner(); // AI 컨트롤러 가져오기
APawn* NPC = AIController->GetPawn(); // AI 폰 가져오기
// AI의 시야에 플레이어가 보이면
if (AIController->LineOfSightTo(Player))
{
UWorld* World = NPC->GetWorld(); // AI 가 속한 월드 가져오기
FName PlayerPositionName = TEXT("PlayerPos");
FVector PlayerPosition = Player->GetActorLocation(); // 플레이어 위치 가져오기
OwnerComp.GetBlackboardComponent()->SetValueAsVector(PlayerPositionName, Player->GetActorLocation()); // 플레이어 위치 저장(Set은 변수에 못 담는다.)
FName TargetName = TEXT("Target");
OwnerComp.GetBlackboardComponent()->SetValueAsObject(TargetName, Player); // 타겟을 Player로 설정
// 플레이어와의 위치를 선과 점으로 표현
DrawDebugPoint(World, Player->GetActorLocation(), 10.0f, FColor::Green, false, 0.2f);
DrawDebugLine(World, NPC->GetActorLocation(), Player->GetActorLocation(), FColor::Green, false, 0.27f);
}
else
{
FName TargetName = TEXT("Target");
OwnerComp.GetBlackboardComponent()->SetValueAsObject(TargetName, nullptr); // 타겟을 null로 설정
}
}
bool UBTDecorator_AttackRange::CalculateRawConditionValue(UBehaviorTreeComponent& OwnerComp, uint8* NodeMemory) const
{
Super::CalculateRawConditionValue(OwnerComp, NodeMemory);
APawn* NPC = OwnerComp.GetAIOwner()->GetPawn();
if (NPC == nullptr)
{
UE_LOG(LogTemp, Error, TEXT("No NPC"));
return false;
}
FName PlayerName = TEXT("Target");
APawn* Player = Cast<APawn>(OwnerComp.GetBlackboardComponent()->GetValueAsObject(PlayerName)); // 타겟인 플레이어 가져오기(캐스팅하기)
if (Player == nullptr)
{
UE_LOG(LogTemp, Error, TEXT("No Target"));
return false;
}
IOLNPCInterface* NPCInterface = Cast<IOLNPCInterface>(NPC); // NPC가 인터페이스를 생성한 경우 캐스팅이 됨
// nullptr로 인터페이스가 없는지 확인을 해야 하는데 착각하고 nullptr을 넣지 않아서 인터페이스가 존재하는 상태에서 false가 되버림(그래서 npc가 자꾸 나를 쫓아오게 됨)
if (NPCInterface == nullptr)
{
UE_LOG(LogTemp, Error, TEXT("No NPCInterface"));
return false;
}
float Distance = FVector::Dist(NPC->GetActorLocation(), Player->GetActorLocation()); // NPC와 플레이어 사이의 거리 구하기
float AttackRange = NPCInterface->AttackRange();
bool AttackRangeResult = Distance <= AttackRange;
return AttackRangeResult;
}
If I can explain this code, Service will keep you checking if the player can see it. If you see it, let’s make the target value the player. And then if it comes within the range of the attack, it attacks and if it doesn’t, it’s the same code that keeps you going.
I don’t know how to use English, so the sentence can be awkward because I use a translator. I’m sorry.
Are you saying that the Behavior Tree in the picture works, but your BT_NPC (not pictured here) isn’t working, and that’s the one you need help with? Could you post a picture of the broken one? Sorry, maybe I’m not understanding because of translation! Could you clear this up?
I’m sorry for the confusion 
The picture I posted is BT_NPC (not working). That action tree in the picture stopped at the root. I just wanted to say that BT_Attack is made the same as the picture. The picture I just posted is BT_NPC, and it’s made the same as BT_Attack.
The help I need is that BT_Attack and BT_NPC made the same as in the picture, but only BT_NPC doesn’t work. It’s true that BT_NPC doesn’t work. BT_NPC stops at the root and doesn’t come down to the lower node as in the picture..
I’m sorry to say the same thing many times..
Okay! I get it now!
So try this:
The reason to do this is the root seems like it’s not finding a way through to do any tasks. This is called a “Fallback”, and what it does is it will highlight the “Wait” node and do that if it can’t reach anything else, just to tell you that it IS working. Try that and see if it does anything (and bring a picture to make sure you set it up right! )
Thank you again for your answer!
So this is definitely not a glitch!
What is happening is on this Sequence node is the Decorator is saying “False” and cannot continue down. The red bar shows us that.
On the OTHER side, “Attack Range” is returning False, preventing it from continuing down.
The behavior tree isn’t ever reaching a task to execute. What I understand from this is The Target is set, but is out of range, so it cannot do anything, and sits at root until one of those turns true.
I hope that makes sense!
Thanks to you, I understand! Thank you!
So is there a way to fix that red bar
If you see a player in the service, they set the target as well, so how did it become false? And if it’s out of the Attack Range, it’s False, so shouldn’t the TargetChase node run?
Was the code a problem?
I understand why it’s not working, but I still have a lot of questions. I’m sorry.
In this graph, the target is seen and set. Therefore it has to go down the left path.
Then it is out of range, so it cannot attack.
It isn’t going to the Movement node that is next because these aren’t connected, that’s why it’s dark gray instead of light gray.
Mind-Brain!!! I have good news.
When I checked after play, if the node is not connected, the red bar appears, and if I connect the node, the red bar does not appear.
Thank you so much. Thanks to you, I solved my troubles and I learned a lot! 
