[UE4]網遊中角色Pawn的移動位置同步以及RTS多角色同時移動的解決方案

下面方案的思路是：
每個Actor，爲其定義一個代理（ActorProxy），真實的Actor放在服務端，代理ActorProxy放在客戶端，移動Actor時，實際是移動服務端上的Actor，然後對客戶端ActorProxy的位置進行同步。

攝像機綁定的是ActorProxy，服務端的真實Actor不用攝像機；而AIController實際控制的是服務端Actor，客戶端其實沒有AIController。

另外，下面例子的同步機制使用的UE4自身集成的Replication（也就是常用的UFUNCTION(Server, Reliable, WithValidation)），這個是非常耗費帶寬的，因爲是定時且頻繁的同步數據。這個如果是做局域網服務端還可以，但是如果是大型高負載服務端，建議自己實現同步機制。另外，v4.4開始，shipping編譯出來的版本會自動刪掉UE4的server模式。原因肯定是官方也不希望這個方便測試的同步機制被開發者應用到生產環境中。所以下面例子中，參考下它的思路即可，具體的同步處理的細節問題可以忽略。

 

RTS遊戲中多角色同時移動的方案：

爲在每個自定義Pawn類定義個AIController，羣體移動時，遍歷所有Pawn，依次調用各自的AIController->MoveToLocation。

 

另外注意點：AIController->MoveToLocation無法像UNavigationSystem->SimpleMoveToLocation()那樣可以主動繞開障礙物，一般建議在服務端通過UNavigationSystem獲取移動路徑的數據，然後將這些數據與客戶端同步。

可參考：
Creating a Movement Component for an RTS in UE4 
http://www.gamedev.net/page/resources/_/technical/game-programming/creating-a-movement-component-for-an-rts-in-ue4-r4019

 

 

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下面文章有點不足的問題是：服務端是通過AIController->MoveToLocation來尋路的，如果對於一個有障礙物的地圖來啊，移動的時候會出現停滯。另外文章建議說服務端不要用UNavigationSystem>SimpleMoveToLocation，這個可能是誤解，服務端是可以使用的。

正文：

[UE4] Getting Multiplayer Player Pawn AI Navigation to work (C++)

http://droneah.com/content/ue4-getting-multiplayer-player-pawn-ai-navigation-work-c

 

Unreal Engine is an awesome piece of technology making it easy to do almost anything you might want.

 

When using the Top Down view however, there is a hurdle to get over when trying to get multiplayer to work. This is a C++ project solution to this problem based on a BluePrints solution.

 

The basic problem stems from the fact that

 

"SimpleMoveToLocation was never intended to be used in a network environment. It's simple after all ;) Currently there's no dedicated engine way of making player pawn follow a path. " (from the same page)

 

To be able to get a working version of SimpleMoveToLocation, we need to do the following:

 

Create a proxy player class (BP_WarriorProxy is BP solution)

Set the proxy class as the default player controller class

Move the camera to the proxy (Since the actual player class is on the server, we can't put a camera on it to display on the client)

The BP solution talks about four classes - our counterparts are as follows:

 

BP_WarriorProxy: ADemoPlayerProxy

BP_WarriorController: ADemoPlayerController (Auto-created when creating a c++ top down project)

BP_Warrior: ADemoCharacter (Auto-created when creating a C++ top down project)

BP_WarriorAI: AAIController - we have no reason to subclass it.

So, from a standard c++ top down project, the only class we need to add is the ADemoPlayerProxy - so go ahead and do that first.

 

The first thing we'll do is rewire the ADemoGameMode class to initialise the proxy class instead of the default MyCharacter Blueprint.

ADemoGameMode::ADemoGameMode(const class FPostConstructInitializeProperties& PCIP) : Super(PCIP)
{
    // use our custom PlayerController class
    PlayerControllerClass = ADemoPlayerController::StaticClass();

    // set default pawn class to our Blueprinted character
    /* static ConstructorHelpers::FClassFinder<apawn> PlayerPawnBPClass(TEXT("/Game/Blueprints/MyCharacter"));
    if (PlayerPawnBPClass.Class != NULL)
    {
        DefaultPawnClass = PlayerPawnBPClass.Class;
    }*/

    DefaultPawnClass = ADemoPlayerProxy::StaticClass();
}

 

 

Our Player Proxy class declaration

/* This class will work as a proxy on the client - tracking the movements of the
 * real Character on the server side and sending back controls. */
UCLASS() class Demo_API ADemoPlayerProxy : public APawn
{
    GENERATED_UCLASS_BODY()
    /** Top down camera */
    UPROPERTY(VisibleAnywhere, BlueprintReadOnly, Category = Camera) TSubobjectPtr<class ucameracomponent> TopDownCameraComponent;

    /** Camera boom positioning the camera above the character */
    UPROPERTY(VisibleAnywhere, BlueprintReadOnly, Category = Camera) TSubobjectPtr<class uspringarmcomponent> CameraBoom;

    // Needed so we can pick up the class in the constructor and spawn it elsewhere
    TSubclassOf<aactor> CharacterClass;

    // Pointer to the actual character. We replicate it so we know its location for the camera on the client
    UPROPERTY(Replicated) ADemoCharacter* Character;

    // The AI Controller we will use to auto-navigate the player
    AAIController* PlayerAI;

    // We spawn the real player character and other such elements here
    virtual void BeginPlay() override;

    // Use do keep this actor in sync with the real one
    void Tick(float DeltaTime);

    // Used by the controller to get moving to work
    void MoveToLocation(const FVector& vector);
};

 

 

and the definition:

#include "Demo.h"
#include "DemoCharacter.h"
#include "AIController.h"
#include "DemoPlayerProxy.h"
#include "UnrealNetwork.h"


ADemoPlayerProxy::ADemoPlayerProxy(const class FPostConstructInitializeProperties& PCIP)
: Super(PCIP)
{
    // Don't rotate character to camera direction
    bUseControllerRotationPitch = false;
    bUseControllerRotationYaw = false;
    bUseControllerRotationRoll = false;

    // It seems that without a RootComponent, we can't place the Actual Character easily
    TSubobjectPtr<UCapsuleComponent> TouchCapsule = PCIP.CreateDefaultSubobject<ucapsulecomponent>(this, TEXT("dummy"));
    TouchCapsule->InitCapsuleSize(1.0f, 1.0f);
    TouchCapsule->SetCollisionEnabled(ECollisionEnabled::NoCollision);
    TouchCapsule->SetCollisionResponseToAllChannels(ECR_Ignore);
    RootComponent = TouchCapsule;

    // Create a camera boom...
    CameraBoom = PCIP.CreateDefaultSubobject<USpringArmComponent>(this, TEXT("CameraBoom"));
    CameraBoom->AttachTo(RootComponent);
    CameraBoom->bAbsoluteRotation = true; // Don't want arm to rotate when character does
    CameraBoom->TargetArmLength = 800.f;
    CameraBoom->RelativeRotation = FRotator(-60.f, 0.f, 0.f);
    CameraBoom->bDoCollisionTest = false; // Don't want to pull camera in when it collides with level

    // Create a camera...
    TopDownCameraComponent = PCIP.CreateDefaultSubobject<UCameraComponent>(this, TEXT("TopDownCamera"));
    TopDownCameraComponent->AttachTo(CameraBoom, USpringArmComponent::SocketName);
    TopDownCameraComponent->bUseControllerViewRotation = false; // Camera does not rotate relative to arm

    if (Role == ROLE_Authority)
    {
        static ConstructorHelpers::FObjectFinder<UClass> PlayerPawnBPClass(TEXT("/Game/Blueprints/MyCharacter.MyCharacter_C"));
        CharacterClass = PlayerPawnBPClass.Object;
    }

}

void ADemoPlayerProxy::BeginPlay()
{
    Super::BeginPlay();
    if (Role == ROLE_Authority)
    {
        // Get current location of the Player Proxy
        FVector Location =  GetActorLocation();
        FRotator Rotation = GetActorRotation();

        FActorSpawnParameters SpawnParams;
        SpawnParams.Owner = this;
        SpawnParams.Instigator = Instigator;
        SpawnParams.bNoCollisionFail = true;

        // Spawn the actual player character at the same location as the Proxy
        Character = Cast<ADemoCharacter>(GetWorld()->SpawnActor(CharacterClass, &Location, &Rotation, SpawnParams));

        // We use the PlayerAI to control the Player Character for Navigation
        PlayerAI = GetWorld()->SpawnActor<AAIController>(GetActorLocation(), GetActorRotation());
        PlayerAI->Possess(Character);
    }

}

void ADemoPlayerProxy::Tick(float DeltaTime)
{

    Super::Tick(DeltaTime);
    if (Character)
    {
        // Keep the Proxy in sync with the real character
        FTransform CharTransform = Character->GetTransform();
        FTransform MyTransform = GetTransform();

        FTransform Transform;
        Transform.LerpTranslationScale3D(CharTransform, MyTransform, ScalarRegister(0.5f));

        SetActorTransform(Transform);

    }
}

void ADemoPlayerProxy::MoveToLocation(const FVector& DestLocation)
{
    /** Looks easy - doesn't it.
     *  What this does is to engage the AI to pathfind.
     *  The AI will then "route" the character correctly.
     *  The Proxy (and with it the camera), on each tick, moves to the location of the real character
     *
     *  And thus, we get the illusion of moving with the Player Character
     */
    PlayerAI->MoveToLocation(DestLocation);
}

void ADemoPlayerProxy::GetLifetimeReplicatedProps(TArray< class FLifetimeProperty > & OutLifetimeProps) const
{

    Super::GetLifetimeReplicatedProps(OutLifetimeProps);

    // Replicate to Everyone
    DOREPLIFETIME(ADemoPlayerProxy, Character);
}

 

 

We'll now cover changes to the Player Controller. We'll rewire it here to ask the proxy to move, which will in turn ask the AIController to find a path and move the real player character. 

 

This involves changing the SetMoveDestination method to call a server side method to move the character. When the character moves, the player Proxy will automatically mirror the movements.

 

In the header file, add the following function

/** Navigate player to the given world location (Server Version) */
UFUNCTION(reliable, server, WithValidation)
void ServerSetNewMoveDestination(const FVector DestLocation);

 

 

 

Now let's implement it (DemoPlayerController.cpp):

bool ADemoPlayerController::ServerSetNewMoveDestination_Validate(const FVector DestLocation)
{
    return true;
}

/* Actual implementation of the ServerSetMoveDestination method */
void ADemoPlayerController::ServerSetNewMoveDestination_Implementation(const FVector DestLocation)
{
    ADemoPlayerProxy* Pawn = Cast<ademoplayerproxy>(GetPawn());
    if (Pawn)
    {
        UNavigationSystem* const NaDemoys = GetWorld()->GetNavigationSystem();
        float const Distance = FVector::Dist(DestLocation, Pawn->GetActorLocation());

        // We need to issue move command only if far enough in order for walk animation to play correctly
        if (NaDemoys && (Distance > 120.0f))
        {
            //NaDemoys->SimpleMoveToLocation(this, DestLocation);
            Pawn->MoveToLocation(DestLocation);
        }
    }

}

 

 

And finally, the rewiring of the original method:

void ADemoPlayerController::SetNewMoveDestination(const FVector DestLocation)
{
    ServerSetNewMoveDestination(DestLocation);
}