关于网络同步中，Character的Rotation同步

笔者最近正在从头开始搭建一个多人射击游戏，用于熟悉UE4 DS的方方面面，以及设计/性能优化等方面的课题，做些零碎的笔记

3.关于网络同步中，Character的Rotation同步。

在搭建游戏过程中，笔者发现直接设置Character的Rotation，并不能同步到服务器及其他客户端，所以趴一趴UE4对位置同步中Rotation的处理。
这里给各位的童鞋推荐大佬博客 https://blog.csdn.net/u012999985/article/details/78669947，对移动同步方向写的很详细，所以我这里只对 Rotation 的问题进说明。
首先找到服务器同步的移动数据ReplicatedMovement，ReplicatedUsing类型的同步变量：

image.png

在服务器进行Actor同步的时候，会采集Movement信息，进行Movement同步，从代码中发现，同步的Rotation直接使用的RootComponent的Rotation，下面继续从客户端发送移动请求寻找来源。

image.png

首先找到客户端发给服务器的同步请求servemove：

void UCharacterMovementComponent::ServerMove(float TimeStamp, FVector_NetQuantize10 InAccel, 
  FVector_NetQuantize100 ClientLoc, uint8 CompressedMoveFlags, uint8 ClientRoll, uint32 View, 
  UPrimitiveComponent* ClientMovementBase, FName ClientBaseBoneName, uint8 ClientMovementMode)
{
    if (MovementBaseUtility::IsDynamicBase(ClientMovementBase))
    {
        CharacterOwner->ServerMove(TimeStamp, InAccel, ClientLoc, CompressedMoveFlags, ClientRoll, View, ClientMovementBase, ClientBaseBoneName, ClientMovementMode);
    }
    else
    {
        CharacterOwner->ServerMoveNoBase(TimeStamp, InAccel, ClientLoc, CompressedMoveFlags, ClientRoll, View, ClientMovementMode);
    }
}

发现 Rotation 相关数据来自参数 uint32 View，向上追溯参数来源，可以看出其实客户端发给服务器的Rotation只是ControlRotation。

void UCharacterMovementComponent::CallServerMove
    (
    const class FSavedMove_Character* NewMove,
    const class FSavedMove_Character* OldMove
    )
{
    check(NewMove != nullptr);

    // Compress rotation down to 5 bytes
    const uint32 ClientYawPitchINT = PackYawAndPitchTo32(NewMove->SavedControlRotation.Yaw, NewMove->SavedControlRotation.Pitch);
    const uint8 ClientRollBYTE = FRotator::CompressAxisToByte(NewMove->SavedControlRotation.Roll);
    ...

在服务器调用RPC处理客户端移动请求时调用UpdateRotation，在UpdateRotation中直接设置了Actor的Rotation为ControlRotation（当然会考虑bUseControllerRotationPitch/bUseControllerRotationYaw/bUseControllerRotationRoll）的设置，所以说了一大堆，就是DS同步以ControlRotation为基础。

void UCharacterMovementComponent::ServerMove_Implementation(
    float TimeStamp,
    FVector_NetQuantize10 InAccel,
    FVector_NetQuantize100 ClientLoc,
    uint8 MoveFlags,
    uint8 ClientRoll,
    uint32 View,
    UPrimitiveComponent* ClientMovementBase,
    FName ClientBaseBoneName,
    uint8 ClientMovementMode)
{
  ...
  // Perform actual movement
    if ((MyWorld->GetWorldSettings()->Pauser == NULL) && (DeltaTime > 0.f))
    {
        if (PC)
        {
            PC->UpdateRotation(DeltaTime);
        }

        MoveAutonomous(TimeStamp, DeltaTime, MoveFlags, Accel);
    }
  ...
}

void APlayerController::UpdateRotation( float DeltaTime )
{
    // Calculate Delta to be applied on ViewRotation
    FRotator DeltaRot(RotationInput);

    FRotator ViewRotation = GetControlRotation();

    if (PlayerCameraManager)
    {
        PlayerCameraManager->ProcessViewRotation(DeltaTime, ViewRotation, DeltaRot);
    }

    AActor* ViewTarget = GetViewTarget();
    if (!PlayerCameraManager || !ViewTarget || !ViewTarget->HasActiveCameraComponent() || ViewTarget->HasActivePawnControlCameraComponent())
    {
        if (IsLocalPlayerController() && GEngine->XRSystem.IsValid() && GEngine->XRSystem->IsHeadTrackingAllowed())
        {
            auto XRCamera = GEngine->XRSystem->GetXRCamera();
            if (XRCamera.IsValid())
            {
                XRCamera->ApplyHMDRotation(this, ViewRotation);
            }
        }
    }

    SetControlRotation(ViewRotation);

    APawn* const P = GetPawnOrSpectator();
    if (P)
    {
        P->FaceRotation(ViewRotation, DeltaTime);
    }
}

void APawn::FaceRotation(FRotator NewControlRotation, float DeltaTime)
{
    // Only if we actually are going to use any component of rotation.
    if (bUseControllerRotationPitch || bUseControllerRotationYaw || bUseControllerRotationRoll)
    {
        const FRotator CurrentRotation = GetActorRotation();

        if (!bUseControllerRotationPitch)
        {
            NewControlRotation.Pitch = CurrentRotation.Pitch;
        }

        if (!bUseControllerRotationYaw)
        {
            NewControlRotation.Yaw = CurrentRotation.Yaw;
        }

        if (!bUseControllerRotationRoll)
        {
            NewControlRotation.Roll = CurrentRotation.Roll;
        }

#if ENABLE_NAN_DIAGNOSTIC
        if (NewControlRotation.ContainsNaN())
        {
            logOrEnsureNanError(TEXT("APawn::FaceRotation about to apply NaN-containing rotation to actor! New:(%s), Current:(%s)"), *NewControlRotation.ToString(), *CurrentRotation.ToString());
        }
#endif

        SetActorRotation(NewControlRotation);
    }
}

对于这种情况，可以有几种方法同步ActorRotation：
1.如果对Controller Rotation没有特殊限制，可以设置 bUseControllerRotationYaw = true，在需要修改转向时直接SetControlRotation 即可；
2.不通过Controller的Rotation同步，设置bUseControllerRotationYaw = false，设置CharacterMovementCompoennt中的bOrientRotationToMovement = true，这个变量的意思是在移动时自动转向你移动的方向，可以通过RotationRate控制转向速度；
3.添加自定义变量ActorYaw，在需要修改时给服务器发RPC。