UE4BeginPlay执行流程

文章目录

UE4 BeginPlay执行流程
- 源代码
- - UGameInstance::StartPlayInEditorGameInstance:
  - UWorld::BeginPlay
  - AGameModeBase::StartPlay
  - AGameStateBase::HandleBeginPlay
  - AWorldSettings::NotifyBeginPlay
  - AActor::DispatchBeginPlay

UE4 BeginPlay执行流程

Actor BeginPlay调用流程

源代码

UGameInstance::StartPlayInEditorGameInstance:

FGameInstancePIEResult UGameInstance::StartPlayInEditorGameInstance(ULocalPlayer* LocalPlayer, const FGameInstancePIEParameters& Params)
{if (!Params.EditorPlaySettings){return FGameInstancePIEResult::Failure(NSLOCTEXT("UnrealEd", "Error_InvalidEditorPlaySettings", "Invalid Editor Play Settings!"));}if (PIEStartTime == 0){PIEStartTime = Params.PIEStartTime;}BroadcastOnStart();UEditorEngine* const EditorEngine = CastChecked<UEditorEngine>(GetEngine());// for clients, just connect to the serverif (Params.NetMode == PIE_Client){FString Error;FURL BaseURL = WorldContext->LastURL;FString URLString(TEXT("127.0.0.1"));uint16 ServerPort = 0;if (Params.EditorPlaySettings->GetServerPort(ServerPort)){URLString += FString::Printf(TEXT(":%hu"), ServerPort);}if (Params.EditorPlaySettings->IsNetworkEmulationEnabled()){if (Params.EditorPlaySettings->NetworkEmulationSettings.IsEmulationEnabledForTarget(NetworkEmulationTarget::Client)){URLString += Params.EditorPlaySettings->NetworkEmulationSettings.BuildPacketSettingsForURL();}}if (EditorEngine->Browse(*WorldContext, FURL(&BaseURL, *URLString, (ETravelType)TRAVEL_Absolute), Error) == EBrowseReturnVal::Pending){EditorEngine->TransitionType = ETransitionType::WaitingToConnect;}else{return FGameInstancePIEResult::Failure(FText::Format(NSLOCTEXT("UnrealEd", "Error_CouldntLaunchPIEClient", "Couldn't Launch PIE Client: {0}"), FText::FromString(Error)));}}else{// we're going to be playing in the current world, get it ready for playUWorld* const PlayWorld = GetWorld();FString ExtraURLOptions;if (Params.EditorPlaySettings->IsNetworkEmulationEnabled()){NetworkEmulationTarget CurrentTarget = Params.NetMode == PIE_ListenServer ? NetworkEmulationTarget::Server : NetworkEmulationTarget::Client;if (Params.EditorPlaySettings->NetworkEmulationSettings.IsEmulationEnabledForTarget(CurrentTarget)){ExtraURLOptions += Params.EditorPlaySettings->NetworkEmulationSettings.BuildPacketSettingsForURL();}}// make a URLFURL URL;// If the user wants to start in spectator mode, do not use the custom play world for nowif (EditorEngine->UserEditedPlayWorldURL.Len() > 0 || Params.OverrideMapURL.Len() > 0){FString UserURL = EditorEngine->UserEditedPlayWorldURL.Len() > 0 ? EditorEngine->UserEditedPlayWorldURL : Params.OverrideMapURL;UserURL += ExtraURLOptions;// If the user edited the play world url. Verify that the map name is the same as the currently loaded map.URL = FURL(NULL, *UserURL, TRAVEL_Absolute);if (URL.Map != PIEMapName){// Ensure the URL map name is the same as the generated play world map name.URL.Map = PIEMapName;}}else{// The user did not edit the url, just build one from scratch.URL = FURL(NULL, *EditorEngine->BuildPlayWorldURL(*PIEMapName, Params.bStartInSpectatorMode, ExtraURLOptions), TRAVEL_Absolute);}// If a start location is specified, spawn a temporary PlayerStartPIE actor at the start location and use it as the portal.AActor* PlayerStart = NULL;if (!EditorEngine->SpawnPlayFromHereStart(PlayWorld, PlayerStart)){// failed to create "play from here" playerstartreturn FGameInstancePIEResult::Failure(NSLOCTEXT("UnrealEd", "Error_FailedCreatePlayFromHerePlayerStart", "Failed to create PlayerStart at desired starting location."));}if (!PlayWorld->SetGameMode(URL)){// Setting the game mode failed so bail return FGameInstancePIEResult::Failure(NSLOCTEXT("UnrealEd", "Error_FailedCreateEditorPreviewWorld", "Failed to create editor preview world."));}FGameInstancePIEResult PostCreateGameModeResult = PostCreateGameModeForPIE(Params, PlayWorld->GetAuthGameMode<AGameModeBase>());if (!PostCreateGameModeResult.IsSuccess()){return PostCreateGameModeResult;}// Make sure "always loaded" sub-levels are fully loadedPlayWorld->FlushLevelStreaming(EFlushLevelStreamingType::Visibility);PlayWorld->CreateAISystem();PlayWorld->InitializeActorsForPlay(URL);// calling it after InitializeActorsForPlay has been called to have all potential bounding boxed initializedFNavigationSystem::AddNavigationSystemToWorld(*PlayWorld, LocalPlayers.Num() > 0 ? FNavigationSystemRunMode::PIEMode : FNavigationSystemRunMode::SimulationMode);// @todo, just use WorldContext.GamePlayer[0]?if (LocalPlayer){FString Error;if (!LocalPlayer->SpawnPlayActor(URL.ToString(1), Error, PlayWorld)){return FGameInstancePIEResult::Failure(FText::Format(NSLOCTEXT("UnrealEd", "Error_CouldntSpawnPlayer", "Couldn't spawn player: {0}"), FText::FromString(Error)));}}UGameViewportClient* const GameViewport = GetGameViewportClient();if (GameViewport != NULL && GameViewport->Viewport != NULL){// Stream any levels now that need to be loaded before the game startsGEngine->BlockTillLevelStreamingCompleted(PlayWorld);}if (Params.NetMode == PIE_ListenServer){// Add portuint16 ServerPort = 0;if (Params.EditorPlaySettings->GetServerPort(ServerPort)){URL.Port = ServerPort;}// start listen server with the built URLPlayWorld->Listen(URL);}PlayWorld->BeginPlay();}// Give the deprecated method a chance to fail as wellFGameInstancePIEResult StartResult = FGameInstancePIEResult::Success();if (StartResult.IsSuccess()){PRAGMA_DISABLE_DEPRECATION_WARNINGSStartResult = StartPIEGameInstance(LocalPlayer, Params.bSimulateInEditor, Params.bAnyBlueprintErrors, Params.bStartInSpectatorMode) ?FGameInstancePIEResult::Success() :FGameInstancePIEResult::Failure(NSLOCTEXT("UnrealEd", "Error_CouldntInitInstance", "The game instance failed to Play/Simulate In Editor"));PRAGMA_ENABLE_DEPRECATION_WARNINGS}return StartResult;
}

UWorld::BeginPlay

void UWorld::BeginPlay()
{AGameModeBase* const GameMode = GetAuthGameMode();if (GameMode){GameMode->StartPlay();if (GetAISystem()){GetAISystem()->StartPlay();}}OnWorldBeginPlay.Broadcast();#if WITH_CHAOSif(PhysicsScene){PhysicsScene->OnWorldBeginPlay();}
#endif
}

AGameModeBase::StartPlay

void AGameModeBase::StartPlay()
{GameState->HandleBeginPlay();
}

AGameStateBase::HandleBeginPlay

void AGameStateBase::HandleBeginPlay()
{bReplicatedHasBegunPlay = true;GetWorldSettings()->NotifyBeginPlay();GetWorldSettings()->NotifyMatchStarted();
}

AWorldSettings::NotifyBeginPlay

void AWorldSettings::NotifyBeginPlay()
{UWorld* World = GetWorld();if (!World->bBegunPlay){for (FActorIterator It(World); It; ++It){SCOPE_CYCLE_COUNTER(STAT_ActorBeginPlay);const bool bFromLevelLoad = true;It->DispatchBeginPlay(bFromLevelLoad);}World->bBegunPlay = true;}
}

FActorIterator 是actor的遍历器,它继承自 TActorIteratorBase<FActorIterator>，TActorIteratorBase里面存储了World的指针，并重写了++符号，所以这样写能遍历Actor
ActorIteratorBase重写的方法：

void operator++()
{// Use local version to avoid LHSs as compiler is not required to write out member variables to memory.AActor*           LocalCurrentActor      = nullptr;int32             LocalIndex             = State->Index;TArray<UObject*>& LocalObjectArray       = State->ObjectArray;TArray<AActor*>&  LocalSpawnedActorArray = State->SpawnedActorArray;UWorld*           LocalCurrentWorld      = State->CurrentWorld;while(++LocalIndex < (LocalObjectArray.Num() + LocalSpawnedActorArray.Num())){if (LocalIndex < LocalObjectArray.Num()){LocalCurrentActor = static_cast<AActor*>(LocalObjectArray[LocalIndex]);}else{LocalCurrentActor = LocalSpawnedActorArray[LocalIndex - LocalObjectArray.Num()];}State->ConsideredCount++;ULevel* ActorLevel = LocalCurrentActor ? LocalCurrentActor->GetLevel() : nullptr;if ( ActorLevel&& static_cast<const Derived*>(this)->IsActorSuitable(LocalCurrentActor)&& static_cast<const Derived*>(this)->CanIterateLevel(ActorLevel)&& ActorLevel->GetWorld() == LocalCurrentWorld){// ignore non-persistent world settingsif (ActorLevel == LocalCurrentWorld->PersistentLevel || !LocalCurrentActor->IsA(AWorldSettings::StaticClass())){State->CurrentActor = LocalCurrentActor;State->Index = LocalIndex;return;}}}State->CurrentActor = NULL;State->ReachedEnd = true;
}

AActor::DispatchBeginPlay

void AActor::DispatchBeginPlay(bool bFromLevelStreaming)
{UWorld* World = (!HasActorBegunPlay() && !IsPendingKill() ? GetWorld() : nullptr);if (World){ensureMsgf(ActorHasBegunPlay == EActorBeginPlayState::HasNotBegunPlay, TEXT("BeginPlay was called on actor %s which was in state %d"), *GetPathName(), (int32)ActorHasBegunPlay);const uint32 CurrentCallDepth = BeginPlayCallDepth++;bActorBeginningPlayFromLevelStreaming = bFromLevelStreaming;ActorHasBegunPlay = EActorBeginPlayState::BeginningPlay;BeginPlay();ensure(BeginPlayCallDepth - 1 == CurrentCallDepth);BeginPlayCallDepth = CurrentCallDepth;if (bActorWantsDestroyDuringBeginPlay){// Pass true for bNetForce as either it doesn't matter or it was true the first time to even // get to the point we set bActorWantsDestroyDuringBeginPlay to trueWorld->DestroyActor(this, true); }if (!IsPendingKill()){// Initialize overlap stateUpdateInitialOverlaps(bFromLevelStreaming);}bActorBeginningPlayFromLevelStreaming = false;}
}