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---
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title: Untitled
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date: 2025-07-25 14:49:41
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excerpt:
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tags:
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rating: ⭐
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---
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# 前言
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社区文章：
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- [虚幻杂记4 PreLoadScreen与_LoadingScreen_](https://zhuanlan.zhihu.com/p/608502007)
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- [UE5 _Lyra_项目的解析与学习三：加载屏幕与RootLayoutUI创建流程](https://zhuanlan.zhihu.com/p/18123648655)
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- 其他相关
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- [UE4 MoviePlayer](https://zhuanlan.zhihu.com/p/346492104)
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# 相关CVar参数
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- CommonLoadingScreen.AlwaysShow：总是显示
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- CommonLoadingScreen.LogLoadingScreenReasonEveryFrame
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- CommonLoadingScreen.HoldLoadingScreenAdditionalSecs：载入完成后的等待时间。
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# Lyra引用逻辑
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ULyraExperienceManagerComponent
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PreLoadMapWithContext委托会在UEngine::LoadMap()中被调用。
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# 相关逻辑
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- CommonLoadingScreen：常规LoadingScreen。
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- ***ULoadingScreenManager***：核心逻辑。
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- UCommonLoadingScreenSettings：各种设置参数。
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- ULoadingProcessTask：继承ILoadingProcessInterface接口，只需覆盖ShouldShowLoadingScreen()。
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- CommonStartupLoadingScreen模块：游戏启动时的LoadingScreen。
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- FCommonStartupLoadingScreenModule：StartupModule()、FPreLoadScreenManager::OnPreLoadScreenManagerCleanUp()绑定OnPreLoadScreenManagerCleanUp()。
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- SCommonPreLoadingScreenWidget：LoadingScreen Slate控件。
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## ULoadingScreenManager(UGameInstanceSubsystem)
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- Initialize()：绑定PreLoadMapWithContext与PostLoadMapWithWorld委托。
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- Deinitialize()：移除BlockInput、移除Widget、移除委托、关闭Tickable。
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- ShouldCreateSubsystem()：覆盖接口函数，对于非Server端都会加载LoadingScreen。
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- FTickableGameObject
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- Tick()：调用**ShouldCreateSubsystem()**，计算TimeUntilNextLogHeartbeatSeconds。
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- GetTickableTickType()
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- IsTickable()：如果GameInstance有效且拥有游戏窗口就可以进行Tick。
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- GetStatId()：STATGROUP_Tickables
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- GetTickableGameObjectWorld()：GetGameInstance()->GetWorld();
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- RegisterLoadingProcessor()：用于坐车任务，在ULoadingProcessTask::CreateLoadingScreenProcessTask()被调用。
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- UnregisterLoadingProcessor()：用于卸载任务，在ULoadingProcessTask::Unregister()被调用。
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- **HandlePreLoadMap()**：修改bCurrentlyInLoadMap为true，之后调用UpdateLoadingScreen()。
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- **HandlePostLoadMap()**：修改bCurrentlyInLoadMap为false。
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- **UpdateLoadingScreen()**：通过ShouldShowLoadingScreen()来判断是ShowLoadingScreen()还是HideLoadingScreen()。并且中间使用FThreadHeartBeat::Get().MonitorCheckpointStart() / MonitorCheckpointEnd()来检查线程心跳？
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- ***CheckForAnyNeedToShowLoadingScreen()***：
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- **ShouldShowLoadingScreen**()：主要通过***CheckForAnyNeedToShowLoadingScreen()*** 判断是否应该显示LoadingScreen。如果HoldLoadingScreenAdditionalSecs大于0，且当前经过时间依然小于HoldLoadingScreenAdditionalSecs，也会显示LoadingScreen。
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- IsShowingInitialLoadingScreen()：判断是否正在显示初始化LoadingScreen。
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- [[#ShowLoadingScreen()]]
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- [[#HideLoadingScreen()]]
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- RemoveWidgetFromViewport()：从Viewport上移除LoadingScreenWidget。
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- StartBlockingInput()：通过FSlateApplication::Get().RegisterInputPreProcessor(MakeShareable< FLoadingScreenInputPreProcessor >(new FLoadingScreenInputPreProcessor()))来Block所有输入。
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- StopBlockingInput()：FSlateApplication::Get().UnregisterInputPreProcessor()接触Block。
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- [[#ChangePerformanceSettings()]]：修改性能相关设置。
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- TODO
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- @TODO: Why can GetLocalPlayers() have nullptr entries? Can it really?
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- @TODO: Test with PIE mode set to simulate and decide how much (if any) loading screen action should occur
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- @TODO: Allow other things implementing ILoadingProcessInterface besides GameState/PlayerController (and owned components) to register as interested parties
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- @TODO: ChangeMusicSettings (either here or using the LoadingScreenVisibilityChanged delegate)
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- @TODO: Studio analytics (FireEvent_PIEFinishedLoading / tracking PIE startup time for regressions, either here or using the LoadingScreenVisibilityChanged delegate)
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### ShowLoadingScreen()
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```c++
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void ULoadingScreenManager::ShowLoadingScreen()
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{
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if (bCurrentlyShowingLoadingScreen)
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{
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return;
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}
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//在Engine载入阶段不会执行后续ShowLoadingScreen逻辑
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if (FPreLoadScreenManager::Get() && FPreLoadScreenManager::Get()->HasActivePreLoadScreenType(EPreLoadScreenTypes::EngineLoadingScreen))
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{
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return;
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}
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TimeLoadingScreenShown = FPlatformTime::Seconds();
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bCurrentlyShowingLoadingScreen = true;
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CSV_EVENT(LoadingScreen, TEXT("Show"));
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const UCommonLoadingScreenSettings* Settings = GetDefault<UCommonLoadingScreenSettings>();
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if (IsShowingInitialLoadingScreen())//已经显示LoadingScreen
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{
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UE_LOG(LogLoadingScreen, Log, TEXT("Showing loading screen when 'IsShowingInitialLoadingScreen()' is true."));
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UE_LOG(LogLoadingScreen, Log, TEXT("%s"), *DebugReasonForShowingOrHidingLoadingScreen);
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}
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else
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{
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UE_LOG(LogLoadingScreen, Log, TEXT("Showing loading screen when 'IsShowingInitialLoadingScreen()' is false."));
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UE_LOG(LogLoadingScreen, Log, TEXT("%s"), *DebugReasonForShowingOrHidingLoadingScreen);
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UGameInstance* LocalGameInstance = GetGameInstance();
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// LoadingScreen显示时Block所有Input
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StartBlockingInput();
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LoadingScreenVisibilityChanged.Broadcast(/*bIsVisible=*/ true);
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// 创建LoadingScreen Widget
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TSubclassOf<UUserWidget> LoadingScreenWidgetClass = Settings->LoadingScreenWidget.TryLoadClass<UUserWidget>();
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if (UUserWidget* UserWidget = UUserWidget::CreateWidgetInstance(*LocalGameInstance, LoadingScreenWidgetClass, NAME_None))
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{
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LoadingScreenWidget = UserWidget->TakeWidget();
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}
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else
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{
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UE_LOG(LogLoadingScreen, Error, TEXT("Failed to load the loading screen widget %s, falling back to placeholder."), *Settings->LoadingScreenWidget.ToString());
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LoadingScreenWidget = SNew(SThrobber);
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}
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// Add to the viewport at a high ZOrder to make sure it is on top of most things
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// 将LoadingScreenWidget显示到Viewport上。
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UGameViewportClient* GameViewportClient = LocalGameInstance->GetGameViewportClient();
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GameViewportClient->AddViewportWidgetContent(LoadingScreenWidget.ToSharedRef(), Settings->LoadingScreenZOrder);
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ChangePerformanceSettings(/*bEnableLoadingScreen=*/ true);
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if (!GIsEditor || Settings->ForceTickLoadingScreenEvenInEditor)
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{
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// Tick Slate to make sure the loading screen is displayed immediately
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FSlateApplication::Get().Tick();
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}
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}
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}
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```
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### HideLoadingScreen()
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```c++
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void ULoadingScreenManager::HideLoadingScreen()
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{
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if (!bCurrentlyShowingLoadingScreen)
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{
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return;
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}
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//取消Block Input
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StopBlockingInput();
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if (IsShowingInitialLoadingScreen())
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{
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UE_LOG(LogLoadingScreen, Log, TEXT("Hiding loading screen when 'IsShowingInitialLoadingScreen()' is true."));
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UE_LOG(LogLoadingScreen, Log, TEXT("%s"), *DebugReasonForShowingOrHidingLoadingScreen);
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}
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else
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{
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UE_LOG(LogLoadingScreen, Log, TEXT("Hiding loading screen when 'IsShowingInitialLoadingScreen()' is false."));
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UE_LOG(LogLoadingScreen, Log, TEXT("%s"), *DebugReasonForShowingOrHidingLoadingScreen);
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UE_LOG(LogLoadingScreen, Log, TEXT("Garbage Collecting before dropping load screen"));
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//更新垃圾回收之间的计时器，以便在下一次机会时运行垃圾回收。
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GEngine->ForceGarbageCollection(true);
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RemoveWidgetFromViewport();
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ChangePerformanceSettings(/*bEnableLoadingScreen=*/ false);
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// Let observers know that the loading screen is done
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LoadingScreenVisibilityChanged.Broadcast(/*bIsVisible=*/ false);
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}
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CSV_EVENT(LoadingScreen, TEXT("Hide"));
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const double LoadingScreenDuration = FPlatformTime::Seconds() - TimeLoadingScreenShown;
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UE_LOG(LogLoadingScreen, Log, TEXT("LoadingScreen was visible for %.2fs"), LoadingScreenDuration);
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bCurrentlyShowingLoadingScreen = false;
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}
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```
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### ChangePerformanceSettings()
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```c++
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void ULoadingScreenManager::ChangePerformanceSettings(bool bEnabingLoadingScreen)
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{
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UGameInstance* LocalGameInstance = GetGameInstance();
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UGameViewportClient* GameViewportClient = LocalGameInstance->GetGameViewportClient();
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//设置Shader编译模式，默认为后台编译，显示LoadingScreen时切换成Fast模式。
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FShaderPipelineCache::SetBatchMode(bEnabingLoadingScreen ? FShaderPipelineCache::BatchMode::Fast : FShaderPipelineCache::BatchMode::Background);
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//在LoadingScreen显示阶段阶段关闭世界渲染。
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GameViewportClient->bDisableWorldRendering = bEnabingLoadingScreen;
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//如果加载界面显示，请确保优先级为流式传输。
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if (UWorld* ViewportWorld = GameViewportClient->GetWorld())
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{
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if (AWorldSettings* WorldSettings = ViewportWorld->GetWorldSettings(false, false))
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{
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WorldSettings->bHighPriorityLoadingLocal = bEnabingLoadingScreen;
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}
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}
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if (bEnabingLoadingScreen)
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{
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// 当加载屏幕可见时，设置新的挂起检测超时倍数
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double HangDurationMultiplier;
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if (!GConfig || !GConfig->GetDouble(TEXT("Core.System"), TEXT("LoadingScreenHangDurationMultiplier"), /*out*/ HangDurationMultiplier, GEngineIni))
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{
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HangDurationMultiplier = 1.0;
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}
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FThreadHeartBeat::Get().SetDurationMultiplier(HangDurationMultiplier);
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// 在加载界面显示时，请勿报告任何问题。
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FGameThreadHitchHeartBeat::Get().SuspendHeartBeat();
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}
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else
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{
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// Restore the hang detector timeout when we hide the loading screen
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FThreadHeartBeat::Get().SetDurationMultiplier(1.0);
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// 现在加载屏幕已关闭，简历报告出现故障。
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FGameThreadHitchHeartBeat::Get().ResumeHeartBeat();
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}
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}
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```
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### FPreLoadScreenManager
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