Lyra学习笔记1地图角色加载流程

纯个人笔记，有错误欢迎指正，学习阶段基本看到不会的就写一写，最后有时间会梳理整体结构

先看完了官方的演讲

1 地图加载流程

1.1 默认Experience的加载

  这里先不从GameInstance开始，中间的CommonUser等流程暂时不谈（有点多暂时不想看0w0），编辑器默认地图L_DefaultEditorOverview中没有重载游戏模式，所以用项目默认的B_LyraGameMode。
  ALyraGameMode::InitGame()

// Wait for the next frame to give time to initialize startup settings
GetWorld()->GetTimerManager().SetTimerForNextTick(this, &ThisClass::HandleMatchAssignmentIfNotExpectingOne);

可见逻辑转到了ALyraGameMode::HandleMatchAssignmentIfNotExpectingOne()
(这里走的默认分支）

void ALyraGameMode::HandleMatchAssignmentIfNotExpectingOne()
{
	...
	ExperienceId = FPrimaryAssetId(FPrimaryAssetType("LyraExperienceDefinition"), FName("B_LyraDefaultExperience"));
	ExperienceIdSource = TEXT("Default");
	...
	OnMatchAssignmentGiven(ExperienceId, ExperienceIdSource);
}

  之后的调用栈大概是

OnMatchAssignmentGiven(ExperienceId, ExperienceIdSource)->
void ULyraExperienceManagerComponent::SetCurrentExperience(ExperienceId)->
void ULyraExperienceManagerComponent::StartExperienceLoad()->
void ULyraExperienceManagerComponent::OnExperienceLoadComplete()

  过程大体是设置当前ExperienceId，异步加载Experience相关资源，调用加载完成的回调.
  OnExperienceLoadComplete()函数收集GameFeaturePluginURL，最终调用

UGameFeaturesSubsystem::Get().
LoadAndActivateGameFeaturePlugin(PluginURL,  
FGameFeaturePluginLoadComplete::CreateUObject(this, 
&ThisClass::OnGameFeaturePluginLoadComplete));

  触发默认Feature的Action

这里记录一下几个Action函数的调用顺序， 防止我忘了
在这个函数中：
void ULyraExperienceManagerComponent::OnExperienceFullLoadCompleted()
ActivateListOfActions的定义

	auto ActivateListOfActions = [&Context](const TArray<UGameFeatureAction*>& ActionList)
	{
		for (UGameFeatureAction* Action : ActionList)
		{
			if (Action != nullptr)
			{
				//@TODO: The fact that these don't take a world are potentially problematic in client-server PIE
				// The current behavior matches systems like gameplay tags where loading and registering apply to the entire process,
				// but actually applying the results to actors is restricted to a specific world
				Action->OnGameFeatureRegistering();
				Action->OnGameFeatureLoading();
				Action->OnGameFeatureActivating(Context);
			}
		}
	};

逐一调用顺序
自己的Actions先调用，再遍历调用ActionSets

ActivateListOfActions(CurrentExperience->Actions);
	for (const TObjectPtr<ULyraExperienceActionSet>& ActionSet : CurrentExperience->ActionSets)
	{
		if (ActionSet != nullptr)
		{
			ActivateListOfActions(ActionSet->Actions);
		}
	}

三个多播顺序

	OnExperienceLoaded_HighPriority.Broadcast(CurrentExperience);
	OnExperienceLoaded_HighPriority.Clear();

	OnExperienceLoaded.Broadcast(CurrentExperience);
	OnExperienceLoaded.Clear();

	OnExperienceLoaded_LowPriority.Broadcast(CurrentExperience);
	OnExperienceLoaded_LowPriority.Clear();

1.2 加载角色

B_LyraDefaultExperience中：

SimplePawnData：

可以发现通过这个就找到了创建的金属Pawn，而不是GameMode中的角色类（是其蓝图子类）

但是为什么这里的配置能够生效呢？
因为ALyraGameMode重写了这个实现：

APawn* ALyraGameMode::SpawnDefaultPawnAtTransform_Implementation(AController* NewPlayer, const FTransform& SpawnTransform){
...
if (UClass* PawnClass = GetDefaultPawnClassForController(NewPlayer))
	{
		if (APawn* SpawnedPawn = GetWorld()->SpawnActor<APawn>(PawnClass, SpawnTransform, SpawnInfo))
...
}

UClass* ALyraGameMode::GetDefaultPawnClassForController_Implementation(AController* InController)
{
	if (const ULyraPawnData* PawnData = GetPawnDataForController(InController))
	{
		if (PawnData->PawnClass)
		{
			return PawnData->PawnClass;
		}
	}
...
}

const ULyraPawnData* ALyraGameMode::GetPawnDataForController(const AController* InController) const
{
...
return Experience->DefaultPawnData;
...
}

1.3 加载场景中的几个传送点

由场景中这个Actor控制：

生成逻辑没什么该注意的，注意生成时传入了LyraUserfacingExperienceDefinition类型的变量，Widget信息都是根据这个配置的。
主要看加载地图：

可见信息都在LyraUserfacingExperienceDefinition中，例如这个下边这个，可以看到
要去的地图信息都有。

2 几个内建类的笔记

2.1 UDataAsset

刚拿到项目无从下手，就去看了启动默认地图L_LyraFrontEnd,没有重载GameMode，即用的项目设置的B_LyraGameMode,暂时先不看GameMode，然后基于演讲去看了DefaultGameplayExperience，一路看过去

B_LyraFrontEnd_Experience->
ULyraExperienceDefinition->
UPrimaryDataAsset->
UDataAsset->
UObject

这时候我发现我对DataAsset没什么了解，只好先去学习一下：

UCLASS(abstract, MinimalAPI, Meta = (LoadBehavior = "LazyOnDemand"))
class UDataAsset : public UObject

abstract：

MinimalAPI没太看懂，大概是优化编译相关的：

LoadBehavior
UPrimaryDataAsset：
UE5–PrimaryDataAsset资产包更新UpdateAssetBundleData源码分析
看完这几篇后我的理解这个类就是数据资产。

2.2 UAssetManager

暂时停留在使用层理解。
UE5 AssetManager类使用详解

参考文章：
UE5 Lyra项目学习（零） 开篇&目录