UE4的World

1 类图

首先看类关系图

2 World

在前面随笔中提到世界是由一个或多个关卡组成。在这里给出部分world的源码以进一步做理解和探究

2.1 World介绍

World代码过长，只给出部分代码。

/** 
 * The World is the top level object representing a map or a sandbox in which Actors and Components will exist and be rendered.  
 *
 * A World can be a single Persistent Level with an optional list of streaming levels that are loaded and unloaded via volumes and blueprint functions
 * or it can be a collection of levels organized with a World Composition.
 *
 * In a standalone game, generally only a single World exists except during seamless area transitions when both a destination and current world exists.
 * In the editor many Worlds exist: The level being edited, each PIE instance, each editor tool which has an interactive rendered viewport, and many more.
 *
 */

UCLASS(customConstructor, config=Engine)
class ENGINE_API UWorld final : public UObject, public FNetworkNotify
{
	GENERATED_UCLASS_BODY()

	~UWorld();
	
	/** Array of levels currently in this world. Not serialized to disk to avoid hard references. */
	UPROPERTY(Transient)
	TArray<class ULevel*>						Levels;
	
	/** The current GameMode, valid only on the server */
	UPROPERTY(Transient)
	class AGameModeBase*						AuthorityGameMode;

	/** The replicated actor which contains game state information that can be accessible to clients. Direct access is not allowed, use GetGameState<>() */
	UPROPERTY(Transient)
	class AGameStateBase*						GameState;
	
	/** All levels information from which our world is composed */
	UPROPERTY()
	class UWorldComposition* WorldComposition;
	
	/** Physics scene for this world. */
	FPhysScene*									PhysicsScene;
	
	/**
	 * The persistent level associated with this collection.
	 * The source collection and the duplicated collection will have their own instances.
	 */
	UPROPERTY()
	class ULevel* PersistentLevel;
	
	/** Priority sorted array of streaming levels actively being considered. */
	UPROPERTY()
	TArray<ULevelStreaming*> StreamingLevels;
	
	UPROPERTY(Transient)
	class UGameInstance*						OwningGameInstance;
	
	/** Pointer to the current level being edited. Level has to be in the Levels array and == PersistentLevel in the game. */
	UPROPERTY(Transient)
	class ULevel*								CurrentLevel;
	
	/** List of all the controllers in the world. */
	TArray<TWeakObjectPtr<class AController> > ControllerList;

	/** List of all the player controllers in the world. */
	TArray<TWeakObjectPtr<class APlayerController> > PlayerControllerList;

	/** List of all the cameras in the world that auto-activate for players. */
	TArray<TWeakObjectPtr<ACameraActor> > AutoCameraActorList;

首先看源码中对World类的注释：

• World是顶级的关卡对象，它表现为地图或者沙盒。Actor和Component存在于这个地图或者沙盒中，并且对Actor和Component渲染也是在这里完成。

• World可以是由单个Persistent Level和一系列可选的streaming Level组成。这些streaming Level可以通过体积或者函数进行加载和卸载，或者World可以是一个由World Composition组织起来的Level集合。

• 在独立游戏中，通常只存在一个世界，除非在无缝区域转换期间同时存在目的地和当前世界。

• 在编辑器中存在许多世界：正在编辑的关卡、每个 PIE 实例、每个具有交互式渲染视口的编辑器工具等等。

一个World由一个或多个Level组成，那么自然而然地，World就需要管理这些Level，负责它们的加载和释放。在UE中，每个World支持一个PersistentLevel和多个其他Level：PersistentLevel在开始时就加载进World，Streaming Level则是后续动态加载的level。Levels保存当前World中已经加载的Level，StreamingLevels则保存整个World的Levels配置列表。PersistentLevel和CurrentLevel是快速引用。在编辑器中，CurrentLevel可以指向其他Level，在运行时CurrentLevel只能是指向PersistentLevel。

思考： World由多个Level拼接而成，由前讲述可知，每个Level都有自己的Worldsetting，那World的配置怎么进行？

World的Settings是PersistentLevel的Worldsetting为主的，但同时其他Level的Worldsetting也发挥着作用。就是需要在整个世界范围内起作用的配置选项（比如VR的WorldToMeters，KillZ，WorldGravity其他大部分都是）从PersistentLevel的Worldsetting配置中提取。而在各自Level中起作用的配置选项则从它们各自的Worldsetting中提取。

2.2 World类型

从前面的解释中，可以知道，作为一个游戏玩家，最直观的体验就是一个地图就是一个World，游戏玩家在玩游戏时在地图上进行游戏。所以，在游戏中不止有一个，比如吃鸡游戏中就有多个地图。但同时，World也不止有一种类型，看下面源码即可知UE中World类型。

/** Specifies the goal/source of a UWorld object */
namespace EWorldType
{
	enum Type
	{
		/** An untyped world, in most cases this will be the vestigial worlds of streamed in sub-levels */
		None,

		/** The game world */
		Game,

		/** A world being edited in the editor */
		Editor,

		/** A Play In Editor world */
		PIE,

		/** A preview world for an editor tool */
		EditorPreview,

		/** A preview world for a game */
		GamePreview,

		/** A minimal RPC world for a game */
		GameRPC,

		/** An editor world that was loaded but not currently being edited in the level editor */
		Inactive
	};

	UE_DEPRECATED(4.14, "EWorldType::Preview is deprecated. Please use either EWorldType::EditorPreview or EWorldType::GamePreview")
	const EWorldType::Type Preview = EWorldType::EditorPreview;
}