相机系统

整体流程#

UE的相机系统相比于更加复杂，涉及到 CameraComponent，CameraActor，PlayerController，PlayerCameraManager 几个类。

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classDiagram
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    UWorld --> APlayerController
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    UGameViewportClient --> ULocalPlayer : 渲染画面时获取摄像机的POV
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    ULocalPlayer --> APlayerController : 获取POV
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    APlayerController "1" <--> "1" APlayerCameraManager : APlayerController创建并驱动PlayerCameraManager
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    APlayerCameraManager ..> AActor : 更新ViewTarget
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    AActor o--> UCameraComponent : 计算POV
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    APlayerCameraManager <--> UCameraModifier : 最后修改POV
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    UCameraModifier --> UCameraModifier_CameraShake : 示例说明
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    class UWorld {
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        +Tick(...)
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    }
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    class UGameViewportClient {
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        +Draw()
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    }
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    class ULocalPlayer {
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        +CalcSceneView(...)
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        +GetViewPoint(...)
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    }
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    class APlayerController {
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        +SpawnPlayerCameraManager()
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        +UpdateCameraManager()
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        +GetPlayerViewPoint(...)
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    }
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    class APlayerCameraManager {
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        +UpdateCamera(...)
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        +UpdateViewTarget(...)
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        +GetCameraCacheView()
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    }
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    class AActor {
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        +CalcCamera()
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    }
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    class UCameraComponent {
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        +GetCameraView(...)
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    }
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    class UCameraModifier {
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        +ModifyCamera()
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    }
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    class UCameraModifier_CameraShake {
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    }

CameraActor
1. CameraComponent 的包装容器，以使相机可以放置在关卡中。
CameraComponent
1. 代表相机的各种数据。
2. 并不直接处理数据。
PlayerCameraManager
1. 相机系统的核心，处理相机数据并应用到 ViewTarget。
2. 管理 ViewTarget，记录摄像机跟随对象Target和摄像机POV。

总体流程上：

初始化ViewTarget：

PlayerController 会在 PostInitializeComponents 函数中调用 SpawnPlayerCameraManager 函数。

SpawnPlayerCameraManager

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// servers and owning clients get cameras
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// If no archetype specified, spawn an Engine.PlayerCameraManager.  NOTE all games should specify an archetype.
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FActorSpawnParameters SpawnInfo;
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SpawnInfo.Owner = this;
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SpawnInfo.Instigator = GetInstigator();
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SpawnInfo.ObjectFlags |= RF_Transient;  // We never want to save camera managers into a map
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if (PlayerCameraManagerClass != NULL)
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{
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    PlayerCameraManager = GetWorld()->SpawnActor<APlayerCameraManager>(PlayerCameraManagerClass, SpawnInfo);
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}
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else
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{
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    PlayerCameraManager = GetWorld()->SpawnActor<APlayerCameraManager>(SpawnInfo);
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}
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if (PlayerCameraManager != NULL)
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{
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    PlayerCameraManager->InitializeFor(this);
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}
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else
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{
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    // log
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}

每个 PlayerController 都会在世界创建一个 PlayerCameraManager Actor。
针对每个创建的 PlayerCameraManager，都会调用 InitializeFor 函数初始化。

InitializeFor

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FMinimalViewInfo DefaultFOVCache = GetCameraCacheView();
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DefaultFOVCache.FOV = DefaultFOV;
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SetCameraCachePOV(DefaultFOVCache);
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PCOwner = PC;
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SetViewTarget(PC);
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// set the level default scale
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SetDesiredColorScale(GetWorldSettings()->DefaultColorScale, 5.f);
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// Force camera update so it doesn't sit at (0,0,0) for a full tick.
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// This can have side effects with streaming.
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UpdateCamera(0.f);

更新ViewTarget：

UWorld 会在 Tick 函数中调用 AplayerController::UpdateCameraManager，驱动 PlayerCameraManager::UpdateCamera 更新 ViewTarget。

World Tick

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//...
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for (int32 i = 0; i < LevelCollections.Num(); ++i)
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{
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    //...
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    // Update cameras last. This needs to be done before NetUpdates, and after all actors have been ticked.
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    for( FConstPlayerControllerIterator Iterator = GetPlayerControllerIterator(); Iterator; ++Iterator )
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    {
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        if (APlayerController* PlayerController = Iterator->Get())
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        {
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            if (!bIsPaused || PlayerController->ShouldPerformFullTickWhenPaused())
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            {
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                PlayerController->UpdateCameraManager(DeltaSeconds);
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            }
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            else if (PlayerController->PlayerCameraManager && FCameraPhotographyManager::IsSupported(this))
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            {
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                PlayerController->PlayerCameraManager->UpdateCameraPhotographyOnly();
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            }
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        }
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    }
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    //...
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}
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//...

PlayerController UpdateCameraManager

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if (PlayerCameraManager != NULL)
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{
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    PlayerCameraManager->UpdateCamera(DeltaSeconds);
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}

PlayerCameraManager UpdateCamera

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if ((PCOwner->Player && PCOwner->IsLocalPlayerController()) || !bUseClientSideCameraUpdates || bDebugClientSideCamera)
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{
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    DoUpdateCamera(DeltaTime);
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    //...
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}

应用ViewTarget：

UGameViewportClient 的 Draw 方法渲染画面时，会通过 ULocalPlayer::CalcSceneView 方法，最终从 APlayerCameraManager 中获取 ViewTarget 中的POV数据用于渲染。

处理ViewTarget#

FViewTarget 在 APlayerCameraManager::UpdateViewTarget 函数中进行更新。ViewTarget核心关注两个参数。

Target 相机看向的目标，后面的POV基于此进行计算。

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USTRUCT(BlueprintType)
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struct FTViewTarget
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{
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    // ...
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    /** Target Actor used to compute POV */
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    UPROPERTY(EditAnywhere, BlueprintReadWrite, Category=TViewTarget)
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    TObjectPtr<class AActor> Target;
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    // ...
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};

POV 相对看向目标的各种参数。

整体流程#

处理ViewTarget#

摄像机控制#

角色旋转控制#

摄像机旋转控制#