UE4 View & State

* FSceneView 包含Family,ViewState,ViewUniformBuffer

* FViewInfo

* FSceneViewFamily 包含Views,Scene,RenderTarget

* FSceneViewStateInterface

* FSceneViewState 存储渲染相关的**跨帧**资源（TAA历史信息、遮挡剔除信息、HLOD可见性、阴影等）

* FSceneInterface

* FScene 场景管理接口，物件和光源，特效以及阴影资源，绘制列表，光线追踪资源（场景加速结构）

* FSceneRenderer 渲染器实例（**每帧都会销毁重建**，同时绘制多个View）

常见的用法

auto RT = NewObject<UTextureRenderTarget2D>();

RT->AddToRoot();

RT->ClearColor = FLinearColor::Transparent;

RT->TargetGamma = TargetGamma;

RT->InitCustomFormat(TargetSize.X, TargetSize.Y, PF_FloatRGBA, false);

FTextureRTResource* RTResource = RT->GameThread_GetRTResource();

FSceneViewFamilyContext ViewFamily(

FSceneViewFamily::ConstructionValues(RTResource, Scene, FEngineShowFlags(ESFIM_Game))

.SetWorldTimes(FApp::GetCurrentTime() - GStartTime, FApp::GetDeltaTime(), FApp::GetCurrentTime() - GStartTime)

);

// To enable visualization mode

ViewFamily.EngineShowFlags.SetPostProcessing(true);

ViewFamily.EngineShowFlags.SetVisualizeBuffer(true);

ViewFamily.EngineShowFlags.SetTonemapper(false);

ViewFamily.EngineShowFlags.SetScreenPercentage(false);

FSceneViewInitOptions ViewInitOptions;

ViewInitOptions.SetViewRectangle(FIntRect(0, 0, TargetSize.X, TargetSize.Y));

ViewInitOptions.ViewFamily = &ViewFamily;

ViewInitOptions.HiddenPrimitives = HiddenPrimitives;

ViewInitOptions.ViewOrigin = ViewOrigin;

ViewInitOptions.ViewRotationMatrix = ViewRotationMatrix;

ViewInitOptions.ProjectionMatrix = ProjectionMatrix;

FSceneView* NewView = new FSceneView(ViewInitOptions);

NewView->CurrentBufferVisualizationMode = VisualizationMode;

ViewFamily.Views.Add(NewView);

ViewFamily.SetScreenPercentageInterface(new FLegacyScreenPercentageDriver(

ViewFamily, /* GlobalResolutionFraction = */ 1.0f, /* AllowPostProcessSettingsScreenPercentage = */ false));

FCanvas Canvas(RTResource, NULL, FApp::GetCurrentTime() - GStartTime, FApp::GetDeltaTime(), FApp::GetCurrentTime() - GStartTime, Scene->GetFeatureLevel());

Canvas.Clear(FLinearColor::Transparent);

GetRendererModule().BeginRenderingViewFamily(&Canvas, &ViewFamily);

// Copy the contents of the remote texture to system memory

OutSamples.SetNumUninitialized(TargetSize.X*TargetSize.Y);

FReadSurfaceDataFlags ReadSurfaceDataFlags;

ReadSurfaceDataFlags.SetLinearToGamma(false);

RTResource->ReadPixelsPtr(OutSamples.GetData(), ReadSurfaceDataFlags, FIntRect(0, 0, TargetSize.X, TargetSize.Y));

FlushRenderingCommands();

RT->RemoveFromRoot();

RT = nullptr;