[commit] 迭代文档

Author: Italink

Docs/04-UnrealEngine/0.基础编程.md

@@ -538,6 +538,40 @@ FUNCTION_NON_NULL_RETURN_START
 
 -   **可以通过UClass来创建对象** ：`NewObject<UCustomObject>()`等价于`NewObject<UObject>(GetTransientPackage(), UCustomObject::StaticClass())`
 
+通常，我们在虚幻引擎中接触到的绝大部分对象，它都是一个**UObject**，在代码层面，要创建任意的UObject，我们一般会使用这种方式：
+
+``` c++
+UObject* MyObject = NewObject<UObject>();
+
+UTexture2D* MyTexture = NewObject<UTexture2D>();
+
+UBlueprint* MyBlueprint = NewObject<UBlueprint>();
+
+UStaticMesh* MyStaticMesh = NewObject<UStaticMesh>();
+
+UNiagaraSystem* MyNiagaraSystem = NewObject<UNiagaraSystem>();
+
+AActor* MyActor = NewObject<AActor>();
+
+UStaticMeshComponent* MyStaticMeshComponent = NewObject<StaticMeshComponent>();
+
+UWorld* World = NewObject<UWorld>();
+
+...
+```
+
+这些语句在虚幻中并没有语法上的错误，它是可以编译通过的。
+
+但熟悉虚幻的小伙伴可能比较清楚，如果直接这样去创建对象，虽然确实能创建成功，但它的某些机制很有可能不能正常工作，因为那些类型伴随着特定的构造数据和逻辑，而引擎往往会将它包裹成新的接口，比如：
+
+- 使用 `UWorld::CreateWorld(...)` 构造 UWolrd
+- 使用 `UWorld::SpawnActor( ... )`在对应世界中创建Actor
+- 使用`FKismetEditorUtilities::CreateBlueprint(...)` 在编辑器下创建蓝图（UBlueprint）
+- 在Actor的构造函数中使用`UObject::CreateDefaultSubobject(...)` 来创建隶属于当前Actor的组件结构
+- ...
+
+因此如果使用`NewObject()`创建的对象某些机制不能正常工作，很有可能引擎封装了特定的构造逻辑，如果没找到，可以试着寻找那些初始化和注册的逻辑，然后手动执行它。
+
 ### 销毁
 
 除了UObject对象的创建，它的销毁，即生命周期的管理，也非常重要。
@@ -1379,6 +1413,131 @@ UObject* LoadedAsset = LoadObject<UObject>(nullptr,TEXT("/Game/CustomPackage.Cus
 - [知乎 - 海狗大人 | UEGamePlay框架：Pawn，Controller，APlayerState](https://zhuanlan.zhihu.com/p/16087843925)
 - [知乎 - 海狗大人 | UEGamePlay框架：GameMode，GameState](https://zhuanlan.zhihu.com/p/16089018768)
 
+当我们了解了这些结构体系之后，也就可以尝试去写一些大胆的代码，比如这是一段离线渲染静态模型的示例：
+
+``` c++
+void Render(UStaticMesh* StaticMesh, FString OutFileName, FTransform CameraTransform, int32 InResolution)
+{
+	EWorldType::Type WorldType = EWorldType::Editor;
+	UWorld* World = UWorld::CreateWorld(WorldType, false, "RenderWorld");		// 手动创建UWorld
+	
+    UWorld* LastWorld = GWorld;
+	GWorld = World;         
+	
+    FWorldContext& EditorContext = GEditor->GetEditorWorldContext();
+	EditorContext.SetCurrentWorld(World);   // Sky Light 的更新依赖于 GEgnine 的 Tick，它需要保证 GWorld == EditorContext.World() 
+
+	const FURL URL;
+	World->InitializeActorsForPlay(URL);
+	World->BeginPlay();															// 手动执行UWorld的开始事件
+
+    FakeEngineTick(World, 0.03f);
+    
+	AStaticMeshActor* Actor = World->SpawnActor<AStaticMeshActor>();
+	UStaticMeshComponent* StaticMeshComp = Actor->GetStaticMeshComponent();
+
+	ASkyAtmosphere* SkyAtmosphereActor = World->SpawnActor<ASkyAtmosphere>();
+	AExponentialHeightFog* ExponentialHeightFogActor = World->SpawnActor<AExponentialHeightFog>();
+
+	ADirectionalLight* DirectionalLightActor = World->SpawnActor<ADirectionalLight>();
+	UDirectionalLightComponent* DirectionalLightComponent = DirectionalLightActor->GetComponent();
+	DirectionalLightComponent->SetIntensity(12);
+
+	ASkyLight* SkyLightActor = World->SpawnActor<ASkyLight>();
+	USkyLightComponent* SkyLightComponent = SkyLightActor->GetLightComponent();
+	SkyLightComponent->SetMobility(EComponentMobility::Movable);
+	SkyLightComponent->bLowerHemisphereIsBlack = false;
+	SkyLightComponent->SetIntensity(2);
+	SkyLightComponent->RecaptureSky();											// 请求刷新天光
+    
+	FakeEngineTick(World, 0.03f);												// 执行等待渲染更新的Tick完成
+
+	UTextureRenderTarget2D* RenderTarget = NewObject<UTextureRenderTarget2D>();	// 初始化RT的数据
+	RenderTarget->RenderTargetFormat = ETextureRenderTargetFormat::RTF_RGBA16f;
+	RenderTarget->InitAutoFormat(InResolution, InResolution);
+	RenderTarget->UpdateResourceImmediate(true);
+
+    FakeEngineTick(World, 0.03f);												// 等待RT的资源提交
+    
+    ETextureRenderTargetFormat RenderTargetFormat = RenderTarget->RenderTargetFormat;
+	FTextureRenderTargetResource* RenderTargetResource = RenderTarget->GameThread_GetRenderTargetResource();
+    
+	ASceneCapture2D* SceneCaptureActor = World->SpawnActor<ASceneCapture2D>();
+	USceneCaptureComponent2D* SceneCaptureComp = SceneCaptureActor->GetCaptureComponent2D();
+	SceneCaptureComp->TextureTarget = RenderTarget;
+	SceneCaptureComp->bCaptureEveryFrame = false;
+	SceneCaptureComp->bOverride_CustomNearClippingPlane = true;
+	SceneCaptureComp->CustomNearClippingPlane = 0.01f;
+	SceneCaptureComp->CaptureSource = ESceneCaptureSource::SCS_FinalColorLDR;
+	SceneCaptureComp->ShowFlagSettings.Add(FEngineShowFlagsSetting{ TEXT("DistanceFieldAO"), false });
+	SceneCaptureComp->SetShowFlagSettings(SceneCaptureComp->ShowFlagSettings);
+
+	FakeEngineTick(World);											// 等待SceneCapture的状态更新
+
+	SceneCaptureActor->SetActorTransform(CameraTransform); 			// 执行捕获
+	SceneCaptureComp->CaptureScene();
+   
+    TArray<FLinearColor> Colors;
+	FReadSurfaceDataFlags ReadPixelFlags(RCM_MinMax);
+	FIntRect IntRegion(0, 0, RenderTarget->SizeX, RenderTarget->SizeY);
+	RenderTargetResource->ReadLinearColorPixels(Colors, ReadPixelFlags, IntRegion);
+    
+	FImageView ImageView(Colors.GetData(), RenderTarget->SizeX, RenderTarget->SizeY);
+	FImageUtils::SaveImageByExtension(*OutFileName, ImageView);	 	// 保存图像
+
+	World->DestroyWorld(false);										// 还原状态
+	GEngine->DestroyWorldContext(World);
+	GWorld = LastWorld;
+}
+
+// 手动执行引擎的Tick更新
+static void FakeEngineTick(UWorld* InWorld, float InDelta = 0.03f)    
+	FApp::SetDeltaTime(InDelta);
+
+    GEngine->EmitDynamicResolutionEvent(EDynamicResolutionStateEvent::EndFrame);
+    GEngine->Tick(InDelta, false);									// 其中包含了当前World的更新
+
+    FSlateApplication::Get().PumpMessages();
+    FSlateApplication::Get().Tick();
+
+    GFrameCounter++;
+
+    bool bIsTicking = FSlateApplication::Get().IsTicking();
+    if (!bIsTicking && GIsRHIInitialized) {
+        if (FSceneInterface* Scene = InWorld->Scene) {
+            ENQUEUE_RENDER_COMMAND(BeginFrame)([](FRHICommandListImmediate& RHICmdList) {
+                GFrameNumberRenderThread++;
+                GFrameCounterRenderThread++;
+                FCoreDelegates::OnBeginFrameRT.Broadcast();
+            });
+
+            ENQUEUE_RENDER_COMMAND(EndFrame)([](FRHICommandListImmediate& RHICmdList) {
+                FCoreDelegates::OnEndFrameRT.Broadcast();
+                RHICmdList.EndFrame();
+            });
+            FlushRenderingCommands();
+        }
+        ENQUEUE_RENDER_COMMAND(VirtualTextureScalability_Release)([](FRHICommandList& RHICmdList) {
+            GetRendererModule().ReleaseVirtualTexturePendingResources();
+        });
+    }
+
+    FTaskGraphInterface::Get().ProcessThreadUntilIdle(ENamedThreads::GameThread);
+
+    FSlateApplication::Get().GetRenderer()->Sync();
+
+    FThreadManager::Get().Tick();
+
+    FTSTicker::GetCoreTicker().Tick(InDelta);
+
+    GEngine->TickDeferredCommands();
+
+    GEngine->EmitDynamicResolutionEvent(EDynamicResolutionStateEvent::EndFrame);
+
+    FAssetCompilingManager::Get().FinishAllCompilation();
+}
+```
+
 ## 其他
 
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