BlueRoseNote/03-UnrealEngine/Rendering/RenderFeature/ShaderWorldPlugin/ShaderWorld.md

---
title: Untitled
date: 2025-06-03 10:19:25
excerpt: 
tags: 
rating: ⭐
---
# 前言
1. ShaderWorldPCGInterop：
2. ShaderWorld：
3. ShaderWorldCore：

# ShaderWorld
- Class 
	- Actor
		- ShaderWorldActor.h:[[#AShaderWorldActor]]
		- SWorld.h:[[#ASWorld]]

# USWorldSubsystem
主要管理：
- TArray<USWContextBase*> SW_Contexts 
- 渲染相关变量：RT_Ready、RenderThreadPoked、RenderThreadResponded处理。
# ASWorld

# AShaderWorldActor
## 大致启动流程
大致启动流程：
- BeginPlay()
	1. 设置SWCamera Location。
	2. 清空所有数据。
	3. InitiateWorld()
		1. 更新相关变量：GenerateCollision_last、VerticalRangeMeters_last、WorldHasBounds_OnRebuild。**Segmented_Initialized** 、**bExportPhysicalMaterialID_cached**
		2. 设置高度生成用材质变量 Generator;bool bHadGeneratorAtRebuildTime = IsValid(Generator);
		3. LOD_Num与WorldDimensionMeters计算。
		4. 重新生成若干数组：
			1. LODs_DimensionsMeters
			2. ClipMapToUpdateAndMove
			3. ClipMapToUpdate
			4. NeedSegmentedUpdate
			5. AdaptiveTopology
		5. 相关线程安全变量：
			1. Shareable_ID_FarLOD
			2. UpdateHOverTime
		6. ComputeOptimalVirtualCacheSize()
		7. for (int32 i = (WorldHasBounds_OnRebuild ? -1 : 0); i < LOD_Num; i++)
		8. Toggle Async creation of Clipmap Meshes
		9. Async TaskGraph ClipMapMeshCreation
- Tick()
	- 初始化
		1. 取得USWorldSubsystem指针，并且进行初始化。
	- ReadbacksManagement()
	- CollisionManagement()
	- SpawnablesManagement()
	- TerrainAndSpawnablesManagement()

### ReadbacksManagement()
主要用于回读RetrieveHeightAt()调用后GPU计算出来的Position信息。在**用于计算HeightReadBack的渲染线程、RHI、GPU都执行完成**后，从ReadBackHeightData的像素点（最多25个）中读取Z轴信息，之后和PointsPendingReadBacks中的X、Y轴信息合并成一个Vector3 Position。

- ThreadSafe
	 - bool
		 - **bProcessingHeightRetrieval**
		 - **bProcessingHeightRetrievalRT**
	 - FSWShareableSamplePoints
		 - PointsPendingReadBacks
	 - FSWColorRead
		 - ReadBackHeightData
 - FRenderCommandFence
	 - HeightReadBackFence

```c++
void AShaderWorldActor::ReadbacksManagement()
{
	if (!bProcessingHeightRetrieval.IsValid())
		bProcessingHeightRetrieval = MakeShared<FThreadSafeBool, ESPMode::ThreadSafe>();
	if (!bProcessingHeightRetrievalRT.IsValid())
		bProcessingHeightRetrievalRT = MakeShared<FThreadSafeBool, ESPMode::ThreadSafe>();
	
	//PointsPendingReadBacks存储从GPU回读的采样坐标位置;在RetrieveHeightAt()调用HeightReadBackFence.BeginFence(true)开启渲染栅栏，不开启这段逻辑不会执行。
	if ((*bProcessingHeightRetrieval.Get()) && (*bProcessingHeightRetrievalRT.Get()) && HeightReadBackFence.IsFenceComplete() && PointsPendingReadBacks.IsValid())
	{
		// ReadBackHeightData uin8 贴图数据
		if (!ReadBackHeightData.IsValid())
			return;
		
		//For now we do Compute samples on a rendertarget 5x5, therefore 25 positions evaluated per request.
		//每次请求可以读取25个点。
		const int NumOfVertex = 25;

		PositionsOfReadBacks.Empty();
		PositionsOfReadBacks.AddUninitialized(25);

		uint8* ReadData8 = (uint8*)ReadBackHeightData->ReadData.GetData();
			uint16 MaterialIndice = 0;
		for (int32 k = 0; k < NumOfVertex; k++)
		{
			FVector3f& PositionSample = PositionsOfReadBacks[k];

			if (RendererAPI == EGeoRenderingAPI::OpenGL)
			{
				int X = k % 5;
				int Y = k / 5;

				int index = X + Y * 5;

				Y = (5 - 1) - Y;

				index = X + Y * 5;

				PositionSample = FVector3f(PointsPendingReadBacks->PositionsXY[2 * k], PointsPendingReadBacks->PositionsXY[2 * k + 1], GetHeightFromGPURead(&ReadData8[index * 4], MaterialIndice) / HeightScale);
			}
			else
				PositionSample = FVector3f(PointsPendingReadBacks->PositionsXY[2 * k], PointsPendingReadBacks->PositionsXY[2 * k + 1], GetHeightFromGPURead(&ReadData8[k * 4], MaterialIndice) / HeightScale);

		}

		if(HeightRetrieveDelegate.ExecuteIfBound(PositionsOfReadBacks))
		{
			//SW_LOG("HeightRetrieveDelegate.ExecuteIfBound(PositionsOfReadBacks) PositionsOfReadBacks[0] %s",*PositionsOfReadBacks[0].ToString())
		}
		else
		{
			//SW_LOG("Fail HeightRetrieveDelegate.ExecuteIfBound(PositionsOfReadBacks)")
		}

		bProcessingHeightRetrieval->AtomicSet(false);
		bProcessingHeightRetrievalRT->AtomicSet(false);
	}

	//For now MinMax is here
	//处理FClipMapMeshElement的最大最小队列？
	if (UseSegmented())
	{
		if(WorldHasBounds_OnRebuild)
		{
			FClipMapMeshElement& MeshEl = FarLOD_BoundedWorld;

			if (MeshEl.MinMaxQueue.Num() > 0)
			{
				MeshEl.ProcessMinMaxQueue(SWorldSubsystem);
			}
		}
		
		for (FClipMapMeshElement& MeshEl : Meshes)
		{

			if (MeshEl.MinMaxQueue.Num() > 0)
			{
				MeshEl.ProcessMinMaxQueue(SWorldSubsystem);
			}
		}
	}
}
```

### CollisionManagement()
- ThreadSafe
	 - bool
		 - ***bProcessingGroundCollision***：处理地面碰撞。
		 - bPreprocessingCollisionUpdate
		 - EditRebuild：传递Bool值给 rebuild。
	 - FSWCollisionManagementShareableData
		 - CollisionShareable
 - FRenderCommandFence
	- 1
- bool 
	- RedbuildCollisionContext
- Array
	- CollisionReadToProcess：
	- CollisionWorkQueue：类型为FCollisionProcessingWork，碰撞处理任务队列，将回读的
- FCollisionMeshElement
	- ReadBackCompletion：碰撞数据GPU回读是否完成。


相关条件
if ((*bPreprocessingCollisionUpdate.Get()) ||  
    CollisionShareable->CollisionMeshToUpdate.Num() > 0 ||  
    CollisionShareable->CollisionMeshToRenameMoveUpdate.Num() > 0 ||  
    CollisionShareable->CollisionMeshToCreate.Num() > 0)  
    return;

	if (CollisionUpdateTimeAcu <= 1.f / 10.f || CollisionWorkQueue.Num() > 0 || !CollisionProcess.IsFenceComplete())


```c++
void AShaderWorldActor::CollisionManagement(float& DeltaT)
{
	SCOPED_NAMED_EVENT_TEXT("AShaderWorldActor::CollisionManagement", FColor::Magenta);
	SW_FCT_CYCLE()

	/*
	 * Can we execute compute shader?
	 * Do we need to rebuild collision?
	 * Did ShaderWorld toggled collision generation On/Off?
	 * Are we pending a full rebuild of the Shader World?
	 */
	if (!SetupCollisions())
		return;

	/*
	 * Using collision updates, update Collision meshes
	 */
	if (!CollisionFinalizeWork())
		return;

	if (CollisionProcess.IsFenceComplete())
	{
		/*
		 * Convert Compute shader results to actionable collision updates
		 */
		if (!CollisionPreprocessGPU())
		{
			CollisionProcess.BeginFence(true);
			return;
		}
	}

	/*
	 * Process GPU work queue by launching GPU tasks to evaluate the collision of new tiles
	 */
	CollisionGPU();

	// Timer
	// 碰撞生成与Update计时
	{
		CollisionUpdateTimeAcu += DeltaT;

		//CollisionUpdateTimeAcu如果超过0.1s，或者CollisionWorkQueue的任务都完成了。CollisionProcess已经完成。
		if (CollisionUpdateTimeAcu <= 1.f / 10.f || CollisionWorkQueue.Num() > 0 || !CollisionProcess.IsFenceComplete())
			return;

		CollisionUpdateTimeAcu = 0.f;
	}

	/*
	 * Gather relevant collision tiles
	 * If an old tile is not relevant anymore, release it.
	 * If a new location needs to be computed: allocate a tile and add its relevant computation work to the GPU work queue
	 */
	CollisionCPU();
}
```

#### SetupCollisions()
设置相关变量。
```c++
bool AShaderWorldActor::SetupCollisions()
{
	SW_FCT_CYCLE()

	if (!bHadGeneratorAtRebuildTime)
		return false;

	if (!Shareable_ID.IsValid() || Meshes.Num() <= 0)
		return false;

	//初始化线程安全变量
	if (!bProcessingGroundCollision.IsValid())
		bProcessingGroundCollision = MakeShared<FThreadSafeBool, ESPMode::ThreadSafe>();
	if (!bPreprocessingCollisionUpdate.IsValid())
		bPreprocessingCollisionUpdate = MakeShared<FThreadSafeBool, ESPMode::ThreadSafe>();

	if (EditRebuild)
	{
		EditRebuild.AtomicSet(false);
		rebuild = true;
	}

	if (rebuild)
		RedbuildCollisionContext = true;
	//重建相关变量初始化
	if (RedbuildCollisionContext)
	{
		if (!(*bProcessingGroundCollision.Get()) && !(*bPreprocessingCollisionUpdate.Get())
			&& CollisionProcess.IsFenceComplete()
			&& (CollisionMesh.Num() <= 0)
			&& (UsedCollisionMesh.Num() <= 0))
		{

			CollisionShareable = nullptr;

			CollisionWorkQueue.Empty();
			CollisionReadToProcess.Empty();

			RedbuildCollisionContext = false;

		}
	}

	if (RedbuildCollisionContext)
		return false;

	if (!GenerateCollision)
		return false;

	//创建全线程碰撞生成相关数据结构体CollisionShareable
	if (!CollisionShareable.IsValid())
		CollisionShareable = MakeShared<FSWCollisionManagementShareableData, ESPMode::ThreadSafe>(CollisionResolution, CollisionVerticesPerPatch);

	if ((*bProcessingGroundCollision.Get()) || (*bPreprocessingCollisionUpdate.Get()) || !CameraSet || (Meshes.Num() == 0))
		return false;

	//Let the data layer be computed before generating collisions and trying to extract material IDs
	if (bExportPhysicalMaterialID && (WorldCycle < 2))
		return false;


	if (CollisionVisibleChanged)
	{
		if (GetWorld())
		{
			for (auto& ColM : CollisionMesh)
			{
				if (auto& Mesh = ColM.Value.Mesh)
				{
					Mesh->SetMeshSectionVisible(0, CollisionVisible);
				}
			}
		}
		CollisionVisibleChanged.AtomicSet(false);
	}

	return true;
}
```

#### CollisionFinalizeWork() 笔记为3.8.6版本非最新
结束碰撞生成任务，true为完成，false为任务超时未完成。**主要的逻辑是将之前的数据设置为脏，并且更新FShaderWProceduralMeshSceneProxy,5.4 Finaly版本里这里已经移除了碰撞相关逻辑**
- TMap<FName,FCollisionMeshElement> CollisionMesh：碰撞Name => 碰撞Mesh Map。
	- FCollisionMeshElement：管理单个碰撞数据的结构体。
- UBodySetup：虚幻引擎中一个重要的物理相关类，主要用于定义和存储物体的物理属性和碰撞设置

```c++
bool AShaderWorldActor::CollisionFinalizeWork()
{
	SCOPED_NAMED_EVENT_TEXT("AShaderWorldActor::CollisionFinalizeWork()", FColor::Magenta);
	SW_FCT_CYCLE()
	
	if (!CollisionReadToProcess.IsEmpty())
		return true;

	const double GameThreadBudget_ms = SWGameThreadBudgetCollision_ms.GetValueOnGameThread();

	double TimeStart = FPlatformTime::Seconds();

	//判断处理队列是否为空
	if(CollisionWorkQueue.Num()<=0)
		return true;

	{
		FScopeLock CollisionMeshArrayAccess(&CollisionMeshAccessLock);
		for (int i = CollisionWorkQueue.Num() - 1; i >= 0; i--)
		{
			//判断生成时间是否是否超过预设数值，如果超过就直接返回。默认为1 ms。
			if ((FPlatformTime::Seconds() - TimeStart) * 1000.0 > GameThreadBudget_ms)
				return false;

			//将生成的碰撞数据赋予给对应的碰撞Mesh，最后移除任务队列中的任务。
			FCollisionProcessingWork& Work = CollisionWorkQueue[i];
			ensure(CollisionMesh.Find(Work.MeshID));
			FCollisionMeshElement& Mesh = CollisionMesh[Work.MeshID];
			Mesh.Mesh->UpdateSectionTriMesh(Work.DestB);
			CollisionWorkQueue.RemoveAt(i);
		}
	}

	CollisionWorkQueue.Empty();
	return true;
}

void UShaderWorldCollisionComponent::UpdateSectionTriMesh(TSharedPtr<FSWShareableVerticePositionBuffer, ESPMode::ThreadSafe>& Positions)
{	
	//当UBodySetup更新队列还有任务时，执行改函数会将FSWShareableVerticePositionBuffer加入到UpdatesReceivedDuringCompute数组中并且退出。
	if (AsyncBodySetupQueue.Num() > 0)
	{
#if SWDEBUG
		SW_LOG("Collision Update received during alreayd occuring computation %s",*GetName())
#endif

		UpdatesReceivedDuringCompute.Add(Positions);

		return;
	}
	
	UpdatesReceivedDuringCompute.Empty();
	
	//使用FSWShareableVerticePositionBuffer数据来更新当前UShaderWorldCollisionComponent
	bool EnsureSameBuffers = ProcMeshSections.Num() > 0 && ProcMeshSections[0].PositionBuffer.IsValid() && (ProcMeshSections[0].PositionBuffer->Positions3f.Num() == 0 || ProcMeshSections[0].PositionBuffer->Positions3f.Num() == Positions->Positions.Num());
	if(!EnsureSameBuffers)
	{
#if SWDEBUG
		UE_LOG(LogTemp,Warning,TEXT("Error UpdateSectionTriMesh : buffers incompatible"));
#endif

	}
	else
	{
		ProcMeshSections[0].PositionBuffer.Reset();
		ProcMeshSections[0].Normals.Reset();

		ProcMeshSections[0].PositionBuffer = Positions;
		ProcMeshSections[0].SectionLocalBox = Positions->Bound;
		ProcMeshSections[0].bEnableCollision = true;

		Async(EAsyncExecution::TaskGraph, [WeakThis = MakeWeakObjectPtr(this), PBuffer = Positions, IndexB = ProcMeshSections[0].IndexBuffer]
		{
				TSharedPtr<TArray<FVector>, ESPMode::ThreadSafe> Normals = SWComputeNormalsForPatch(PBuffer, IndexB);

				AsyncTask(ENamedThreads::GameThread, [WeakThis,PBuffer, Normals]()
				{
						if (WeakThis.IsValid())
						{
							if (UShaderWorldCollisionComponent* Comp = Cast<UShaderWorldCollisionComponent>(WeakThis.Get()))
							{
								//塞入Normal
								if(IsValid(Comp))
									Comp->ReceiveComputedNormals(PBuffer, Normals);
							}
						}
				});
		});
	}
	
	//Materials
	// Pass new positions to trimesh
	UpdateCollision();//1. 异步Cook UBodySetup 2. 删除原本的碰撞 3. UseBodySetup->CreatePhysicsMeshesAsync()，使用UBodySetup异步创建新的碰撞网格。
	UpdateLocalBounds();//更新UShaderWorldCollisionComponent的LocalBoundingBox
	UpdateNavigation();

	if (ProcMeshSections.Num() > 0 && (ProcMeshSections[0].bSectionVisible || (GetWorld() && !GetWorld()->IsGameWorld())))
	{
		// If we have a valid proxy and it is not pending recreation
		if (SceneProxy && !IsRenderStateDirty())
		{
			//SW_LOG("Update trimesh SceneProxy && !IsRenderStateDirty()")
			// Create data to update section
			FShaderWColProcMeshSectionUpdateData* SectionData = new FShaderWColProcMeshSectionUpdateData;
			SectionData->TargetSection = 0;
			SectionData->NewPositionBuffer = ProcMeshSections[0].PositionBuffer;

			//更新SceneProxy FShaderWProceduralMeshSceneProxy的NewPositionBuffer，也就是UpdateSection
			if(AShaderWorldActor* owner = Cast<AShaderWorldActor>(GetOwner()))
			{
				{
					// Enqueue command to send to render thread
					FShaderWProceduralMeshSceneProxy* ProcMeshSceneProxy = (FShaderWProceduralMeshSceneProxy*)(SceneProxy && !IsRenderStateDirty() ? SceneProxy : nullptr);
					ENQUEUE_RENDER_COMMAND(FGeoCProcMeshSectionUpdate)
						([ProcMeshSceneProxy, SectionData](FRHICommandListImmediate& RHICmdList)
						{
							if(ProcMeshSceneProxy)
								ProcMeshSceneProxy->UpdateSection_RenderThread(SectionData);
						});
				}				
			}
			else
			{
				//SW_LOG("Update trimesh !owner")
			}
		}
		else
		{
			//SW_LOG("Update trimesh !(SceneProxy && !IsRenderStateDirty())")
		}

		MarkRenderTransformDirty();
	}
}
```

#### CollisionPreprocessGPU()
GPU生成碰撞 的预处理阶段。
将从GPU回读的碰撞顶点Z轴数据***uint8* ReadData8*** 反序列化成double，之后再还原成***FCollisionProcessingWork.DestB***的Positions、Normals、Positions3f、MaterialIndices、Bound。

```c++
bool AShaderWorldActor::CollisionPreprocessGPU()
{
	SCOPED_NAMED_EVENT_TEXT("AShaderWorldActor::CollisionPreprocessGPU()", FColor::Magenta);
	SW_FCT_CYCLE()

	for (int32 CollID = CollisionReadToProcess.Num() - 1; CollID >= 0; CollID--)
	{
		const FName& ElID = CollisionReadToProcess[CollID];


		if (!CollisionMesh.Find(ElID))
		{
			CollisionWorkQueue.Empty();
			CollisionReadToProcess.RemoveAt(CollID);
			continue;
		}

		//判断FCollisionMeshElement是否有效，以及是否将碰撞数据回读完成，如果完成，则将数据添加到碰撞处理队列CollisionWorkQueue，并且从碰撞回读队列CollisionReadToProcess
		FCollisionMeshElement& Mesh = *CollisionMesh.Find(ElID);
		if ((*Mesh.ReadBackCompletion.Get()))
		{
			ensure(Mesh.Mesh);

			if(FGeoCProcMeshSection* Section = Mesh.Mesh->GetProcMeshSection(0))
			{
				if(CollisionMesh.Contains(CollisionBufferHolder))
				{
					CollisionWorkQueue.Emplace(
						ElID
						, Mesh.HeightData
						, (*CollisionMesh.Find(CollisionBufferHolder)).Mesh->VerticesTemplate
						, (*CollisionMesh.Find(CollisionBufferHolder)).Mesh->TrianglesTemplate);
				}
				else
				{
					SW_LOG("!CollisionMesh.Contains(CollisionBufferHolder)")
				}

			}
			else
			{
				SW_LOG("CollisionPreprocessGPU :: Mesh.Mesh->GetProcMeshSection(0) = nullptr")
			}
			
			CollisionReadToProcess.RemoveAt(CollID);
		}
	}
	//回读队列处理完毕后之后执行后续逻辑
	if (!CollisionReadToProcess.IsEmpty())
	{
		return false;
	}

	//开始执行碰撞处理队列逻辑
	CollisionReadToProcess.Empty();
	if (CollisionWorkQueue.Num() > 0)
	{
		(*bProcessingGroundCollision.Get()) = true;

		AShaderWorldActor* SWContext = this;
		//异步并行 反序列化Ground碰撞数据
		Async(EAsyncExecution::TaskGraph, [Completion = bProcessingGroundCollision, RenderAPI = RendererAPI, VerticesPerPatch = CollisionVerticesPerPatch, Work = CollisionWorkQueue]
			{

				ParallelFor(Work.Num(), [&](int32 WorkIndex)
					{						
						
						const FCollisionProcessingWork& WorkEl = Work[WorkIndex];


						if (!WorkEl.Read.IsValid() || !WorkEl.SourceB.IsValid() || !WorkEl.DestB.IsValid())
							return;

						const int NumOfVertex = WorkEl.SourceB->Positions.Num();

						WorkEl.DestB->Positions.SetNum(NumOfVertex);
						WorkEl.DestB->Positions3f.SetNum(NumOfVertex);
						WorkEl.DestB->MaterialIndices.SetNum(NumOfVertex);
						WorkEl.DestB->Bound = FBox(EForceInit::ForceInit);

						FVector LocationfVertice_WS(0);
						uint16 MaterialIndice = 0;

						//取得从GPU回读的序列化数据
						uint8* ReadData8 = (uint8*)WorkEl.Read->ReadData.GetData();

						TSet<int32>& TrianglesAffectedByHoles = WorkEl.DestB->TrianglesAffectedByHoles;
						TrianglesAffectedByHoles.Empty();

						//#TODO ISPC slower ?
#if 0 // INTEL_ISPC
							if (RenderAPI == EGeoRenderingAPI::OpenGL)
							{
								ispc::ShaderWorld_HeightFromGPUReadOpenGL(NumOfVertex, VerticesPerPatch, ReadData8,(ispc::FVector*)WorkEl.SourceB->Positions.GetData(), (ispc::FVector*)WorkEl.DestB->Positions.GetData(), (ispc::FVector3f*)WorkEl.DestB->Positions3f.GetData(), WorkEl.DestB->MaterialIndices.GetData());
								
							}
							else
							{
								ispc::ShaderWorld_HeightFromGPURead(NumOfVertex, VerticesPerPatch, ReadData8, (ispc::FVector3f*)WorkEl.SourceB->Positions3f.GetData(), (ispc::FVector*)WorkEl.DestB->Positions.GetData(), (ispc::FVector3f*)WorkEl.DestB->Positions3f.GetData(), WorkEl.DestB->MaterialIndices.GetData());
							}
#else

						//从对序列化碰撞Z轴数据进行反序列化，还原成double，再之后还原成FCollisionProcessingWork.DestB
						for (int32 k = 0; k < NumOfVertex; k++)
							{

								if (RenderAPI == EGeoRenderingAPI::OpenGL)
								{
									const int index = k % VerticesPerPatch + (VerticesPerPatch - 1 - (k / VerticesPerPatch)) * VerticesPerPatch;

									LocationfVertice_WS = FVector(WorkEl.SourceB->Positions[k].X, WorkEl.SourceB->Positions[k].Y, GetHeightFromGPURead(&ReadData8[4 * index], MaterialIndice));
								}
								else
									LocationfVertice_WS = FVector(WorkEl.SourceB->Positions[k].X, WorkEl.SourceB->Positions[k].Y, GetHeightFromGPURead(&ReadData8[4 * k], MaterialIndice));

								WorkEl.DestB->Positions[k] = LocationfVertice_WS;
								WorkEl.DestB->Positions3f[k] = FVector3f(LocationfVertice_WS);
								WorkEl.DestB->MaterialIndices[k] = MaterialIndice;

								
								/*
								 * Height below -7km means terrain hole
								 */
								if(WorkEl.DestB->Positions[k].Z < -700000.0)
								{
									/*
									 * Find triangles including this vertex and add them to removed triangles
									 */

									if(WorkEl.SourceB->PositionToTriangle.Contains(k))
									{
										TrianglesAffectedByHoles.Append(*WorkEl.SourceB->PositionToTriangle.Find(k));
									}
								}
								else
								{
									WorkEl.DestB->Bound += WorkEl.DestB->Positions[k];
								}
							}

#endif
						/*
						 * If the terrain has holes, create a custom index buffer with the related triangles removed
						 * 地形挖洞，碰撞逻辑处理。
						 */
						if(TrianglesAffectedByHoles.Num() > 0)
						{
							WorkEl.DestB->FilteredTriangles = MakeShared<FSWShareableIndexBuffer, ESPMode::ThreadSafe>();

							for(int32 Triangle = 0; Triangle < WorkEl.TriangleTemplate->Indices.Num()/3; Triangle++)
							{
								if(!TrianglesAffectedByHoles.Contains(Triangle))
								{
									WorkEl.DestB->FilteredTriangles->Indices.Add(WorkEl.TriangleTemplate->Indices[Triangle * 3]);
									WorkEl.DestB->FilteredTriangles->Indices.Add(WorkEl.TriangleTemplate->Indices[Triangle * 3 + 1]);
									WorkEl.DestB->FilteredTriangles->Indices.Add(WorkEl.TriangleTemplate->Indices[Triangle * 3 + 2]);

									WorkEl.DestB->FilteredTriangles->Triangles_CollisionOnly.Add(WorkEl.TriangleTemplate->Triangles_CollisionOnly[Triangle]);
								}
							}
						}
						else
						{
							WorkEl.DestB->FilteredTriangles.Reset();
						}


						//WorkEl.DestB->Bound = FBox(WorkEl.DestB->Positions);
					}
				);

				//执行完成后将Completion（bProcessingGroundCollision）设置为false代表处理完成。
				if (Completion.IsValid())
					Completion->AtomicSet(false);

			});
	}

	return true;
}
```



#### CollisionGPU()
```c++

void AShaderWorldActor::CollisionGPU()
{
	SCOPED_NAMED_EVENT_TEXT("AShaderWorldActor::CollisionGPU()", FColor::Magenta);
	SW_FCT_CYCLE()

	double CurrentTime = FPlatformTime::Seconds();

		if (!(!(*bPreprocessingCollisionUpdate.Get()) && (
			CollisionShareable->CollisionMeshToUpdate.Num() > 0 ||
			CollisionShareable->CollisionMeshToRenameMoveUpdate.Num() > 0 ||
			CollisionShareable->CollisionMeshToCreate.Num() > 0)))
		{
			/*
			 * No collision Preprocessing running, we can safely access the data in the shared pointer without risking race condition
			 * 确保没有PreprocessingCollision任务在运行
			 */
			if(!(*bPreprocessingCollisionUpdate.Get()))
			{
				FScopeLock CollisionMeshArrayAccess(CollisionMeshAccessLock.Get());

				TArray<FName> NameToRemove;
				//遍历AvailableCollisionMesh
				for (const FName& AvailableID : CollisionShareable->AvailableCollisionMesh)
				{
					FCollisionMeshElement& Elem = *CollisionMesh.Find(AvailableID);
					//更新时间戳
					if (Elem.SleepTime < 0.0)
						Elem.SleepTime = CurrentTime;
					else if ((abs(CurrentTime - Elem.SleepTime) >= 1.0) && (CollisionBufferHolder == "" || AvailableID != CollisionBufferHolder) && (!Elem.Mesh || (Elem.Mesh && !Elem.Mesh->HasAsyncWorkPending())))//如果生成超时，则销毁对应变量
					{
						if (IsValid(Elem.Mesh))						
							Elem.Mesh->DestroyComponent();							
						
						Elem.Mesh = nullptr;

						DecountRTAllocatedMemory(Elem.CollisionRT)
						DecountRTAllocatedMemory(Elem.CollisionRT_Duplicate)

						Elem.CollisionRT = nullptr;
						Elem.CollisionRT_Duplicate = nullptr;
						Elem.DynCollisionCompute = nullptr;
						Elem.LayerComputeForPhysicalMaterial.Empty();

						CollisionMesh.Remove(AvailableID);

						if (UsedCollisionMesh.Contains(AvailableID))
						{
							UsedCollisionMesh.Remove(AvailableID);
						}

						CollisionShareable->CollisionMeshData.Remove(AvailableID);
						CollisionShareable->UsedCollisionMesh.Remove(AvailableID);
						NameToRemove.Add(AvailableID);
					}
					else
					{
					}
				}
				for (auto& TR : NameToRemove)
				{
					CollisionShareable->AvailableCollisionMesh.Remove(TR);
				}
			}

			return;
		}
			


	UWorld* World = GetWorld();

	bool RequireRenderFence = false;
	int32 CollisionDrawCallCount = 0;


	UsedCollisionMesh = CollisionShareable->UsedCollisionMesh;

	/*
	 * Async task created proxy CollisionMesh and associated IDs to them, create actual GameThread collision using the provided IDs
	 * 异步任务创建了代理碰撞网格，并将相关 ID 与它们关联起来，使用提供的 ID 在游戏线程中创建实际的碰撞。
	 */
	for (FName& ID : CollisionShareable->CollisionMeshToCreate)
	{
		//使用需要创建碰撞的ID（Name）来获取碰撞MeshData.
		const FSWCollisionMeshElemData& Mesh_Shareable = *CollisionShareable->CollisionMeshData.Find(ID);

		FCollisionMeshElement& Mesh = GetACollisionMesh(ID);//GetACollisionMesh()取得现有FCollisionMeshElement或者创建新的，代码贼长。

		Mesh.Location = Mesh_Shareable.Location;
		Mesh.MeshLocation = Mesh_Shareable.MeshLocation;

		Mesh.Mesh->SetWorldTransform(FTransform(Mesh_Shareable.MeshLocation));
		Mesh.Mesh->SetCollisionProfileName(UCollisionProfile::BlockAll_ProfileName);
		Mesh.Mesh->Mobility = EComponentMobility::Static;
	}

	//清空创建列表。
	CollisionShareable->CollisionMeshToCreate.Empty();

	//处理CollisionMeshToUpdate 碰撞数据更新队列
	for (int i = CollisionShareable->CollisionMeshToUpdate.Num() - 1; i >= 0; i--)
	{
		FName& CollisionIDToUpdate = CollisionShareable->CollisionMeshToUpdate[i];
		FCollisionMeshElement& El = *CollisionMesh.Find(CollisionIDToUpdate);
		UpdateCollisionMeshData(El);//核心函数

		CollisionShareable->CollisionMeshToUpdate.RemoveAt(i);

		RequireRenderFence = true;
		CollisionDrawCallCount++;

		if (CollisionDrawCallCount >= CollisionMaxDrawCallPerFrame)
			break;
	}

	//处理CollisionMeshToRenameMoveUpdate 碰撞数据重命名&移动更新队列
	for (int i = CollisionShareable->CollisionMeshToRenameMoveUpdate.Num() - 1; i >= 0; i--)
	{
		FName& CollisionIDToUpdate = CollisionShareable->CollisionMeshToRenameMoveUpdate[i];

		ensure(CollisionMesh.Find(CollisionIDToUpdate) != nullptr);
		ensure(CollisionShareable->CollisionMeshData.Find(CollisionIDToUpdate) != nullptr);

		FCollisionMeshElement& El = *CollisionMesh.Find(CollisionIDToUpdate);
		const FSWCollisionMeshElemData& El_Shareable = *CollisionShareable->CollisionMeshData.Find(CollisionIDToUpdate);

		El.Location = El_Shareable.Location;
		El.MeshLocation = El_Shareable.MeshLocation;

		El.Mesh->SetLocationOnPhysicCookComplete(El.MeshLocation);

		UpdateCollisionMeshData(El);

		CollisionShareable->CollisionMeshToRenameMoveUpdate.RemoveAt(i);

		RequireRenderFence = true;
		CollisionDrawCallCount++;

		if (CollisionDrawCallCount >= CollisionMaxDrawCallPerFrame)
			break;
	}

	//开启CollisionProcess，需要等到执行完之后，才能执行CollisionPreprocessGPU()
	if (RequireRenderFence)
	{
		CollisionProcess.BeginFence();
	}
		
}
```

```c++
FCollisionMeshElement& AShaderWorldActor::GetACollisionMesh(FName Name/*, FGuid AlreadyCreatedID*/)
{
	UWorld* World = GetWorld();

	//存在可用CollisionMesh时，使用ID去寻找，如果找到则直接返回。并将AvailableCollisionMesh中的ID 转移到 UsedCollisionMesh
	if (CollisionShareable.IsValid() && CollisionShareable->AvailableCollisionMesh.Num() > 0 )
	{
		if(FName* FoundName = CollisionShareable->AvailableCollisionMesh.Find(Name))
		{
			
			if (FCollisionMeshElement* Elem = CollisionMesh.Find(Name))
			{
				UsedCollisionMesh.Add(Name);
				CollisionShareable->UsedCollisionMesh.Add(Name);
				CollisionShareable->AvailableCollisionMesh.Remove(Name);
				Elem->SleepTime = -1.0;
				return *Elem;
			}			
		}
	}

	FScopeLock CollisionMeshArrayAccess(CollisionMeshAccessLock.Get());
	//往CollisionMesh Map添加新元素(FCollisionMeshElement)并设置其属性。
	CollisionMesh.Add(Name, {});
	FCollisionMeshElement& NewElem = *CollisionMesh.Find(Name);
	NewElem.ID = Name;


	uint32 SizeT = (uint32)CollisionVerticesPerPatch;
	NewElem.CollisionVerticesPerPatch = SizeT;


	NewElem.HeightData = MakeShared<FSWColorRead, ESPMode::ThreadSafe>();
	NewElem.HeightData->ReadData.SetNum(CollisionVerticesPerPatch * CollisionVerticesPerPatch);

	NewElem.Mesh = NewObject<UShaderWorldCollisionComponent>(this, Name, RF_Transient | RF_TextExportTransient);

	NewElem.Mesh->SetUsedPhysicalMaterial(RootComp->PhysicalMaterials);

	NewElem.Mesh->bUseAsyncCooking = true;

	NewElem.Mesh->SetSWWorldVersion(Shareable_ID);

	if (RootComp)
	{
		NewElem.Mesh->ComponentTags = RootComp->ComponentTags;
		NewElem.Mesh->BodyInstance.CopyBodyInstancePropertiesFrom(&RootComp->BodyInstance);

		NewElem.Mesh->ComponentTags = RootComp->ComponentTags;
	}
	else
	{
		UE_LOG(LogTemp, Warning, TEXT("UShaderWorldCollisionComponent Creation : invalid RootComp"))
	}

	NewElem.Mesh->SetCollisionObjectType(CollisionChannel);
	NewElem.Mesh->SetGenerateOverlapEvents(true);
	NewElem.Mesh->SetupAttachment(RootComponent);

	//NewElem.Mesh->SetRelativeLocation(FVector(0.f, 0.f, 0.f));
	NewElem.Mesh->bUseComplexAsSimpleCollision = true;
	/*
	NewElem.Mesh->SetUsingAbsoluteLocation(true);
	NewElem.Mesh->SetUsingAbsoluteRotation(true);
	*/
	//NewElem.Mesh->bTraceComplexOnMove = false;
	NewElem.MeshLocation = NewElem.Mesh->GetComponentLocation();

#if WITH_EDITORONLY_DATA
	NewElem.Mesh->bConsiderForActorPlacementWhenHidden = true;
#endif

	NewElem.Mesh->RegisterComponent();

	TSharedPtr<FSWShareableVerticePositionBuffer, ESPMode::ThreadSafe> Vertices = MakeShared<FSWShareableVerticePositionBuffer, ESPMode::ThreadSafe>();
	TSharedPtr<FSWShareableIndexBuffer, ESPMode::ThreadSafe> Triangles = MakeShared<FSWShareableIndexBuffer, ESPMode::ThreadSafe>();

	float Spacing = CollisionResolution;

	if(CollisionBufferHolder.IsValid() && (!CollisionMesh.Find(CollisionBufferHolder) || (CollisionMesh.Find(CollisionBufferHolder) && !CollisionMesh.Find(CollisionBufferHolder)->Mesh)))
		CollisionBufferHolder = "";

	//符合条件则重新创建碰撞GPU计算用RT。
	if ( CollisionBufferHolder == "" || (CollisionBufferHolder != "" && CollisionBufferHolder == Name))
	{
		CollisionBufferHolder = Name;

		SW_RT(NewElem.CollisionRT, World, Name.ToString() + FString::FromInt(GetUniqueID()), SizeT, TF_Nearest, RTF_RGBA8)
		RTAllocatedMemory(NewElem.CollisionRT)


		if (bExportPhysicalMaterialID_cached && LayerStoringMaterialID != "")
		{
			for (FSWProducers& layer : Producers)
			{
				if (layer.LayerName == "Height" || layer.LayerName == "height")
				{
					continue;
				}

				if (layer.LayerName != "" && layer.MaterialToGenerateLayer)
				{
					NewElem.LayerOrder.Add(layer.LayerName);

					UShaderWorldRT2D* LayerRT = nullptr;
					SW_RT(LayerRT, World, layer.LayerName + "_PhyMat_" + FString::FromInt(GetUniqueID()), SizeT, layer.LayerFiltering, layer.LayerFormat)
						RTAllocatedMemory(LayerRT)

						NewElem.LayerComputeForPhysicalMaterial.Add(layer.LayerName, { LayerRT ,nullptr });
				}

				if (LayerStoringMaterialID == layer.LayerName)
					break;
			}
		}


		SW_RT(NewElem.CollisionRT_Duplicate, World, "RT_Temp_" + Name.ToString() + FString::FromInt(GetUniqueID()), SizeT, TF_Nearest, RTF_RGBA8)
		RTAllocatedMemory(NewElem.CollisionRT_Duplicate)

		TArray<FVector2f> UV;
		USWBlueprintFunctionLibrary::CreateGridMeshWelded(CollisionVerticesPerPatch, CollisionVerticesPerPatch, Triangles, Vertices, UV, Spacing);

		{
			const int32 NumTriangles = Triangles->Indices.Num() / 3;
			Triangles->Triangles_CollisionOnly.Empty();
			Triangles->Triangles_CollisionOnly.Reserve(NumTriangles);
			for (int32 TriIdx = 0; TriIdx < NumTriangles; TriIdx++)
			{
				FTriIndices& Triangle = Triangles->Triangles_CollisionOnly.AddDefaulted_GetRef();
				Triangle.v0 = Triangles->Indices[(TriIdx * 3) + 0] /* + VertexBase */;
				Triangle.v1 = Triangles->Indices[(TriIdx * 3) + 1] /* + VertexBase */;
				Triangle.v2 = Triangles->Indices[(TriIdx * 3) + 2] /* + VertexBase */;
			}
		}

		/*
		 * The data inside the Vertices shared pointer can and will change over time, while VerticesTemplate is immutable,
		 * therefore we are making a persistent copy instead of using Vertices directly
		 */
		NewElem.Mesh->VerticesTemplate = MakeShared<FSWShareableVerticePositionBuffer, ESPMode::ThreadSafe>();
		NewElem.Mesh->VerticesTemplate->Positions = Vertices->Positions;
		NewElem.Mesh->VerticesTemplate->Positions3f = Vertices->Positions3f;
		NewElem.Mesh->VerticesTemplate->MaterialIndices = Vertices->MaterialIndices;

		NewElem.Mesh->VerticesTemplate->PositionToTriangle = Vertices->PositionToTriangle;

		NewElem.Mesh->TrianglesTemplate = Triangles;
	}
	else if(CollisionBufferHolder != "" && CollisionMesh.Find(CollisionBufferHolder) && !CollisionMesh.Find(CollisionBufferHolder)->Mesh->VerticesTemplate.IsValid())
	{
		/*
		 * #TODO Should never occur, remove
		 */
#if SWDEBUG
		SW_LOG("Recreating Collision Vertice template")
#endif
		const FCollisionMeshElement& BufferHolder = *CollisionMesh.Find(CollisionBufferHolder);

		TArray<FVector2f> UV;
		USWBlueprintFunctionLibrary::CreateGridMeshWelded(CollisionVerticesPerPatch, CollisionVerticesPerPatch, Triangles, Vertices, UV, Spacing);

		{
			const int32 NumTriangles = Triangles->Indices.Num() / 3;
			Triangles->Triangles_CollisionOnly.Empty();
			Triangles->Triangles_CollisionOnly.Reserve(NumTriangles);
			for (int32 TriIdx = 0; TriIdx < NumTriangles; TriIdx++)
			{
				FTriIndices& Triangle = Triangles->Triangles_CollisionOnly.AddDefaulted_GetRef();
				Triangle.v0 = Triangles->Indices[(TriIdx * 3) + 0] /* + VertexBase */;
				Triangle.v1 = Triangles->Indices[(TriIdx * 3) + 1] /* + VertexBase */;
				Triangle.v2 = Triangles->Indices[(TriIdx * 3) + 2] /* + VertexBase */;
			}
		}

		BufferHolder.Mesh->VerticesTemplate = MakeShared<FSWShareableVerticePositionBuffer, ESPMode::ThreadSafe>();
		BufferHolder.Mesh->VerticesTemplate->Positions = Vertices->Positions;
		BufferHolder.Mesh->VerticesTemplate->Positions3f = Vertices->Positions3f;
		BufferHolder.Mesh->VerticesTemplate->MaterialIndices = Vertices->MaterialIndices;

		BufferHolder.Mesh->VerticesTemplate->PositionToTriangle = Vertices->PositionToTriangle;

		BufferHolder.Mesh->TrianglesTemplate = Triangles;

		Vertices->Positions = BufferHolder.Mesh->VerticesTemplate->Positions;
		Vertices->Positions3f = BufferHolder.Mesh->VerticesTemplate->Positions3f;
		Vertices->MaterialIndices = BufferHolder.Mesh->VerticesTemplate->MaterialIndices;

		Triangles = BufferHolder.Mesh->TrianglesTemplate;


		SW_RT(NewElem.CollisionRT, World, Name.ToString() + FString::FromInt(GetUniqueID()), SizeT, TF_Nearest, RTF_RGBA8)
		RTAllocatedMemory(NewElem.CollisionRT)


		if (bExportPhysicalMaterialID_cached && LayerStoringMaterialID != "")
		{
			for (FSWProducers& layer : Producers)
			{
				if (layer.LayerName == "Height" || layer.LayerName == "height")
				{
					continue;
				}

				if (layer.LayerName != "" && layer.MaterialToGenerateLayer)
				{
					NewElem.LayerOrder.Add(layer.LayerName);

					UShaderWorldRT2D* LayerRT = nullptr;
					SW_RT(LayerRT, World, layer.LayerName + "_PhyMat_" + FString::FromInt(GetUniqueID()), SizeT, layer.LayerFiltering, layer.LayerFormat)
						RTAllocatedMemory(LayerRT)

						NewElem.LayerComputeForPhysicalMaterial.Add(layer.LayerName, { LayerRT ,nullptr });
				}

				if (LayerStoringMaterialID == layer.LayerName)
					break;
			}
		}
	}
	else
	{
		check(CollisionMesh.Contains(CollisionBufferHolder))

		const FCollisionMeshElement& BufferHolder = *CollisionMesh.Find(CollisionBufferHolder);

		check(BufferHolder.Mesh->VerticesTemplate.IsValid())
		/*
		 * No point copying irrelevant data that will be overriden once the computation is complete.
		 */
		Triangles = BufferHolder.Mesh->TrianglesTemplate;

		NewElem.CollisionRT = BufferHolder.CollisionRT;
		NewElem.LayerOrder = BufferHolder.LayerOrder;
		NewElem.LayerComputeForPhysicalMaterial = BufferHolder.LayerComputeForPhysicalMaterial;
	}

	NewElem.Mesh->CreateMeshSection(0, Vertices, Triangles, false);

	/*
	 * If not in editor mode, only make collision blue mesh visible if we asked for collisions to be visible
	 * The renderthread will otherwise completely skip the collision meshes
	 */
	NewElem.Mesh->SetMeshSectionVisible(0, CollisionVisible);


	if (!CollisionMat)
	{
#if SWDEBUG
		SW_LOG("Material for Collision mesh not available for Shader World %s", *GetName())
#endif
	}
	else
	{
#if WITH_EDITOR
		if ((CollisionBufferHolder != Name)
			&& CollisionMesh.Contains(CollisionBufferHolder)
			&& (*CollisionMesh.Find(CollisionBufferHolder)).Mesh)
		{

			NewElem.Mesh->SetMaterialFromOwner(0, (*CollisionMesh.Find(CollisionBufferHolder)).Mesh->GetMaterial(0));
		}
		else
		{
			UMaterialInstanceDynamic* DynColMat = SWTakeCareOfMID(CollisionMat.Get(), this);
			SWorldSubsystem->SetScalarParameterValue(DynColMat, "MakeCollisionVisible", 1.0);
			SWorldSubsystem->SetScalarParameterValue(DynColMat, "CollisionResolution", CollisionResolution);
			NewElem.Mesh->SetMaterialFromOwner(0, DynColMat);
		}
#endif
	}

	UsedCollisionMesh.Add(Name);
	CollisionShareable->UsedCollisionMesh.Add(Name);

	//if (CollisionShareable->CollisionMeshData.Num() < CollisionMesh.Num())
	{
		if(!CollisionShareable->CollisionMeshData.Contains(Name))
			CollisionShareable->CollisionMeshData.Add(Name, NewElem);
	}

	return *CollisionMesh.Find(Name);
	//return CollisionMesh[CollisionMesh.Num() - 1];
}
```

```c++
void AShaderWorldActor::UpdateCollisionMeshData(FCollisionMeshElement& Mesh)
{
	FVector MesgLoc = FVector((Mesh.Location * CollisionResolution * (CollisionVerticesPerPatch - 1) + FIntVector(0.f, 0.f, 1) * HeightOnStart));

	if (!Generator)
	{
#if SWDEBUG
		SW_LOG("Generator Material not available for Shader World %s", *GetName())
#endif
	}
	else
	{
		UWorld* World = GetWorld();

		//OPTION A : Compute collision form GPU readback
		UMaterialInstanceDynamic* DynCollisionMat = Mesh.DynCollisionCompute;
		//如果生成高度材质无效，这里将会进行初始化。
		if (!DynCollisionMat)
		{	
			DynCollisionMat = SWTakeCareOfMID(Generator.Get(), this);
			Mesh.DynCollisionCompute = DynCollisionMat;

			SWorldSubsystem->SetScalarParameterValue(DynCollisionMat, "NoMargin", 1.f);
			SWorldSubsystem->SetScalarParameterValue(DynCollisionMat, "TexelPerSide", CollisionVerticesPerPatch);
			SWorldSubsystem->SetScalarParameterValue(DynCollisionMat, "PatchFullSize", CollisionResolution * (CollisionVerticesPerPatch - 1));
			SWorldSubsystem->SetScalarParameterValue(DynCollisionMat, "MeshScale", CollisionResolution * (CollisionVerticesPerPatch <= 1 ? 1 : CollisionVerticesPerPatch));

			SWorldSubsystem->SetScalarParameterValue(DynCollisionMat, "N", CollisionVerticesPerPatch);
			SWorldSubsystem->SetScalarParameterValue(DynCollisionMat, "CacheRes", CollisionVerticesPerPatch);
			SWorldSubsystem->SetScalarParameterValue(DynCollisionMat, "LocalGridScaling", CollisionResolution);

			

			if (bExportPhysicalMaterialID_cached && LayerStoringMaterialID != "")
			{
				for (FSWProducers& Layer : Producers)
				{
					if (Layer.LayerName == "Height" || Layer.LayerName == "height")
					{
						continue;
					}

					if (Layer.LayerName != "" && Layer.MaterialToGenerateLayer)
					{
						check(Mesh.LayerComputeForPhysicalMaterial.Contains(Layer.LayerName))						

						UMaterialInstanceDynamic* LayerPartitionDynMat = SWTakeCareOfMID(Layer.MaterialToGenerateLayer, this);

						FSWCollisionLayerData& CLayerData = *Mesh.LayerComputeForPhysicalMaterial.Find(Layer.LayerName);
						CLayerData.DynMat = LayerPartitionDynMat;

						SWorldSubsystem->SetScalarParameterValue(LayerPartitionDynMat, "PatchFullSize", CollisionResolution* (CollisionVerticesPerPatch - 1));
						SWorldSubsystem->SetScalarParameterValue(LayerPartitionDynMat, "TexelPerSide", CollisionVerticesPerPatch);
						SWorldSubsystem->SetScalarParameterValue(LayerPartitionDynMat, "NoMargin", 1.f);

						SWorldSubsystem->SetScalarParameterValue(LayerPartitionDynMat, "MeshScale", CollisionResolution * (CollisionVerticesPerPatch <= 1 ? 1 : CollisionVerticesPerPatch));

					
						SWorldSubsystem->SetScalarParameterValue(LayerPartitionDynMat, "N", CollisionVerticesPerPatch);
						SWorldSubsystem->SetScalarParameterValue(LayerPartitionDynMat, "CacheRes", CollisionVerticesPerPatch);
						SWorldSubsystem->SetScalarParameterValue(LayerPartitionDynMat, "LocalGridScaling", CollisionResolution);

						SWorldSubsystem->SetScalarParameterValue(LayerPartitionDynMat, "NormalMapSelect", 1.f);						
					}

					if (LayerStoringMaterialID == Layer.LayerName)
						break;
				}
			}

			if (bUseMaterialCollection)
			{
				if (UShaderWorld_Material_Collection* MC = GetValid(MaterialCollection))
				{
					for (auto& IDMat : MC->MaterialNameToID)
					{
						SWorldSubsystem->SetScalarParameterValue(DynCollisionMat, FName(IDMat.Key), IDMat.Value);

						for (auto& CollisionLayerC : Mesh.LayerComputeForPhysicalMaterial)
						{
							if (CollisionLayerC.Value.DynMat)
								SWorldSubsystem->SetScalarParameterValue(CollisionLayerC.Value.DynMat, FName(IDMat.Key), IDMat.Value);
						}
					}
				}
			}
			else
			{
				for (auto& IDMat : MaterialNameToID)
				{
					SWorldSubsystem->SetScalarParameterValue(DynCollisionMat, FName(IDMat.Key), IDMat.Value);

					for (auto& CollisionLayerC : Mesh.LayerComputeForPhysicalMaterial)
					{
						if (CollisionLayerC.Value.DynMat)
							SWorldSubsystem->SetScalarParameterValue(CollisionLayerC.Value.DynMat, FName(IDMat.Key), IDMat.Value);
					}
				}
			}

			TSet<FName> UsedNames;
			for (FInstancedStruct& Seed : CurrentSeedsArray.SeedsArray)
			{
				if (Seed.IsValid())
				{
					const UScriptStruct* Type = Seed.GetScriptStruct();
					CA_ASSUME(Type);
					if (Type->IsChildOf(FTextureSeed::StaticStruct()))
					{
						FTextureSeed& TypedSeed = Seed.GetMutable<FTextureSeed>();
						if (!UsedNames.Contains(TypedSeed.SeedName))
						{
							UsedNames.Add(TypedSeed.SeedName);
							SWorldSubsystem->SetTextureParameterValue(Mesh.DynCollisionCompute, TypedSeed.SeedName, TypedSeed.Value);

							for (auto& LayerEl : Mesh.LayerComputeForPhysicalMaterial)
							{
								SWorldSubsystem->SetTextureParameterValue(LayerEl.Value.DynMat, TypedSeed.SeedName, TypedSeed.Value);
							}
						}
					}
					else if (Type->IsChildOf(FLinearColorSeed::StaticStruct()))
					{
						FLinearColorSeed& TypedSeed = Seed.GetMutable<FLinearColorSeed>();
						if (!UsedNames.Contains(TypedSeed.SeedName))
						{
							UsedNames.Add(TypedSeed.SeedName);
							SWorldSubsystem->SetVectorParameterValue(Mesh.DynCollisionCompute, TypedSeed.SeedName, TypedSeed.Value);

							for (auto& LayerEl : Mesh.LayerComputeForPhysicalMaterial)
							{
								SWorldSubsystem->SetVectorParameterValue(LayerEl.Value.DynMat, TypedSeed.SeedName, TypedSeed.Value);
							}
						}
					}
					else if (Type->IsChildOf(FScalarSeed::StaticStruct()))
					{
						FScalarSeed& TypedSeed = Seed.GetMutable<FScalarSeed>();
						if (!UsedNames.Contains(TypedSeed.SeedName))
						{
							UsedNames.Add(TypedSeed.SeedName);
							SWorldSubsystem->SetScalarParameterValue(Mesh.DynCollisionCompute, TypedSeed.SeedName, TypedSeed.Value);

							for (auto& LayerEl : Mesh.LayerComputeForPhysicalMaterial)
							{
								SWorldSubsystem->SetScalarParameterValue(LayerEl.Value.DynMat, TypedSeed.SeedName, TypedSeed.Value);
							}
						}
					}
					else
					{
#if SWDEBUG
						SW_LOG("Invalid Seed type found: '%s'", *GetPathNameSafe(Type));
#endif
					}
				}
			}
		}

		SWorldSubsystem->SetVectorParameterValue(DynCollisionMat,"PatchLocation", MesgLoc);

		//UKismetRenderingLibrary::ClearRenderTarget2D(this, Mesh.CollisionRT, FLinearColor::Black);

#if SW_COMPUTE_GENERATION
		//使用CS计算碰撞数据，最后写入FCollisionMeshElement.CollisionRT
		SWorldSubsystem->DrawMaterialToRenderTarget(
			{ false,
				 false,
				GetWorld()->Scene,
				(float)GetWorld()->TimeSeconds,
				false,
				true,
				Mesh.CollisionRT->SizeX,
				(int32)(CollisionVerticesPerPatch - 1) * CollisionResolution,
				FVector(MesgLoc),
				FIntPoint(0),
				FIntPoint(Mesh.CollisionVerticesPerPatch,Mesh.CollisionVerticesPerPatch),
				false,
				ReadRequestLocation,
				DynCollisionMat,
				 Mesh.CollisionRT
			});
#else
		UKismetRenderingLibrary::DrawMaterialToRenderTarget(this, Mesh.CollisionRT, DynCollisionMat);
#endif

		if (IsValid(BrushManager))
			BrushManager->ApplyBrushStackToHeightMap(this, 0, Mesh.CollisionRT, Mesh.CollisionVerticesPerPatch, MesgLoc, CollisionResolution, CollisionVerticesPerPatch, true /*Collision heightmap have no border*/);

		//输出物理材质ID缓存，bExportPhysicalMaterialID_cached默认为false。
		if (bExportPhysicalMaterialID_cached && (LayerStoringMaterialID != ""))
		{
			{
				int32 DrawCallCount = 0;
				TArray<UShaderWorldRT2D*> PreviousLayer;
				PreviousLayer.Reserve(Mesh.LayerOrder.Num());

				int32 LayerIndice = 0;

				for (int k = 0; k < Mesh.LayerOrder.Num(); k++)
				{
					FString LayerName = Mesh.LayerOrder[k];

					check(Mesh.LayerComputeForPhysicalMaterial.Contains(LayerName))

					FSWCollisionLayerData& CLayerData = *Mesh.LayerComputeForPhysicalMaterial.Find(LayerName);

					if (!CLayerData.DynMat)
					{
						UE_LOG(LogTemp, Warning, TEXT("ERROR drawing layers for Physical material: !CLayerData.DynMat[%d]"), k);
						continue;
					}

					if (UShaderWorldRT2D* Layer_RT_To_Produce = CLayerData.RT)
					{
						SWorldSubsystem->SetVectorParameterValue(CLayerData.DynMat, "PatchLocation", MesgLoc);
						SWorldSubsystem->SetTextureParameterValue(CLayerData.DynMat, "HeightMap", Mesh.CollisionRT);
						SWorldSubsystem->SetTextureParameterValue(CLayerData.DynMat, "NormalMap", Mesh.CollisionRT);//#TODO Support normal map for collision ?
						for (int u = 0; u < LayerIndice; u++)
						{
							SWorldSubsystem->SetTextureParameterValue(CLayerData.DynMat, FName(*Mesh.LayerOrder[u]), PreviousLayer[u]);
						}
#if SW_COMPUTE_GENERATION
						SWorldSubsystem->DrawMaterialToRenderTarget(
							{ false,
								 false,
								GetWorld()->Scene,
								(float)GetWorld()->TimeSeconds,
								false,
								true,
								Layer_RT_To_Produce->SizeX,
								(int32)(CollisionVerticesPerPatch - 1) * CollisionResolution,
								MesgLoc,
								FIntPoint(0),
				FIntPoint(Mesh.CollisionVerticesPerPatch,Mesh.CollisionVerticesPerPatch),
								false,
								ReadRequestLocation,
								 CLayerData.DynMat,
								Layer_RT_To_Produce,
								Mesh.CollisionRT,
								Mesh.CollisionRT//#TODO Support normal map for collision ?
							});
#else
						UKismetRenderingLibrary::DrawMaterialToRenderTarget(this, Layer_RT_To_Produce, Elem.LayerPartitionMatDyn[k]);
#endif
						DrawCallCount++;
						

						if (IsValid(BrushManager))
							DrawCallCount += BrushManager->ApplyBrushStackToLayer(this, 0, Layer_RT_To_Produce, Mesh.CollisionVerticesPerPatch, MesgLoc, CollisionResolution, CollisionVerticesPerPatch, LayerName);

						PreviousLayer.Add(Layer_RT_To_Produce);
						LayerIndice++;

						if (LayerStoringMaterialID == LayerName)
						{
							float PatchSize = (CollisionVerticesPerPatch - 1) * CollisionResolution;

							SWorldSubsystem->CopyAtoB(Mesh.CollisionRT, (*CollisionMesh.Find(CollisionBufferHolder)).CollisionRT_Duplicate);

							uint8 channel = (static_cast<uint8>(LayerChannelStoringID)) + 1;

							SWorldSubsystem->CopyAtoB(Layer_RT_To_Produce, Mesh.CollisionRT, (*CollisionMesh.Find(CollisionBufferHolder)).CollisionRT_Duplicate, 0, channel, FVector2D(MesgLoc), FVector2D(MesgLoc), PatchSize, PatchSize, SWCopyConfig::AlphaChannelCombine);

							break;
						}
					}
				}
			}
		}

		if (false && bExportPhysicalMaterialID_cached && (LayerStoringMaterialID != "") && GetMeshNum() > 0 && CollisionMesh.Num() > 0 && (*CollisionMesh.Find(CollisionBufferHolder)).CollisionRT_Duplicate)
		{


			if (USWorldSubsystem* ShaderWorldSubsystem = SWorldSubsystem)
			{

				bool LayerIsRelevant = false;
				FString LayerSource = LayerStoringMaterialID.ToString();

				for (auto& La : Producers)
				{
					if (La.LayerName == "Height" || La.LayerName == "height")
						continue;

					if (La.LayerName == LayerSource)
					{
						LayerIsRelevant = true;
						break;
					}
				}

				if (LayerIsRelevant)
				{
					FVector2D Location_Mesh(MesgLoc);
					FVector2D Extent = CollisionResolution * (CollisionVerticesPerPatch - 1) / 2.f * FVector2D(1.f, 1.f);//Margin
					FBox2D LocalMeshBox(Location_Mesh - Extent, Location_Mesh + Extent);

					int LOD_Candidate = -1;
					///////////////////////////////

					for (int k = 0; k < GetMeshNum(); k++)
					{
						FClipMapMeshElement& Elem_Local = GetMesh(k);
						FIntVector ClipMapLocation = Elem_Local.Location - GetWorld()->OriginLocation;

						FVector2D Location_Elem_Local(ClipMapLocation.X, ClipMapLocation.Y);
						FVector2D Extent_Elem_Local = Elem_Local.GridSpacing * ((Elem_Local.N - 1) / 2) * FVector2D(1.f, 1.f);
						FBox2D Elem_Local_Footprint(Location_Elem_Local - Extent_Elem_Local, Location_Elem_Local + Extent_Elem_Local);

						if (Elem_Local_Footprint.IsInside(LocalMeshBox) && (Elem_Local.IsSectionVisible(0) || Elem_Local.IsSectionVisible(1)))
						{
							LOD_Candidate = k;
						}
						else
						{
							break;
						}
					}

					if (LOD_Candidate >= 0)
					{
						FClipMapMeshElement& Elem_Local = GetMesh(LOD_Candidate);
						float PatchSize = (Elem_Local.N - 1) * Elem_Local.GridSpacing;

						for (int k = 0; k < Elem_Local.LandLayers.Num(); k++)
						{
							if (Elem_Local.LandLayers_names[k] == LayerStoringMaterialID)
							{
								ShaderWorldSubsystem->CopyAtoB(Mesh.CollisionRT, (*CollisionMesh.Find(CollisionBufferHolder)).CollisionRT_Duplicate);

								uint8 channel = (static_cast<uint8>(LayerChannelStoringID)) + 1;

								ShaderWorldSubsystem->CopyAtoB(Elem_Local.LandLayers[k], Mesh.CollisionRT, (*CollisionMesh.Find(CollisionBufferHolder)).CollisionRT_Duplicate, 0, channel, FVector2D(FVector(Elem_Local.Location)), FVector2D(MesgLoc), PatchSize, CollisionResolution * (CollisionVerticesPerPatch - 1), SWCopyConfig::AlphaChannelCombine);

								break;
							}
						}

					}
					else
					{
						//UE_LOG(LogTemp, Warning, TEXT("Non Admissible LOD_Candidate %d"), LOD_Candidate);
					}
				}
				else
				{
					UE_LOG(LogTemp, Warning, TEXT("No relevant data layer"));
				}
			}

		}

		if (!Mesh.HeightData.IsValid())
		{
			Mesh.HeightData = MakeShared<FSWColorRead, ESPMode::ThreadSafe>();
			Mesh.HeightData->ReadData.SetNum(CollisionVerticesPerPatch * CollisionVerticesPerPatch);
		}

		if (!Mesh.ReadBackCompletion.IsValid())
		{
			Mesh.ReadBackCompletion = MakeShared<FThreadSafeBool, ESPMode::ThreadSafe>();
		}

		//设置 碰撞GPU数据回读完成 变量为false
		Mesh.ReadBackCompletion->AtomicSet(false);


		//ShaderWorld::ReadPixelsFromRT(Mesh.CollisionRT, Mesh);
		//ShaderWorld::AsyncReadPixelsFromRT(Mesh.CollisionRT, Mesh.HeightData, Mesh.ReadBackCompletion);
		//从FCollisionMeshElement.CollisionRT读取数据并且写入FCollisionMeshElement.HeightData。
		SWorldSubsystem->AsyncReadPixelsFromRT(Mesh.CollisionRT, Mesh.HeightData, Mesh.ReadBackCompletion);

		//将ID添加到CollisionReadToProcess 碰撞数据回读队列，
		CollisionReadToProcess.Add(Mesh.ID);

		return;
	}

	return;
}

```
### CollisionCPU
```c++

void AShaderWorldActor::CollisionCPU()
{
	SCOPED_NAMED_EVENT_TEXT("AShaderWorldActor::CollisionCPU()", FColor::Magenta);
	SW_FCT_CYCLE()

		if ((*bPreprocessingCollisionUpdate.Get()) ||
			CollisionShareable->CollisionMeshToUpdate.Num() > 0 ||
			CollisionShareable->CollisionMeshToRenameMoveUpdate.Num() > 0 ||
			CollisionShareable->CollisionMeshToCreate.Num() > 0)
			return;


	UWorld* World = GetWorld();

	//SW Brush相关
	bool bBrushManagerAskedRedraw = BrushManager && (BrushManagerRedrawScopes_collision.Num() > 0);
	FVector LocalActorLocation = GetActorLocation();
	FIntVector LocalOriginLocation = GetWorld()->OriginLocation;

	TArray<FBox2D> BrushRedrawScope;

	if (bBrushManagerAskedRedraw)
	{
		BrushRedrawScope = MoveTemp(BrushManagerRedrawScopes_collision);
		BrushManagerRedrawScopes_collision.Empty();
	}



	bool bExternalCollisionRebuildRequest = !CollisionUpdateRequest.IsEmpty();
	FBox2D BPCollisionRebuildRequest(ForceInit);

	if (bExternalCollisionRebuildRequest)
		CollisionUpdateRequest.Dequeue(BPCollisionRebuildRequest);

	TArray<ShaderWorld::FVisitor> VisitorLocations;

	// Use latest camera we know if current array is empty

	if (CameraLocations.Num() <= 0)
		VisitorLocations.Add(CamLocation);

	VisitorLocations.Append(CameraLocations);

	(*bPreprocessingCollisionUpdate.Get()) = true;

	Async(EAsyncExecution::TaskGraph, [Completion = bPreprocessingCollisionUpdate, CollData = CollisionShareable,
		VisitorLocations, bBrushManagerAskedRedraw, BrushScope = MoveTemp(BrushRedrawScope), bExternalCollisionRebuildRequest,
		BPRecomputeScope = BPCollisionRebuildRequest, ColRingCount = CollisionGridMaxRingNumber, LocalActorLocation, LocalOriginLocation,
		Height0 = HeightOnStart,  Bounded = WorldHasBounds_OnRebuild, GBounds = WorldBoundsOnRebuild, Lock = CollisionMeshAccessLock]
		{
			if (!CollData.IsValid())
			{
				if (Completion.IsValid())
					(*Completion.Get()) = false;
				return;
			}

			FScopeLock CollisionMeshArrayAccess(Lock.Get());

			double CollisionWidth = CollData->CollisionResolution * (CollData->VerticePerPatch - 1);

			TMap<FIntVector, FVector> BrushRedraws;

			for (const FBox2d& B : BrushScope)
			{
				const int32 MinBoxX_local = FMath::FloorToInt(((double)(B.Min.X + LocalOriginLocation.X)) / CollisionWidth + 0.45);
				const int32 MinBoxY_local = FMath::FloorToInt(((double)(B.Min.Y + LocalOriginLocation.Y)) / CollisionWidth + 0.45);

				const int32 MaxBoxX_local = FMath::FloorToInt(((double)(B.Max.X + LocalOriginLocation.X)) / CollisionWidth + 0.55);
				const int32 MaxBoxY_local = FMath::FloorToInt(((double)(B.Max.Y + LocalOriginLocation.Y)) / CollisionWidth + 0.55);

				for (int32 X_iter = MinBoxX_local; X_iter <= MaxBoxX_local; X_iter++)
				{
					for (int32 Y_iter = MinBoxY_local; Y_iter <= MaxBoxY_local; Y_iter++)
					{
						BrushRedraws.Add(FIntVector(X_iter, Y_iter, 0));
					}
				}
			}

			/*
			 * Get World Bounds in centimeters
			 */
			FBox SWorldBounds = GBounds;
			SWorldBounds.Min *= 100.0;
			SWorldBounds.Max *= 100.0;

			TSet<FIntVector> ExternalCollisionsBounds;

			for (const ShaderWorld::FVisitor& SingleCamLoc : VisitorLocations)
			{
				if (SingleCamLoc.Bounds.IsValid)
				{
					ExternalCollisionsBounds.Append(USWBlueprintFunctionLibrary::GetCollisionMeshesLayout(CollisionWidth, SingleCamLoc.Bounds, SWorldBounds));
				}
			}

			CollData->MultipleCamera.Empty();
			CollData->LocRefs.Empty();

			for (const ShaderWorld::FVisitor& SingleCamLoc : VisitorLocations)
			{			
				if (SingleCamLoc.Bounds.IsValid)
					continue;

				double Cam_X_local = SingleCamLoc.Location.X + LocalOriginLocation.X;
				double Cam_Y_local = SingleCamLoc.Location.Y + LocalOriginLocation.Y;

				if (Bounded)
				{
					Cam_X_local = FMath::Max(FMath::Min(Cam_X_local, GBounds.Max.X * 100.0), GBounds.Min.X * 100.0);
					Cam_Y_local = FMath::Max(FMath::Min(Cam_Y_local, GBounds.Max.Y * 100.0), GBounds.Min.Y * 100.0);					
				}

				const int CamX_local = FMath::RoundToInt(Cam_X_local / CollisionWidth);
				const int CamY_local = FMath::RoundToInt(Cam_Y_local / CollisionWidth);

				FIntVector LocRef_local = FIntVector(CamX_local, CamY_local, 0.f) * CollisionWidth + FIntVector(0.f, 0.f, 1) * Height0 - LocalOriginLocation;


				int32 LocalRingCount = FMath::Clamp(FMath::Floor(FMath::Abs(SingleCamLoc.Range * 100.0) / CollisionWidth), 1, ColRingCount);

				CollData->LocRefs.Add(LocRef_local, LocalRingCount);
				CollData->MultipleCamera.Add(FIntVector(CamX_local, CamY_local, 0), LocalRingCount);
			}

			TArray<FName> NameToRemove;
			for (const FName& CollID : CollData->UsedCollisionMesh)
			{
				FSWCollisionMeshElemData& El = *CollData->CollisionMeshData.Find(CollID);

				bool BeyondCriteria_local = !ExternalCollisionsBounds.Contains(El.Location);


				for (auto& Elem : CollData->LocRefs)
				{
					FIntVector& SingleLocRef = Elem.Key;
					int32& LocalRingCount = Elem.Value;

					const FVector ToCompLocal = FVector(FIntVector(El.MeshLocation) - SingleLocRef) / CollisionWidth;
					BeyondCriteria_local = BeyondCriteria_local && (FMath::Abs(ToCompLocal.X) > LocalRingCount + .1f || FMath::Abs(ToCompLocal.Y) > LocalRingCount + .1f);
					if (!BeyondCriteria_local)
						break;
				}


				if (BeyondCriteria_local)
				{					
					CollData->AvailableCollisionMesh.Add(CollID);
					NameToRemove.Add(CollID);

					for (auto It = CollData->GroundCollisionLayout.CreateConstIterator(); It; ++It)
					{
						if(It->Value == CollID)
						{
							CollData->GroundCollisionLayout.Remove(It->Key);
							break;
						}
					}
				}
				else
				{

					if (bBrushManagerAskedRedraw || bExternalCollisionRebuildRequest)
					{

						bool UpdateRequested = false;
						if (bBrushManagerAskedRedraw)
						{
							if (BrushRedraws.Contains(El.Location))
							{
								CollData->CollisionMeshToUpdate.Add(CollID);
								UpdateRequested = true;
							}
						}

						if (!UpdateRequested && bExternalCollisionRebuildRequest)
						{
							const FVector Location_LocalOrigin = FVector(El.Location * CollisionWidth + FIntVector(0, 0, 1) * LocalActorLocation.Z - LocalOriginLocation);

							FVector2D Location_Mesh(Location_LocalOrigin.X, Location_LocalOrigin.Y);
							FVector2D Extent = CollisionWidth / 2.f * FVector2D(1.f, 1.f);
							FBox2D LocalCollisionMeshBox(Location_Mesh - Extent, Location_Mesh + Extent);

							if (BPRecomputeScope.Intersect(LocalCollisionMeshBox))
							{
								CollData->CollisionMeshToUpdate.Add(CollID);
							}
						}
					}

				}

			}

			for (const FName& TR : NameToRemove)
			{
				CollData->UsedCollisionMesh.Remove(TR);
			}

			BrushRedraws.Empty();

			FBox WorldBounds = GBounds;
			WorldBounds.Min *= 100.0;
			WorldBounds.Max *= 100.0;

			for (auto& ExternalBounds : ExternalCollisionsBounds)
			{
				FIntVector LocMeshInt = ExternalBounds;
				FIntVector MeshLoc = LocMeshInt * CollisionWidth + FIntVector(0.f, 0.f, 1) * Height0 - LocalOriginLocation;

				if (Bounded && !WorldBounds.IntersectXY(FBox((FVector(LocMeshInt) - FVector(0.5, 0.5, 0.0)) * CollisionWidth, (FVector(LocMeshInt) + FVector(0.5, 0.5, 0.0)) * CollisionWidth)))
					continue;

				if (!CollData->GroundCollisionLayout.Contains(LocMeshInt))
				{
					const FString CollisionMeshString = "SW_Collision_X_" + FString::FromInt(LocMeshInt.X) + "_Y_" + FString::FromInt(LocMeshInt.Y) + "_Z_" + FString::FromInt(LocMeshInt.Z);

					const FName CollisionMeshName = FName(*CollisionMeshString);

					if (CollData->AvailableCollisionMesh.Num() > 0 && CollData->AvailableCollisionMesh.Contains(CollisionMeshName))
					{
						FSWCollisionMeshElemData& ElemData = *CollData->CollisionMeshData.Find(CollisionMeshName);
						CollData->UsedCollisionMesh.Add(CollisionMeshName);
						CollData->AvailableCollisionMesh.Remove(CollisionMeshName);

						ElemData.Location = LocMeshInt;
						ElemData.MeshLocation = FVector(MeshLoc);

						CollData->CollisionMeshToRenameMoveUpdate.AddUnique(CollisionMeshName);

						CollData->GroundCollisionLayout.Add(LocMeshInt, CollisionMeshName);
					}
					else
					{
						FCollisionMeshElement NewElem;
						NewElem.ID = CollisionMeshName;

						NewElem.Location = LocMeshInt;
						NewElem.MeshLocation = FVector(MeshLoc);

						CollData->UsedCollisionMesh.Add(CollisionMeshName);
						CollData->CollisionMeshData.Add(CollisionMeshName, NewElem);

						CollData->CollisionMeshToCreate.AddUnique(CollisionMeshName);
						CollData->CollisionMeshToRenameMoveUpdate.AddUnique(CollisionMeshName);

						CollData->GroundCollisionLayout.Add(LocMeshInt, CollisionMeshName);
					}
				}
			}

			for (auto& Elem : CollData->MultipleCamera)
			{
				FIntVector& SingleCam = Elem.Key;
				int32& LocalRingCount = Elem.Value;

				for (int r = LocalRingCount; r >= 0; r--)
				{
					for (int i = -r; i <= r; i++)
					{
						for (int j = -r; j <= r; j++)
						{
							if (abs(j) != r && abs(i) != r)
								continue;

							FIntVector LocMeshInt = FIntVector(SingleCam.X + i, SingleCam.Y + j, 0);
							FIntVector MeshLoc = LocMeshInt * CollisionWidth + FIntVector(0.f, 0.f, 1) * Height0 - LocalOriginLocation;

							if (Bounded && !WorldBounds.IntersectXY(FBox((FVector(LocMeshInt) - FVector(0.5, 0.5, 0.0)) * CollisionWidth, (FVector(LocMeshInt) + FVector(0.5, 0.5, 0.0)) * CollisionWidth)))
								continue;

							if (!CollData->GroundCollisionLayout.Contains(LocMeshInt))
							{							
								const FString CollisionMeshString = "SW_Collision_X_" + FString::FromInt(LocMeshInt.X) + "_Y_" + FString::FromInt(LocMeshInt.Y) + "_Z_" + FString::FromInt(LocMeshInt.Z);

								const FName CollisionMeshName = FName(*CollisionMeshString);

								if(CollData->AvailableCollisionMesh.Num() > 0 && CollData->AvailableCollisionMesh.Contains(CollisionMeshName))
								{
									FSWCollisionMeshElemData& ElemData = *CollData->CollisionMeshData.Find(CollisionMeshName);
									CollData->UsedCollisionMesh.Add(CollisionMeshName);
									CollData->AvailableCollisionMesh.Remove(CollisionMeshName);

									ElemData.Location = LocMeshInt;
									ElemData.MeshLocation = FVector(MeshLoc);

									CollData->CollisionMeshToRenameMoveUpdate.AddUnique(CollisionMeshName);

									CollData->GroundCollisionLayout.Add(LocMeshInt, CollisionMeshName);
								}
								else
								{
									FCollisionMeshElement NewElem;
									NewElem.ID = CollisionMeshName;

									NewElem.Location = LocMeshInt;
									NewElem.MeshLocation = FVector(MeshLoc);

									CollData->UsedCollisionMesh.Add(CollisionMeshName);
									CollData->CollisionMeshData.Add(CollisionMeshName, NewElem);

									CollData->CollisionMeshToCreate.AddUnique(CollisionMeshName);
									CollData->CollisionMeshToRenameMoveUpdate.AddUnique(CollisionMeshName);

									CollData->GroundCollisionLayout.Add(LocMeshInt, CollisionMeshName);
								}								
							}
						}
					}
				}
			}

			if (Completion.IsValid())
				(*Completion.Get()) = false;
		}
	);
}
```

### SpawnablesManagement()

### TerrainAndSpawnablesManagement()

## PreEditChange() / PostEditChangeProperty()
**PreEditChange()** 主要针对以下两个变量的设置：
- PreventReRegistration：防止重新注册。
- RuntimePropertyEditing：实时属性修改。

**PostEditChangeProperty()** 
里面比较关键的逻辑有：
- EditRebuildVegetation.AtomicSet(true);
	- 在Setup()中清空Bioms数组。
- EditRebuild.AtomicSet(true);
	- 在SetupCollisions()设置rebuild = true。

如果RuntimePropertyEditing为true，在最后会将RuntimePropertyEditing设置为false。PreventReRegistration也会设置为false。

## Rebuild变量
主要出现在：
- Setup():调用RebuildCleanup()清空所有数据。
- SetupCollision(): RedbuildCollisionContext = true。
- ProcessSpawnablePending():如果处于重建状态就直接返回。
- InitiateClipMapMeshes():如果处于重建状态就直接返回。
- FinalizeAsyncWork():如果处于重建状态就直接返回。

## DrawMaterialToRenderTarget
USWorldSubsystem::DrawMaterialToRenderTarget
=>
SWShaderToolBox::DrawMaterial
=>
DrawMaterial_CS_RT

调用路径：
- AShaderWorldActor::[[#RetrieveHeightAt]]（好像没有引用）：检索高度
- AShaderWorldActor::ComputeHeight_Segmented_MapForClipMap
	- AShaderWorldActor::ProcessSegmentedComputation() <- AShaderWorldActor::TerrainAndSpawnablesManagement() <- AShaderWorldActor::Tick()
- AShaderWorldActor::ComputeHeightMapForClipMap
	- AShaderWorldActor::UpdateClipMap() <- AShaderWorldActor::TerrainAndSpawnablesManagement() <- AShaderWorldActor::Tick()
- AShaderWorldActor::ComputeDataLayersForClipMap
	- AShaderWorldActor::UpdateClipMap() <- AShaderWorldActor::TerrainAndSpawnablesManagement() <- AShaderWorldActor::Tick()
- AShaderWorldActor::UpdateCollisionMeshData：更新碰撞模型数据。
	- AShaderWorldActor::CollisionGPU() <- AShaderWorldActor::CollisionManagement() <- AShaderWorldActor::Tick()
- FSpawnableMesh::UpdateSpawnableData
	- AShaderWorldActor::ProcessSegmentedComputation() <- AShaderWorldActor::TerrainAndSpawnablesManagement() <- AShaderWorldActor::Tick()


## Cache机制
AShaderWorldActor::ProcessSegmentedComputation() <- AShaderWorldActor::TerrainAndSpawnablesManagement() <- AShaderWorldActor::Tick()


# 其他Bug


## SetTextureParameterValue相关逻辑排查
- AShaderWorldActor中的SetTextureParameterValue
	- ~~ExportCacheInBounds~~
	- ~~AssignHeightMapToDynamicMaterial~~
	- UpdateStaticDataFor
	- ComputeHeight_Segmented_MapForClipMap：似乎会设置
	- ~~UpdateCollisionMeshData~~
	- [x] [[#InitializeReadBackDependencies]]
	- [x] InitiateMaterials

### UpdateStaticDataFor


### ComputeHeight_Segmented_MapForClipMap
- 作用：
- 调用顺序：AShaderWorldActor::Tick() -> AShaderWorldActor::TerrainAndSpawnablesManagement() -> AShaderWorldActor::ProcessSegmentedComputation() -> ComputeHeight_Segmented_MapForClipMap


>// 1) Intersect clipmap with grid quad  
  // 2) Gather non computed quads   
  // 3) Allocated Compute element to missing Quad   
  // 4) Update the indirection data to the new elements  
  // 5) Update the Clipmap Heightmap with the grid data
 

### UpdateCollisionMeshData
 - 作用：
	 1. 判断DynCollisionMat是否有效，无效就使用`Generator`（高度数据生成材质）来创建。
	 2. 设置材质参数NoMargin、TexelPerSide、PatchFullSize、MeshScale。
	 3. 设置随机种子相关的材质参数。
	 4. 设置材质参数PatchLocation。
	 5. 生成碰撞数据到`CollisionRT`。
	 6. 笔刷功能逻辑：ApplyBrushStackToHeightMap()。
	 7. ExportPhysicalMaterialID逻辑。
	 8. GPU碰撞数据回读：ShaderWorld::AsyncReadPixelsFromRT()。
		 1. ShaderWorld::GSWReadbackManager.AddPendingReadBack()，将回读Task增加`TArray<FReadBackTask> PendingReads;`。
		 2. 之后会在USWorldSubsystem::Tick()中调用ShaderWorld::GSWReadbackManager.TickReadBack()，不断检查是否可回读，并进行最终回读。
 - 调用顺序：Tick() -> CollisionManagement() -> CollisionGPU() -> UpdateCollisionMeshData()

```c++
namespace ShaderWorld
{
	FORCEINLINE void AsyncReadPixelsFromRT(UShaderWorldRT2D* InRT, TSharedPtr<FSWColorRead, ESPMode::ThreadSafe> Destination, TSharedPtr < FThreadSafeBool, ESPMode::ThreadSafe> Completion)
	{

		ENQUEUE_RENDER_COMMAND(ReadGeoClipMapRTCmd)(
			[InRT, HeightData = Destination, Completion = Completion](FRHICommandListImmediate& RHICmdList)
			{
				check(IsInRenderingThread());

				if (HeightData.IsValid() && InRT->GetResource())
				{
					FRDGBuilder GraphBuilder(RHICmdList);
					TSharedPtr<FRHIGPUTextureReadback> ReadBackStaging = MakeShared<FRHIGPUTextureReadback>(TEXT("SWGPUTextureReadback"));
					FRDGTextureRef RDGSourceTexture = RegisterExternalTexture(GraphBuilder, InRT->GetResource()->TextureRHI, TEXT("SWSourceTextureToReadbackTexture"));
					AddEnqueueCopyPass(GraphBuilder, ReadBackStaging.Get(), RDGSourceTexture);
					GraphBuilder.Execute();

					ShaderWorld::GSWReadbackManager.AddPendingReadBack(RHICmdList, GPixelFormats[RDGSourceTexture->Desc.Format].BlockBytes, RDGSourceTexture->Desc.Extent.X, RDGSourceTexture->Desc.Extent.Y, ReadBackStaging, const_cast<TSharedPtr<FSWColorRead, ESPMode::ThreadSafe>&>(HeightData), const_cast<TSharedPtr < FThreadSafeBool, ESPMode::ThreadSafe>&>(Completion));
				}

			});	
	}
```


### InitializeReadBackDependencies
- 作用：初始化几个GPU数据回读用的RT。
- 调用顺序：BeginPlay() -> InitiateWorld() -> InitializeReadBackDependencies()

1. 初始化3个RT：ReadRequestLocation、ReadRequestLocationHeightmap、GeneratorDynamicForReadBack。
2. 会设置`TObjectPtr < UMaterialInstanceDynamic> GeneratorDynamicForReadBack`各种变量
```c++
GeneratorDynamicForReadBack->SetScalarParameterValue("HeightReadBack", 1.f);  
GeneratorDynamicForReadBack->SetTextureParameterValue("SpecificLocationsRT", ReadRequestLocation);  
GeneratorDynamicForReadBack->SetScalarParameterValue("NoMargin", 0.f);  
GeneratorDynamicForReadBack->SetScalarParameterValue("N", N);  
GeneratorDynamicForReadBack->SetScalarParameterValue("NormalMapSelect", 0.f);  
GeneratorDynamicForReadBack->SetScalarParameterValue("HeightMapToggle", 1.f);
```
3. 设置随机种子相关Shader Parameter。
### InitiateMaterials
作用：初始化`TArray<FClipMapMeshElement> Meshes;`的Material、`Producers`
调用顺序：BeginPlay() -> InitiateWorld() -> InitiateMaterials()

经过断点调试，会设置WorldSettings里的Material（地形Material）的HeightMap与NormalMap。


# 
SWorldSubsystem->DrawMaterialToRenderTarget


# Rebuild逻辑
## 重要函数
- AShaderWorldActor::BeginPlay()
- AShaderWorldActor::Setup()（<- TerrainAndSpawnablesManagement(float& DeltaT) <- Tick()）

## Rebuild逻辑顺序
1. AShaderWorldActor::BeginPlay()
	1. 


# Debug
1. AShaderWorldActor::ComputeHeight_Segmented_MapForClipMap 十多次
2. UpdateCollisionMeshData
3. AShaderWorldActor::ComputeHeight_Segmented_MapForClipMap  十多次
4. [[#RetrieveHeightAt]]
5. UpdateCollisionMeshData 3次
6. AShaderWorldActor::ComputeHeight_Segmented_MapForClipMap  十多次

# RetrieveHeightAt
可能存在bug待排查的：
- ShaderWorldSubsystem->LoadSampleLocationsInRT()
- ShaderWorldSubsystem->DrawMaterialToRenderTarget()

## 相关变量
- FThreadSafeBool
	- bProcessingHeightRetrieval
	- bProcessingHeightRetrievalRT
- MID
	- GeneratorDynamicForReadBack
- UShaderWorldRT2D（`UTextureRenderTarget2D`）
	- ReadRequestLocation：RTF_RG32f，初始化于`InitializeReadBackDependencies() <- InitiateWorld()`
	- ReadRequestLocationHeightmap：RTF_RGBA8，初始化于`InitializeReadBackDependencies() <- InitiateWorld()`



## 代码
```c++
bool AShaderWorldActor::RetrieveHeightAt(const TArray<FVector>& Origin, const FSWHeightRetrievalDelegate& Callback)
{	
	if (!GeneratorDynamicForReadBack || !SWorldSubsystem)
		return false;

	if (!bProcessingHeightRetrieval.IsValid())
	{
		bProcessingHeightRetrieval = MakeShared<FThreadSafeBool, ESPMode::ThreadSafe>();
		bProcessingHeightRetrieval->AtomicSet(false);
	}
	if (!bProcessingHeightRetrievalRT.IsValid())
	{
		bProcessingHeightRetrievalRT = MakeShared<FThreadSafeBool, ESPMode::ThreadSafe>();
		bProcessingHeightRetrievalRT->AtomicSet(false);
	}


	if (!(*bProcessingHeightRetrieval.Get()) && ReadRequestLocation && ReadRequestLocationHeightmap && GeneratorDynamicForReadBack)
	{
		bProcessingHeightRetrieval->AtomicSet(true);
		bProcessingHeightRetrievalRT->AtomicSet(false);
		HeightRetrieveDelegate = Callback;

		//初始化采样点数组结构体FSWShareableSamplePoints
		PointsPendingReadBacks = MakeShared<FSWShareableSamplePoints, ESPMode::ThreadSafe>();
		TSharedPtr<FSWShareableSamplePoints>& Samples = PointsPendingReadBacks;

		FBox BoundingBoxRead(Origin);

		Samples->PositionsXY.SetNum(25 * 2);
		for (int i = 0; i < 25; i++)
		{
			if (i < Origin.Num())
			{
				Samples->PositionsXY[i * 2] = Origin[i].X;
				Samples->PositionsXY[i * 2 + 1] = Origin[i].Y;
			}
			else
			{
				Samples->PositionsXY[i * 2] = 0.f;
				Samples->PositionsXY[i * 2 + 1] = 0.f;
			}
		}

		if (USWorldSubsystem* ShaderWorldSubsystem = SWorldSubsystem)
		{
			//从渲染线程
			ShaderWorldSubsystem->LoadSampleLocationsInRT(ReadRequestLocation, Samples);

#if SW_COMPUTE_GENERATION
			ShaderWorldSubsystem->DrawMaterialToRenderTarget(
			{   false,
				 false,
				GetWorld()->Scene,
				(float)GetWorld()->TimeSeconds,
				false,
				true,
				ReadRequestLocationHeightmap->SizeX,
				10,
				FVector(0.f),
				true,
				ReadRequestLocation,
				GeneratorDynamicForReadBack,
				ReadRequestLocationHeightmap
			});
#else
			UKismetRenderingLibrary::DrawMaterialToRenderTarget(this, ReadRequestLocationHeightmap, GeneratorDynamicForReadBack);
#endif

			int32 Size_RT_Readback = ReadRequestLocationHeightmap.Get()->SizeX;

			FVector Barycentre = BoundingBoxRead.GetCenter();
			FVector Extent = BoundingBoxRead.GetExtent();
			float gridspacing = Extent.X * 2.0 / (Size_RT_Readback - 1);

			if (IsValid(BrushManager))
				BrushManager->ApplyBrushStackToHeightMap(this, 0, ReadRequestLocationHeightmap.Get(), Barycentre, gridspacing, Size_RT_Readback, true, true, ReadRequestLocation.Get());


			ReadBackHeightData = MakeShared<FSWColorRead, ESPMode::ThreadSafe>();
			ReadBackHeightData->ReadData.SetNum(25);

			ENQUEUE_RENDER_COMMAND(ReadGeoClipMapRTCmd)(
				[InRT = ReadRequestLocationHeightmap, HeightData = ReadBackHeightData, Completion = bProcessingHeightRetrievalRT](FRHICommandListImmediate& RHICmdList)
				{
					check(IsInRenderingThread());

					if (HeightData.IsValid() && InRT->GetResource())
					{
						FRDGBuilder GraphBuilder(RHICmdList);

						TSharedPtr<FRHIGPUTextureReadback> ReadBackStaging = MakeShared<FRHIGPUTextureReadback>(TEXT("SWGPUTextureReadback"));

						FRDGTextureRef RDGSourceTexture = RegisterExternalTexture(GraphBuilder, InRT->GetResource()->TextureRHI, TEXT("SWSourceTextureToReadbackTexture"));

						AddEnqueueCopyPass(GraphBuilder, ReadBackStaging.Get(), RDGSourceTexture);

						GraphBuilder.Execute();

						ShaderWorld::GSWReadbackManager.AddPendingReadBack(RHICmdList, GPixelFormats[RDGSourceTexture->Desc.Format].BlockBytes, RDGSourceTexture->Desc.Extent.X, RDGSourceTexture->Desc.Extent.Y, ReadBackStaging, const_cast<TSharedPtr<FSWColorRead, ESPMode::ThreadSafe>&>(HeightData), const_cast<TSharedPtr < FThreadSafeBool, ESPMode::ThreadSafe>&>(Completion));

					}

				});

			HeightReadBackFence.BeginFence(true);
		}

		return true;
	}

	return false;
}
```


### RequestReadBackLoad
```c++
bool USWorldSubsystem::LoadSampleLocationsInRT(UShaderWorldRT2D* LocationsRequestedRT,
                                               TSharedPtr<FSWShareableSamplePoints>& Samples)
{
	if (!RenderThreadResponded)
		return false;

	const SWSampleRequestComputeData ReadBackData(LocationsRequestedRT, Samples);
	SWToolBox->RequestReadBackLoad(ReadBackData);
	return true;
}
```
# SWShaderToolBox
## RequestReadBackLoad
```c++
void SWShaderToolBox::RequestReadBackLoad(const SWSampleRequestComputeData& Data) const
{
	if (Data.CPU)
		return CPUTools.RequestReadBackLoad(Data);

	ENQUEUE_RENDER_COMMAND(ShaderTools_copy_rt)
		([this, Data](FRHICommandListImmediate& RHICmdList)
			{
				if (Data.SamplesXY && Data.SamplesXY->GetResource())
				RequestReadBackLoad_RT(RHICmdList,Data);
			}
	);

}

void SWShaderToolBox::RequestReadBackLoad_RT(FRHICommandListImmediate& RHICmdList, const SWSampleRequestComputeData& Data) const
{
	if (!(Data.SamplesXY && Data.SamplesXY->GetResource()))
		return;

	FRDGBuilder GraphBuilder(RHICmdList);

		{
			RDG_EVENT_SCOPE(GraphBuilder, "ShaderWorld  PositionReadBack");
			RDG_GPU_STAT_SCOPE(GraphBuilder, ShaderWorldReadBack);

			FIntVector GroupCount;
			GroupCount.X = FMath::DivideAndRoundUp((float)Data.SamplesXY->GetResource()->GetSizeX(), (float)SW_LoadReadBackLocations_GroupSizeX);
			GroupCount.Y = FMath::DivideAndRoundUp((float)Data.SamplesXY->GetResource()->GetSizeY(), (float)SW_LoadReadBackLocations_GroupSizeY);
			GroupCount.Z = 1;

			const FUnorderedAccessViewRHIRef RT_UAV = GraphBuilder.RHICmdList.CreateUnorderedAccessView(Data.SamplesXY->GetResource()->TextureRHI);

			const FRDGBufferRef LocationRequest = CreateUploadBuffer(
				GraphBuilder,
				TEXT("SWLoadSampleLocations"),
				sizeof(float),
				Data.SamplesSource->PositionsXY.Num(),
				Data.SamplesSource->PositionsXY.GetData(),
				Data.SamplesSource->PositionsXY.Num() * Data.SamplesSource->PositionsXY.GetTypeSize()
			);

			const FRDGBufferSRVRef LocationRequestSRV = GraphBuilder.CreateSRV(FRDGBufferSRVDesc(LocationRequest, PF_R32_FLOAT));;

			FLoadReadBackLocations_CS::FPermutationDomain PermutationVector;
			TShaderMapRef<FLoadReadBackLocations_CS> ComputeShader(GetGlobalShaderMap(GMaxRHIFeatureLevel), PermutationVector);
	
			FLoadReadBackLocations_CS::FParameters* PassParameters = GraphBuilder.AllocParameters<FLoadReadBackLocations_CS::FParameters>();
			PassParameters->SampleDim = Data.SamplesXY->GetResource()->GetSizeX();
			PassParameters->DestLocationsTex = RT_UAV;
			PassParameters->SourceLocationBuffer = LocationRequestSRV;


			GraphBuilder.AddPass(
				RDG_EVENT_NAME("ShaderWorld LoadReadBacklocations_CS"),
				PassParameters,
				ERDGPassFlags::Compute |
				ERDGPassFlags::NeverCull,
				[PassParameters, ComputeShader, GroupCount](FRHICommandList& RHICmdList)
				{
					FComputeShaderUtils::Dispatch(RHICmdList, ComputeShader, *PassParameters, GroupCount);
				});

		}

	GraphBuilder.Execute();
}
```

FLoadReadBackLocations_CS
```c++
uint SampleDim;
RWTexture2D<float2> DestLocationsTex;
Buffer<float> SourceLocationBuffer;

[numthreads(THREADGROUP_SIZEX, THREADGROUP_SIZEY, THREADGROUP_SIZEZ)]
void SampleLocationLoaderCS(uint3 ThreadId : SV_DispatchThreadID)
{
    if (any(ThreadId.xy >= SampleDim.xx))
        return;

	uint IndexPixel = (ThreadId.x + ThreadId.y * SampleDim) * 2;
	
	DestLocationsTex[ThreadId.xy] = float2(SourceLocationBuffer[IndexPixel],SourceLocationBuffer[IndexPixel + 1]);
}
```


# FSWDrawMaterial_SL_CS
IMPLEMENT_MATERIAL_SHADER_TYPE(template<>, FSWDrawMaterial_SL_CS, TEXT("/ShaderWorld/ShaderWorldUtilities.usf"), TEXT("DrawMaterialCS"), SF_Compute);

FMeshMaterialShader::ModifyCompilationEnvironment(Parameters, OutEnvironment);  
OutEnvironment.SetDefine(TEXT("SW_DRAW_WITH_HEIGHTNORMAL"), 0);  
OutEnvironment.SetDefine(TEXT("SW_DRAWMATERIAL"), 1);  
OutEnvironment.SetDefine(TEXT("SW_SPECIFIC_LOCATION_DRAW"), 1);  
  
OutEnvironment.SetDefine(TEXT("THREADGROUP_SIZEX"), bIsMobileRenderer ? SW_MobileLowSharedMemory_GroupSizeX : FComputeShaderUtils::kGolden2DGroupSize);  
OutEnvironment.SetDefine(TEXT("THREADGROUP_SIZEY"), bIsMobileRenderer ? SW_MobileLowSharedMemory_GroupSizeY : FComputeShaderUtils::kGolden2DGroupSize);  
OutEnvironment.SetDefine(TEXT("THREADGROUP_SIZEZ"), 1);

# 
- M_Blank_HeightLayer
	- MFC_WorldPositionNormal_Layer
		- M_Blank_HeightLayer（未连接）
	- MFC_Position_ForCache
- 其他
	- MF_CacheRead_Reference_Tessellation
	- MFC_CacheRead：没有其他引用
	- MFC_CacheRead_Tessellationt
	- MFC_CacheReadNoVertexManipulation
	- MFC_ExternalCacheRead



# 植被生成逻辑
Tick() => TerrainAndSpawnablesManagement() => UpdateSpawnables() => UpdateSpawnable()


# 碰撞Python逻辑

```python
def TickCheckWorldReady(self, dt: float) -> bool:  
    is_shader_world_ready = self.ShaderWorldActor.WorldAndCollisionGeneratedReady()  
    if not is_shader_world_ready:  
        return True  
    is_ready = self.ShaderWorldActor.CheckCollisionGeneratedReady(self.AvatarBornPosition)  
    print("LBK --------  TickCheckWorldReady", self.FailedCheckCnt, is_ready)  
    if is_ready:  
        self.OnWorldMeshReady()  
        ue.RemoveTicker(self.worldTickHander)  
        # 等待地形物理加载完毕  
        if self.OtherLoadFinshed:  
            GlobalData.TimerSystem.AddTimer(1, self.ReallyStartDriving)  
        else:  
            self.OtherLoadFinshed = True  
        print('LBK -------------- DrivingModeSystem: TickCheckWorldReady', GlobalData.p.pos, self.AvatarBornPosition)  
        return False  
    self.FailedCheckCnt += 1  
    if self.FailedCheckCnt > self.FailedAttemptCnt:  #self.FailedAttemptCnt为40
        self.ShaderWorldActor.RebuildWorld()  
        self.FailedCheckCnt = 0  
    return True

# 通过LineTraceSingleForObjects检测碰撞高度是否超过5，来判断碰撞是否生成。
def CheckCollisionGeneratedReady(self, checkPosition: ue.Vector) -> bool:  
    HitStartLocation = checkPosition + ue.Vector(0, 0, 50000.0)  
    HitEndLocation = checkPosition + ue.Vector(0, 0, -50000.0)  
    hitState, hitResult = ue.KismetSystemLibrary.LineTraceSingleForObjects(  
       self.GetWorld(),  
       HitStartLocation,  
       HitEndLocation,  
       [ue.EObjectTypeQuery.ObjectTypeQuery1, ue.EObjectTypeQuery.ObjectTypeQuery13],  # Ground  
       False,  # 是否追踪复杂碰撞  
       [],  
       ue.EDrawDebugTrace.ForDuration if GlobalData.IsDebugMode else ue.EDrawDebugTrace.NONE,  # 调试可视化  
       True,  # 忽略自身  
       ue.LinearColor(1.0, 0.0, 0.0, 1.0),  # 红色  
       ue.LinearColor(0.0, 1.0, 0.0, 1.0),  # 绿色  
       20.0  # 调试线条持续时间  
    )  
    if not hitState:  
       return False  
    # TODO LBK 这个射线检测的方式不太准确，那个物理生成，会从平面开始  
    return hitResult.Location.Z > 5.0
```

```c++
bool AShaderWorldActor::WorldAndCollisionGeneratedReady()
{
	if (!WorldGeneratedAndReady())
		return false;
	if (!CollisionShareable.IsValid())
		return false;

	FScopeLock CollisionMeshArrayAccess(CollisionMeshAccessLock.Get());

	// 1. 必须有碰撞布局
	if (CollisionShareable->GroundCollisionLayout.Num() == 0)
		return false;

	// 2. 检查所有Patch都ready
	for (const auto& Pair : CollisionShareable->GroundCollisionLayout)
	{
		const FIntVector& Loc = Pair.Key;
		const FName& CollisionName = Pair.Value;

		// Patch必须存在
		if (!CollisionMesh.Contains(CollisionName))
			return false;

		// Patch必须在已用集合
		if (!CollisionShareable->UsedCollisionMesh.Contains(CollisionName))
			return false;

		// Patch必须ReadBack完成
		const FCollisionMeshElement& CollisionElement = *CollisionMesh.Find(CollisionName);
		if (!CollisionElement.ReadBackCompletion.IsValid() || !(*CollisionElement.ReadBackCompletion.Get()))
			return false;

		// Patch不能在待处理队列
		if (CollisionReadToProcess.Contains(CollisionName))
			return false;
		if (!UsedCollisionMesh.Contains(CollisionName))
			return false;

		// Patch不能在工作队列
		for (const auto& WQ : CollisionWorkQueue)
			if (WQ.MeshID == CollisionName)
				return false;
	}

	return true;
}
```