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

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title	date	excerpt	tags	rating
Untitled	2025-06-03 10:19:25			⭐

前言

1. ShaderWorldPCGInterop：
2. ShaderWorld：
3. ShaderWorldCore：

ShaderWorld

• Class
  • Actor
    • ShaderWorldActor.h:#AShaderWorldActor
    • SWorld.h:#ASWorld

ASWorld

AShaderWorldActor

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
  • #InitializeReadBackDependencies
  • 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()

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

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