BlueRoseNote/03-UnrealEngine/Rendering/RenderingPipeline/Materials/MeshDraw.md

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title: Untitled
date: 2024-09-25 14:59:32
excerpt: 
tags: 
rating: ⭐
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# 前言
可以使用DrawDynamicMeshPass()，实现在插件中使用MeshDraw绘制Pass。

参考文章：
- ***UE5，为HairStrands添加自定义深度与模板***:https://zhuanlan.zhihu.com/p/689578355

# MeshDraw
推荐学习：
- CustomDepth
- RenderBasePassInternal()
- RenderAnisotropyPass()

Shader推荐：
- DepthOnlyVertexShader.usf
- DepthOnlyPixelShader.usf

# NaniteMeshDraw
`Engine\Source\Runtime\Renderer\Private\Nanite\`NaniteMaterials.h & NaniteMaterials.cpp

PS.使用的Shader必须是`FNaniteGlobalShader`的子类。

## BasePass
### DrawBasePass()
该函数在FDeferredShadingSceneRenderer::RenderBasePassInternal()中调用。

DrawNaniteMaterialPass() => SubmitNaniteIndirectMaterial()
## PSO
-  RDG 04 Graphics Pipeline State Initializer https://zhuanlan.zhihu.com/p/582020846 

- FGraphicsPipelineStateInitializer
	- FRHIDepthStencilState*           DepthStencilState
	- FRHIBlendState*                       BlendState
	- FRHIRasterizerState*                RasterizerState
	- EPrimitiveType                           PrimitiveType
	- FBoundShaderStateInput         BoundShaderState.VertexDeclarationRHI
	- FBoundShaderStateInput         BoundShaderState.VertexShaderRHI
	- FBoundShaderStateInput         BoundShaderState.PixelShaderRHI
	- ……

// 应用
SetGraphicsPipelineState(RHICmdList, GraphicsPSOInit,0);

## FMeshPassProcessorRenderState
- FMeshPassProcessorRenderState
	- FRHIBlendState*                         BlendState
	- FRHIDepthStencilState*             DepthStencilState
	- FExclusiveDepthStencil::Type    DepthStencilAccess
	- FRHIUniformBuffer*                    ViewUniformBuffer
	- FRHIUniformBuffer*                    InstancedViewUniformBuffer
	- FRHIUniformBuffer*                    PassUniformBuffer
	- FRHIUniformBuffer*                    NaniteUniformBuffer
	- uint32                                          StencilRef = 0;

### FRHIBlendState
### FRHIDepthStencilState
***TStaticDepthStencilState***



```c++
DrawRenderState.SetDepthStencilState(TStaticDepthStencilState<false, CF_Equal>::GetRHI());

template<bool bDepthTest, ECompareFunction CompareFunction, uint32 StencilWriteMask>
void SetDepthStencilStateForBasePass_Internal(FMeshPassProcessorRenderState& InDrawRenderState)
{
	InDrawRenderState.SetDepthStencilState(TStaticDepthStencilState<
		bDepthTest, CompareFunction,
		true, CF_Always, SO_Keep, SO_Keep, SO_Replace,
		false, CF_Always, SO_Keep, SO_Keep, SO_Keep,
		0xFF, StencilWriteMask>::GetRHI());
}

template<bool bDepthTest, ECompareFunction CompareFunction>
void SetDepthStencilStateForBasePass_Internal(FMeshPassProcessorRenderState& InDrawRenderState, ERHIFeatureLevel::Type FeatureLevel)
{	
	const static bool bStrataDufferPassEnabled = Strata::IsStrataEnabled() && Strata::IsDBufferPassEnabled(GShaderPlatformForFeatureLevel[FeatureLevel]);
	if (bStrataDufferPassEnabled)
	{
		SetDepthStencilStateForBasePass_Internal<bDepthTest, CompareFunction, GET_STENCIL_BIT_MASK(STRATA_RECEIVE_DBUFFER_NORMAL, 1) | GET_STENCIL_BIT_MASK(STRATA_RECEIVE_DBUFFER_DIFFUSE, 1) | GET_STENCIL_BIT_MASK(STRATA_RECEIVE_DBUFFER_ROUGHNESS, 1) | GET_STENCIL_BIT_MASK(DISTANCE_FIELD_REPRESENTATION, 1) | STENCIL_LIGHTING_CHANNELS_MASK(0x7)>(InDrawRenderState);
	}
	else
	{
		SetDepthStencilStateForBasePass_Internal<bDepthTest, CompareFunction, GET_STENCIL_BIT_MASK(RECEIVE_DECAL, 1) | GET_STENCIL_BIT_MASK(DISTANCE_FIELD_REPRESENTATION, 1) | STENCIL_LIGHTING_CHANNELS_MASK(0x7)>(InDrawRenderState);
	}
}

void SetDepthStencilStateForBasePass(
	FMeshPassProcessorRenderState& DrawRenderState,
	ERHIFeatureLevel::Type FeatureLevel,
	bool bDitheredLODTransition,
	const FMaterial& MaterialResource,
	bool bEnableReceiveDecalOutput,
	bool bForceEnableStencilDitherState)
{
	const bool bMaskedInEarlyPass = (MaterialResource.IsMasked() || bDitheredLODTransition) && MaskedInEarlyPass(GShaderPlatformForFeatureLevel[FeatureLevel]);
	if (bEnableReceiveDecalOutput)
	{
		if (bMaskedInEarlyPass)
		{
			SetDepthStencilStateForBasePass_Internal<false, CF_Equal>(DrawRenderState, FeatureLevel);
		}
		else if (DrawRenderState.GetDepthStencilAccess() & FExclusiveDepthStencil::DepthWrite)
		{
			SetDepthStencilStateForBasePass_Internal<true, CF_GreaterEqual>(DrawRenderState, FeatureLevel);
		}
		else
		{
			SetDepthStencilStateForBasePass_Internal<false, CF_GreaterEqual>(DrawRenderState, FeatureLevel);
		}
	}
	else if (bMaskedInEarlyPass)
	{
		DrawRenderState.SetDepthStencilState(TStaticDepthStencilState<false, CF_Equal>::GetRHI());
	}

	if (bForceEnableStencilDitherState)
	{
		SetDepthStencilStateForBasePass_Internal<false, CF_Equal>(DrawRenderState, FeatureLevel);
	}
}
```

### CustomStencil
#### InitCustomDepthStencilContext()
根据当前平台是否支持使用ComputeShader直接输出结果（bComputeExport）、以及是否写入Stencil缓存，以此来创建不同的资源。最终输出FCustomDepthContext。
```c++
struct FCustomDepthContext  
{  
    FRDGTextureRef InputDepth = nullptr;  
    FRDGTextureSRVRef InputStencilSRV = nullptr;  
    FRDGTextureRef DepthTarget = nullptr;  
    FRDGTextureRef StencilTarget = nullptr;  
    bool bComputeExport = true;  
};
```

#### EmitCustomDepthStencilTargets()
根据bComputeExport，分别使用RDG的ComputeShader与PixelShader输出DepthStencil。 
- CS使用FComputeShaderUtils::AddPass()
- PS使用NaniteExportGBuffer.usf的**EmitCustomDepthStencilPS()**，FPixelShaderUtils::AddFullscreenPass()

以**FEmitCustomDepthStencilPS**(NaniteExportGBuffer.usf)为例，额外输入的Nanite相关变量：
- FSceneUniformParameters Scene
- StructuredBuffer`<`FPackedView`>` InViews
- ByteAddressBuffer VisibleClustersSWHW？
- FIntVector4, PageConstants
- Texture2D`<`UlongType`>`, VisBuffer64
- ByteAddressBuffer MaterialSlotTable

#### FinalizeCustomDepthStencil()
替换输出的Depth&Stencil。

# FViewInfo
FViewInfo& ViewInfo
- WriteView.bSceneHasSkyMaterial |= bSceneHasSkyMaterial;
- WriteView.bHasSingleLayerWaterMaterial |= bHasSingleLayerWaterMaterial;
- WriteView.bHasCustomDepthPrimitives |= bHasCustomDepthPrimitives;
- WriteView.bHasDistortionPrimitives |= bHasDistortionPrimitives;
- WriteView.bUsesCustomDepth |= bUsesCustomDepth;  
- WriteView.bUsesCustomStencil |= bUsesCustomStencil;

- FRelevancePacket::Finalize()

相关性：
- 相关性定义
	- FStaticMeshBatchRelevance
	- FMaterialRelevance
- View相关计算
	- FViewInfo::Init()
	- FRelevancePacket
	- FRelevancePacket::Finalize()

# 相关宏定义
- SCOPE_CYCLE_COUNTER(STAT_BasePassDrawTime);：
	- DECLARE_CYCLE_STAT_EXTERN(TEXT("Base pass drawing"),STAT_BasePassDrawTime,STATGROUP_SceneRendering, RENDERCORE_API);
	- DEFINE_STAT(STAT_BasePassDrawTime);
- DEFINE_GPU_STAT(NaniteBasePass);
	- DECLARE_GPU_STAT_NAMED_EXTERN(NaniteBasePass, TEXT("Nanite BasePass"));
- GET_STATID(STAT_CLP_BasePass)
	- FRDGParallelCommandListSet ParallelCommandListSet(InPass, RHICmdList, GET_STATID(STAT_CLP_BasePass), View, FParallelCommandListBindings(PassParameters));
	- DECLARE_CYCLE_STAT(TEXT("BasePass"), STAT_CLP_BasePass, STATGROUP_ParallelCommandListMarkers);