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

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title	date	excerpt	tags	rating
Untitled	2024-09-25 14:59:32			⭐

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()

DepthStencil

TStaticDepthStencilState

• RDG 04 Graphics Pipeline State Initializer https://zhuanlan.zhihu.com/p/582020846

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);
	}
}

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。

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);