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

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2025-08-02 12:09:34 +08:00
---
title: Untitled
date: 2024-09-25 14:59:32
excerpt:
tags:
rating: ⭐
---
# 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
## 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
使用***FBlendStateInitializerRHI()*** 进行初始化。
它定义了8个渲染对象，一般我们只用第一组，它的七个参数分别是：
- Color
- Color Write Mask
- Color Blend 混合类型
- Color Src 混合因子
- Color Dest 混合因子
- Alpha
- Alpha Blend 混合类型
- Alpha Src 混合因子
- Alpha Dest 混合因子
```c++
FRHIBlendState* CopyBlendState = TStaticBlendState<CW_RGB, BO_Add, BF_SourceAlpha, BF_InverseSourceAlpha, BO_Add, BF_Zero, BF_One>::GetRHI();
```
颜色写入蒙版：
```c++
enum EColorWriteMask
{
CW_RED = 0x01,
CW_GREEN = 0x02,
CW_BLUE = 0x04,
CW_ALPHA = 0x08,
CW_NONE = 0,
CW_RGB = CW_RED | CW_GREEN | CW_BLUE,
CW_RGBA = CW_RED | CW_GREEN | CW_BLUE | CW_ALPHA,
CW_RG = CW_RED | CW_GREEN,
CW_BA = CW_BLUE | CW_ALPHA,
EColorWriteMask_NumBits = 4,
};
```
#### 混合运算
混合运算符对于颜色混合方程和Alpha混合方程效果是一样的，这里就只用颜色混合方程来做讲解。
| BlendOperation | 颜色混合方程 |
| -------------------- | ---------------------------------------------------------------------------------- |
| BO_Add | $$C=C_{src} \otimes F_{src} + C_{dst} \otimes F_{dst}Csrc​⊗Fsrc​+Cdst​⊗Fdst$$​ |
| BO_Subtract | $$C = C_{src} \otimes F_{src} - C_{dst} \otimes F_{dst}C=Csrc​⊗Fsrc​−Cdst​⊗Fdst$$​ |
| BO_ReverseSubtract | $$C = C_{dst} \otimes F_{dst} - C_{src} \otimes F_{src}C=Cdst​⊗Fdst​−Csrc​⊗Fsrc$$​ |
| BO_Min | $$C = Min(C_{src} , C_{dst} )C=Min(Csrc​,Cdst​)$$ |
| BO_Max | $$C = Max(C_{src} , C_{dst} )C=Max(Csrc​,Cdst​)$$ |
| BO_Min和BO_Max忽略了混合因子 | |
#### 混合因子
| BlendFactor | 颜色混合因子 | Alpha混合因子 |
| ----------------------------- | ---------------------------------------------------------------- | ------------------------ |
| BF_Zero | $$F = (0,0,0)F=(0,0,0)$$ | $$F=0F=0$$ |
| BF_One | $$F=(1,1,1)F=(1,1,1)$$ | $$F=1F=1$$ |
| BF_SourceColor | $$F=(r_{src},g_{src},b_{src})F=(rsrc​,gsrc​,bsrc​)$$ | – |
| BF_InverseSourceColor | $$F=(1-r_{src},1-g_{src},1-b_{src})F=(1−rsrc​,1−gsrc​,1−bsrc​)$$ | – |
| BF_SourceAlpha | $$F=(a_{src},a_{src},a_{src})F=(asrc​,asrc​,asrc​)$$ | $$F=a_{src}F=asrc$$​ |
| BF_InverseSourceAlpha | $$F=(1-a_{src},1-a_{src},1-a_{src})F=(1−asrc​,1−asrc​,1−asrc​)$$ | $$F=1-a_{src}F=1−asrc$$​ |
| BF_DestAlpha | $$F=(a_{dst},a_{dst},a_{dst})F=(adst​,adst​,adst​)$$ | $$F=a_{dst}F=adst$$​ |
| BF_InverseDestAlpha | $$F=(1-a_{dst},1-a_{dst},1-a_{dst})F=(1−adst​,1−adst​,1−adst​)$$ | $$F=1-a_{dst}F=1−adst$$​ |
| BF_DestColor | $$F=(r_{dst},g_{dst},b_{dst})F=(rdst​,gdst​,bdst​)$$ | – |
| BF_InverseDestColor | $$F=(1-r_{dst},1-g_{dst},1-b_{dst})F=(1−rdst​,1−gdst​,1−bdst​)$$ | – |
| BF_ConstantBlendFactor | F=(r,g,b)F=(r,g,b) | F=aF=a |
| BF_InverseConstantBlendFactor | F=(1-r,1-g,1-b)F=(1−r,1−g,1−b) | F=1-aF=1−a |
| BF_Source1Color | 未知 | 未知 |
| BF_InverseSource1Color | 未知 | 未知 |
| BF_Source1Alpha | 未知 | 未知 |
| BF_InverseSource1Alpha | 未知 | 未知 |
最后四个选项没有在DirectX中找到对应的选项，没有继续探究，前面的应该足够一般使用了。
### FRHIDepthStencilState
```c++
TStaticDepthStencilState<
bEnableDepthWrite, // 是否启用深度写入
DepthTest, // 深度测试比较函数
bEnableFrontFaceStencil, // (正面)启用模板
FrontFaceStencilTest, // (正面)模板测试操作
FrontFaceStencilFailStencilOp, //(正面)模板测试失败时如何更新模板缓冲区
FrontFaceDepthFailStencilOp, //(正面)深度测试失败时如何更新模板缓冲区
FrontFacePassStencilOp, //(正面)通过模板测试时如何更新模板缓冲区
bEnableBackFaceStencil, // (背面)启用模板
BackFaceStencilTest, // (背面)模板失败操作
BackFaceStencilFailStencilOp, //(背面)模板测试失败时如何更新模板缓冲区
BackFaceDepthFailStencilOp, //(背面)深度测试失败时如何更新模板缓冲区
BackFacePassStencilOp, //(背面)通过模板测试时如何更新模板红冲去
StencilReadMask, // 模板读取Mask
StencilWriteMask // 模板写入Mask
>
```
```c++
//一般使用这个
TStaticDepthStencilState<true, CF_DepthNearOrEqual>::GetRHI();
//CustomStencil中使用的
TStaticDepthStencilState<true, CF_DepthNearOrEqual, true, CF_Always, SO_Keep, SO_Keep, SO_Replace, false, CF_Always, SO_Keep, SO_Keep, SO_Keep, 255, 255>::GetRHI()
```
#### DepthTest
深度测试比较函数。
```c++
enum ECompareFunction
{
CF_Less,
CF_LessEqual,
CF_Greater,
CF_GreaterEqual,
CF_Equal,
CF_NotEqual,
CF_Never, // 总是返回false
CF_Always, // 总是返回true
ECompareFunction_Num,
ECompareFunction_NumBits = 3,
// Utility enumerations
CF_DepthNearOrEqual = (((int32)ERHIZBuffer::IsInverted != 0) ? CF_GreaterEqual : CF_LessEqual),
CF_DepthNear = (((int32)ERHIZBuffer::IsInverted != 0) ? CF_Greater : CF_Less),
CF_DepthFartherOrEqual = (((int32)ERHIZBuffer::IsInverted != 0) ? CF_LessEqual : CF_GreaterEqual),
CF_DepthFarther = (((int32)ERHIZBuffer::IsInverted != 0) ? CF_Less : CF_Greater),
};
```
```c++
enum EStencilOp
{
SO_Keep,
SO_Zero,
SO_Replace,
SO_SaturatedIncrement,
SO_SaturatedDecrement,
SO_Invert,
SO_Increment,
SO_Decrement,
EStencilOp_Num,
EStencilOp_NumBits = 3,
};
```
### 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);
# NaniteMeshDraw
`Engine\Source\Runtime\Renderer\Private\Nanite\`NaniteMaterials.h & NaniteMaterials.cpp
PS.使用的Shader必须是`FNaniteGlobalShader`的子类。
以下是Nanite物体的CustomDepth绘制过程：
```c++
bool FSceneRenderer::RenderCustomDepthPass(
FRDGBuilder& GraphBuilder,
FCustomDepthTextures& CustomDepthTextures,
const FSceneTextureShaderParameters& SceneTextures,
TConstArrayView<Nanite::FRasterResults> PrimaryNaniteRasterResults,
TConstArrayView<Nanite::FPackedView> PrimaryNaniteViews)
{
if (!CustomDepthTextures.IsValid())
{
return false;
}
// Determine if any of the views have custom depth and if any of them have Nanite that is rendering custom depth
// 构建NaniteDrawLists，用于后面的绘制
bool bAnyCustomDepth = false;
TArray<FNaniteCustomDepthDrawList, SceneRenderingAllocator> NaniteDrawLists;
NaniteDrawLists.AddDefaulted(Views.Num());
uint32 TotalNaniteInstances = 0;
for (int32 ViewIndex = 0; ViewIndex < Views.Num(); ++ViewIndex)
{
FViewInfo& View = Views[ViewIndex];
if (View.ShouldRenderView() && View.bHasCustomDepthPrimitives)
{
if (PrimaryNaniteRasterResults.IsValidIndex(ViewIndex))
{
const FNaniteVisibilityResults& VisibilityResults = PrimaryNaniteRasterResults[ViewIndex].VisibilityResults;
// Get the Nanite instance draw list for this view. (NOTE: Always use view index 0 for now because we're not doing
// multi-view yet).
NaniteDrawLists[ViewIndex] = BuildNaniteCustomDepthDrawList(View, 0u, VisibilityResults);
TotalNaniteInstances += NaniteDrawLists[ViewIndex].Num();
}
bAnyCustomDepth = true;
}
}
SET_DWORD_STAT(STAT_NaniteCustomDepthInstances, TotalNaniteInstances);
..
if (TotalNaniteInstances > 0)
{
RDG_EVENT_SCOPE(GraphBuilder, "Nanite CustomDepth");
const FIntPoint RasterTextureSize = CustomDepthTextures.Depth->Desc.Extent;
FIntRect RasterTextureRect(0, 0, RasterTextureSize.X, RasterTextureSize.Y);
if (Views.Num() == 1)
{
const FViewInfo& View = Views[0];
if (View.ViewRect.Min.X == 0 && View.ViewRect.Min.Y == 0)
{
RasterTextureRect = View.ViewRect;
}
}
const bool bWriteCustomStencil = IsCustomDepthPassWritingStencil();
Nanite::FSharedContext SharedContext{};
SharedContext.FeatureLevel = Scene->GetFeatureLevel();
SharedContext.ShaderMap = GetGlobalShaderMap(SharedContext.FeatureLevel);
SharedContext.Pipeline = Nanite::EPipeline::Primary;
// TODO: If !bWriteCustomStencil, we could copy off the depth and rasterize depth-only (probable optimization)
//初始化Nanite::FRasterContext RasterContext。
Nanite::FRasterContext RasterContext = Nanite::InitRasterContext(
GraphBuilder,
SharedContext,
ViewFamily,
RasterTextureSize,
RasterTextureRect,
false, // bVisualize
Nanite::EOutputBufferMode::VisBuffer,
true, // bClearTarget
nullptr, // RectMinMaxBufferSRV
0, // NumRects
nullptr, // ExternalDepthBuffer
true // bCustomPass
);
//用于构建FCustomDepthContext结构体，创建对应的贴图资源。主要包含了InputDepth、InputStencilSRV、DepthTarget、StencilTarget以及bComputeExport（是否使用ComputeShader输出）。
Nanite::FCustomDepthContext CustomDepthContext = Nanite::InitCustomDepthStencilContext(
GraphBuilder,
CustomDepthTextures,
bWriteCustomStencil);
Nanite::FConfiguration CullingConfig = { 0 };//Nanite剔除设置，用的较多的是bUpdateStreaming、bPrimaryContext、bTwoPassOcclusion，设置为true。
CullingConfig.bUpdateStreaming = true;
for (int32 ViewIndex = 0; ViewIndex < Views.Num(); ++ViewIndex)
{
RDG_EVENT_SCOPE_CONDITIONAL(GraphBuilder, Views.Num() > 1, "View%d", ViewIndex);
FViewInfo& View = Views[ViewIndex];
if (!View.ShouldRenderView() || NaniteDrawLists[ViewIndex].Num() == 0)
{
continue;
}
//创建Nanite渲染器
auto NaniteRenderer = Nanite::IRenderer::Create(
GraphBuilder,
*Scene,
View,
GetSceneUniforms(),
SharedContext,
RasterContext,
CullingConfig,
View.ViewRect,
/* PrevHZB = */ nullptr
);
NaniteRenderer->DrawGeometry(
Scene->NaniteRasterPipelines[ENaniteMeshPass::BasePass],
PrimaryNaniteRasterResults[ViewIndex].VisibilityResults,
*Nanite::FPackedViewArray::Create(GraphBuilder, PrimaryNaniteViews[ViewIndex]),
NaniteDrawLists[ViewIndex]
);
Nanite::FRasterResults RasterResults;
NaniteRenderer->ExtractResults( RasterResults );
// Emit depth
Nanite::EmitCustomDepthStencilTargets(
GraphBuilder,
*Scene,
View,
RasterResults.PageConstants,
RasterResults.VisibleClustersSWHW,
RasterResults.ViewsBuffer,
RasterContext.VisBuffer64,
CustomDepthContext
);
}
Nanite::FinalizeCustomDepthStencil(GraphBuilder, CustomDepthContext, CustomDepthTextures);
}
...
}
```
- Nanite::InitRasterContext()：初始化Nanite::FRasterContext RasterContext。
- Nanite::InitCustomDepthStencilContext()：位于NaniteMaterials.cpp，用于构建FCustomDepthContext结构体，创建对应的贴图资源。主要包含了InputDepth、InputStencilSRV、DepthTarget、StencilTarget以及bComputeExport（是否使用ComputeShader输出）。
- auto NaniteRenderer = Nanite::IRenderer::Create()：创建Nanite渲染器
- NaniteRenderer->DrawGeometry()：Nanite物体绘制
- NaniteRenderer->ExtractResults( RasterResults )：提取渲染结果。
- ***Nanite::EmitCustomDepthStencilTargets()***：使用提取到的Nanite::FRasterResults RasterResults，输出CustomDepth。结果存储在 FCustomDepthContext& CustomDepthContext中。
- FDepthExportCS / FEmitCustomDepthStencilPS
- Nanite::FinalizeCustomDepthStencil()：将CustomDepthContext中的结果输出到CustomDepthTextures上。
## BasePass Nanite
1. Render()中向RenderBasePass()传入const TArrayView<Nanite::FRasterResults>& NaniteRasterResults。
2. 调用Lambda RenderNaniteBasePass()，本质上是调用Nanite::DrawBasePass()进行渲染。
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