413 lines
17 KiB
Markdown
413 lines
17 KiB
Markdown
---
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title: Untitled
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date: 2024-09-25 14:59:32
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excerpt:
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tags:
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rating: ⭐
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---
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# 前言
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可以使用DrawDynamicMeshPass()，实现在插件中使用MeshDraw绘制Pass。
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参考文章：
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- ***UE5，为HairStrands添加自定义深度与模板***:https://zhuanlan.zhihu.com/p/689578355
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# MeshDraw
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推荐学习：
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- CustomDepth
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- RenderBasePassInternal()
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- RenderAnisotropyPass()
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Shader推荐：
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- DepthOnlyVertexShader.usf
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- DepthOnlyPixelShader.usf
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## BasePass
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### DrawBasePass()
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该函数在FDeferredShadingSceneRenderer::RenderBasePassInternal()中调用。
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DrawNaniteMaterialPass() => SubmitNaniteIndirectMaterial()
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## PSO
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- RDG 04 Graphics Pipeline State Initializer https://zhuanlan.zhihu.com/p/582020846
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- FGraphicsPipelineStateInitializer
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- FRHIDepthStencilState* DepthStencilState
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- FRHIBlendState* BlendState
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- FRHIRasterizerState* RasterizerState
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- EPrimitiveType PrimitiveType
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- FBoundShaderStateInput BoundShaderState.VertexDeclarationRHI
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- FBoundShaderStateInput BoundShaderState.VertexShaderRHI
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- FBoundShaderStateInput BoundShaderState.PixelShaderRHI
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- ……
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// 应用
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SetGraphicsPipelineState(RHICmdList, GraphicsPSOInit,0);
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## FMeshPassProcessorRenderState
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- FMeshPassProcessorRenderState
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- FRHIBlendState* BlendState
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- FRHIDepthStencilState* DepthStencilState
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- FExclusiveDepthStencil::Type DepthStencilAccess
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- FRHIUniformBuffer* ViewUniformBuffer
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- FRHIUniformBuffer* InstancedViewUniformBuffer
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- FRHIUniformBuffer* PassUniformBuffer
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- FRHIUniformBuffer* NaniteUniformBuffer
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- uint32 StencilRef = 0;
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### FRHIBlendState
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使用***FBlendStateInitializerRHI()*** 进行初始化。
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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：
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- Color
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- Color Write Mask
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- Color Blend 混合类型
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- Color Src 混合因子
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- Color Dest 混合因子
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- Alpha
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- Alpha Blend 混合类型
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- Alpha Src 混合因子
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- Alpha Dest 混合因子
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```c++
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FRHIBlendState* CopyBlendState = TStaticBlendState<CW_RGB, BO_Add, BF_SourceAlpha, BF_InverseSourceAlpha, BO_Add, BF_Zero, BF_One>::GetRHI();
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```
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颜色写入蒙版：
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```c++
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enum EColorWriteMask
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{
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CW_RED = 0x01,
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CW_GREEN = 0x02,
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CW_BLUE = 0x04,
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CW_ALPHA = 0x08,
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CW_NONE = 0,
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CW_RGB = CW_RED | CW_GREEN | CW_BLUE,
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CW_RGBA = CW_RED | CW_GREEN | CW_BLUE | CW_ALPHA,
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CW_RG = CW_RED | CW_GREEN,
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CW_BA = CW_BLUE | CW_ALPHA,
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EColorWriteMask_NumBits = 4,
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};
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```
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#### 混合运算
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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。
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| BlendOperation | 颜色混合方程 |
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| -------------------- | ---------------------------------------------------------------------------------- |
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| BO_Add | $$C=C_{src} \otimes F_{src} + C_{dst} \otimes F_{dst}Csrc⊗Fsrc+Cdst⊗Fdst$$ |
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| BO_Subtract | $$C = C_{src} \otimes F_{src} - C_{dst} \otimes F_{dst}C=Csrc⊗Fsrc−Cdst⊗Fdst$$ |
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| BO_ReverseSubtract | $$C = C_{dst} \otimes F_{dst} - C_{src} \otimes F_{src}C=Cdst⊗Fdst−Csrc⊗Fsrc$$ |
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| BO_Min | $$C = Min(C_{src} , C_{dst} )C=Min(Csrc,Cdst)$$ |
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| BO_Max | $$C = Max(C_{src} , C_{dst} )C=Max(Csrc,Cdst)$$ |
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| BO_Min和BO_Max忽略了混合因子 | |
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#### 混合因子
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| BlendFactor | 颜色混合因子 | Alpha混合因子 |
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| ----------------------------- | ---------------------------------------------------------------- | ------------------------ |
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| BF_Zero | $$F = (0,0,0)F=(0,0,0)$$ | $$F=0F=0$$ |
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| BF_One | $$F=(1,1,1)F=(1,1,1)$$ | $$F=1F=1$$ |
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| BF_SourceColor | $$F=(r_{src},g_{src},b_{src})F=(rsrc,gsrc,bsrc)$$ | – |
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| BF_InverseSourceColor | $$F=(1-r_{src},1-g_{src},1-b_{src})F=(1−rsrc,1−gsrc,1−bsrc)$$ | – |
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| BF_SourceAlpha | $$F=(a_{src},a_{src},a_{src})F=(asrc,asrc,asrc)$$ | $$F=a_{src}F=asrc$$ |
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| BF_InverseSourceAlpha | $$F=(1-a_{src},1-a_{src},1-a_{src})F=(1−asrc,1−asrc,1−asrc)$$ | $$F=1-a_{src}F=1−asrc$$ |
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| BF_DestAlpha | $$F=(a_{dst},a_{dst},a_{dst})F=(adst,adst,adst)$$ | $$F=a_{dst}F=adst$$ |
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| BF_InverseDestAlpha | $$F=(1-a_{dst},1-a_{dst},1-a_{dst})F=(1−adst,1−adst,1−adst)$$ | $$F=1-a_{dst}F=1−adst$$ |
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| BF_DestColor | $$F=(r_{dst},g_{dst},b_{dst})F=(rdst,gdst,bdst)$$ | – |
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| BF_InverseDestColor | $$F=(1-r_{dst},1-g_{dst},1-b_{dst})F=(1−rdst,1−gdst,1−bdst)$$ | – |
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| BF_ConstantBlendFactor | F=(r,g,b)F=(r,g,b) | F=aF=a |
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| BF_InverseConstantBlendFactor | F=(1-r,1-g,1-b)F=(1−r,1−g,1−b) | F=1-aF=1−a |
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| BF_Source1Color | 未知 | 未知 |
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| BF_InverseSource1Color | 未知 | 未知 |
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| BF_Source1Alpha | 未知 | 未知 |
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| BF_InverseSource1Alpha | 未知 | 未知 |
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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。
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### FRHIDepthStencilState
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```c++
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TStaticDepthStencilState<
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bEnableDepthWrite, // 是否启用深度写入
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DepthTest, // 深度测试比较函数
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bEnableFrontFaceStencil, // (正面)启用模板
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FrontFaceStencilTest, // (正面)模板测试操作
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FrontFaceStencilFailStencilOp, //(正面)模板测试失败时如何更新模板缓冲区
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FrontFaceDepthFailStencilOp, //(正面)深度测试失败时如何更新模板缓冲区
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FrontFacePassStencilOp, //(正面)通过模板测试时如何更新模板缓冲区
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bEnableBackFaceStencil, // (背面)启用模板
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BackFaceStencilTest, // (背面)模板失败操作
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BackFaceStencilFailStencilOp, //(背面)模板测试失败时如何更新模板缓冲区
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BackFaceDepthFailStencilOp, //(背面)深度测试失败时如何更新模板缓冲区
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BackFacePassStencilOp, //(背面)通过模板测试时如何更新模板红冲去
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StencilReadMask, // 模板读取Mask
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StencilWriteMask // 模板写入Mask
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>
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```
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```c++
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//一般使用这个
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TStaticDepthStencilState<true, CF_DepthNearOrEqual>::GetRHI();
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//CustomStencil中使用的
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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()
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```
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#### DepthTest
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深度测试比较函数。
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```c++
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enum ECompareFunction
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{
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CF_Less,
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CF_LessEqual,
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CF_Greater,
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CF_GreaterEqual,
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CF_Equal,
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CF_NotEqual,
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CF_Never, // 总是返回false
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CF_Always, // 总是返回true
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ECompareFunction_Num,
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ECompareFunction_NumBits = 3,
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// Utility enumerations
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CF_DepthNearOrEqual = (((int32)ERHIZBuffer::IsInverted != 0) ? CF_GreaterEqual : CF_LessEqual),
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CF_DepthNear = (((int32)ERHIZBuffer::IsInverted != 0) ? CF_Greater : CF_Less),
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CF_DepthFartherOrEqual = (((int32)ERHIZBuffer::IsInverted != 0) ? CF_LessEqual : CF_GreaterEqual),
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CF_DepthFarther = (((int32)ERHIZBuffer::IsInverted != 0) ? CF_Less : CF_Greater),
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};
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```
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```c++
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enum EStencilOp
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{
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SO_Keep,
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SO_Zero,
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SO_Replace,
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SO_SaturatedIncrement,
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SO_SaturatedDecrement,
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SO_Invert,
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SO_Increment,
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SO_Decrement,
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EStencilOp_Num,
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EStencilOp_NumBits = 3,
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};
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```
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### CustomStencil
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#### InitCustomDepthStencilContext()
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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。
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```c++
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struct FCustomDepthContext
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{
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FRDGTextureRef InputDepth = nullptr;
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FRDGTextureSRVRef InputStencilSRV = nullptr;
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FRDGTextureRef DepthTarget = nullptr;
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FRDGTextureRef StencilTarget = nullptr;
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bool bComputeExport = true;
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};
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```
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#### EmitCustomDepthStencilTargets()
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根据bComputeExport，分别使用RDG的ComputeShader与PixelShader输出DepthStencil。
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- CS使用FComputeShaderUtils::AddPass()
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- PS使用NaniteExportGBuffer.usf的**EmitCustomDepthStencilPS()**，FPixelShaderUtils::AddFullscreenPass()
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以**FEmitCustomDepthStencilPS**(NaniteExportGBuffer.usf)为例，额外输入的Nanite相关变量：
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- FSceneUniformParameters Scene
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- StructuredBuffer`<`FPackedView`>` InViews
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- ByteAddressBuffer VisibleClustersSWHW？
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- FIntVector4, PageConstants
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- Texture2D`<`UlongType`>`, VisBuffer64
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- ByteAddressBuffer MaterialSlotTable
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#### FinalizeCustomDepthStencil()
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替换输出的Depth&Stencil。
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# FViewInfo
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FViewInfo& ViewInfo
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- WriteView.bSceneHasSkyMaterial |= bSceneHasSkyMaterial;
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- WriteView.bHasSingleLayerWaterMaterial |= bHasSingleLayerWaterMaterial;
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- WriteView.bHasCustomDepthPrimitives |= bHasCustomDepthPrimitives;
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- WriteView.bHasDistortionPrimitives |= bHasDistortionPrimitives;
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- WriteView.bUsesCustomDepth |= bUsesCustomDepth;
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- WriteView.bUsesCustomStencil |= bUsesCustomStencil;
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- FRelevancePacket::Finalize()
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相关性：
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- 相关性定义
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- FStaticMeshBatchRelevance
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- FMaterialRelevance
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- View相关计算
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- FViewInfo::Init()
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- FRelevancePacket
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- FRelevancePacket::Finalize()
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# 相关宏定义
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- SCOPE_CYCLE_COUNTER(STAT_BasePassDrawTime);：
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- DECLARE_CYCLE_STAT_EXTERN(TEXT("Base pass drawing"),STAT_BasePassDrawTime,STATGROUP_SceneRendering, RENDERCORE_API);
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- DEFINE_STAT(STAT_BasePassDrawTime);
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- DEFINE_GPU_STAT(NaniteBasePass);
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- DECLARE_GPU_STAT_NAMED_EXTERN(NaniteBasePass, TEXT("Nanite BasePass"));
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- GET_STATID(STAT_CLP_BasePass)
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- FRDGParallelCommandListSet ParallelCommandListSet(InPass, RHICmdList, GET_STATID(STAT_CLP_BasePass), View, FParallelCommandListBindings(PassParameters));
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- DECLARE_CYCLE_STAT(TEXT("BasePass"), STAT_CLP_BasePass, STATGROUP_ParallelCommandListMarkers);
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# NaniteMeshDraw
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`Engine\Source\Runtime\Renderer\Private\Nanite\`NaniteMaterials.h & NaniteMaterials.cpp
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PS.使用的Shader必须是`FNaniteGlobalShader`的子类。
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以下是Nanite物体的CustomDepth绘制过程：
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```c++
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bool FSceneRenderer::RenderCustomDepthPass(
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FRDGBuilder& GraphBuilder,
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FCustomDepthTextures& CustomDepthTextures,
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const FSceneTextureShaderParameters& SceneTextures,
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TConstArrayView<Nanite::FRasterResults> PrimaryNaniteRasterResults,
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TConstArrayView<Nanite::FPackedView> PrimaryNaniteViews)
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{
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if (!CustomDepthTextures.IsValid())
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{
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return false;
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}
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// Determine if any of the views have custom depth and if any of them have Nanite that is rendering custom depth
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// 构建NaniteDrawLists，用于后面的绘制
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bool bAnyCustomDepth = false;
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TArray<FNaniteCustomDepthDrawList, SceneRenderingAllocator> NaniteDrawLists;
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NaniteDrawLists.AddDefaulted(Views.Num());
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uint32 TotalNaniteInstances = 0;
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for (int32 ViewIndex = 0; ViewIndex < Views.Num(); ++ViewIndex)
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{
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FViewInfo& View = Views[ViewIndex];
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if (View.ShouldRenderView() && View.bHasCustomDepthPrimitives)
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{
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if (PrimaryNaniteRasterResults.IsValidIndex(ViewIndex))
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{
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const FNaniteVisibilityResults& VisibilityResults = PrimaryNaniteRasterResults[ViewIndex].VisibilityResults;
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// Get the Nanite instance draw list for this view. (NOTE: Always use view index 0 for now because we're not doing
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// multi-view yet).
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NaniteDrawLists[ViewIndex] = BuildNaniteCustomDepthDrawList(View, 0u, VisibilityResults);
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TotalNaniteInstances += NaniteDrawLists[ViewIndex].Num();
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}
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bAnyCustomDepth = true;
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}
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}
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SET_DWORD_STAT(STAT_NaniteCustomDepthInstances, TotalNaniteInstances);
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..
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if (TotalNaniteInstances > 0)
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{
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RDG_EVENT_SCOPE(GraphBuilder, "Nanite CustomDepth");
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const FIntPoint RasterTextureSize = CustomDepthTextures.Depth->Desc.Extent;
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FIntRect RasterTextureRect(0, 0, RasterTextureSize.X, RasterTextureSize.Y);
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if (Views.Num() == 1)
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{
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const FViewInfo& View = Views[0];
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if (View.ViewRect.Min.X == 0 && View.ViewRect.Min.Y == 0)
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{
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RasterTextureRect = View.ViewRect;
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}
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}
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const bool bWriteCustomStencil = IsCustomDepthPassWritingStencil();
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Nanite::FSharedContext SharedContext{};
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SharedContext.FeatureLevel = Scene->GetFeatureLevel();
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SharedContext.ShaderMap = GetGlobalShaderMap(SharedContext.FeatureLevel);
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SharedContext.Pipeline = Nanite::EPipeline::Primary;
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// TODO: If !bWriteCustomStencil, we could copy off the depth and rasterize depth-only (probable optimization)
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//初始化Nanite::FRasterContext RasterContext。
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Nanite::FRasterContext RasterContext = Nanite::InitRasterContext(
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GraphBuilder,
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SharedContext,
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ViewFamily,
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RasterTextureSize,
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RasterTextureRect,
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false, // bVisualize
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Nanite::EOutputBufferMode::VisBuffer,
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true, // bClearTarget
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nullptr, // RectMinMaxBufferSRV
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0, // NumRects
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nullptr, // ExternalDepthBuffer
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true // bCustomPass
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);
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//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）。
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Nanite::FCustomDepthContext CustomDepthContext = Nanite::InitCustomDepthStencilContext(
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GraphBuilder,
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CustomDepthTextures,
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bWriteCustomStencil);
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Nanite::FConfiguration CullingConfig = { 0 };//Nanite剔除设置，用的较多的是bUpdateStreaming、bPrimaryContext、bTwoPassOcclusion，设置为true。
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CullingConfig.bUpdateStreaming = true;
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for (int32 ViewIndex = 0; ViewIndex < Views.Num(); ++ViewIndex)
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{
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RDG_EVENT_SCOPE_CONDITIONAL(GraphBuilder, Views.Num() > 1, "View%d", ViewIndex);
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FViewInfo& View = Views[ViewIndex];
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if (!View.ShouldRenderView() || NaniteDrawLists[ViewIndex].Num() == 0)
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{
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continue;
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}
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//创建Nanite渲染器
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auto NaniteRenderer = Nanite::IRenderer::Create(
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GraphBuilder,
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*Scene,
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View,
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GetSceneUniforms(),
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SharedContext,
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RasterContext,
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CullingConfig,
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View.ViewRect,
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/* PrevHZB = */ nullptr
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);
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NaniteRenderer->DrawGeometry(
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Scene->NaniteRasterPipelines[ENaniteMeshPass::BasePass],
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PrimaryNaniteRasterResults[ViewIndex].VisibilityResults,
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*Nanite::FPackedViewArray::Create(GraphBuilder, PrimaryNaniteViews[ViewIndex]),
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NaniteDrawLists[ViewIndex]
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);
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Nanite::FRasterResults RasterResults;
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NaniteRenderer->ExtractResults( RasterResults );
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// Emit depth
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Nanite::EmitCustomDepthStencilTargets(
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GraphBuilder,
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*Scene,
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View,
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RasterResults.PageConstants,
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RasterResults.VisibleClustersSWHW,
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RasterResults.ViewsBuffer,
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RasterContext.VisBuffer64,
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CustomDepthContext
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);
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}
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Nanite::FinalizeCustomDepthStencil(GraphBuilder, CustomDepthContext, CustomDepthTextures);
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}
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...
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}
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```
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- Nanite::InitRasterContext()：初始化Nanite::FRasterContext RasterContext。
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- 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）。
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- auto NaniteRenderer = Nanite::IRenderer::Create()：创建Nanite渲染器
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- NaniteRenderer->DrawGeometry()：Nanite物体绘制
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- NaniteRenderer->ExtractResults( RasterResults )：提取渲染结果。
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- ***Nanite::EmitCustomDepthStencilTargets()***：使用提取到的Nanite::FRasterResults RasterResults，输出CustomDepth。结果存储在 FCustomDepthContext& CustomDepthContext中。
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- FDepthExportCS / FEmitCustomDepthStencilPS
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- Nanite::FinalizeCustomDepthStencil()：将CustomDepthContext中的结果输出到CustomDepthTextures上。
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## BasePass Nanite
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1. Render()中向RenderBasePass()传入const TArrayView<Nanite::FRasterResults>& NaniteRasterResults。
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2. 调用Lambda RenderNaniteBasePass()，本质上是调用Nanite::DrawBasePass()进行渲染。 |