vault backup: 2024-02-06 20:08:30
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@ -661,4 +661,236 @@ private:
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上面展示了Vertex Factory的很多类型，有好几个是核心类，比如FVertexFactory、FVertexElement、FRHIVertexDeclaration、FRHIVertexBuffer、FVertexFactoryType、FVertexStreamComponent、FVertexInputStream、FVertexFactoryShaderParameters等。那么它们之间的关系是什么呢？
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为了更好地说明它们之间的关系，以静态模型的FStaticMeshDataType为例：
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![[UE_VertexFactory_FStaticMeshDataType.jpg]]
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![[UE_VertexFactory_FStaticMeshDataType.jpg]]
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FStaticMeshDataType会包含若干个FVertexStreamComponent实例，每个FVertexStreamComponent包含了一个在**FVertexDeclarationElementList**的**FVertexElement实例索引**和一个在**FVertexInputStreamArray**列表的**FVertexStream实例索引**。
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此外，FVertexFactory是个基类，内置的子类主要有：
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- FGeometryCacheVertexVertexFactory：几何缓存顶点的顶点工厂，常用于预生成的布料、动作等网格类型。
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- FGPUBaseSkinVertexFactory：GPU蒙皮骨骼网格的父类，它的子类有：
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- TGPUSkinVertexFactory：可指定骨骼权重方式的GPU蒙皮的顶点工厂。
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- FLocalVertexFactory：局部顶点工厂，常用于**静态网格**，它拥有**数量较多的子类**：
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- FInstancedStaticMeshVertexFactory：实例化的静态网格顶点工厂。
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- FSplineMeshVertexFactory：样条曲线网格顶点工厂。
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- FGeometryCollectionVertexFactory：几何收集顶点工厂。
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- FGPUSkinPassthroughVertexFactory：启用了Skin Cache模式的蒙皮骨骼顶点工厂。
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- FSingleTriangleMeshVertexFactory：单个三角形网格的顶点工厂，用于体积云渲染。
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- ......
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- FParticleVertexFactoryBase：用于粒子渲染的顶点工厂基类。
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- FLandscapeVertexFactory：用于渲染地形的顶点工厂。
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除了以上继承自FVertexFactory，还有一些不是继承自FVertexFactory的类型，如：
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- FGPUBaseSkinAPEXClothVertexFactory：布料顶点工厂。
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- TGPUSkinAPEXClothVertexFactory：可带骨骼权重模式的布料顶点工厂。
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除了FVertexFactory，相应的其它核心类也有继承体系。比如FVertexFactoryShaderParameters的子类有：
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- FGeometryCacheVertexFactoryShaderParameters
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- FGPUSkinVertexFactoryShaderParameters
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- FMeshParticleVertexFactoryShaderParameters
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- FParticleSpriteVertexFactoryShaderParameters
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- FGPUSpriteVertexFactoryShaderParametersVS
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- FGPUSpriteVertexFactoryShaderParametersPS
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- FSplineMeshVertexFactoryShaderParameters
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- FLocalVertexFactoryShaderParametersBase
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- FLandscapeVertexFactoryVertexShaderParameters
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- FLandscapeVertexFactoryPixelShaderParameters
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- ......
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另外，有部分顶点工厂还会在内部派生FStaticMeshDataType的类型，以复用静态网格相关的数据成员。为了更好地说明顶点工厂的使用方式，下面就以最常见的FLocalVertexFactory和使用了FLocalVertexFactory的CableComponent为例：
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```c++
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class ENGINE_API FLocalVertexFactory : public FVertexFactory
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{
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public:
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FLocalVertexFactory(ERHIFeatureLevel::Type InFeatureLevel, const char* InDebugName)；
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// 派生自FStaticMeshDataType的数据类型.
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struct FDataType : public FStaticMeshDataType
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{
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FRHIShaderResourceView* PreSkinPositionComponentSRV = nullptr;
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};
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// 环境变量更改和校验.
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static bool ShouldCompilePermutation(const FVertexFactoryShaderPermutationParameters& Parameters);
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static void ModifyCompilationEnvironment(const FVertexFactoryShaderPermutationParameters& Parameters, FShaderCompilerEnvironment& OutEnvironment);
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static void ValidateCompiledResult(const FVertexFactoryType* Type, EShaderPlatform Platform, const FShaderParameterMap& ParameterMap, TArray<FString>& OutErrors);
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// 由TSynchronizedResource从游戏线程更新而来的数据.
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void SetData(const FDataType& InData);
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// 从其它顶点工厂复制数据.
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void Copy(const FLocalVertexFactory& Other);
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// FRenderResource接口.
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virtual void InitRHI() override;
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virtual void ReleaseRHI() override
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{
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UniformBuffer.SafeRelease();
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FVertexFactory::ReleaseRHI();
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}
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// 顶点颜色接口.
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void SetColorOverrideStream(FRHICommandList& RHICmdList, const FVertexBuffer* ColorVertexBuffer) const;
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void GetColorOverrideStream(const FVertexBuffer* ColorVertexBuffer, FVertexInputStreamArray& VertexStreams) const;
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// 着色器参数和其它数据接口.
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inline FRHIShaderResourceView* GetPositionsSRV() const;
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inline FRHIShaderResourceView* GetPreSkinPositionSRV() const;
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inline FRHIShaderResourceView* GetTangentsSRV() const;
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inline FRHIShaderResourceView* GetTextureCoordinatesSRV() const;
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inline FRHIShaderResourceView* GetColorComponentsSRV() const;
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inline const uint32 GetColorIndexMask() const;
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inline const int GetLightMapCoordinateIndex() const;
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inline const int GetNumTexcoords() const;
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FRHIUniformBuffer* GetUniformBuffer() const;
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(......)
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protected:
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// 从游戏线程传入的数据. FDataType是FStaticMeshDataType的子类.
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FDataType Data;
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// 局部顶点工厂的着色器参数.
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TUniformBufferRef<FLocalVertexFactoryUniformShaderParameters> UniformBuffer;
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// 顶点颜色流索引.
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int32 ColorStreamIndex;
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(......)
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};
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// Engine\Source\Runtime\Engine\Public\LocalVertexFactory.cpp
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void FLocalVertexFactory::InitRHI()
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{
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// 是否使用gpu场景.
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const bool bCanUseGPUScene = UseGPUScene(GMaxRHIShaderPlatform, GMaxRHIFeatureLevel);
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// 初始化位置流和位置声明.
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if (Data.PositionComponent.VertexBuffer != Data.TangentBasisComponents[0].VertexBuffer)
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{
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// 增加顶点声明.
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auto AddDeclaration = [this, bCanUseGPUScene](EVertexInputStreamType InputStreamType, bool bAddNormal)
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{
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// 顶点流元素.
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FVertexDeclarationElementList StreamElements;
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StreamElements.Add(AccessStreamComponent(Data.PositionComponent, 0, InputStreamType));
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bAddNormal = bAddNormal && Data.TangentBasisComponents[1].VertexBuffer != NULL;
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if (bAddNormal)
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{
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StreamElements.Add(AccessStreamComponent(Data.TangentBasisComponents[1], 2, InputStreamType));
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}
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const uint8 TypeIndex = static_cast<uint8>(InputStreamType);
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PrimitiveIdStreamIndex[TypeIndex] = -1;
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if (GetType()->SupportsPrimitiveIdStream() && bCanUseGPUScene)
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{
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// When the VF is used for rendering in normal mesh passes, this vertex buffer and offset will be overridden
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StreamElements.Add(AccessStreamComponent(FVertexStreamComponent(&GPrimitiveIdDummy, 0, 0, sizeof(uint32), VET_UInt, EVertexStreamUsage::Instancing), 1, InputStreamType));
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PrimitiveIdStreamIndex[TypeIndex] = StreamElements.Last().StreamIndex;
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}
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// 初始化声明.
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InitDeclaration(StreamElements, InputStreamType);
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};
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// 增加PositionOnly和PositionAndNormalOnly两种顶点声明, 其中前者不需要法线.
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AddDeclaration(EVertexInputStreamType::PositionOnly, false);
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AddDeclaration(EVertexInputStreamType::PositionAndNormalOnly, true);
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}
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// 顶点声明元素列表.
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FVertexDeclarationElementList Elements;
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// 顶点位置
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if(Data.PositionComponent.VertexBuffer != NULL)
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{
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Elements.Add(AccessStreamComponent(Data.PositionComponent,0));
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}
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// 图元id
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{
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const uint8 Index = static_cast<uint8>(EVertexInputStreamType::Default);
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PrimitiveIdStreamIndex[Index] = -1;
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if (GetType()->SupportsPrimitiveIdStream() && bCanUseGPUScene)
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{
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// When the VF is used for rendering in normal mesh passes, this vertex buffer and offset will be overridden
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Elements.Add(AccessStreamComponent(FVertexStreamComponent(&GPrimitiveIdDummy, 0, 0, sizeof(uint32), VET_UInt, EVertexStreamUsage::Instancing), 13));
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PrimitiveIdStreamIndex[Index] = Elements.Last().StreamIndex;
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}
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}
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// 切线和法线, 切线法线才需要被顶点流使用, 副法线由shader生成.
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uint8 TangentBasisAttributes[2] = { 1, 2 };
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for(int32 AxisIndex = 0;AxisIndex < 2;AxisIndex++)
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{
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if(Data.TangentBasisComponents[AxisIndex].VertexBuffer != NULL)
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{
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Elements.Add(AccessStreamComponent(Data.TangentBasisComponents[AxisIndex],TangentBasisAttributes[AxisIndex]));
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}
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}
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if (Data.ColorComponentsSRV == nullptr)
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{
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Data.ColorComponentsSRV = GNullColorVertexBuffer.VertexBufferSRV;
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Data.ColorIndexMask = 0;
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}
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// 顶点颜色
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ColorStreamIndex = -1;
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if(Data.ColorComponent.VertexBuffer)
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{
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Elements.Add(AccessStreamComponent(Data.ColorComponent,3));
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ColorStreamIndex = Elements.Last().StreamIndex;
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}
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else
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{
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FVertexStreamComponent NullColorComponent(&GNullColorVertexBuffer, 0, 0, VET_Color, EVertexStreamUsage::ManualFetch);
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Elements.Add(AccessStreamComponent(NullColorComponent, 3));
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ColorStreamIndex = Elements.Last().StreamIndex;
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}
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// 纹理坐标
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if(Data.TextureCoordinates.Num())
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{
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const int32 BaseTexCoordAttribute = 4;
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for(int32 CoordinateIndex = 0;CoordinateIndex < Data.TextureCoordinates.Num();CoordinateIndex++)
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{
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Elements.Add(AccessStreamComponent(
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Data.TextureCoordinates[CoordinateIndex],
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BaseTexCoordAttribute + CoordinateIndex
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));
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}
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for (int32 CoordinateIndex = Data.TextureCoordinates.Num(); CoordinateIndex < MAX_STATIC_TEXCOORDS / 2; CoordinateIndex++)
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{
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Elements.Add(AccessStreamComponent(
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Data.TextureCoordinates[Data.TextureCoordinates.Num() - 1],
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BaseTexCoordAttribute + CoordinateIndex
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));
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}
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}
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// 光照图
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if(Data.LightMapCoordinateComponent.VertexBuffer)
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{
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Elements.Add(AccessStreamComponent(Data.LightMapCoordinateComponent,15));
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}
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else if(Data.TextureCoordinates.Num())
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{
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Elements.Add(AccessStreamComponent(Data.TextureCoordinates[0],15));
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}
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// 初始化顶点声明
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InitDeclaration(Elements);
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const int32 DefaultBaseVertexIndex = 0;
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const int32 DefaultPreSkinBaseVertexIndex = 0;
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if (RHISupportsManualVertexFetch(GMaxRHIShaderPlatform) || bCanUseGPUScene)
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{
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SCOPED_LOADTIMER(FLocalVertexFactory_InitRHI_CreateLocalVFUniformBuffer);
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UniformBuffer = CreateLocalVFUniformBuffer(this, Data.LODLightmapDataIndex, nullptr, DefaultBaseVertexIndex, DefaultPreSkinBaseVertexIndex);
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}
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}
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// 实现FLocalVertexFactory的参数类型.
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IMPLEMENT_VERTEX_FACTORY_PARAMETER_TYPE(FLocalVertexFactory, SF_Vertex, FLocalVertexFactoryShaderParameters);
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// 实现FLocalVertexFactory.
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IMPLEMENT_VERTEX_FACTORY_TYPE_EX(FLocalVertexFactory,"/Engine/Private/LocalVertexFactory.ush",true,true,true,true,true,true,true);
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```
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