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03-UnrealEngine/Rendering/RenderingPipeline/向往渲染系列文章阅读笔记/剖析虚幻渲染体系（08）- Shader体系.md

@@ -193,4 +193,472 @@ private:
     // 缓冲区尺寸.
     uint32 LayoutConstantBufferSize;
 };
+
+// 定义FRHIUniformBuffer的引用类型.
+typedef TRefCountPtr<FRHIUniformBuffer> FUniformBufferRHIRef;
+
+// Engine\Source\Runtime\RenderCore\Public\ShaderParameterMacros.h
+// 引用了指定类型的FRHIUniformBuffer的实例资源. 注意是继承了FUniformBufferRHIRef.
+template<typename TBufferStruct>
+class TUniformBufferRef : public FUniformBufferRHIRef
+{
+public:
+    TUniformBufferRef();
+
+    // 根据给定的值创建Uniform Buffer, 并返回结构体引用. (模板)
+    static TUniformBufferRef<TBufferStruct> CreateUniformBufferImmediate(const TBufferStruct& Value, EUniformBufferUsage Usage, EUniformBufferValidation Validation = EUniformBufferValidation::ValidateResources);
+    // 根据给定的值创建[局部]的Uniform Buffer, 并返回结构体引用.
+    static FLocalUniformBuffer CreateLocalUniformBuffer(FRHICommandList& RHICmdList, const TBufferStruct& Value, EUniformBufferUsage Usage);
+
+    // 立即刷新缓冲区数据到RHI.
+    void UpdateUniformBufferImmediate(const TBufferStruct& Value);
+
+private:
+    // 私有构造体, 只能给TUniformBuffer和TRDGUniformBuffer创建.
+    TUniformBufferRef(FRHIUniformBuffer* InRHIRef);
+
+    template<typename TBufferStruct2>
+    friend class TUniformBuffer;
+
+    friend class TRDGUniformBuffer<TBufferStruct>;
+};
 ```
+
+最后TUniformBuffer和TRDGUniformBuffer引用了FUniformBufferRHIRef。TUniformBuffer为`TUniformBufferRef<TBufferStruct> UniformBufferRHI`成员变量；TRDGUniformBuffer为`TRefCountPtr<FRHIUniformBuffer> UniformBufferRHI`。
+
+![[UE_Uniform.png]]
+
+### 定义宏
+- SHADER_PARAMETER_STRUCT_REF：引用着色器参数结构体(全局的才行)
+- SHADER_PARAMETER_STRUCT_INCLUDE：包含着色器参数结构体(局部或全局都行)
+
+# Vertex Factory
+我们知道，在引擎中存在着静态网格、蒙皮骨骼、程序化网格以及地形等等类型的网格类型，而材质就是通过顶点工厂FVertexFactory来支持这些网格类型。实际上，顶点工厂要涉及各方面的数据和类型，包含但不限于：
+- 顶点着色器。顶点着色器的输入输出需要顶点工厂来表明数据的布局。
+- 顶点工厂的参数和RHI资源。这些数据将从C++层传入到顶点着色器中进行处理。
+- 顶点缓冲和顶点布局。通过顶点布局，我们可以自定义和扩展顶点缓冲的输入，从而实现定制化的Shader代码。
+- 几何预处理。顶点缓冲、网格资源、材质参数等等都可以在真正渲染前预处理它们。
+![[UE_VertexFactory.png]]
+
+**顶点工厂在渲染层级中的关系。由图可知，顶点工厂是渲染线程的对象，横跨于CPU和GPU两端。**
+
+```c++
+// Engine\Source\Runtime\RHI\Public\RHI.h
+// 顶点元素.
+struct FVertexElement
+{
+    uint8 StreamIndex;      // 流索引
+    uint8 Offset;          // 偏移
+    TEnumAsByte<EVertexElementType> Type; // 类型
+    uint8 AttributeIndex;// 属性索引
+    uint16 Stride;          // 步长
+    // 实例索引或顶点索引是否实例化的, 若是0, 则元素会对每个实例进行重复.
+    uint16 bUseInstanceIndex;
+
+    FVertexElement();
+    FVertexElement(uint8 InStreamIndex, ...);
+    
+    void operator=(const FVertexElement& Other);
+    friend FArchive& operator<<(FArchive& Ar,FVertexElement& Element);
+    
+    FString ToString() const;
+    void FromString(const FString& Src);
+    void FromString(const FStringView& Src);
+};
+
+// 顶点声明元素列表的类型.
+typedef TArray<FVertexElement,TFixedAllocator<MaxVertexElementCount> > FVertexDeclarationElementList;
+
+// Engine\Source\Runtime\RHI\Public\RHIResources.h
+// 顶点声明的RHI资源
+class FRHIVertexDeclaration : public FRHIResource
+{
+public:
+    virtual bool GetInitializer(FVertexDeclarationElementList& Init) { return false; }
+};
+
+// 顶点缓冲区
+class FRHIVertexBuffer : public FRHIResource
+{
+public:
+    FRHIVertexBuffer(uint32 InSize,uint32 InUsage);
+
+    uint32 GetSize() const;
+    uint32 GetUsage() const;
+
+protected:
+    FRHIVertexBuffer();
+
+    void Swap(FRHIVertexBuffer& Other);
+    void ReleaseUnderlyingResource();
+
+private:
+    // 尺寸.
+    uint32 Size;
+    // 缓冲区标记, 如BUF_UnorderedAccess
+    uint32 Usage;
+};
+
+// Engine\Source\Runtime\RenderCore\Public\VertexFactory.h
+// 顶点输入流.
+struct FVertexInputStream
+{
+    // 顶点流索引
+    uint32 StreamIndex : 4;
+    // 在VertexBuffer的偏移.
+    uint32 Offset : 28;
+    // 顶点缓存区
+    FRHIVertexBuffer* VertexBuffer;
+
+    FVertexInputStream();
+    FVertexInputStream(uint32 InStreamIndex, uint32 InOffset, FRHIVertexBuffer* InVertexBuffer);
+
+    inline bool operator==(const FVertexInputStream& rhs) const;
+    inline bool operator!=(const FVertexInputStream& rhs) const;
+};
+
+// 顶点输入流数组.
+typedef TArray<FVertexInputStream, TInlineAllocator<4>> FVertexInputStreamArray;
+
+// 顶点流标记
+enum class EVertexStreamUsage : uint8
+{
+    Default            = 0 << 0, // 默认
+    Instancing        = 1 << 0, // 实例化
+    Overridden        = 1 << 1, // 覆盖
+    ManualFetch        = 1 << 2  // 手动获取
+};
+
+// 顶点输入流类型.
+enum class EVertexInputStreamType : uint8
+{
+    Default = 0,  // 默认
+    PositionOnly, // 只有位置
+    PositionAndNormalOnly // 只有位置和法线
+};
+
+// 顶点流组件.
+struct FVertexStreamComponent
+{
+    // 流数据的顶点缓冲区, 如果为null, 则不会有数据从此顶点流被读取.
+    const FVertexBuffer* VertexBuffer = nullptr;
+
+    // vertex buffer的偏移.
+    uint32 StreamOffset = 0;
+    // 数据的偏移, 相对于顶点缓冲区中每个元素的开头.
+    uint8 Offset = 0;
+    // 数据的步长.
+    uint8 Stride = 0;
+    // 从流读取的数据类型.
+    TEnumAsByte<EVertexElementType> Type = VET_None;
+    // 顶点流标记.
+    EVertexStreamUsage VertexStreamUsage = EVertexStreamUsage::Default;
+
+    (......)
+};
+
+// 着色器使用的顶点工厂的参数绑定接口.
+class FVertexFactoryShaderParameters
+{
+public:
+    // 绑定参数到ParameterMap. 具体逻辑由子类完成.
+    void Bind(const class FShaderParameterMap& ParameterMap) {}
+
+    // 获取顶点工厂的着色器绑定和顶点流. 具体逻辑由子类完成.
+    void GetElementShaderBindings(
+        const class FSceneInterface* Scene,
+        const class FSceneView* View,
+        const class FMeshMaterialShader* Shader,
+        const EVertexInputStreamType InputStreamType,
+        ERHIFeatureLevel::Type FeatureLevel,
+        const class FVertexFactory* VertexFactory,
+        const struct FMeshBatchElement& BatchElement,
+        class FMeshDrawSingleShaderBindings& ShaderBindings,
+        FVertexInputStreamArray& VertexStreams) const {}
+
+    (......)
+};
+
+// 用来表示顶点工厂类型的类.
+class FVertexFactoryType
+{
+public:
+    // 类型定义
+    typedef FVertexFactoryShaderParameters* (*ConstructParametersType)(EShaderFrequency ShaderFrequency, const class FShaderParameterMap& ParameterMap);
+    typedef const FTypeLayoutDesc* (*GetParameterTypeLayoutType)(EShaderFrequency ShaderFrequency);
+    (......)
+
+    // 获取顶点工厂类型数量.
+    static int32 GetNumVertexFactoryTypes();
+
+    // 获取全局的着色器工厂列表.
+    static RENDERCORE_API TLinkedList<FVertexFactoryType*>*& GetTypeList();
+    // 获取已存的材质类型列表.
+    static RENDERCORE_API const TArray<FVertexFactoryType*>& GetSortedMaterialTypes();
+    // 通过名字查找FVertexFactoryType
+    static RENDERCORE_API FVertexFactoryType* GetVFByName(const FHashedName& VFName);
+
+    // 初始化FVertexFactoryType静态成员, 必须在VF类型创建之前调用.
+    static void Initialize(const TMap<FString, TArray<const TCHAR*> >& ShaderFileToUniformBufferVariables);
+    static void Uninitialize();
+
+    // 构造/析构函数.
+    RENDERCORE_API FVertexFactoryType(...);
+    virtual ~FVertexFactoryType();
+
+    // 数据获取接口.
+    const TCHAR* GetName() const;
+    FName GetFName() const;
+    const FHashedName& GetHashedName() const;
+    const TCHAR* GetShaderFilename() const;
+
+    // 着色器参数接口.
+    FVertexFactoryShaderParameters* CreateShaderParameters(...) const;
+    const FTypeLayoutDesc* GetShaderParameterLayout(...) const;
+    void GetShaderParameterElementShaderBindings(...) const;
+
+    // 标记访问.
+    bool IsUsedWithMaterials() const;
+    bool SupportsStaticLighting() const;
+    bool SupportsDynamicLighting() const;
+    bool SupportsPrecisePrevWorldPos() const;
+    bool SupportsPositionOnly() const;
+    bool SupportsCachingMeshDrawCommands() const;
+    bool SupportsPrimitiveIdStream() const;
+
+    // 获取哈希.
+    friend uint32 GetTypeHash(const FVertexFactoryType* Type);
+    // 基于顶点工厂类型的源码和包含计算出来的哈希.
+    const FSHAHash& GetSourceHash(EShaderPlatform ShaderPlatform) const;
+    // 是否需要缓存材质的着色器类型.
+    bool ShouldCache(const FVertexFactoryShaderPermutationParameters& Parameters) const;
+
+    void ModifyCompilationEnvironment(...);
+    void ValidateCompiledResult(EShaderPlatform Platform, ...);
+
+    bool SupportsTessellationShaders() const;
+
+    // 增加引用的Uniform Buffer包含.
+    void AddReferencedUniformBufferIncludes(...);
+    void FlushShaderFileCache(...);
+    const TMap<const TCHAR*, FCachedUniformBufferDeclaration>& GetReferencedUniformBufferStructsCache() const;
+
+private:
+    static uint32 NumVertexFactories;
+    static bool bInitializedSerializationHistory;
+
+    // 顶点工厂类型的各类数据和标记.
+    const TCHAR* Name;
+    const TCHAR* ShaderFilename;
+    FName TypeName;
+    FHashedName HashedName;
+    uint32 bUsedWithMaterials : 1;
+    uint32 bSupportsStaticLighting : 1;
+    uint32 bSupportsDynamicLighting : 1;
+    uint32 bSupportsPrecisePrevWorldPos : 1;
+    uint32 bSupportsPositionOnly : 1;
+    uint32 bSupportsCachingMeshDrawCommands : 1;
+    uint32 bSupportsPrimitiveIdStream : 1;
+    ConstructParametersType ConstructParameters;
+    GetParameterTypeLayoutType GetParameterTypeLayout;
+    GetParameterTypeElementShaderBindingsType GetParameterTypeElementShaderBindings;
+    ShouldCacheType ShouldCacheRef;
+    ModifyCompilationEnvironmentType ModifyCompilationEnvironmentRef;
+    ValidateCompiledResultType ValidateCompiledResultRef;
+    SupportsTessellationShadersType SupportsTessellationShadersRef;
+
+    // 全局顶点工厂类型列表.
+    TLinkedList<FVertexFactoryType*> GlobalListLink;
+    // 缓存引用的Uniform Buffer的包含.
+    TMap<const TCHAR*, FCachedUniformBufferDeclaration> ReferencedUniformBufferStructsCache;
+    // 跟踪ReferencedUniformBufferStructsCache缓存了哪些平台的声明.
+    bool bCachedUniformBufferStructDeclarations;
+};
+
+// ------顶点工厂的工具宏------
+// 实现顶点工厂参数类型
+#define IMPLEMENT_VERTEX_FACTORY_PARAMETER_TYPE(FactoryClass, ShaderFrequency, ParameterClass)
+// 顶点工厂类型的声明
+#define DECLARE_VERTEX_FACTORY_TYPE(FactoryClass)
+// 顶点工厂类型的实现
+#define IMPLEMENT_VERTEX_FACTORY_TYPE(FactoryClass,ShaderFilename,bUsedWithMaterials,bSupportsStaticLighting,bSupportsDynamicLighting,bPrecisePrevWorldPos,bSupportsPositionOnly)
+// 顶点工厂的虚函数表实现
+#define IMPLEMENT_VERTEX_FACTORY_VTABLE(FactoryClass
+
+// 顶点工厂
+class FVertexFactory : public FRenderResource
+{
+public:
+    FVertexFactory(ERHIFeatureLevel::Type InFeatureLevel);
+
+    virtual FVertexFactoryType* GetType() const;
+
+    // 获取顶点数据流.
+    void GetStreams(ERHIFeatureLevel::Type InFeatureLevel, EVertexInputStreamType VertexStreamType, FVertexInputStreamArray& OutVertexStreams) const
+    {
+        // Default顶点流类型
+        if (VertexStreamType == EVertexInputStreamType::Default)
+        {
+            bool bSupportsVertexFetch = SupportsManualVertexFetch(InFeatureLevel);
+
+            // 将顶点工厂的数据构造到FVertexInputStream中并添加到输出列表
+            for (int32 StreamIndex = 0;StreamIndex < Streams.Num();StreamIndex++)
+            {
+                const FVertexStream& Stream = Streams[StreamIndex];
+
+                if (!(EnumHasAnyFlags(EVertexStreamUsage::ManualFetch, Stream.VertexStreamUsage) && bSupportsVertexFetch))
+                {
+                    if (!Stream.VertexBuffer)
+                    {
+                        OutVertexStreams.Add(FVertexInputStream(StreamIndex, 0, nullptr));
+                    }
+                    else
+                    {
+                        if (EnumHasAnyFlags(EVertexStreamUsage::Overridden, Stream.VertexStreamUsage) && !Stream.VertexBuffer->IsInitialized())
+                        {
+                            OutVertexStreams.Add(FVertexInputStream(StreamIndex, 0, nullptr));
+                        }
+                        else
+                        {
+                            OutVertexStreams.Add(FVertexInputStream(StreamIndex, Stream.Offset, Stream.VertexBuffer->VertexBufferRHI));
+                        }
+                    }
+                }
+            }
+        }
+        // 只有位置和的顶点流类型
+        else if (VertexStreamType == EVertexInputStreamType::PositionOnly)
+        {
+            // Set the predefined vertex streams.
+            for (int32 StreamIndex = 0; StreamIndex < PositionStream.Num(); StreamIndex++)
+            {
+                const FVertexStream& Stream = PositionStream[StreamIndex];
+                OutVertexStreams.Add(FVertexInputStream(StreamIndex, Stream.Offset, Stream.VertexBuffer->VertexBufferRHI));
+            }
+        }
+        // 只有位置和法线的顶点流类型
+        else if (VertexStreamType == EVertexInputStreamType::PositionAndNormalOnly)
+        {
+            // Set the predefined vertex streams.
+            for (int32 StreamIndex = 0; StreamIndex < PositionAndNormalStream.Num(); StreamIndex++)
+            {
+                const FVertexStream& Stream = PositionAndNormalStream[StreamIndex];
+                OutVertexStreams.Add(FVertexInputStream(StreamIndex, Stream.Offset, Stream.VertexBuffer->VertexBufferRHI));
+            }
+        }
+        else
+        {
+            // NOT_IMPLEMENTED
+        }
+    }
+    
+    // 偏移实例的数据流.
+    void OffsetInstanceStreams(uint32 InstanceOffset, EVertexInputStreamType VertexStreamType, FVertexInputStreamArray& VertexStreams) const;
+    
+    static void ModifyCompilationEnvironment(...);
+    static void ValidateCompiledResult(...);
+
+    static bool SupportsTessellationShaders();
+
+    // FRenderResource接口, 释放RHI资源.
+    virtual void ReleaseRHI();
+
+    // 设置/获取顶点声明的RHI引用.
+    FVertexDeclarationRHIRef& GetDeclaration();
+    void SetDeclaration(FVertexDeclarationRHIRef& NewDeclaration);
+
+    // 根据类型获取顶点声明的RHI引用.
+    const FVertexDeclarationRHIRef& GetDeclaration(EVertexInputStreamType InputStreamType) const 
+    {
+        switch (InputStreamType)
+        {
+        case EVertexInputStreamType::Default:                return Declaration;
+        case EVertexInputStreamType::PositionOnly:            return PositionDeclaration;
+        case EVertexInputStreamType::PositionAndNormalOnly:    return PositionAndNormalDeclaration;
+        }
+        return Declaration;
+    }
+
+    // 各类标记.
+    virtual bool IsGPUSkinned() const;
+    virtual bool SupportsPositionOnlyStream() const;
+    virtual bool SupportsPositionAndNormalOnlyStream() const;
+    virtual bool SupportsNullPixelShader() const;
+
+    // 用面向摄像机精灵的方式渲染图元.
+    virtual bool RendersPrimitivesAsCameraFacingSprites() const;
+
+    // 是否需要顶点声明.
+    bool NeedsDeclaration() const;
+    // 是否支持手动的顶点获取.
+    inline bool SupportsManualVertexFetch(const FStaticFeatureLevel InFeatureLevel) const;
+    // 根据流类型获取索引.
+    inline int32 GetPrimitiveIdStreamIndex(EVertexInputStreamType InputStreamType) const;
+
+protected:
+    inline void SetPrimitiveIdStreamIndex(EVertexInputStreamType InputStreamType, int32 StreamIndex)
+    {
+        PrimitiveIdStreamIndex[static_cast<uint8>(InputStreamType)] = StreamIndex;
+    }
+
+    // 为顶点流组件创建顶点元素.
+    FVertexElement AccessStreamComponent(const FVertexStreamComponent& Component,uint8 AttributeIndex);
+    FVertexElement AccessStreamComponent(const FVertexStreamComponent& Component, uint8 AttributeIndex, EVertexInputStreamType InputStreamType);
+    // 初始化顶点声明.
+    void InitDeclaration(const FVertexDeclarationElementList& Elements, EVertexInputStreamType StreamType = EVertexInputStreamType::Default)
+    {
+        if (StreamType == EVertexInputStreamType::PositionOnly)
+        {
+            PositionDeclaration = PipelineStateCache::GetOrCreateVertexDeclaration(Elements);
+        }
+        else if (StreamType == EVertexInputStreamType::PositionAndNormalOnly)
+        {
+            PositionAndNormalDeclaration = PipelineStateCache::GetOrCreateVertexDeclaration(Elements);
+        }
+        else // (StreamType == EVertexInputStreamType::Default)
+        {
+            // Create the vertex declaration for rendering the factory normally.
+            Declaration = PipelineStateCache::GetOrCreateVertexDeclaration(Elements);
+        }
+    }
+
+    // 顶点流, 需要设置到顶点流的信息体.
+    struct FVertexStream
+    {
+        const FVertexBuffer* VertexBuffer = nullptr;
+        uint32 Offset = 0;
+        uint16 Stride = 0;
+        EVertexStreamUsage VertexStreamUsage = EVertexStreamUsage::Default;
+        uint8 Padding = 0;
+
+        friend bool operator==(const FVertexStream& A,const FVertexStream& B);
+        FVertexStream();
+    };
+
+    // 用于渲染顶点工厂的顶点流.
+    TArray<FVertexStream,TInlineAllocator<8> > Streams;
+
+    // VF(顶点工厂)可以显式地将此设置为false，以避免在没有声明的情况下出现错误. 主要用于需要直接从缓冲区获取数据的VF(如Niagara).
+    bool bNeedsDeclaration = true;
+    bool bSupportsManualVertexFetch = false;
+    int8 PrimitiveIdStreamIndex[3] = { -1, -1, -1 };
+
+private:
+    // 只有位置的顶点流, 用于渲染深度Pass的顶点工厂.
+    TArray<FVertexStream,TInlineAllocator<2> > PositionStream;
+    // 只有位置和法线的顶点流.
+    TArray<FVertexStream, TInlineAllocator<3> > PositionAndNormalStream;
+
+    // 用于常规渲染顶点工厂的RHI顶点声明.
+    FVertexDeclarationRHIRef Declaration;
+
+    // PositionStream和PositionAndNormalStream对应的RHI资源.
+    FVertexDeclarationRHIRef PositionDeclaration;
+    FVertexDeclarationRHIRef PositionAndNormalDeclaration;
+};
+```
+
+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？
+
+为了更好地说明它们之间的关系，以静态模型的FStaticMeshDataType为例：
+![[UE_VertexFactory_FStaticMeshDataType.jpg]]