196 lines
8.6 KiB
Markdown
196 lines
8.6 KiB
Markdown
---
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title: 剖析虚幻渲染体系（08）- Shader体系
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date: 2024-02-04 21:44:10
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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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原文地址:https://www.cnblogs.com/timlly/p/15092257.html
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# FShader
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```c++
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class FShader
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{
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public:
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// 在编译触发之前修改编译环境参数, 可由子类覆盖.
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static void ModifyCompilationEnvironment(const FShaderPermutationParameters&, FShaderCompilerEnvironment&) {}
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// 是否需要编译指定的排列, 可由子类覆盖.
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static bool ShouldCompilePermutation(const FShaderPermutationParameters&) { return true; }
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// 检测编译结果是否有效, 可由子类覆盖.
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static bool ValidateCompiledResult(EShaderPlatform InPlatform, const FShaderParameterMap& InParameterMap, TArray<FString>& OutError) { return true; }
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// 取得RayTracingPayloadType
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static ERayTracingPayloadType GetRayTracingPayloadType(const int32 PermutationId) { return static_cast<ERayTracingPayloadType>(0); }
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// 获取各类数据的Hash的接口.
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RENDERCORE_API const FSHAHash& GetHash() const;
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RENDERCORE_API const FSHAHash& GetVertexFactoryHash() const;
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RENDERCORE_API const FSHAHash& GetOutputHash() const;
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/** Returns an identifier suitable for deterministic sorting of shaders between sessions. */
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uint32 GetSortKey() const { return SortKey; }
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// 保存并检测shader代码的编译结果.
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RENDERCORE_API void Finalize(const FShaderMapResourceCode* Code);
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// 数据获取接口.
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inline FShaderType* GetType(const FShaderMapPointerTable& InPointerTable) const { return Type.Get(InPointerTable.ShaderTypes); }
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inline FShaderType* GetType(const FPointerTableBase* InPointerTable) const { return Type.Get(InPointerTable); }
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inline FVertexFactoryType* GetVertexFactoryType(const FShaderMapPointerTable& InPointerTable) const { return VFType.Get(InPointerTable.VFTypes); }
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inline FVertexFactoryType* GetVertexFactoryType(const FPointerTableBase* InPointerTable) const { return VFType.Get(InPointerTable); }
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inline FShaderType* GetTypeUnfrozen() const { return Type.GetUnfrozen(); }
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inline int32 GetResourceIndex() const { checkSlow(ResourceIndex != INDEX_NONE); return ResourceIndex; }
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inline EShaderPlatform GetShaderPlatform() const { return Target.GetPlatform(); }
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inline EShaderFrequency GetFrequency() const { return Target.GetFrequency(); }
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inline const FShaderTarget GetTarget() const { return Target; }
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inline bool IsFrozen() const { return Type.IsFrozen(); }
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inline uint32 GetNumInstructions() const { return NumInstructions; }
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#if WITH_EDITORONLY_DATA
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inline uint32 GetNumTextureSamplers() const { return NumTextureSamplers; }
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inline uint32 GetCodeSize() const { return CodeSize; }
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inline void SetNumInstructions(uint32 Value) { NumInstructions = Value; }
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#else
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inline uint32 GetNumTextureSamplers() const { return 0u; }
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inline uint32 GetCodeSize() const { return 0u; }
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#endif
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// 尝试返回匹配指定类型的自动绑定的Uniform Buffer, 如果不存在则返回未绑定的.
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template<typename UniformBufferStructType>
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FORCEINLINE_DEBUGGABLE const TShaderUniformBufferParameter<UniformBufferStructType>& GetUniformBufferParameter() const
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{
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const FShaderUniformBufferParameter& FoundParameter = GetUniformBufferParameter(UniformBufferStructType::FTypeInfo::GetStructMetadata());
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return static_cast<const TShaderUniformBufferParameter<UniformBufferStructType>&>(FoundParameter);
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}
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FORCEINLINE_DEBUGGABLE const FShaderUniformBufferParameter& GetUniformBufferParameter(const FShaderParametersMetadata* SearchStruct) const
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{
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const FHashedName SearchName = SearchStruct->GetShaderVariableHashedName();
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return GetUniformBufferParameter(SearchName);
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}
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FORCEINLINE_DEBUGGABLE const FShaderUniformBufferParameter& GetUniformBufferParameter(const FHashedName SearchName) const
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{
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int32 FoundIndex = INDEX_NONE;
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TArrayView<const FHashedName> UniformBufferParameterStructsView(UniformBufferParameterStructs);
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for (int32 StructIndex = 0, Count = UniformBufferParameterStructsView.Num(); StructIndex < Count; StructIndex++)
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{
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if (UniformBufferParameterStructsView[StructIndex] == SearchName)
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{
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FoundIndex = StructIndex;
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break;
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}
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}
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if (FoundIndex != INDEX_NONE)
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{
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const FShaderUniformBufferParameter& FoundParameter = UniformBufferParameters[FoundIndex];
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return FoundParameter;
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}
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else
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{
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// This can happen if the uniform buffer was not bound
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// There's no good way to distinguish not being bound due to temporary debugging / compiler optimizations or an actual code bug,
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// Hence failing silently instead of an error message
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static FShaderUniformBufferParameter UnboundParameter;
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return UnboundParameter;
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}
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}
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RENDERCORE_API const FShaderParametersMetadata* FindAutomaticallyBoundUniformBufferStruct(int32 BaseIndex) const;
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RENDERCORE_API void DumpDebugInfo(const FShaderMapPointerTable& InPtrTable);
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#if WITH_EDITOR
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RENDERCORE_API void SaveShaderStableKeys(const FShaderMapPointerTable& InPtrTable, EShaderPlatform TargetShaderPlatform, int32 PermutationId, const struct FStableShaderKeyAndValue& SaveKeyVal);
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#endif // WITH_EDITOR
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/** Returns the meta data for the root shader parameter struct. */
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static inline const FShaderParametersMetadata* GetRootParametersMetadata()
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{
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return nullptr;
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}
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private:
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RENDERCORE_API void BuildParameterMapInfo(const TMap<FString, FParameterAllocation>& ParameterMap);
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public:
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// 着色器参数绑定.
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LAYOUT_FIELD(FShaderParameterBindings, Bindings);
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// 着色器参数绑定的映射信息.
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LAYOUT_FIELD(FShaderParameterMapInfo, ParameterMapInfo);
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protected:
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LAYOUT_FIELD(TMemoryImageArray<FHashedName>, UniformBufferParameterStructs);
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LAYOUT_FIELD(TMemoryImageArray<FShaderUniformBufferParameter>, UniformBufferParameters);
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// 下面3个是编辑器参数.
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// 着色器的编译输出和结果参数映射的哈希值, 用于查找匹配的资源.
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LAYOUT_FIELD_EDITORONLY(FSHAHash, OutputHash);
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// 顶点工厂资源哈希值
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LAYOUT_FIELD_EDITORONLY(FSHAHash, VFSourceHash);
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// Shader资源哈希值.
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LAYOUT_FIELD_EDITORONLY(FSHAHash, SourceHash);
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private:
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// 着色器类型.
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LAYOUT_FIELD(TIndexedPtr<FShaderType>, Type);
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// 顶点工厂类型.
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LAYOUT_FIELD(TIndexedPtr<FVertexFactoryType>, VFType);
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// 目标平台和着色频率(frequency).
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LAYOUT_FIELD(FShaderTarget, Target);
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// 在FShaderMapResource的shader索引.
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LAYOUT_FIELD(int32, ResourceIndex);
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// shader指令数.
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LAYOUT_FIELD(uint32, NumInstructions);
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/** Truncated version of OutputHash, intended for sorting. Not suitable for unique shader identification. */
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LAYOUT_FIELD(uint32, SortKey);
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// 纹理采样器数量.
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LAYOUT_FIELD_EDITORONLY(uint32, NumTextureSamplers);
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// shader代码尺寸.
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LAYOUT_FIELD_EDITORONLY(uint32, CodeSize);
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};
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```
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以上可知，FShader存储着Shader关联的绑定参数、顶点工厂、编译后的各类资源等数据，并提供了编译器修改和检测接口，还有各类数据获取接口。
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FShader实际上是个基础父类，它的子类有：
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- **FGlobalShader**：全局着色器，它的子类在内存中只有唯一的实例，常用于屏幕方块绘制、后处理等。相比父类FShader，增加了SetParameters设置视图统一缓冲的接口。FGlobalShader包含了后处理、光照、工具类、可视化、地形、虚拟纹理等方面的Shader代码，可以是VS、PS、CS，但CS必然是FGlobalShader的子类
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- **FMaterialShader**：材质着色器，由FMaterialShaderType指定的材质引用的着色器，是材质蓝图在实例化后的一个shader子集。FMaterialShader主要包含了模型、专用Pass、体素化等方面的Shader代码，可以是VS、PS、GS等，但不会有CS。
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## Shader Parameter
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位于`Engine\Source\Runtime\RenderCore\Public\ShaderParameters.h`。
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- FShaderParameter：着色器的寄存器绑定参数, 它的类型可以是float1/2/3/4，数组等。
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- FShaderResourceParameter：着色器资源绑定(纹理或采样器)。
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- FRWShaderParameter：绑定了UAV或SRV资源的类型。
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- FShaderUniformBufferParameter：着色器统一缓冲参数。
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## Uniform Buffer
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位于`Engine\Source\Runtime\RHI\Public\RHIResources.h`。
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UE的Uniform Buffer涉及了几个核心的概念，最底层的是RHI层的FRHIUniformBuffer，封装了各种图形API的统一缓冲区（也叫Constant Buffer）。
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```c++
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class FRHIUniformBuffer : public FRHIResource
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{
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public:
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// 构造函数.
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FRHIUniformBuffer(const FRHIUniformBufferLayout& InLayout);
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// 引用计数操作.
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uint32 AddRef() const;
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uint32 Release() const;
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// 数据获取接口.
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uint32 GetSize() const;
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const FRHIUniformBufferLayout& GetLayout() const;
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bool IsGlobal() const;
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private:
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// RHI Uniform Buffer的布局.
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const FRHIUniformBufferLayout* Layout;
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// 缓冲区尺寸.
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uint32 LayoutConstantBufferSize;
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};
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``` |