ue metal feature level

   if (Input.ShaderFormat == NAME_SF_METAL || Input.ShaderFormat == NAME_SF_METAL_TVOS)
    {
        UE_CLOG(VersionEnum < 2, LogShaders, Warning, TEXT("Metal shader version must be Metal v1.2 or higher for format %s!"), VersionEnum, *Input.ShaderFormat.ToString());
        VersionEnum = VersionEnum >= 2 ? VersionEnum : 2;
        AdditionalDefines.SetDefine(TEXT("METAL_PROFILE"), 1);
    }
    else if (Input.ShaderFormat == NAME_SF_METAL_MRT || Input.ShaderFormat == NAME_SF_METAL_MRT_TVOS)
    {
        UE_CLOG(VersionEnum < 2, LogShaders, Warning, TEXT("Metal shader version must be Metal v1.2 or higher for format %s!"), VersionEnum, *Input.ShaderFormat.ToString());
        AdditionalDefines.SetDefine(TEXT("METAL_MRT_PROFILE"), 1);
        VersionEnum = VersionEnum >= 2 ? VersionEnum : 2;
        MetalCompilerTarget = HCT_FeatureLevelSM5;
        Semantics = EMetalGPUSemanticsTBDRDesktop;
    }
    else if (Input.ShaderFormat == NAME_SF_METAL_MACES3_1)
    {
        UE_CLOG(VersionEnum < 3, LogShaders, Warning, TEXT("Metal shader version must be Metal v2.0 or higher for format %s!"), VersionEnum, *Input.ShaderFormat.ToString());
        AdditionalDefines.SetDefine(TEXT("METAL_PROFILE"), 1);
        VersionEnum = VersionEnum > 3 ? VersionEnum : 3;
        MetalCompilerTarget = HCT_FeatureLevelES3_1;
        Semantics = EMetalGPUSemanticsImmediateDesktop;
    }
    else if (Input.ShaderFormat == NAME_SF_METAL_SM5_NOTESS)
    {
        UE_CLOG(VersionEnum < 3, LogShaders, Warning, TEXT("Metal shader version must be Metal v2.0 or higher for format %s!"), VersionEnum, *Input.ShaderFormat.ToString());
        AdditionalDefines.SetDefine(TEXT("METAL_SM5_NOTESS_PROFILE"), 1);
        AdditionalDefines.SetDefine(TEXT("USING_VERTEX_SHADER_LAYER"), 1);
        VersionEnum = VersionEnum > 3 ? VersionEnum : 3;
        MetalCompilerTarget = HCT_FeatureLevelSM5;
        Semantics = EMetalGPUSemanticsImmediateDesktop;
    }
    else if (Input.ShaderFormat == NAME_SF_METAL_SM5)
    {
        UE_CLOG(VersionEnum < 3, LogShaders, Warning, TEXT("Metal shader version must be Metal v2.0 or higher for format %s!"), VersionEnum, *Input.ShaderFormat.ToString());
        AdditionalDefines.SetDefine(TEXT("METAL_SM5_PROFILE"), 1);
        AdditionalDefines.SetDefine(TEXT("USING_VERTEX_SHADER_LAYER"), 1);
        VersionEnum = VersionEnum > 3 ? VersionEnum : 3;
        MetalCompilerTarget = HCT_FeatureLevelSM5;
        Semantics = EMetalGPUSemanticsImmediateDesktop;
    }
    else if (Input.ShaderFormat == NAME_SF_METAL_MRT_MAC)
    {
        UE_CLOG(VersionEnum < 3, LogShaders, Warning, TEXT("Metal shader version must be Metal v2.0 or higher for format %s!"), VersionEnum, *Input.ShaderFormat.ToString());
        AdditionalDefines.SetDefine(TEXT("METAL_MRT_PROFILE"), 1);
        VersionEnum = VersionEnum > 3 ? VersionEnum : 3;
        MetalCompilerTarget = HCT_FeatureLevelSM5;
        Semantics = EMetalGPUSemanticsTBDRDesktop;
    }

#if PS4_PROFILE
    #define FEATURE_LEVEL FEATURE_LEVEL_SM5

#elif SM5_PROFILE
    // SM5 = full dx11 features (high end UE4 rendering)
    #define FEATURE_LEVEL FEATURE_LEVEL_SM5

#elif SM4_PROFILE
    #define FEATURE_LEVEL FEATURE_LEVEL_SM4

#elif SWITCH_PROFILE || SWITCH_PROFILE_FORWARD
    #undef ES3_1_PROFILE

    #if SWITCH_PROFILE
        #define FEATURE_LEVEL FEATURE_LEVEL_SM5
    #else
        #define FEATURE_LEVEL FEATURE_LEVEL_ES3_1
        // @todo switch: maybe all uses of this should check feature level not profile?
        #define ES3_1_PROFILE 1
    #endif

#elif VULKAN_PROFILE
    #define FEATURE_LEVEL FEATURE_LEVEL_ES3_1
    // @todo: replace usage of ES3_1_PROFILE with FEATURE_LEVEL where appropriate
    #undef ES3_1_PROFILE
    #define ES3_1_PROFILE 1 

#elif VULKAN_PROFILE_SM5
    #define FEATURE_LEVEL FEATURE_LEVEL_SM5
    #define STENCIL_COMPONENT_SWIZZLE .x

#elif METAL_PROFILE
    #define FEATURE_LEVEL  FEATURE_LEVEL_ES3_1
    // @todo metal: remove this and make sure all uses handle METAL_PROFILE
    #undef ES3_1_PROFILE
    #define ES3_1_PROFILE 1
#if MAX_SHADER_LANGUAGE_VERSION >= 3
    #define FCOLOR_COMPONENT_SWIZZLE .rgba
#else
    #define FCOLOR_COMPONENT_SWIZZLE .bgra
#endif
    #define FMANUALFETCH_COLOR_COMPONENT_SWIZZLE .bgra
    #define STENCIL_COMPONENT_SWIZZLE .x

#elif METAL_MRT_PROFILE
    #define FEATURE_LEVEL FEATURE_LEVEL_SM5
#if MAX_SHADER_LANGUAGE_VERSION >= 3
    #define FCOLOR_COMPONENT_SWIZZLE .rgba
#else
    #define FCOLOR_COMPONENT_SWIZZLE .bgra
#endif
    #define FMANUALFETCH_COLOR_COMPONENT_SWIZZLE .bgra
    #define STENCIL_COMPONENT_SWIZZLE .x

#elif METAL_SM5_NOTESS_PROFILE
    #define FEATURE_LEVEL FEATURE_LEVEL_SM5
    #define FCOLOR_COMPONENT_SWIZZLE .rgba
    #define FMANUALFETCH_COLOR_COMPONENT_SWIZZLE .bgra
    #define STENCIL_COMPONENT_SWIZZLE .x

#elif METAL_SM5_PROFILE
    #define FEATURE_LEVEL FEATURE_LEVEL_SM5
    #define FCOLOR_COMPONENT_SWIZZLE .rgba
    #define FMANUALFETCH_COLOR_COMPONENT_SWIZZLE .bgra
    #define STENCIL_COMPONENT_SWIZZLE .x

#elif ES3_1_PROFILE
    #define FEATURE_LEVEL FEATURE_LEVEL_ES3_1

    #if COMPILER_GLSL_ES3_1
        #define FCOLOR_COMPONENT_SWIZZLE .bgra  
        #define FMANUALFETCH_COLOR_COMPONENT_SWIZZLE .bgra
    #else 
        #define FCOLOR_COMPONENT_SWIZZLE .rgba
        #define FMANUALFETCH_COLOR_COMPONENT_SWIZZLE .bgra
    #endif

    #if COMPILER_GLSL || COMPILER_GLSL_ES3_1
        // A8 textures when sampled have their component in R
        #define A8_SAMPLE_MASK .r
    #endif
#elif VECTORVM_PROFILE
    #define FEATURE_LEVEL FEATURE_LEVEL_SM5
#endif

SM5---dx11

metal_MRT_Profile  sm5 tbdrDesktop 这俩不确定

metal_sm5_noTess_Profile   no tessellation

metal_sm5_profile 就是ios desktop renderer 的sm5  

metal_Profile es31

shader这里 metal的有三种

 metal sm5 ---basepass desktop  mac上的desktop renderer

metal ---metal低版本---mobilebasepass ---gl_LastFragDataR_4 SceneDepth放这里 Mobile deferred 也是这个 ps里用这个(METAL_PROFILE && !MAC) && PIXELSHADER

metal MRT---basepass   Mobile deferred SceneTextureStruct_SceneDepthTexture. ---这个就是mobile desktop renderer on mobile (METAL_MRT_PROFILE&& !MAC) && PIXELSHADER

 不一样的shader编号

不同quality同样编号