Shader compilation code flow

  • Initializes FHLSLMaterialTranslator()

  • Set up which material properties are shared (ex: SharedPixelProperties[MP_Normal] = true;)

  • Calls FHLSLMaterialTranslator::Translate(): Translate from Material Node graph into textual shader code representation

  • Material->GatherExpressionsForCustomInterpolators(Expressions);

  • GatherCustomVertexInterpolators(Expressions);

  • Material->GatherCustomOutputExpressions(CustomOutputExpressions);

  • CompileCustomOutputs(CustomOutputExpressions, SeenCustomOutputExpressionsClases, true);

  • Material->CompilePropertyAndSetMaterialProperty() on MP_Normal, MP_DiffuseColor, MP_Specular, MP_Roughness, etc

  • Determines if properties are actually used && validation checking. Eg:

    bUsesEmissiveColor = IsMaterialPropertyUsed(MP_EmissiveColor, Chunk[MP_EmissiveColor], FLinearColor(0, 0, 0, 0), 3);

  • Determines number of vertex interpolators/uv tex coords/etc

  • MaterialCompilationOutput.UniformExpressionSet.SetParameterCollections(ParameterCollections);

  • MaterialCompilationOutput.UniformExpressionSet.CreateBufferStruct();

  • Calls FHLSLMaterialTranslator::GetMaterialEnvironment()

  • Sets more fundamental defines such as: NEEDS_PARTICLE_POSITION, NEEDS_SCENE_TEXTURES, USES_TRANSFORM_VECTOR, USES_EMISSIVE_COLOR

  • Add uniform buffer declarations for any parameter collections referenced

    const FString CollectionName = FString::Printf(TEXT(“MaterialCollection%u”), CollectionIndex);

    FShaderUniformBufferParameter::ModifyCompilationEnvironment(*CollectionName, ParameterCollections[CollectionIndex]->GetUniformBufferStruct(), InPlatform, OutEnvironment); - Calls FHLSLMaterialTranslator::GetMaterialShaderCode():

  • Responsible for compiling and filling MaterialTemplate.ush

  • Uses LazyPrintf.PushParam() and Printf() to stringify everything into the generated Material.ush file

  • GetSharedInputsMaterialCode():

    • Generates the fields for FPixelMaterialInputs which are shared properties across the shader (like MP_Normal, MP_BaseColor, MP_Roughness, etc)

    • Generates initializers for them too

  • Calls main compilation in NewShaderMap->Compile():

  • Material->SetupMaterialEnvironment(): Sets majority of shader defines (including material specific ones like staticswitches, etc) by calling. Ex:

  • Defines from the umaterial uproperties such as: MATERIAL_TWOSIDED, MATERIAL_NONMETAL, MATERIAL_HQ_FORWARD_REFLECTIONS

  • Defines from the material itself such as: GetBlendMode() => MATERIALBLENDING_MASKED|MATERIALBLENDING_SOLID, MATERIAL_FULLY_ROUGH

  • Defines also fundamental things such as MATERIAL_DOMAIN_SURFACE|MATERIAL_DOMAIN_DEFERREDDECAL|… & MATERIAL_SHADINGMODEL_UNLIT|MATERIAL_SHADINGMODEL_DEFAULT_LIT|…

  • Also uses cvar values to determine whether to set defines or not: r.StencilForLODDither => USE_STENCIL_LOD_DITHER_DEFAULT

  • Iterate over all vertex factories and materials and compile them together if this material applies


Last update: November 14, 2019