Adding a new Shading Model

本文主要记录了UE5如何通过修改源代码添加自己的shadingmodel~本文会先梳理下添加ShadingModel所需文件及其相关用途再进行相关介绍，了解过的朋友可直接跳转第二章开始。

1.文件梳理

EngineTypes.h ：存储引擎中类型集合，在这里需要添加ShaderingModel
MaterialShader.cpp : 负责材质相关属性声明
HLSLMaterialTranslator.cpp : 负责控制材质C++侧到hlsl侧的数据传递
ShaderMaterial.h : 声明材质相关定义
Material.cpp ：Material 相关设置
ShaderMaterialDerivedHelpers.cpp ：声明处理相关材质parameter
ShadingCommon.ush : Shading Common 数据包括共用的ShadingModel 和相关函数
BasePassPixelShader.usf ：Base Pass Pixel Shader 相关
ShadingModelsMaterial.ush ：对GBuffer相关设置
BasePassCommon.ush ：BasePass相关共用数据声明
DeferredShadingCommon.ush ：声明GBuffer数据及相关DeferredRendering数据函数
Definitions.usf ：定义各种材质的宏
ClusteredDeferredShadingPixelShader.usf ：Defer Rendering Pixel Shader相关光照处理
ShadingModels.ush : 负责处理不同ShadingModel分类

2.新增 MaterialShadingModel

在 EngineTypes.h 中新增自己的ShadingModel类型

添加后编译即可在ShadingModel中找到自己的ShadingModel

Note ：这里需要在MSM_NUM 之前进行添加，否则会报check(InShadingModel < MSM_NUM)检查导致没法Hack

然后在 MaterialShader.cpp 文件中GetShadingModelString中添加相关声明，Note：名字必须相同

在 HLSLMaterialTranslator.cpp 文件，这里需要找到FHLSLMaterialTranslator::GetMaterialEnvironment 函数并为shadingmodel添加相关defined

在 ShaderMaterial.h 中 FShaderMaterialPropertyDefines 声明映射：

3.开启CustomData 接口

在 Material.cpp 中找到IsPropertyActive_Internal函数，在switch中找到相关接口，并输入自己新shadingModel。

这一步是为了激活接口在不同ShadingModel中的使用情况。

2.1 设置CustomData接口名字

打开 MaterialShared.cpp ，在GetAttributeOverrideForMaterial函数中case MP_CustomData0中添加CustomPinNames。该函数控制在Editor中切换不同模式下Pin接口的可用情况。这里Add第一个是ShadingModel , 第二个是接口展示的名字。

case MP_CustomData0:	
		CustomPinNames.Add({ MSM_ClearCoat, "Clear Coat" });
		CustomPinNames.Add({MSM_Hair, "Backlit"});
		CustomPinNames.Add({MSM_Cloth, "Cloth"});
		CustomPinNames.Add({MSM_Eye, "Iris Mask"});
		CustomPinNames.Add({MSM_SubsurfaceProfile, "Curvature" });
		CustomPinNames.Add({MSM_StylizedShadow, "MyStylizedShadow" });
		return FText::FromString(GetPinNameFromShadingModelField(Material->GetShadingModels(), CustomPinNames, "Custom Data 0"));

在 ShaderMaterialDerivedHelpers.cpp 文件中修改Custom Node 相关映射。

1
2

// Only some shader models actually need custom data.
	Dst.WRITES_CUSTOMDATA_TO_GBUFFER = (Dst.USES_GBUFFER && (Mat.MATERIAL_SHADINGMODEL_SUBSURFACE || Mat.MATERIAL_SHADINGMODEL_PREINTEGRATED_SKIN || Mat.MATERIAL_SHADINGMODEL_SUBSURFACE_PROFILE || Mat.MATERIAL_SHADINGMODEL_CLEAR_COAT || Mat.MATERIAL_SHADINGMODEL_TWOSIDED_FOLIAGE || Mat.MATERIAL_SHADINGMODEL_HAIR || Mat.MATERIAL_SHADINGMODEL_CLOTH || Mat.MATERIAL_SHADINGMODEL_EYE || Mat.MATERIAL_SHADINGMODEL_STYLIZED_SHAODW));

3.设置 GBuffer Shading Model ID

打开 ShadingCommone.ush 文件在Shading Model的定义中添加自己的定义

然后在GetShadingModelColor(uint ShadingModelID) 中修改 ShadingModel ID的颜色

然后在 BasePassPixelShader.usf 中找到GetMaterialShadingModel 并进行声明 ShadingModel

#if MATERIAL_SHADINGMODEL_STYLIZED_SHADOW
	uint ShadingModel = SHADINGMODELID_STYLIZED_SHADOW;
#else
	uint ShadingModel = GetMaterialShadingModel(PixelMaterialInputs);
#endif

3.1将CustomData数据写入GBuffer

接下来打开 ShadingModelsMaterial.ush 。查看SetGBufferForShadingModel函数。该函数控制不同shadingModel写入FGbufferData的数据。

#if MATERIAL_SHADINGMODEL_STYLIZED_SHADOW
	else if (ShadingModel == SHADINGMODEL_STYLIZED_SHADOW)
	{
		GBuffer.ShadingModelID = SHADINGMODELID_STYLIZED_SHADOW;
		GBuffer.CustomData.x = GetMaterialCustomData0(MaterialParameters);
	}
#endif

这里使用GetMaterialCustomData0来获取CustomData0的输入，并将其存放到GBuffer.CustomData中

然后在 BasePassCommon.ush 中的#define WRITES_CUSTOMDATA_TO_GBUFFER 添加 MATERIAL_SHADINGMODEL_STYLIZED_SHADOW。

#define WRITES_CUSTOMDATA_TO_GBUFFER        (USES_GBUFFER && (MATERIAL_SHADINGMODEL_SUBSURFACE || MATERIAL_SHADINGMODEL_PREINTEGRATED_SKIN || MATERIAL_SHADINGMODEL_SUBSURFACE_PROFILE || MATERIAL_SHADINGMODEL_CLEAR_COAT || MATERIAL_SHADINGMODEL_TWOSIDED_FOLIAGE || MATERIAL_SHADINGMODEL_HAIR || MATERIAL_SHADINGMODEL_CLOTH || MATERIAL_SHADINGMODEL_EYE || SHADINGMODELID_STYLIZED_SHADOW))

4.修改 CustomGBufferData 数据

DeferredShadingCommon.ush 修改HasCustomGBufferData函数，支持SHADINGMODELID_STYLIZED_SHADOW写入

bool HasCustomGBufferData(int ShadingModelID)
{
  return ShadingModelID == SHADINGMODELID_SUBSURFACE
    || ShadingModelID == SHADINGMODELID_PREINTEGRATED_SKIN
    || ShadingModelID == SHADINGMODELID_CLEAR_COAT
    || ShadingModelID == SHADINGMODELID_SUBSURFACE_PROFILE
    || ShadingModelID == SHADINGMODELID_TWOSIDED_FOLIAGE
    || ShadingModelID == SHADINGMODELID_HAIR
    || ShadingModelID == SHADINGMODELID_CLOTH
    || ShadingModelID == SHADINGMODELID_EYE
    || ShadingModelID == SHADINGMODELID_STYLIZED_SHADOW;
}

5.其他声明

打开 ShaderGenerationUtil.cpp 文件，找到ApplyFetchEnvironment 并在其中声明 Shader Compile

同时到 DetermineUsedMaterialSlots 函数中添加对象slot

然后在 Definitions.usf 中声明

6.光照修改

从这里开始计算光照部分的修改：

6.1获取光源数据

在 Engine\Shaders\Private\ClusteredDeferredShadingPixelShader.usf 的 ClusteredShadingPixelShader 函数中添加我们的着色模型。

6.2着色计算

打开 ShadingModels.ush 在其中的IntegrateBxDF 函数中添加相关着色类型：

接下来是StylizedShadowBxDF 相关渲染代码，这里直接参考dalao文章

code

FDirectLighting StylizedShadowBxDF(FGBufferData GBuffer, half3 N, half3 V, half3 L, float Falloff, float NoL, FAreaLight AreaLight, FShadowTerms Shadow)
{
#if GBUFFER_HAS_TANGENT
	half3 X = GBuffer.WorldTangent;
	half3 Y = normalize(cross(N, X));
#else
	half3 X = 0;
	half3 Y = 0;
#endif
	
	BxDFContext Context;

	Init(Context, N, X, Y, V, L);
	
	SphereMaxNoH(Context, AreaLight.SphereSinAlpha, true);
	Context.NoV = saturate(abs(Context.NoV) + 0.00001);

	float SpecularOffset = 0.5;
	float SpecularRange = GBuffer.CustomData.x;

	float3 ShadowColor = 0;
	
	ShadowColor = GBuffer.DiffuseColor * ShadowColor;
	float offset = GBuffer.CustomData.y;
	float SoftScatterStrength = 0;

	offset = offset * 2 - 1;
	half3 H = normalize(V + L);
	float NoH = saturate(dot(N, H));
	NoL = (dot(N, L) + 1) / 2; // overwrite NoL To Get more range out Of it
	half NoLOffset = saturate(NoL + offset);
	
	FDirectLighting Lighting;
	Lighting.Diffuse = AreaLight.FalloffColor * (smoothstep(0, 1, NoLOffset) * Falloff) * Diffuse_Lambert(GBuffer.DiffuseColor) * 2.2;
	float InScatter = pow(saturate(dot(L, -V)), 12) * lerp(3, 0.1F, 1);
	float NormalContribution = saturate(dot(N, H));
	float BackScatter = GBuffer.GBufferAO * NormalContribution / (PI * 2);
	Lighting.Specular = ToonStep(SpecularRange, (saturate(D_GGX(SpecularOffset, NoH)))) * (AreaLight.FalloffColor * GBuffer.SpecularColor * Falloff * 8);
	float3 TransmissionSoft = AreaLight.FalloffColor * (Falloff * lerp(BackScatter, 1, InScatter)) * ShadowColor * SoftScatterStrength;
	float3 ShadowLightener = 0;
	ShadowLightener = (saturate(smoothstep(0, 1, saturate(1 - NoLOffset))) * ShadowColor * 0.1);
	
	Lighting.Transmission = (ShadowLightener + TransmissionSoft) * Falloff;
	return Lighting;
}

打开DeferredLightingCommon.ush ，并找到GetDynamicLighting函数，在其中的 GetDynamicLightingSplit，添加相关case 进行分类

code

/** Calculates lighting for a given position, normal, etc with a fully featured lighting model designed for quality. */
FDeferredLightingSplit GetDynamicLightingSplit(
	float3 TranslatedWorldPosition, float3 CameraVector, FGBufferData GBuffer, float AmbientOcclusion, uint ShadingModelID, 
	FDeferredLightData LightData, float4 LightAttenuation, float Dither, uint2 SVPos, FRectTexture SourceTexture,
	inout float SurfaceShadow)
{
	FLightAccumulator LightAccumulator = (FLightAccumulator)0;

	float3 V = -CameraVector;
	float3 N = GBuffer.WorldNormal;
	BRANCH if( GBuffer.ShadingModelID == SHADINGMODELID_CLEAR_COAT && CLEAR_COAT_BOTTOM_NORMAL)
	{
		const float2 oct1 = ((float2(GBuffer.CustomData.a, GBuffer.CustomData.z) * 2) - (256.0/255.0)) + UnitVectorToOctahedron(GBuffer.WorldNormal);
		N = OctahedronToUnitVector(oct1);			
	}
	
	float3 L = LightData.Direction;	// Already normalized
	float3 ToLight = L;
	
	float LightMask = 1;
	if (LightData.bRadialLight)
	{
		LightMask = GetLocalLightAttenuation( TranslatedWorldPosition, LightData, ToLight, L );
	}

	LightAccumulator.EstimatedCost += 0.3f;		// running the PixelShader at all has a cost
	
	BRANCH
	if( LightMask > 0 )
	{
		FShadowTerms Shadow;
		Shadow.SurfaceShadow = AmbientOcclusion;
		Shadow.TransmissionShadow = 1;
		Shadow.TransmissionThickness = 1;
		Shadow.HairTransmittance.OpaqueVisibility = 1;
		const float ContactShadowOpacity = GBuffer.CustomData.a;
		GetShadowTerms(GBuffer.Depth, GBuffer.PrecomputedShadowFactors, GBuffer.ShadingModelID, ContactShadowOpacity,
			LightData, TranslatedWorldPosition, L, LightAttenuation, Dither, Shadow);
		SurfaceShadow = Shadow.SurfaceShadow;

		LightAccumulator.EstimatedCost += 0.3f;		// add the cost of getting the shadow terms

		BRANCH
		if( Shadow.SurfaceShadow + Shadow.TransmissionShadow > 0 )
		{
			const bool bNeedsSeparateSubsurfaceLightAccumulation = UseSubsurfaceProfile(GBuffer.ShadingModelID);
			float3 LightColor = LightData.Color;

			// ****************** start here  ********************* //
			// STYLIZEDSHADOW SHADING 
			float3 Attenuation = 1;
			BRANCH
			if (GBuffer.ShadingModelID == SHADINGMODELID_STYLIZED_SHADOW)
			{
				 
				  float offset = GBuffer.CustomData.x;
				  float TerminatorRange = saturate(GBuffer.Roughness - 0.5);
  
				  offset = offset * 2 - 1;
  
				  BRANCH
				  if (offset >= 1)
				  {
					Attenuation = 1;
				  }
				  else
				  {
					float NoL = (dot(N, L) + 1) / 2;
					float NoLOffset = saturate(NoL + offset);
					float LightAttenuationOffset = saturate( Shadow.SurfaceShadow + offset);
					float ToonSurfaceShadow = smoothstep(0.5 - TerminatorRange, 0.5 + TerminatorRange, LightAttenuationOffset);

					Attenuation = smoothstep(0.5 - TerminatorRange, 0.5 + TerminatorRange, NoLOffset) * ToonSurfaceShadow;
				  }
			}
		// ****************** end here  ********************* //
		#if NON_DIRECTIONAL_DIRECT_LIGHTING
			float Lighting;

			if( LightData.bRectLight )
			{
				FRect Rect = GetRect( ToLight, LightData );

				Lighting = IntegrateLight( Rect, SourceTexture);
			}
			else
			{
				FCapsuleLight Capsule = GetCapsule( ToLight, LightData );

				Lighting = IntegrateLight( Capsule, LightData.bInverseSquared );
			}

			float3 LightingDiffuse = Diffuse_Lambert( GBuffer.DiffuseColor ) * Lighting;
		// ****************** start here  ********************* //
			LightAccumulator_AddSplit(LightAccumulator, LightingDiffuse, 0.0f, 0, LightColor * LightMask * Shadow.SurfaceShadow * Attenuation, bNeedsSeparateSubsurfaceLightAccumulation);
		// ****************** end here  ********************* //
		#else
			FDirectLighting Lighting;

			if (LightData.bRectLight)
			{
				FRect Rect = GetRect( ToLight, LightData );

				#if REFERENCE_QUALITY
					Lighting = IntegrateBxDF( GBuffer, N, V, Rect, Shadow, SourceTexture, SVPos );
				#else
					Lighting = IntegrateBxDF( GBuffer, N, V, Rect, Shadow, SourceTexture);
				#endif
			}
			else
			{
				FCapsuleLight Capsule = GetCapsule( ToLight, LightData );

				#if REFERENCE_QUALITY
					Lighting = IntegrateBxDF( GBuffer, N, V, Capsule, Shadow, SVPos );
				#else
					Lighting = IntegrateBxDF( GBuffer, N, V, Capsule, Shadow, LightData.bInverseSquared );
				#endif
			}

			Lighting.Specular *= LightData.SpecularScale;
			// ****************** start here  ********************* //
			LightAccumulator_AddSplit( LightAccumulator, Lighting.Diffuse, Lighting.Specular, Lighting.Diffuse, LightColor * LightMask * Shadow.SurfaceShadow  * Attenuation, bNeedsSeparateSubsurfaceLightAccumulation );
				
			LightAccumulator_AddSplit( LightAccumulator, Lighting.Transmission, 0.0f, Lighting.Transmission, LightColor * LightMask * Shadow.TransmissionShadow, bNeedsSeparateSubsurfaceLightAccumulation );
			// ****************** end here  ********************* //

			LightAccumulator.EstimatedCost += 0.4f;		// add the cost of the lighting computations (should sum up to 1 form one light)	
			
		#endif
		}
	}
	
	
	return LightAccumulator_GetResultSplit(LightAccumulator);
}

编译后即可看到效果

7. 总结

初步实现自定义ShadingModel材质渲染。后续可做进一步开发~

8.参考

Unreal Engine 4 Rendering Part 6: Adding a new Shading Model

GitHub - Eragon-Brisingr/ToonShader: cartoon plugins for unreal engine

在UE4中创建新的Shading Model_「已注销」的博客-CSDN博客

UE5自定义着色模型 Unreal Engine 5 custom Shading Model

风中追风

Adding a new Shading Model in Unreal5