BlueRoseNote/03-UnrealEngine/Rendering/RenderingPipeline/Lighting/Lighting.md

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title	date	excerpt	tags	rating
Untitled	2025-02-11 11:30:34			⭐

FSortedLightSetSceneInfo

有序的光源集合相关定义：

/** Data for a simple dynamic light. */  
class FSimpleLightEntry  
{  
public:  
    FVector3f Color;  
    float Radius;  
    float Exponent;  
    float InverseExposureBlend = 0.0f;  
    float VolumetricScatteringIntensity;  
    bool bAffectTranslucency;  
};

struct FSortedLightSceneInfo  
{  
    union  
    {  
       struct  
       {  
          // Note: the order of these members controls the light sort order!  
          // Currently bHandledByLumen is the MSB and LightType is LSB          /** The type of light. */          uint32 LightType : LightType_NumBits;  
          /** Whether the light has a texture profile. */  
          uint32 bTextureProfile : 1;  
          /** Whether the light uses a light function. */  
          uint32 bLightFunction : 1;  
          /** Whether the light uses lighting channels. */  
          uint32 bUsesLightingChannels : 1;  
          /** Whether the light casts shadows. */  
          uint32 bShadowed : 1;  
          /** Whether the light is NOT a simple light - they always support tiled/clustered but may want to be selected separately. */  
          uint32 bIsNotSimpleLight : 1;  
          /* We want to sort the lights that write into the packed shadow mask (when enabled) to the front of the list so we don't waste slots in the packed shadow mask. */  
          uint32 bDoesNotWriteIntoPackedShadowMask : 1;  
          /**   
           * True if the light doesn't support clustered deferred, logic is inverted so that lights that DO support clustered deferred will sort first in list   
           * Super-set of lights supporting tiled, so the tiled lights will end up in the first part of this range.  
           */          
           uint32 bClusteredDeferredNotSupported : 1;  
          /** Whether the light should be handled by Lumen's Final Gather, these will be sorted to the end so they can be skipped */  
          uint32 bHandledByLumen : 1;  
       } Fields;  
       /** Sort key bits packed into an integer. */  
       int32 Packed;  
    } SortKey;  
  
    const FLightSceneInfo* LightSceneInfo;  
    int32 SimpleLightIndex;  
  
    /** Initialization constructor. */  
    explicit FSortedLightSceneInfo(const FLightSceneInfo* InLightSceneInfo)  
       : LightSceneInfo(InLightSceneInfo),  
       SimpleLightIndex(-1)  
    {       
	    SortKey.Packed = 0;  
		SortKey.Fields.bIsNotSimpleLight = 1;  
    }  
    explicit FSortedLightSceneInfo(int32 InSimpleLightIndex)  
       : LightSceneInfo(nullptr),  
       SimpleLightIndex(InSimpleLightIndex)  
    {   
        SortKey.Packed = 0;  
		SortKey.Fields.bIsNotSimpleLight = 0;  
    }};  
  
/**   
 * Stores info about sorted lights and ranges.   
 * The sort-key in FSortedLightSceneInfo gives rise to the following order:  
 *  [SimpleLights,Clustered,UnbatchedLights,LumenLights] * Note that some shadowed lights can be included in the clustered pass when virtual shadow maps and one pass projection are used. */struct FSortedLightSetSceneInfo  
{  
    int32 SimpleLightsEnd;  
    int32 ClusteredSupportedEnd;  
  
    /** First light with shadow map or */  
    int32 UnbatchedLightStart;  
  
    int32 LumenLightStart;  
  
    FSimpleLightArray SimpleLights;  
    TArray<FSortedLightSceneInfo, SceneRenderingAllocator> SortedLights;  
};

开始获取有序光源集合

UE的光源分配由FDeferredShadingSceneRenderer::Render内的bComputeLightGrid变量决定的，bComputeLightGrid的赋值逻辑如下：

void FDeferredShadingSceneRenderer::Render(FRHICommandListImmediate& RHICmdList) {
...
	bool bComputeLightGrid = false;

	if (RendererOutput == ERendererOutput::FinalSceneColor)
	{
		if (bUseVirtualTexturing)
		{
			// Note, should happen after the GPU-Scene update to ensure rendering to runtime virtual textures is using the correctly updated scene
			FVirtualTextureSystem::Get().EndUpdate(GraphBuilder, MoveTemp(VirtualTextureUpdater), FeatureLevel);
		}

#if RHI_RAYTRACING
		GatherRayTracingWorldInstancesForView(GraphBuilder, ReferenceView, RayTracingScene, InitViewTaskDatas.RayTracingRelevantPrimitives);
#endif // RHI_RAYTRACING

		bool bAnyLumenEnabled = false;

		{
			if (bUseGBuffer)
			{
				bComputeLightGrid = bRenderDeferredLighting;
			}
			else
			{
				bComputeLightGrid = ViewFamily.EngineShowFlags.Lighting;
			}

			for (int32 ViewIndex = 0; ViewIndex < Views.Num(); ViewIndex++)
			{
				FViewInfo& View = Views[ViewIndex];
				bAnyLumenEnabled = bAnyLumenEnabled
					|| GetViewPipelineState(View).DiffuseIndirectMethod == EDiffuseIndirectMethod::Lumen
					|| GetViewPipelineState(View).ReflectionsMethod == EReflectionsMethod::Lumen;
			}

			bComputeLightGrid |= (
				ShouldRenderVolumetricFog() ||
				VolumetricCloudWantsToSampleLocalLights(Scene, ViewFamily.EngineShowFlags) ||
				ViewFamily.ViewMode != VMI_Lit ||
				bAnyLumenEnabled ||
				VirtualShadowMapArray.IsEnabled() ||
				ShouldVisualizeLightGrid());
		}
	}
...
}	

获取有序的光源集合

void FDeferredShadingSceneRenderer::Render(FRHICommandListImmediate& RHICmdList) {
...
	// 有序的光源集合.
	FSortedLightSetSceneInfo& SortedLightSet = *GraphBuilder.AllocObject<FSortedLightSetSceneInfo>();  
	{  
	    RDG_CSV_STAT_EXCLUSIVE_SCOPE(GraphBuilder, SortLights);  
	    RDG_GPU_STAT_SCOPE(GraphBuilder, SortLights);  
	    ComputeLightGridOutput = GatherLightsAndComputeLightGrid(GraphBuilder, bComputeLightGrid, SortedLightSet);  
	}
...
}	

PS. 简单光源都可以被分块或分簇渲染，但对于非简单光源，只有满足以下条件的光源才可被分块或分簇渲染：

• 没有使用光源的附加特性（TextureProfile、LightFunction、LightingChannel）。
• 没有开启阴影。
• 非平行光或矩形光。

另外，是否支持分块渲染，还需要光源场景代理的IsTiledDeferredLightingSupported返回true，长度为0的点光源才支持分块渲染。

GatherLightsAndComputeLightGrid

FComputeLightGridOutput FDeferredShadingSceneRenderer::GatherLightsAndComputeLightGrid(FRDGBuilder& GraphBuilder, bool bNeedLightGrid, FSortedLightSetSceneInfo& SortedLightSet)
{
	SCOPED_NAMED_EVENT(GatherLightsAndComputeLightGrid, FColor::Emerald);
	FComputeLightGridOutput Result = {};

	bool bShadowedLightsInClustered = ShouldUseClusteredDeferredShading()
		&& CVarVirtualShadowOnePassProjection.GetValueOnRenderThread()
		&& VirtualShadowMapArray.IsEnabled();

	const bool bUseLumenDirectLighting = ShouldRenderLumenDirectLighting(Scene, Views[0]);

	GatherAndSortLights(SortedLightSet, bShadowedLightsInClustered, bUseLumenDirectLighting);
	
	if (!bNeedLightGrid)
	{
		SetDummyForwardLightUniformBufferOnViews(GraphBuilder, ShaderPlatform, Views);
		return Result;
	}

	bool bAnyViewUsesForwardLighting = false;
	bool bAnyViewUsesLumen = false;
	for (int32 ViewIndex = 0; ViewIndex < Views.Num(); ViewIndex++)
	{
		const FViewInfo& View = Views[ViewIndex];
		bAnyViewUsesForwardLighting |= View.bTranslucentSurfaceLighting || ShouldRenderVolumetricFog() || View.bHasSingleLayerWaterMaterial || VolumetricCloudWantsToSampleLocalLights(Scene, ViewFamily.EngineShowFlags) || ShouldVisualizeLightGrid();
		bAnyViewUsesLumen |= GetViewPipelineState(View).DiffuseIndirectMethod == EDiffuseIndirectMethod::Lumen || GetViewPipelineState(View).ReflectionsMethod == EReflectionsMethod::Lumen;
	}
	
	const bool bCullLightsToGrid = GLightCullingQuality 
		&& (IsForwardShadingEnabled(ShaderPlatform) || bAnyViewUsesForwardLighting || IsRayTracingEnabled() || ShouldUseClusteredDeferredShading() ||
			bAnyViewUsesLumen || ViewFamily.EngineShowFlags.VisualizeMeshDistanceFields || VirtualShadowMapArray.IsEnabled());

	// Store this flag if lights are injected in the grids, check with 'AreLightsInLightGrid()'
	bAreLightsInLightGrid = bCullLightsToGrid;
	
	Result = ComputeLightGrid(GraphBuilder, bCullLightsToGrid, SortedLightSet);

	return Result;
}

• GatherAndSortLights：收集与排序当前场景中所有的可见光源（当前View）。
• ComputeLightGrid：是在锥体空间（frustum space）裁剪局部光源和反射探针到3D格子中，构建每个视图相关的光源列表和格子。

RenderLights() -> RenderLight()

InternalRenderLight()

DeferredLightVertexShaders

// 输入参数.
struct FInputParams
{
    float2 PixelPos;
    float4 ScreenPosition;
    float2 ScreenUV;
    float3 ScreenVector;
};

// 派生参数.
struct FDerivedParams
{
    float3 CameraVector;
    float3 WorldPosition;
};

// 获取派生参数.
FDerivedParams GetDerivedParams(in FInputParams Input, in float SceneDepth)
{
    FDerivedParams Out;
#if LIGHT_SOURCE_SHAPE > 0
    // With a perspective projection, the clip space position is NDC * Clip.w
    // With an orthographic projection, clip space is the same as NDC
    float2 ClipPosition = Input.ScreenPosition.xy / Input.ScreenPosition.w * (View.ViewToClip[3][3] < 1.0f ? SceneDepth : 1.0f);
    Out.WorldPosition = mul(float4(ClipPosition, SceneDepth, 1), View.ScreenToWorld).xyz;
    Out.CameraVector = normalize(Out.WorldPosition - View.WorldCameraOrigin);
#else
    Out.WorldPosition = Input.ScreenVector * SceneDepth + View.WorldCameraOrigin;
    Out.CameraVector = normalize(Input.ScreenVector);
#endif
    return Out;
}

Texture2D<uint> LightingChannelsTexture;

uint GetLightingChannelMask(float2 UV)
{
	uint2 IntegerUV = UV * View.BufferSizeAndInvSize.xy;
	return LightingChannelsTexture.Load(uint3(IntegerUV, 0)).x;
}

float GetExposure()
{
	return View.PreExposure;
}

向往文章中的SetupLightDataForStandardDeferred()变为InitDeferredLightFromUniforms()。位于LightDataUniform.ush。

FDeferredLightData InitDeferredLightFromUniforms(uint InLightType)
{
	const bool bIsRadial = InLightType != LIGHT_TYPE_DIRECTIONAL;

	FDeferredLightData Out;
	Out.TranslatedWorldPosition = GetDeferredLightTranslatedWorldPosition();
	Out.InvRadius				= DeferredLightUniforms.InvRadius;
	Out.Color					= DeferredLightUniforms.Color;
	Out.FalloffExponent			= DeferredLightUniforms.FalloffExponent;
	Out.Direction				= DeferredLightUniforms.Direction;
	Out.Tangent					= DeferredLightUniforms.Tangent;
	Out.SpotAngles				= DeferredLightUniforms.SpotAngles;
	Out.SourceRadius			= DeferredLightUniforms.SourceRadius;
	Out.SourceLength			= bIsRadial ? DeferredLightUniforms.SourceLength : 0;
	Out.SoftSourceRadius		= DeferredLightUniforms.SoftSourceRadius;
	Out.SpecularScale			= DeferredLightUniforms.SpecularScale;
	Out.ContactShadowLength		= abs(DeferredLightUniforms.ContactShadowLength);
	Out.ContactShadowLengthInWS = DeferredLightUniforms.ContactShadowLength < 0.0f;
	Out.ContactShadowCastingIntensity = DeferredLightUniforms.ContactShadowCastingIntensity;
	Out.ContactShadowNonCastingIntensity = DeferredLightUniforms.ContactShadowNonCastingIntensity;
	Out.DistanceFadeMAD			= DeferredLightUniforms.DistanceFadeMAD;
	Out.ShadowMapChannelMask	= DeferredLightUniforms.ShadowMapChannelMask;
	Out.ShadowedBits			= DeferredLightUniforms.ShadowedBits;
	Out.bInverseSquared			= bIsRadial && DeferredLightUniforms.FalloffExponent == 0; // Directional lights don't use 'inverse squared attenuation'
	Out.bRadialLight			= bIsRadial;
	Out.bSpotLight				= InLightType == LIGHT_TYPE_SPOT;
	Out.bRectLight				= InLightType == LIGHT_TYPE_RECT;

	Out.RectLightData.BarnCosAngle				= DeferredLightUniforms.RectLightBarnCosAngle;
	Out.RectLightData.BarnLength				= DeferredLightUniforms.RectLightBarnLength;
	Out.RectLightData.AtlasData.AtlasMaxLevel	= DeferredLightUniforms.RectLightAtlasMaxLevel;
	Out.RectLightData.AtlasData.AtlasUVOffset	= DeferredLightUniforms.RectLightAtlasUVOffset;
	Out.RectLightData.AtlasData.AtlasUVScale	= DeferredLightUniforms.RectLightAtlasUVScale;

	Out.HairTransmittance		= InitHairTransmittanceData();
	return Out;
}

DeferredLightPixelMain

void DeferredLightPixelMain(
#if LIGHT_SOURCE_SHAPE > 0
	float4 InScreenPosition : TEXCOORD0,
#else
	float2 ScreenUV			: TEXCOORD0,
	float3 ScreenVector		: TEXCOORD1,
#endif
	float4 SVPos			: SV_POSITION,
	out float4 OutColor		: SV_Target0
#if STRATA_OPAQUE_ROUGH_REFRACTION_ENABLED
	, out float3 OutOpaqueRoughRefractionSceneColor : SV_Target1
	, out float3 OutSubSurfaceSceneColor : SV_Target2
#endif
	)
{
	const float2 PixelPos = SVPos.xy;
	OutColor = 0;
#if STRATA_OPAQUE_ROUGH_REFRACTION_ENABLED
	OutOpaqueRoughRefractionSceneColor = 0;
	OutSubSurfaceSceneColor = 0;
#endif

	// Convert input data (directional/local light)
	// 计算屏幕UV
	FInputParams InputParams = (FInputParams)0;
	InputParams.PixelPos		= SVPos.xy;
#if LIGHT_SOURCE_SHAPE > 0
	InputParams.ScreenPosition	= InScreenPosition;
	InputParams.ScreenUV		= InScreenPosition.xy / InScreenPosition.w * View.ScreenPositionScaleBias.xy + View.ScreenPositionScaleBias.wz;
	InputParams.ScreenVector	= 0;
#else
	InputParams.ScreenPosition	= 0;
	InputParams.ScreenUV		= ScreenUV;
	InputParams.ScreenVector	= ScreenVector;
#endif

#if STRATA_ENABLED

	FStrataAddressing StrataAddressing = GetStrataPixelDataByteOffset(PixelPos, uint2(View.BufferSizeAndInvSize.xy), Strata.MaxBytesPerPixel);
	FStrataPixelHeader StrataPixelHeader = UnpackStrataHeaderIn(Strata.MaterialTextureArray, StrataAddressing, Strata.TopLayerTexture);

	BRANCH
	if (StrataPixelHeader.BSDFCount > 0	// This test is also enough to exclude sky pixels
#if USE_LIGHTING_CHANNELS
		//灯光通道逻辑
		&& (GetLightingChannelMask(InputParams.ScreenUV) & DeferredLightUniforms.LightingChannelMask)
#endif
		) 
	{
		//通过SceneDepth获取的CameraVector以及当前像素的世界坐标
		const float SceneDepth = CalcSceneDepth(InputParams.ScreenUV);
		const FDerivedParams DerivedParams = GetDerivedParams(InputParams, SceneDepth);

		//设置获取光源各种信息
		FDeferredLightData LightData = InitDeferredLightFromUniforms(CURRENT_LIGHT_TYPE);
		UpdateLightDataColor(LightData, InputParams, DerivedParams);//根据当前世界坐标计算LightData.Color *= 大气&云&阴影的衰减值 * IES灯亮度（非IES灯数值为1） 

		float3 V =-DerivedParams.CameraVector;
		float3 L = LightData.Direction;	// Already normalized
		float3 ToLight = L;
		float LightMask = 1;
		if (LightData.bRadialLight)
		{
			LightMask = GetLocalLightAttenuation(DerivedParams.TranslatedWorldPosition, LightData, ToLight, L);
		}

		if (LightMask > 0)
		{
			FShadowTerms ShadowTerms = { StrataGetAO(StrataPixelHeader), 1.0, 1.0, InitHairTransmittanceData() };
			float4 LightAttenuation = GetLightAttenuationFromShadow(InputParams, SceneDepth);

			float Dither = InterleavedGradientNoise(InputParams.PixelPos, View.StateFrameIndexMod8);
			const uint FakeShadingModelID = 0;
			const float FakeContactShadowOpacity = 1.0f;
			float4 PrecomputedShadowFactors = StrataReadPrecomputedShadowFactors(StrataPixelHeader, PixelPos, SceneTexturesStruct.GBufferETexture);
			GetShadowTerms(SceneDepth, PrecomputedShadowFactors, FakeShadingModelID, FakeContactShadowOpacity,
				LightData, DerivedParams.TranslatedWorldPosition, L, LightAttenuation, Dither, ShadowTerms);

			FStrataDeferredLighting StrataLighting = StrataDeferredLighting(
				LightData,
				V,
				L,
				ToLight,
				LightMask,
				ShadowTerms,
				Strata.MaterialTextureArray,
				StrataAddressing,
				StrataPixelHeader);

			OutColor += StrataLighting.SceneColor;
#if STRATA_OPAQUE_ROUGH_REFRACTION_ENABLED
			OutOpaqueRoughRefractionSceneColor += StrataLighting.OpaqueRoughRefractionSceneColor;
			OutSubSurfaceSceneColor += StrataLighting.SubSurfaceSceneColor;
#endif
		}
	}

#else // STRATA_ENABLED
	//取得屏幕空间数据（FGbufferData、AO）
	FScreenSpaceData ScreenSpaceData = GetScreenSpaceData(InputParams.ScreenUV);
	// Only light pixels marked as using deferred shading
	BRANCH if (ScreenSpaceData.GBuffer.ShadingModelID > 0
#if USE_LIGHTING_CHANNELS
		&& (GetLightingChannelMask(InputParams.ScreenUV) & DeferredLightUniforms.LightingChannelMask)
#endif
		)
	{
		//通过SceneDepth获取的CameraVector以及当前像素的世界坐标
		const float SceneDepth = CalcSceneDepth(InputParams.ScreenUV);
		const FDerivedParams DerivedParams = GetDerivedParams(InputParams, SceneDepth);

		//设置获取光源各种信息
		FDeferredLightData LightData = InitDeferredLightFromUniforms(CURRENT_LIGHT_TYPE);
		UpdateLightDataColor(LightData, InputParams, DerivedParams);//根据当前世界坐标计算LightData.Color *= 大气&云&阴影的衰减值 * IES灯亮度（非IES灯数值为1） 


	 #if USE_HAIR_COMPLEX_TRANSMITTANCE
		//针对ShadingModel Hair（同时需要CustomData.a > 0)计算头发散射结果
		if (ScreenSpaceData.GBuffer.ShadingModelID == SHADINGMODELID_HAIR && ShouldUseHairComplexTransmittance(ScreenSpaceData.GBuffer))
		{
			LightData.HairTransmittance = EvaluateDualScattering(ScreenSpaceData.GBuffer, DerivedParams.CameraVector, -DeferredLightUniforms.Direction);
		}
	#endif
		//计算当前像素的抖动值
		float Dither = InterleavedGradientNoise(InputParams.PixelPos, View.StateFrameIndexMod8);

		float SurfaceShadow = 1.0f;
		
		float4 LightAttenuation = GetLightAttenuationFromShadow(InputParams, SceneDepth);//根绝是否开启VSM 分别从VirtualShadowMap 或者 LightAttenuationTexture（上一阶段渲染的ShadowProjction） 获取灯光衰减值。
		float4 Radiance = GetDynamicLighting(DerivedParams.TranslatedWorldPosition, DerivedParams.CameraVector, ScreenSpaceData.GBuffer, ScreenSpaceData.AmbientOcclusion, ScreenSpaceData.GBuffer.ShadingModelID, LightData, LightAttenuation, Dither, uint2(InputParams.PixelPos), SurfaceShadow);

		OutColor += Radiance;
	}

#endif // STRATA_ENABLED

	// RGB:SceneColor Specular and Diffuse
	// A:Non Specular SceneColor Luminance
	// So we need PreExposure for both color and alpha
	OutColor.rgba *= GetExposure();
#if STRATA_OPAQUE_ROUGH_REFRACTION_ENABLED 
	// Idem
	OutOpaqueRoughRefractionSceneColor *= GetExposure();
	OutSubSurfaceSceneColor *= GetExposure();
#endif
}
#endif

GetDynamicLighting() => GetDynamicLightingSplit()

FDeferredLightingSplit GetDynamicLightingSplit(
	float3 TranslatedWorldPosition, float3 CameraVector, FGBufferData GBuffer, float AmbientOcclusion, uint ShadingModelID, 
	FDeferredLightData LightData, float4 LightAttenuation, float Dither, uint2 SVPos, 
	inout float SurfaceShadow)
{
	FLightAccumulator LightAccumulator = AccumulateDynamicLighting(TranslatedWorldPosition, CameraVector, GBuffer, AmbientOcclusion, ShadingModelID, LightData, LightAttenuation, Dither, SVPos, SurfaceShadow);
	return LightAccumulator_GetResultSplit(LightAccumulator);
}

LightAccumulator_GetResultSplit()：针对Subsurface，RetDiffuse.a = In.ScatterableLightLuma; 或者 RetDiffuse.a = Luminance(In.ScatterableLight);

FDeferredLightingSplit LightAccumulator_GetResultSplit(FLightAccumulator In)
{
	float4 RetDiffuse;
	float4 RetSpecular;

	if (VISUALIZE_LIGHT_CULLING == 1)
	{
		// a soft gradient from dark red to bright white, can be changed to be different
		RetDiffuse = 0.1f * float4(1.0f, 0.25f, 0.075f, 0) * In.EstimatedCost;
		RetSpecular = 0.1f * float4(1.0f, 0.25f, 0.075f, 0) * In.EstimatedCost;
	}
	else
	{
		RetDiffuse = float4(In.TotalLightDiffuse, 0);
		RetSpecular = float4(In.TotalLightSpecular, 0);

		//针对Subsurface会额外对RetDiffuse的Alpha设置数值 ScatterableLight的亮度数值
		if (SUBSURFACE_CHANNEL_MODE == 1 )
		{
			if (View.bCheckerboardSubsurfaceProfileRendering == 0)
			{
				// RGB accumulated RGB HDR color, A: specular luminance for screenspace subsurface scattering
				RetDiffuse.a = In.ScatterableLightLuma;
			}
		}
		else if (SUBSURFACE_CHANNEL_MODE == 2)
		{
			// RGB accumulated RGB HDR color, A: view independent (diffuse) luminance for screenspace subsurface scattering
			// 3 add,  1 mul, 2 mad, can be optimized to use 2 less temporary during accumulation and remove the 3 add
			RetDiffuse.a = Luminance(In.ScatterableLight);
			// todo, need second MRT for SUBSURFACE_CHANNEL_MODE==2
		}
	}

	FDeferredLightingSplit Ret;
	Ret.DiffuseLighting = RetDiffuse;
	Ret.SpecularLighting = RetSpecular;

	return Ret;
}

AccumulateDynamicLighting

FLightAccumulator AccumulateDynamicLighting(
	float3 TranslatedWorldPosition, half3 CameraVector, FGBufferData GBuffer, half AmbientOcclusion, uint ShadingModelID,
	FDeferredLightData LightData, half4 LightAttenuation, float Dither, uint2 SVPos, 
	inout float SurfaceShadow)
{
	FLightAccumulator LightAccumulator = (FLightAccumulator)0;

	half3 V = -CameraVector;
	half3 N = GBuffer.WorldNormal;
	//针对开启CLEAR_COAT_BOTTOM_NORMAL的清漆ShadingModel进行Normal处理
	BRANCH if( GBuffer.ShadingModelID == SHADINGMODELID_CLEAR_COAT && CLEAR_COAT_BOTTOM_NORMAL)
	{
		const float2 oct1 = ((float2(GBuffer.CustomData.a, GBuffer.CustomData.z) * 4) - (512.0/255.0)) + UnitVectorToOctahedron(GBuffer.WorldNormal);
		N = OctahedronToUnitVector(oct1);			
	}
	
	float3 L = LightData.Direction;	// Already normalized
	float3 ToLight = L;
	float3 MaskedLightColor = LightData.Color;//灯光颜色
	float LightMask = 1;
	// 获取辐射光源的衰减值，衰减方法根据LightData.bInverseSquared，会分别使用新版衰减方法InverseSquared 或者 旧方法。如果是SpotLight与RectLight就乘以SpotLight、RectLight对应的形状衰减数值。
	if (LightData.bRadialLight)
	{
		LightMask = GetLocalLightAttenuation( TranslatedWorldPosition, LightData, ToLight, L );
		MaskedLightColor *= LightMask;
	}

	LightAccumulator.EstimatedCost += 0.3f;		// running the PixelShader at all has a cost

	BRANCH
	if( LightMask > 0 )//如果不是完全死黑就计算阴影部分逻辑
	{
		FShadowTerms Shadow;
		Shadow.SurfaceShadow = AmbientOcclusion;//GBuffer中的AO
		Shadow.TransmissionShadow = 1;
		Shadow.TransmissionThickness = 1;
		Shadow.HairTransmittance.OpaqueVisibility = 1;
		const float ContactShadowOpacity = GBuffer.CustomData.a;//TODO:修正ToonStandard对应的逻辑
		//
		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

#if SHADING_PATH_MOBILE
		const bool bNeedsSeparateSubsurfaceLightAccumulation = UseSubsurfaceProfile(GBuffer.ShadingModelID);
		
		FDirectLighting Lighting = (FDirectLighting)0;

		half NoL = max(0, dot(GBuffer.WorldNormal, L));
	#if TRANSLUCENCY_NON_DIRECTIONAL
		NoL = 1.0f;
	#endif
		Lighting = EvaluateBxDF(GBuffer, N, V, L, NoL, Shadow);

		Lighting.Specular *= LightData.SpecularScale;
				
		LightAccumulator_AddSplit( LightAccumulator, Lighting.Diffuse, Lighting.Specular, Lighting.Diffuse, MaskedLightColor * Shadow.SurfaceShadow, bNeedsSeparateSubsurfaceLightAccumulation );
		LightAccumulator_AddSplit( LightAccumulator, Lighting.Transmission, 0.0f, Lighting.Transmission, MaskedLightColor * Shadow.TransmissionShadow, bNeedsSeparateSubsurfaceLightAccumulation );
#else // SHADING_PATH_MOBILE
		BRANCH
		if( Shadow.SurfaceShadow + Shadow.TransmissionShadow > 0 )
		{
			const bool bNeedsSeparateSubsurfaceLightAccumulation = UseSubsurfaceProfile(GBuffer.ShadingModelID);

		#if NON_DIRECTIONAL_DIRECT_LIGHTING
			float Lighting;

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

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

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

			float3 LightingDiffuse = Diffuse_Lambert( GBuffer.DiffuseColor ) * Lighting;
			LightAccumulator_AddSplit(LightAccumulator, LightingDiffuse, 0.0f, 0, MaskedLightColor * Shadow.SurfaceShadow, bNeedsSeparateSubsurfaceLightAccumulation);
		#else
			FDirectLighting Lighting;

			if (LightData.bRectLight)
			{
				FRect Rect = GetRect( ToLight, LightData );
				const FRectTexture SourceTexture = ConvertToRectTexture(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;
				
			LightAccumulator_AddSplit( LightAccumulator, Lighting.Diffuse, Lighting.Specular, Lighting.Diffuse, MaskedLightColor * Shadow.SurfaceShadow, bNeedsSeparateSubsurfaceLightAccumulation );
			LightAccumulator_AddSplit( LightAccumulator, Lighting.Transmission, 0.0f, Lighting.Transmission, MaskedLightColor * Shadow.TransmissionShadow, bNeedsSeparateSubsurfaceLightAccumulation );

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

光源新衰减公式，相关计算位于GetLocalLightAttenuation()：

Falloff = \frac{saturate(1-(distance/lightRadius)^4)^2}{distance^2 + 1}

光源旧衰减公式，相关函数位于DynamicLightingCommon.ush中的RadialAttenuation()

Falloff = (1 - saturate(length(WorldLightVector)))^ {FalloffExponent}

GetShadowTerms()