UnrealEngine/Engine/Shaders/Private/Lumen/LumenCardBasePass.ush

// Copyright Epic Games, Inc. All Rights Reserved.

#pragma  once

struct FLumenCardBasePassOutput
{
	float4 Target0;
	float4 Target1;
	float4 Target2;
};

FLumenCardBasePassOutput LumenCardBasePass(FPixelMaterialInputs PixelMaterialInputs, FMaterialPixelParameters MaterialParameters, float4 SvPosition)
{
#if TEMPLATE_USES_SUBSTRATE
	const float3 V = MaterialParameters.WorldNormal; // Use the normal to avoid view dependent transmittance effects when baking non directional card data.
	const float3 L = MaterialParameters.WorldNormal;

	float3 DiffuseColor  = 0;
	float3 SpecularColor = 0;
	float3 WorldNormal   = 0;
	float3 Emissive      = 0;
	float TotalCoverage  = 1.f;

	// Initialise a Substrate header with normal in registers
	FSubstrateData SubstrateData = PixelMaterialInputs.GetFrontSubstrateData();
	FSubstratePixelHeader SubstratePixelHeader = MaterialParameters.GetFrontSubstrateHeader();

  #if SUBSTRATE_OPTIMIZED_UNLIT

	// Unlit BSDF goes through the SubstrateTree to support weighting operations. Technically, layering and mixing could also be supported.
	float3	UnlitSurfaceTransmittancePreCoverage = 0.0f;
	float3	UnlitSurfaceNormal = 0.0f;
	SubstratePixelHeader.SubstrateUpdateTreeUnlit(
		uint2(SvPosition.xy),
		MaterialParameters.CameraVector,
		SubstrateData,
		Emissive,
		TotalCoverage,
		UnlitSurfaceTransmittancePreCoverage,
		UnlitSurfaceNormal);

  #else // SUBSTRATE_OPTIMIZED_UNLIT
	SubstratePixelHeader.IrradianceAO.MaterialAO = GetMaterialAmbientOcclusion(PixelMaterialInputs);
	
	if (SubstratePixelHeader.SubstrateTree.BSDFCount > 0)
	{
		// To have better 'specular as diffuse' response, we use bForceFullyRoughAccurate which computes specular & diffuse separately. 
		// They are both merge them manually at the end, as Lumen card stores only diffuse albedo.
		// Match behavior in LumenHardwareRayTracingCommon.ush
		FSubstrateIntegrationSettings Settings = InitSubstrateIntegrationSettings(true /*bForceFullyRough*/, true /*bRoughDiffuseEnabled*/, 0 /*PeelLayersAboveDepth*/, false/*bRoughnessTracking*/);
		Settings.bForceFullyRoughAccurate = true;

		float3 TotalTransmittancePreCoverage = 0;
		SubstratePixelHeader.SubstrateUpdateTree(SubstrateData, V, Settings, TotalCoverage, TotalTransmittancePreCoverage);


		// Extract averaged DiffuseAlbedo / SpecularColor
		SUBSTRATE_UNROLL_N(SUBSTRATE_CLAMPED_CLOSURE_COUNT)
		for (int BSDFIdx = 0; BSDFIdx < SubstratePixelHeader.SubstrateTree.BSDFCount; ++BSDFIdx)
		{
			#define CurrentBSDF SubstratePixelHeader.SubstrateTree.BSDFs[BSDFIdx]
			if (SubstrateIsBSDFVisible(CurrentBSDF))
			{
				FSubstrateAddressing NullSubstrateAddressing = (FSubstrateAddressing)0;	// Fake unused in SubstrateCreateBSDFContext when using Forward inline shading
				FSubstrateBSDFContext SubstrateBSDFContext = SubstrateCreateBSDFContext(SubstratePixelHeader, CurrentBSDF, NullSubstrateAddressing, V, L);
				FSubstrateEnvLightResult SubstrateEnvLight = SubstrateEvaluateForEnvLight(SubstrateBSDFContext, true /*bEnableSpecular*/, Settings);

				// Use LuminanceWeightV instead of LuminanceWeight(..) as we only need to weight these value with the view transmittance, not the light transmittance;
				const float3 Weight = CurrentBSDF.LuminanceWeightV;

				DiffuseColor  += Weight * (SubstrateEnvLight.DiffuseWeight + SubstrateEnvLight.DiffuseBackFaceWeight); // This is not correct, as the albedo/diffuse color can go above 1. However this is necessary to match legacy behavior.
				SpecularColor += Weight * SubstrateEnvLight.SpecularWeight;
				SpecularColor += Weight * SubstrateEnvLight.SpecularHazeWeight;
				WorldNormal   += Weight * SubstrateBSDFContext.N;
				Emissive      += Weight * CurrentBSDF.Emissive;

				// Lumen card stores only diffuse albedo, so merge specular & diffuse color, 
				// which are propertly weighted respectively to each other
				DiffuseColor = SpecularColor + DiffuseColor;

				// Note : The legacy path uses a different formulation for composition diffuse and specular color. This result in lighter albedo.
				//        If the above formulation causes issues for legacy projects, one could re-enable the code below:
				//  DiffuseColor  = Weight * SubstrateEnvLight.DiffuseColor;
				//  SpecularColor = Weight * SubstrateEnvLight.SpecularColor;
				//  EnvBRDFApproxFullyRough(DiffuseColor, SpecularColor);
			}
			#undef CurrentBSDF
		}
	}
  #endif // SUBSTRATE_OPTIMIZED_UNLIT
	
	float Opacity = 1.0f;
#if MATERIALBLENDING_ANY_TRANSLUCENT
	Opacity = TotalCoverage > 0.5f ? 1.0f : 0.0f;
#elif MATERIALBLENDING_MASKED
	Opacity = GetMaterialMask(PixelMaterialInputs) >= 0.0f ? 1.0f : 0.0f;
#endif

#else // TEMPLATE_USES_SUBSTRATE

	float3 BaseColor = GetMaterialBaseColor(PixelMaterialInputs);
	float Metallic = GetMaterialMetallic(PixelMaterialInputs);
	float Specular = GetMaterialSpecular(PixelMaterialInputs);
	float Roughness = GetMaterialRoughness(PixelMaterialInputs);
	float3 Emissive = GetMaterialEmissive(PixelMaterialInputs);
	float3 WorldNormal = MaterialParameters.WorldNormal;

	float Opacity = 1.0f;
#if MATERIALBLENDING_ANY_TRANSLUCENT
	Opacity = GetMaterialOpacity(PixelMaterialInputs) > 0.5f ? 1.0f : 0.0f;
#elif MATERIALBLENDING_MASKED
	Opacity = GetMaterialMask(PixelMaterialInputs) >= 0.0f ? 1.0f : 0.0f;
#endif

	float3 DiffuseColor = BaseColor - BaseColor * Metallic;
	float3 SpecularColor = lerp(0.08f * Specular.xxx, BaseColor, Metallic.xxx);

	EnvBRDFApproxFullyRough(DiffuseColor, SpecularColor);

	uint ShadingModel = GetMaterialShadingModel(PixelMaterialInputs);

	float3 SubsurfaceColor = 0.0f;
	// Match the logic in BasePassPixelShader.usf. MATERIAL_SHADINGMODEL_SUBSURFACE_PROFILE and MATERIAL_SHADINGMODEL_EYE 
	// are ignored from the following logic as the subsurface color does not contribute to them.
#if MATERIAL_SHADINGMODEL_SUBSURFACE || MATERIAL_SHADINGMODEL_PREINTEGRATED_SKIN || MATERIAL_SHADINGMODEL_TWOSIDED_FOLIAGE || MATERIAL_SHADINGMODEL_CLOTH
	if (ShadingModel == SHADINGMODELID_SUBSURFACE || ShadingModel == SHADINGMODELID_PREINTEGRATED_SKIN || ShadingModel == SHADINGMODELID_TWOSIDED_FOLIAGE || ShadingModel == SHADINGMODELID_CLOTH)
	{
		float4 SubsurfaceData = GetMaterialSubsurfaceData(PixelMaterialInputs);
		DiffuseColor += SubsurfaceData.rgb;
	}
#endif

#endif // TEMPLATE_USES_SUBSTRATE

	// Normals are stored in local card space
	float3 CardSpaceNormal = float3(0, 0, 1);

	// As of 04/06/2022 sometimes we get NaN normals from Nanite meshes with WPO
	if (all(IsFinite(WorldNormal)))
	{
		WorldNormal = normalize(WorldNormal);
		CardSpaceNormal = mul(float4(WorldNormal, 0.0f), ResolvedView.TranslatedWorldToView).xyz;
	}

	FLumenCardBasePassOutput ShadedPixel;
	ShadedPixel.Target0 = float4(sqrt(DiffuseColor), Opacity);
	ShadedPixel.Target1 = float4(CardSpaceNormal.xy * 0.5f + 0.5f, 0.0f, /* bValid */ 1.0f);
	ShadedPixel.Target2 = float4(Emissive * LumenCardPass.CachedLightingPreExposure, 0.0f);
	return ShadedPixel;
}