UnrealEngine/Engine/Shaders/Private/MegaLights/MegaLightsShading.ush

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

#pragma once

// Experimental - Stochastic lighting for Substrate
// Select and light stochastically a single Slab for material containing several layers
#define SUBSTRATE_STOCHASTIC_LIGHTING 0

#include "MegaLights.ush"
#include "MegaLightsMaterial.ush"

FDeferredLightingSplit GetMegaLightsSplitLighting(
	float3 TranslatedWorldPosition,
	float3 CameraVector,
	FMegaLightsMaterial Material,
	float AmbientOcclusion,
	FDeferredLightData LightData,
	float4 LightAttenuation,
	float Dither,
	uint2 ScreenCoord,
	inout float SurfaceShadow)
#if SUBSTRATE_ENABLED && !INPUT_TYPE == INPUT_TYPE_HAIRSTRANDS
{
	const uint2 PixelCoord = ScreenCoord;

	FDeferredLightingSplit Out = (FDeferredLightingSplit)0;
	#if SUBSTRATE_GBUFFER_FORMAT==1 && SUBSTRATE_LOAD_FROM_MATERIALCONTAINER
	FSubstrateAddressing SubstrateAddressing = GetSubstratePixelDataByteOffset(PixelCoord, uint2(View.BufferSizeAndInvSize.xy), Substrate.MaxBytesPerPixel);
	FSubstratePixelHeader SubstratePixelHeader = UnpackSubstrateHeaderIn(Substrate.MaterialTextureArray, SubstrateAddressing, Substrate.TopLayerTexture);
	const bool bIsValid = SubstratePixelHeader.ClosureCount > 0;
	#else
	const bool bIsValid = Material.IsValid();
	#endif

	BRANCH
		if (bIsValid)
		{
			float3 V = -CameraVector;
			float3 L = LightData.Direction;	// Already normalized
			float3 ToLight = L;
			float LightMask = 1;
			if (LightData.bRadialLight)
			{
				LightMask = GetLocalLightAttenuation(TranslatedWorldPosition, LightData, ToLight, L);
#if ADAPTIVE_VOLUMETRIC_SHADOW_MAP
				//LightAttenuation *= ComputeTransmittance(TranslatedWorldPosition, LightData.TranslatedWorldPosition, 256);
				LightAttenuation *= AVSM_SampleTransmittance(TranslatedWorldPosition, LightData.TranslatedWorldPosition);
#endif // ADAPTIVE_VOLUMETRIC_SHADOW_MAP
			}

			if (LightMask > 0)
			{
				FSubstrateShadowTermInputParameters SubstrateShadowTermInputParameters = GetInitialisedSubstrateShadowTermInputParameters();
				SubstrateShadowTermInputParameters.bEvaluateShadowTerm = true;
				SubstrateShadowTermInputParameters.SceneDepth = Material.Depth;
				SubstrateShadowTermInputParameters.PrecomputedShadowFactors = 1.f;  //SubstrateReadPrecomputedShadowFactors(SubstratePixelHeader, PixelCoord, SceneTexturesStruct.GBufferETexture);
				SubstrateShadowTermInputParameters.TranslatedWorldPosition = TranslatedWorldPosition;
				SubstrateShadowTermInputParameters.LightAttenuation = LightAttenuation;
				SubstrateShadowTermInputParameters.Dither = Dither;

				// When using stochastic material selection, 
				// * Seek the selected closure
				// * Force single closure evaluation
				const bool bStochasticLighting = Substrate.bStochasticLighting > 0;
				#if SUBSTRATE_STOCHASTIC_LIGHTING && SUBSTRATE_LOAD_FROM_MATERIALCONTAINER
				if (bStochasticLighting)
				{
					#if SUBSTRATE_MATERIAL_CLOSURE_COUNT > 1
					if (SubstratePixelHeader.ClosureCount > 1)
					{
						const uint AddressOffset = UnpackClosureOffsetAtIndex(Substrate.ClosureOffsetTexture[SubstrateAddressing.PixelCoords], Material.ClosureIndex, SubstratePixelHeader.ClosureCount);
						SubstrateSeekClosure(SubstrateAddressing, AddressOffset);
					}
					#endif
					SubstratePixelHeader.ClosureCount = 1;
				}
				#endif

				FSubstrateDeferredLighting SubstrateLighting = SubstrateDeferredLighting(
					LightData,
					V,
					L,
					ToLight,
					LightMask,
					SubstrateShadowTermInputParameters,
					#if SUBSTRATE_GBUFFER_FORMAT==1 && SUBSTRATE_LOAD_FROM_MATERIALCONTAINER
					Substrate.MaterialTextureArray,
					SubstrateAddressing,
					SubstratePixelHeader
					#else
					Material.BSDF,
					Material.BSDFTangentBasis,
					Material.BSDFAO
					#endif
					);

				// SUBSTRATE_TODO - Add support for SUBSTRATE_OPAQUE_ROUGH_REFRACTION_ENABLED
				Out.DiffuseLighting = float4(SubstrateLighting.TotalDiffuseLighting, 0);
				Out.SpecularLighting = float4(SubstrateLighting.TotalSpecularLighting, 0);
				// SUBSTRATE_TODO - Accumulate Luminance separately
				Out.LightingLuminance = Luminance(SubstrateLighting.TotalDiffuseLighting + SubstrateLighting.TotalSpecularLighting);

				#if SUBSTRATE_STOCHASTIC_LIGHTING
				// Account for the probability of having chosen this slab
				if (bStochasticLighting)
				{
					const float InvPdf = 1.f / Material.PDF;
					Out.DiffuseLighting   *= InvPdf;
					Out.SpecularLighting  *= InvPdf;
					Out.LightingLuminance *= InvPdf;
				}
				#endif
			}
		}
	return Out;
}
#else // INPUT_TYPE == INPUT_TYPE_GBUFFER || INPUT_TYPE == INPUT_TYPE_HAIRSTRANDS
{
	return GetDynamicLightingSplit(
		TranslatedWorldPosition, CameraVector, Material.GBuffer, AmbientOcclusion,
		LightData, LightAttenuation, Dither, ScreenCoord,
		SurfaceShadow);
}
#endif // SUBSTRATE_ENABLED

#if INPUT_TYPE == INPUT_TYPE_HAIRSTRANDS

#include "../HairStrands/HairStrandsVisibilityCommon.ush"
#include "../HairStrands/HairStrandsVisibilityUtils.ush"
#include "../HairStrands/HairStrandsCommon.ush"
#include "../HairStrands/HairStrandsDeepTransmittanceCommon.ush"
#include "../HairStrands/HairStrandsDeepTransmittanceDualScattering.ush" 

// Compute transmittance data from a transmittance mask
FHairTransmittanceData GetTransmittanceDataFromTransmitttanceMask(
	FDeferredLightData LightData, 
	FMegaLightsMaterial Material, 
	FHairTransmittanceMask TransmittanceMask,
	float3 TranslatedWorldPosition, 
	float3 CameraVector)
{
	float3 L = LightData.Direction;
	if (LightData.bRadialLight)
	{
		L = normalize(LightData.TranslatedWorldPosition - TranslatedWorldPosition);
	}
	const float3 V = normalize(-CameraVector);

	return GetHairTransmittance(
		V,
		L,
		Material.GBuffer,
		TransmittanceMask,
		View.HairScatteringLUTTexture,
		HairScatteringLUTSampler,
		View.HairComponents);
}
#endif