UnrealEngineUWP/Engine/Shaders/PostProcessAmbient.usf

// Copyright 1998-2014 Epic Games, Inc. All Rights Reserved.

/*=============================================================================
	PostprocessAmbient.usf: To apply a ambient cubemap as a postprocess
=============================================================================*/

#include "Common.usf"
#include "PostProcessCommon.usf"
#include "DeferredShadingCommon.usf"
#include "CubemapCommon.usf"
#include "Random.usf"
#include "BRDF.usf"
#include "MonteCarlo.usf"

#define IMPORTANCE_SAMPLE		0

float3 DiffuseIBL( uint2 Random, float3 DiffuseColor, float3 N )
{
	float3 DiffuseLighting = 0;

	const uint NumSamples = 32;
	for( uint i = 0; i < NumSamples; i++ )
	{
		float2 E = Hammersley( i, NumSamples, Random );
		float3 L = TangentToWorld( CosineSampleHemisphere( E ).xyz, N );

		float NoL = saturate( dot( N, L ) );
		if( NoL > 0 )
		{
			float3 SampleColor = AmbientCubemap.SampleLevel( AmbientCubemapSampler, L, 0 ).rgb;

			// lambert = DiffuseColor * NoL / PI
			// pdf = NoL / PI
			DiffuseLighting += SampleColor * DiffuseColor;
		}
	}

	return DiffuseLighting / NumSamples;
}

float3 SpecularIBL( uint2 Random, float3 SpecularColor, float Roughness, float3 N, float3 V )
{
	float3 SpecularLighting = 0;

	const uint NumSamples = 32;
	for( uint i = 0; i < NumSamples; i++ )
	{
		float2 E = Hammersley( i, NumSamples, Random );
		float3 H = TangentToWorld( ImportanceSampleGGX( E, Roughness ).xyz, N );
		float3 L = 2 * dot( V, H ) * H - V;

		float NoV = saturate( dot( N, V ) );
		float NoL = saturate( dot( N, L ) );
		float NoH = saturate( dot( N, H ) );
		float VoH = saturate( dot( V, H ) );
		
		if( NoL > 0 )
		{
			float3 SampleColor = AmbientCubemap.SampleLevel( AmbientCubemapSampler, L, 0 ).rgb;

			float Vis = Vis_Smith( Roughness, NoV, NoL );
			float Fc = pow( 1 - VoH, 5 );
			float3 F = (1 - Fc) * SpecularColor + Fc;

			// Incident light = SampleColor * NoL
			// Microfacet specular = D*G*F / (4*NoL*NoV) = D*Vis*F
			// pdf = D * NoH / (4 * VoH)
			SpecularLighting += SampleColor * F * ( NoL * Vis * (4 * VoH / NoH) );
		}
	}

	return SpecularLighting / NumSamples;
}

float3 StandardShading( FGBufferData GBuffer, float Roughness, float3 L, float3 V, half3 N )
{
	float3 H = normalize(V + L);
	float NoL = saturate( dot(N, L) );
	float NoV = saturate( dot(N, V) );
	float NoH = saturate( dot(N, H) );
	float VoH = saturate( dot(V, H) );
	
	// Generalized microfacet specular
	float D = D_GGX( Roughness, NoH );
	float Vis = Vis_Schlick( Roughness, NoV, NoL );
	float3 F = F_Schlick( GBuffer.SpecularColor, VoH );
	
	//float k = Square( Roughness ) * 0.25;
	//float Vis = 0.25 / Square( VoH * (1 - k) + k );
	//float Vis = 0.25 / ( VoH * VoH * (1 - k*k) + k*k );
	//float Vis = Vis_Smith( Roughness, NoV, NoL );

	return Diffuse_Lambert( GBuffer.DiffuseColor ) + (D * Vis) * F;
}

float3 ClearCoatShading( FGBufferData GBuffer, float Roughness, float3 L, float3 V, half3 N )
{
	const float ClearCoat			= GBuffer.CustomData.x;
	const float ClearCoatRoughness	= GBuffer.CustomData.y;
	const float Film = 1 * ClearCoat;
	const float MetalSpec = 0.9;

#if 0
	float3 H = normalize(V + L);
	float NoL = saturate( dot(N, L) );
	float NoV = saturate( dot(N, V) );
	float NoH = saturate( dot(N, H) );
	float VoH = saturate( dot(V, H) );
	
	// Generalized microfacet specular
	float D = D_GGX( ClearCoatRoughness, NoH );
	float Vis = Vis_Kelemen( VoH );
	
	// F_Schlick
	float F0 = 0.04;
	float Fc = pow( 1 - VoH, 5 );
	float F = Fc + (1 - Fc) * F0;
	F *= ClearCoat;

	float Fr1 = D * Vis * F;

	float LayerAttenuation = (1 - F);

	// Generalized microfacet specular
	float D2 = D_GGX( Roughness, NoH );
	float Vis2 = Vis_Schlick( Roughness, NoV, NoL );
	float3 F2 = saturate( 50.0 * GBuffer.SpecularColor.g ) * Fc + (1 - Fc) * GBuffer.SpecularColor;

	float3 Fr2 = Diffuse_Lambert( GBuffer.DiffuseColor ) + (D2 * Vis2) * F2;
	
	return Fr1 + Fr2 * LayerAttenuation;
#else
	float3 H = normalize(V + L);
	float NoL = saturate( dot(N, L) );
	float NoV = saturate( dot(N, V) );
	float NoH = saturate( dot(N, H) );
	float VoH = saturate( dot(V, H) );
	
	// Hard coded IOR of 1.5

	// Generalized microfacet specular
	float D = D_GGX( ClearCoatRoughness, NoH );
	float Vis = Vis_Kelemen( VoH );
	
	// F_Schlick
	float F0 = 0.04;
	float Fc = pow( 1 - VoH, 5 );
	float F = Fc + (1 - Fc) * F0;

	float Fr1 = D * Vis * F;

#if 1
	// Refract rays
	float3 L2 = refract( -L, -H, 1 / 1.5 );
	float3 V2 = refract( -V, -H, 1 / 1.5 );

	// LoH == VoH
	float RefractBlend = sqrt( 4 * VoH*VoH + 5 ) / 3 + 2.0 / 3 * VoH;
	//float3 L2 = RefractBlend * H - L / 1.5;
	//float3 V2 = RefractBlend * H - V / 1.5;

	float3 H2 = normalize( V2 + L2 );
	float NoL2 = saturate( dot(N, L2) );
	float NoV2 = saturate( dot(N, V2) );
	float NoH2 = saturate( dot(N, H2) );
	float VoH2 = saturate( dot(V2, H2) );
#else
	// Approximation
	float RefractBlend = (0.22 * VoH + 0.7) * VoH + 0.745;	// 2 mad
	// Dot products distribute. No need for L2 and V2.
	float RefractNoH = RefractBlend * NoH;					// 1 mul
	float NoL2 = saturate( RefractNoH - (1 / 1.5) * NoL );	// 1 mad
	float NoV2 = saturate( RefractNoH - (1 / 1.5) * NoV );	// 1 mad
	// Should refract H too but unimportant
#endif

	NoL2 = max( 0.001, NoL2 );
	NoV2 = max( 0.001, NoV2 );

	float3 AbsorptionColor = (1 - Film) + GBuffer.BaseColor * ( Film * (1 / MetalSpec) );
	float  AbsorptionDist = rcp(NoV2) + rcp(NoL2);
	float3 Absorption = pow( AbsorptionColor, 0.5 * AbsorptionDist );

	// Approximation
	//float  AbsorptionDist = ( NoV2 + NoL2 ) / ( NoV2 * NoL2 );
	//float3 Absorption = AbsorptionColor * ( AbsorptionColor * (AbsorptionDist * 0.5 - 1) + (2 - 0.5 * AbsorptionDist) );
	//float3 Absorption = AbsorptionColor + AbsorptionColor * (AbsorptionColor - 1) * (AbsorptionDist * 0.5 - 1);	// use for shared version
	
#if 1
	float F21 = F_Schlick( 0.04, saturate( dot(V2, H) ) );

	float k = Square( Roughness ) * 0.5;
	float G_SchlickV2 = NoV2 / ( NoV2 * (1 - k) + k );
	float G_SchlickL2 = NoL2 / ( NoL2 * (1 - k) + k );
	float TotalInternalReflection = 1 - F21 * G_SchlickV2 * G_SchlickL2;
	float3 LayerAttenuation = ( (1 - F) * TotalInternalReflection ) * Absorption;
#else
	// Approximation
	float3 LayerAttenuation = (1 - F) * Absorption;
#endif

	// Approximation for IOR == 1.5
	//SpecularColor = ChangeBaseMedium( SpecularColor, 1.5 );
	//SpecularColor = saturate( ( 0.55 * SpecularColor + (0.45 * 1.08) ) * SpecularColor - (0.45 * 0.08) );
	// Treat SpecularColor as relative to IOR. Artist compensates.
	
	// Generalized microfacet specular
#if 1
	float D2 = D_GGX( Roughness, NoH2 );
	float Vis2 = Vis_Schlick( Roughness, NoV2, NoL2 );
	float3 F2 = F_Schlick( MetalSpec, VoH2 );
#else
	// Approximation
	float D2 = D_GGX( Roughness, NoH );
	float Vis2 = Vis_Schlick( Roughness, NoV2, NoL2 );
	float3 F2 = F_Schlick( GBuffer.SpecularColor, VoH );
#endif

	float3 Fr2 = Diffuse_Lambert( GBuffer.DiffuseColor ) + (D2 * Vis2) * F2;
	
	return Fr1 + Fr2 * LayerAttenuation;
#endif
}


float3 ImageBasedLightingMIS( FGBufferData GBuffer, float3 V, float3 N, uint2 Random )
{
	float3 Lighting = 0;

	float Roughness1 = GBuffer.Roughness;
	float Roughness2 = 0.1;
	
	uint NumSamples[] =
	{
		16,
		16,
		16,
	};

	UNROLL
	for( uint Set = 0; Set < 3; Set++ )
	{
		LOOP
		for( uint i = 0; i < NumSamples[ Set ]; i++ )
		{
			float2 E = Hammersley( i, NumSamples[ Set ], Random );
			
			float3 L, H;
			if( Set == 0 )
			{
				L = TangentToWorld( CosineSampleHemisphere( E ).xyz, N );
				H = normalize(V + L);
			}
			else if( Set == 1 )
			{
				H = TangentToWorld( ImportanceSampleGGX( E, Roughness1 ).xyz, N );
				L = 2 * dot( V, H ) * H - V;
			}
			else
			{
				H = TangentToWorld( ImportanceSampleGGX( E, Roughness2 ).xyz, N );
				L = 2 * dot( V, H ) * H - V;
			}

			float NoL = saturate( dot(N, L) );
			float NoH = saturate( dot(N, H) );
			float VoH = saturate( dot(V, H) );
		
			if( NoL > 0 && VoH > 0 )
			{
				float3 SampleColor = AmbientCubemap.SampleLevel( AmbientCubemapSampler, L, 0 ).rgb;

				float PDF[] =
				{
					NoL / PI,
					D_GGX( Roughness1, NoH ) * NoH / (4 * VoH),
					D_GGX( Roughness2, NoH ) * NoH / (4 * VoH),
				};

				// MIS balance heuristic
				float InvWeight = 0;
				UNROLL for( uint j = 0; j < 3; j++ )
				{
					InvWeight += PDF[j] * NumSamples[j];
				}
				float Weight = rcp( InvWeight );

				float3 Shading = 0;
				BRANCH if( GBuffer.ShadingModelID == SHADINGMODELID_CLEAR_COAT )
				{
					Shading = ClearCoatShading( GBuffer, GBuffer.Roughness, L, V, N );
				}
				else
				{
					Shading = StandardShading( GBuffer, GBuffer.Roughness, L, V, N );
				}
			
				Lighting += SampleColor * Shading * ( NoL * Weight );
			}
		}
	}

	return Lighting;
}

float3 FilterEnvMap( uint2 Random, float Roughness, float3 N, float3 V )
{
	float3 FilteredColor = 0;
	float Weight = 0;

	const uint NumSamples = 64;
	for( uint i = 0; i < NumSamples; i++ )
	{
		float2 E = Hammersley( i, NumSamples, Random );
		float3 H = TangentToWorld( ImportanceSampleGGX( E, Roughness ).xyz, N );
		float3 L = 2 * dot( V, H ) * H - V;

		float NoL = saturate( dot( N, L ) );
		if( NoL > 0 )
		{
			FilteredColor += AmbientCubemap.SampleLevel( AmbientCubemapSampler, L, 0 ).rgb * NoL;
			Weight += NoL;
		}
	}

	return FilteredColor / max( Weight, 0.001 );
}

float3 PrefilterEnvMap( uint2 Random, float Roughness, float3 R )
{
	float3 FilteredColor = 0;
	float Weight = 0;
		
	const uint NumSamples = 64;
	for( uint i = 0; i < NumSamples; i++ )
	{
		float2 E = Hammersley( i, NumSamples, Random );
		float3 H = TangentToWorld( ImportanceSampleGGX( E, Roughness ).xyz, R );
		float3 L = 2 * dot( R, H ) * H - R;

		float NoL = saturate( dot( R, L ) );
		if( NoL > 0 )
		{
			FilteredColor += AmbientCubemap.SampleLevel( AmbientCubemapSampler, L, 0 ).rgb * NoL;
			Weight += NoL;
		}
	}

	return FilteredColor / max( Weight, 0.001 );
}

float2 IntegrateBRDF( uint2 Random, float Roughness, float NoV )
{
	float3 V;
	V.x = sqrt( 1.0f - NoV * NoV );	// sin
	V.y = 0;
	V.z = NoV;						// cos

	float A = 0;
	float B = 0;

	const uint NumSamples = 64;
	for( uint i = 0; i < NumSamples; i++ )
	{
		float2 E = Hammersley( i, NumSamples, Random );
		float3 H = ImportanceSampleGGX( E, Roughness ).xyz;
		float3 L = 2 * dot( V, H ) * H - V;

		float NoL = saturate( L.z );
		float NoH = saturate( H.z );
		float VoH = saturate( dot( V, H ) );

		if( NoL > 0 )
		{
			float Vis = Vis_Schlick( Roughness, NoV, NoL );

			// Incident light = NoL
			// pdf = D * NoH / (4 * VoH)
			// NoL * Vis / pdf
			float NoL_Vis_PDF = NoL * Vis * (4 * VoH / NoH);

			float Fc = pow( 1 - VoH, 5 );
			A += (1 - Fc) * NoL_Vis_PDF;
			B += Fc * NoL_Vis_PDF;
		}
	}

	return float2( A, B ) / NumSamples;
}

float3 ApproximateSpecularIBL( uint2 Random, float3 SpecularColor, float Roughness, float3 N, float3 V )
{
	// Function replaced with prefiltered environment map sample
	float3 R = 2 * dot( V, N ) * N - V;
	float3 PrefilteredColor = PrefilterEnvMap( Random, Roughness, R );
	//float3 PrefilteredColor = FilterEnvMap( Random, Roughness, N, V );

	// Function replaced with 2D texture sample
	float NoV = saturate( dot( N, V ) );
	float2 AB = IntegrateBRDF( Random, Roughness, NoV );

	return PrefilteredColor * ( SpecularColor * AB.x + AB.y );
}

void MainPS(in float4 UVAndScreenPos : TEXCOORD0, out float4 OutColor : SV_Target0)
{
	float2 UV = UVAndScreenPos.xy;

	FScreenSpaceData ScreenSpaceData = GetScreenSpaceData(UV);
	FGBufferData GBuffer = ScreenSpaceData.GBuffer;
	float AbsoluteDiffuseMip = AmbientCubemapMipAdjust.z;

	// screen position in [-1, 1] screen space
	float2 ScreenSpacePos = UVAndScreenPos.zw;
	int2 PixelPos = int2(UVAndScreenPos.zw * ScreenPosToPixel.xy + ScreenPosToPixel.zw + 0.5f);

	float3 ScreenVector = normalize(mul(float4(ScreenSpacePos, 1, 0), View.ScreenToWorld).xyz);
	float NoV = saturate( dot( GBuffer.WorldNormal, -ScreenVector ) );
	float3 R = reflect( ScreenVector, GBuffer.WorldNormal );
	
	uint2 Random = ScrambleTEA( PixelPos );
	Random.x ^= View.Random;
	Random.y ^= View.Random;

	float3 NonSpecularContribution = 0;
	float3 SpecularContribution = 0;

	float3 DiffuseLookup =  TextureCubeSampleLevel(AmbientCubemap, AmbientCubemapSampler, GBuffer.WorldNormal, AbsoluteDiffuseMip).rgb;

	// Diffuse
	{
		// we want to access the mip with the preconvolved diffuse lighting (coneangle=90 degree)
		NonSpecularContribution += GBuffer.DiffuseColor * DiffuseLookup;
	}

	// Specular
	{
		float Mip = ComputeCubemapMipFromRoughness( GBuffer.Roughness, AmbientCubemapMipAdjust.w );
		float3 SampleColor = TextureCubeSampleLevel( AmbientCubemap, AmbientCubemapSampler, R, Mip ).rgb;

		BRANCH if( GBuffer.ShadingModelID == SHADINGMODELID_CLEAR_COAT )
		{
			float ClearCoat = GBuffer.CustomData.x;
			float2 AB = PreIntegratedGF.SampleLevel( PreIntegratedGFSampler, float2( NoV, GBuffer.Roughness ), 0 ).rg;
			SpecularContribution += SampleColor * GBuffer.SpecularColor * AB.x + AB.y * (1 - ClearCoat);
		}
		else
		{
			SpecularContribution += SampleColor * EnvBRDF( GBuffer.SpecularColor, GBuffer.Roughness, NoV );
		}
	}

	BRANCH if( GBuffer.ShadingModelID == SHADINGMODELID_CLEAR_COAT )
	{
		const float ClearCoat			= GBuffer.CustomData.x;
		const float ClearCoatRoughness	= GBuffer.CustomData.y;

		float Mip = ComputeCubemapMipFromRoughness( ClearCoatRoughness, AmbientCubemapMipAdjust.w );
		float3 SampleColor = TextureCubeSampleLevel( AmbientCubemap, AmbientCubemapSampler, R, Mip ).rgb;

		// F_Schlick
		float F0 = 0.04;
		float Fc = pow( 1 - NoV, 5 );
		float F = Fc + (1 - Fc) * F0;
		F *= ClearCoat;

		float LayerAttenuation = (1 - F);

		NonSpecularContribution *= LayerAttenuation;
		SpecularContribution *= LayerAttenuation;
		SpecularContribution += SampleColor * F;
	}

#if IMPORTANCE_SAMPLE
	if( GBuffer.ShadingModelID > 0 )
	{
		NonSpecularContribution = 0;
		SpecularContribution = ImageBasedLightingMIS( GBuffer, -ScreenVector, GBuffer.WorldNormal, Random );
	}
#endif
	
	// apply darkening from ambient occlusion (does not use PostprocessInput1 to set white texture if SSAO is off)
	float AmbientOcclusion = GBuffer.GBufferAO * ScreenSpaceData.AmbientOcclusion;

	// Subsurface
	BRANCH if(GBuffer.ShadingModelID == SHADINGMODELID_SUBSURFACE || GBuffer.ShadingModelID == SHADINGMODELID_PREINTEGRATED_SKIN)
	{
		// some view dependent and some non view dependent (hard coded)
		float DependentSplit = 0.5f;

		float3 SubsurfaceColor = ExtractSubsurfaceColor(GBuffer);

		// view independent (shared lookup for diffuse for better performance
		NonSpecularContribution += DiffuseLookup * SubsurfaceColor * (DependentSplit);
		// view dependent (blurriness is hard coded)
		SpecularContribution += TextureCubeSampleLevel(AmbientCubemap, AmbientCubemapSampler, ScreenVector, AbsoluteDiffuseMip - 2.5f).rgb * SubsurfaceColor * (AmbientOcclusion * (1.0f - DependentSplit));
	}

	FLightAccumulator LightAccumulator = (FLightAccumulator)0;

	LightAccumulator_Add(LightAccumulator, NonSpecularContribution, SpecularContribution, AmbientCubemapColor.rgb);

	OutColor = LightAccumulator_GetResult(LightAccumulator);

	OutColor *= AmbientOcclusion;
}