UnrealEngineUWP/Engine/Shaders/ShadingModels.usf

// Copyright 1998-2015 Epic Games, Inc. All Rights Reserved.

#pragma once

#include "DeferredShadingCommon.usf"
#include "BRDF.usf"

#if 0
void StandardShadingShared( float3 DiffuseColor, float3 SpecularColor, float Roughness, float3 V, half3 N )
{
	//float NoV = saturate( dot(N, V) );
	float NoV = abs( dot(N, V) ) + 1e-5;

	// Diffuse_Lambert
	Shared.DiffuseMul = DiffuseColor * (1.0 / PI);

	// D_GGX, Vis_SmithJointApprox
	float m = Roughness * Roughness;
	Shared.m2 = m * m;
	Shared.SpecularMul = (0.5 / PI) * Shared.m2;
	Shared.VisMad = float2( 2 * NoV * ( 1 - m ) + m, NoV * m );
	
	// F_Schlick
	Shared.SpecularMul *= saturate( 50.0 * SpecularColor.g );
}

void StandardShadingPerLight( Shared, float3 L, float3 V, half3 N )
{
	float3 H = normalize(V + L);			// 3 add, 2 mad, 4 mul, 1 rsqrt
	float NoL = saturate( dot(N, L) );		// 2 mad, 1 mul
	float NoH = saturate( dot(N, H) );		// 2 mad, 1 mul
	float VoH = saturate( dot(V, H) );		// 2 mad, 1 mul

	// D_GGX, Vis_SmithJointApprox
	float d = ( NoH * Shared.m2 - NoH ) * NoH + 1;			// 2 mad
	float v = NoL * Shared.VisMad.x + Shared.VisMad.y;		// 1 mad
	float D_Vis = Shared.SpecularMul * rcp( d * d * v );	// 3 mul, 1 rcp

	// F_Schlick
	float Fc = pow( 1 - VoH, 5 );							// 1 sub, 3 mul
	float3 F = Fc + (1 - Fc) * SpecularColor;				// 1 sub, 3 mad

	return Shared.DiffuseMul + D_Vis * F;					// 3 mad
}
#endif

// @param DiffSpecMask .r: diffuse, .g:specular e.g. float2(1,1) for both, float2(1,0) for diffuse only
float3 StandardShading( FGBufferData GBuffer, float3 LobeRoughness, float3 LobeEnergy, float3 L, float3 V, half3 N, float2 DiffSpecMask )
{
	float3 H = normalize(V + L);
	float NoL = saturate( dot(N, L) );
	//float NoV = saturate( dot(N, V) );
	float NoV = max( dot(N, V), 1e-5 );
	float NoH = saturate( dot(N, H) );
	float VoH = saturate( dot(V, H) );
	
	// Generalized microfacet specular
	float D = D_GGX( LobeRoughness[1], NoH ) * LobeEnergy[1];
	float Vis = Vis_SmithJointApprox( LobeRoughness[1], NoV, NoL );
	float3 F = F_Schlick( GBuffer.SpecularColor, VoH );

	float3 Diffuse = Diffuse_Lambert( GBuffer.DiffuseColor );
	//float3 Diffuse = Diffuse_Burley( GBuffer.DiffuseColor, LobeRoughness[1], NoV, NoL, VoH );
	//float3 Diffuse = Diffuse_OrenNayar( GBuffer.DiffuseColor, LobeRoughness[1], NoV, NoL, VoH );
	
	return Diffuse * (LobeEnergy[2] * DiffSpecMask.r) + (D * Vis * DiffSpecMask.g) * F;
}

float3 SimpleShading( FGBufferData GBuffer, float Roughness, float3 L, float3 V, half3 N )
{
	float3 H = normalize(V + L);
	float NoH = saturate( dot(N, H) );
	
	// Generalized microfacet specular
	float D = D_GGX( Roughness, NoH );
	float Vis = Vis_Implicit();
	float3 F = F_None( GBuffer.SpecularColor );

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

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

#if 1
	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( LobeRoughness[0], NoH ) * LobeEnergy[0];
	float Vis = Vis_Kelemen( VoH );
	
	// F_Schlick
	float F0 = 0.04;
	float Fc = Pow5( 1 - VoH );
	float F = Fc + (1 - Fc) * F0;
	F *= ClearCoat;

	float Fr1 = D * Vis * F;

	float LayerAttenuation = (1 - F);

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

	//float3 Fr2 = Diffuse_Burley( GBuffer.DiffuseColor, LobeRoughness[1], NoV, NoL, VoH ) * LobeEnergy[2] + (D2 * Vis2) * F2;
	float3 Fr2 = Diffuse_Lambert( GBuffer.DiffuseColor ) * LobeEnergy[2] + (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 ) * LobeEnergy[0];
	float Vis = Vis_Kelemen( VoH );
	
	// F_Schlick
	float F0 = 0.04;
	float Fc = Pow5( 1 - VoH );
	float F = Fc + (1 - Fc) * F0;

	float Fr1 = D * Vis * F;

	// 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;
	//float NoL2 = saturate( dot(N, L2) );
	//float NoV2 = saturate( dot(N, V2) );
	
	// 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

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

	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
	
	//float F21 = Fresnel( 1 / 1.5, saturate( dot(V2, H) ) );
	//float TotalInternalReflection = 1 - F21 * G_Schlick( Roughness, NoV2, NoL2 );
	//float3 LayerAttenuation = ( (1 - F12) * TotalInternalReflection ) * Absorption;

	// Approximation
	float3 LayerAttenuation = (1 - F) * Absorption;

	// 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
	float D2 = D_GGX( Roughness, NoH ) * LobeEnergy[2];
	float Vis2 = Vis_Schlick( Roughness, NoV2, NoL2 );
	float3 F2 = F_Schlick( GBuffer.SpecularColor, VoH );

	float3 Fr2 = Diffuse_Lambert( GBuffer.DiffuseColor ) * LobeEnergy[2] + (D2 * Vis2) * F2;
	
	return Fr1 + Fr2 * LayerAttenuation;
#endif
#else //USE_CLEARCOAT
	return float3(0.0f, 0.0f, 0.0f);
#endif //USE_CLEARCOAT
}

float3 SubsurfaceShadingSubsurface( FGBufferData GBuffer, float3 L, float3 V, half3 N )
{
	float3 SubsurfaceColor = ExtractSubsurfaceColor(GBuffer);

	float3 H = normalize(V + L);

	// to get an effect when you see through the material
	// hard coded pow constant
	float InScatter = pow(saturate(dot(L, -V)), 12) * lerp(3, .1f, GBuffer.Opacity);
	// wrap around lighting, /(PI*2) to be energy consistent (hack do get some view dependnt and light dependent effect)
	float OpacityFactor = GBuffer.Opacity;
	// Opacity of 0 gives no normal dependent lighting, Opacity of 1 gives strong normal contribution
	float NormalContribution = saturate(dot(N, H) * OpacityFactor + 1 - OpacityFactor);
	float BackScatter = GBuffer.GBufferAO * NormalContribution / (PI * 2);

	// lerp to never exceed 1 (energy conserving)
	return SubsurfaceColor * lerp(BackScatter, 1, InScatter);
}

float3 SubsurfaceShadingTwoSided( float3 SubsurfaceColor, float3 L, float3 V, half3 N )
{
	// http://blog.stevemcauley.com/2011/12/03/energy-conserving-wrapped-diffuse/
	float Wrap = 0.5;
	float NoL = saturate( ( dot(-N, L) + Wrap ) / Square( 1 + Wrap ) );

	// GGX scatter distribution
	float VoL = saturate( dot(V, -L) );
	float a = 0.6;
	float a2 = a * a;
	float d = ( VoL * a2 - VoL ) * VoL + 1;	// 2 mad
	float GGX = (a2 / PI) / (d * d);		// 2 mul, 1 rcp
	return NoL * GGX * SubsurfaceColor;
}

Texture2D		PreIntegratedBRDF;
SamplerState	PreIntegratedBRDFSampler;

float3 SubsurfaceShadingPreintegratedSkin( FGBufferData GBuffer, float3 L, float3 V, half3 N )
{
	float3 SubsurfaceColor = ExtractSubsurfaceColor(GBuffer);

	float OpacityFactor = GBuffer.Opacity;
	float3 PreintegratedBRDF = Texture2DSampleLevel(PreIntegratedBRDF, PreIntegratedBRDFSampler, float2(saturate(dot(N, L) * .5 + .5), 1 - OpacityFactor), 0).rgb;
	return PreintegratedBRDF * SubsurfaceColor;
}

// @param DiffSpecMask .r: diffuse, .g:specular e.g. float2(1,1) for both, float2(1,0) for diffuse only
float3 SurfaceShading( FGBufferData GBuffer, float3 LobeRoughness, float3 LobeEnergy, float3 L, float3 V, half3 N, float2 DiffSpecMask )
{
	switch( GBuffer.ShadingModelID )
	{
		case SHADINGMODELID_UNLIT:
		case SHADINGMODELID_DEFAULT_LIT:
		case SHADINGMODELID_SUBSURFACE:
		case SHADINGMODELID_PREINTEGRATED_SKIN:
		case SHADINGMODELID_SUBSURFACE_PROFILE:
		case SHADINGMODELID_TWOSIDED_FOLIAGE:
			return StandardShading( GBuffer, LobeRoughness, LobeEnergy, L, V, N, DiffSpecMask);
		case SHADINGMODELID_CLEAR_COAT:
			// this path does not support DiffSpecMask yet
			return ClearCoatShading( GBuffer, LobeRoughness, LobeEnergy, L, V, N );
		default:
			return 0;
	}
}

float3 SubsurfaceShading( FGBufferData GBuffer, float3 L, float3 V, half3 N )
{
	float3 SubsurfaceColor = ExtractSubsurfaceColor(GBuffer);

	switch( GBuffer.ShadingModelID )
	{
		case SHADINGMODELID_SUBSURFACE:
			return SubsurfaceShadingSubsurface( GBuffer, L, V, N );
		case SHADINGMODELID_PREINTEGRATED_SKIN:
			return SubsurfaceShadingPreintegratedSkin( GBuffer, L, V, N );
		case SHADINGMODELID_TWOSIDED_FOLIAGE:
			return SubsurfaceShadingTwoSided( SubsurfaceColor, L, V, N );
		default:
			return 0;
	}
}