UShaderLab/Shaders/Private/Surface_Substrate.ush

// Copyright UShaderLab. All Rights Reserved.
// Substrate-mode surface/BSDF output structs. Included by ShaderLabCommon.ush only when
// SHADERLAB_SUBSTRATE != 0 (i.e. the project runs with r.Substrate=1). The legacy (non-Substrate)
// counterpart is Surface_Legacy.ush. Keeping the two schemes in separate files makes the legacy path
// deletable wholesale once UE drops the non-Substrate rendering path.

#pragma once

// A single Substrate Slab BSDF layer, filled by an SL_SLAB() body in a multi-slab shader. These 18 fields
// mirror the pins of UMaterialExpressionSubstrateSlabBSDF one-for-one (name/order/type). A slab is only a
// BSDF layer — material-level outputs (Opacity/Refraction/...) are NOT slab concerns: set them once per
// material via an SL_MATERIAL() block (FShaderLabMaterialOutput). Defaults mirror the node's pin defaults.
struct FShaderLabSlab
{
	float3 DiffuseAlbedo;
	float3 F0;
	float3 F90;
	float  Roughness;
	float  Anisotropy;
	float3 Normal;
	float3 Tangent;
	float3 SSSMFP;
	float  SSSMFPScale;
	float  SSSPhaseAnisotropy;
	float3 EmissiveColor;
	float  SecondRoughness;
	float  SecondRoughnessWeight;
	float  FuzzRoughness;
	float  FuzzAmount;
	float3 FuzzColor;
	float  GlintValue;
	float2 GlintUV;
};

// Material-level (whole-material) pixel-stage outputs, filled by an SL_MATERIAL() block in a multi-slab
// shader. Each field maps to a main-material-node pin (NOT a slab pin); which are active depends on the
// material Domain/BlendMode (validated by the graph builder mirroring the engine's IsPropertyActive):
//   Opacity          — translucency coverage (routed through a Substrate Weight over the material)
//   OpacityMask      — Masked blend cutout
//   Refraction       — scalar IOR (RefractionMethod = IndexOfRefraction); 1.0 = no bending
//   PixelDepthOffset — world-unit depth push toward camera
//   AmbientOcclusion — ambient occlusion (Lit)
//   SurfaceThickness — thin-surface thickness in cm (only when the material is a thin surface)
struct FShaderLabMaterialOutput
{
	float  Opacity;
	float  OpacityMask;
	float  Refraction;
	float  PixelDepthOffset;
	float  AmbientOcclusion;
	float  SurfaceThickness;
};

// Simple single-entry surface, filled by the SL_SURFACE(...) body. It is the one-stop path: the 18 Slab
// shading fields (== FShaderLabSlab) PLUS the material-level outputs (== FShaderLabMaterialOutput), so a
// simple opaque/masked/translucent material can be written in one block. Multi-slab shaders instead split
// these across SL_SLAB (FShaderLabSlab) + SL_MATERIAL (FShaderLabMaterialOutput). Slab-field defaults
// mirror the SubstrateSlabBSDF pin defaults; material-output defaults mirror the main-node pin defaults.
struct FShaderLabSurface
{
	float3 DiffuseAlbedo;
	float3 F0;
	float3 F90;
	float  Roughness;
	float  Anisotropy;
	float3 Normal;
	float3 Tangent;
	float3 SSSMFP;
	float  SSSMFPScale;
	float  SSSPhaseAnisotropy;
	float3 EmissiveColor;
	float  SecondRoughness;
	float  SecondRoughnessWeight;
	float  FuzzRoughness;
	float  FuzzAmount;
	float3 FuzzColor;
	float  GlintValue;
	float2 GlintUV;
	// Material-level outputs (single-Surface sugar). See FShaderLabMaterialOutput for pin semantics.
	float  Opacity;
	float  OpacityMask;
	float  Refraction;
	float  PixelDepthOffset;
	float  AmbientOcclusion;
	float  SurfaceThickness;
};

// --- Additional Substrate BSDF output structs. Each mirrors the pins of its engine BSDF node; the graph
// builder wires only the fields a body writes, leaving the rest at the node's native default. ---

// Hair BSDF (SL_HAIR): hair-fiber shading.
struct FShaderLabHair
{
	float3 BaseColor;
	float  Scatter;
	float  Specular;
	float  Roughness;
	float3 Backlit;
	float3 Tangent;
	float3 EmissiveColor;
};

// Eye BSDF (SL_EYE): cornea / iris / sclera shading.
struct FShaderLabEye
{
	float3 DiffuseColor;
	float  Roughness;
	float3 CorneaNormal;
	float3 IrisNormal;
	float3 IrisPlaneNormal;
	float  IrisMask;
	float  IrisDistance;
	float3 EmissiveColor;
};

// Single Layer Water BSDF (SL_WATER): water surface + underwater scattering.
struct FShaderLabWater
{
	float3 BaseColor;
	float  Metallic;
	float  Specular;
	float  Roughness;
	float3 Normal;
	float3 EmissiveColor;
	float3 TopMaterialOpacity;
	float3 WaterAlbedo;
	float3 WaterExtinction;
	float  WaterPhaseG;
	float3 ColorScaleBehindWater;
};

// Volumetric-Fog-Cloud BSDF (SL_VOLUME, Domain = Volume): participating media.
struct FShaderLabVolume
{
	float3 Albedo;
	float3 Extinction;
	float3 EmissiveColor;
	float  AmbientOcclusion;
};

// Simple Clear Coat BSDF (SL_CLEARCOAT): bottom layer + clear coat top.
struct FShaderLabClearCoat
{
	float3 DiffuseAlbedo;
	float3 F0;
	float  Roughness;
	float  ClearCoatCoverage;
	float  ClearCoatRoughness;
	float3 Normal;
	float3 EmissiveColor;
	float3 BottomNormal;
};

// Toon BSDF (SL_TOON, experimental): stylized shading.
struct FShaderLabToon
{
	float3 BaseColor;
	float  Metallic;
	float  Specular;
	float  Roughness;
	float3 Normal;
	float3 EmissiveColor;
	float2 PatternUVs;
	float  Anisotropy;
	float3 Tangent;
};

// Light Function (SL_LIGHTFUNCTION, Domain = LightFunction): per-light modulation color.
struct FShaderLabLightFunction
{
	float3 Color;
};

FShaderLabHair ShaderLabDefaultHair()
{
	FShaderLabHair H;
	H.BaseColor = float3(0, 0, 0);
	H.Scatter = 0;
	H.Specular = 0.5;
	H.Roughness = 0.5;
	H.Backlit = float3(0, 0, 0);
	H.Tangent = float3(1, 0, 0);
	H.EmissiveColor = float3(0, 0, 0);
	return H;
}

FShaderLabEye ShaderLabDefaultEye()
{
	FShaderLabEye E;
	E.DiffuseColor = float3(0, 0, 0);
	E.Roughness = 0.5;
	E.CorneaNormal = float3(0, 0, 1);
	E.IrisNormal = float3(0, 0, 1);
	E.IrisPlaneNormal = float3(0, 0, 1);
	E.IrisMask = 0;
	E.IrisDistance = 0;
	E.EmissiveColor = float3(0, 0, 0);
	return E;
}

FShaderLabWater ShaderLabDefaultWater()
{
	FShaderLabWater W;
	W.BaseColor = float3(0, 0, 0);
	W.Metallic = 0;
	W.Specular = 0.5;
	W.Roughness = 0.5;
	W.Normal = float3(0, 0, 1);
	W.EmissiveColor = float3(0, 0, 0);
	W.TopMaterialOpacity = float3(0, 0, 0);
	W.WaterAlbedo = float3(0, 0, 0);
	W.WaterExtinction = float3(0, 0, 0);
	W.WaterPhaseG = 0;
	W.ColorScaleBehindWater = float3(1, 1, 1);
	return W;
}

FShaderLabVolume ShaderLabDefaultVolume()
{
	FShaderLabVolume V;
	V.Albedo = float3(0, 0, 0);
	V.Extinction = float3(0, 0, 0);
	V.EmissiveColor = float3(0, 0, 0);
	V.AmbientOcclusion = 1;
	return V;
}

FShaderLabClearCoat ShaderLabDefaultClearCoat()
{
	FShaderLabClearCoat C;
	C.DiffuseAlbedo = float3(0.18, 0.18, 0.18);
	C.F0 = float3(0.04, 0.04, 0.04);
	C.Roughness = 0.5;
	C.ClearCoatCoverage = 0.5;
	C.ClearCoatRoughness = 0.5;
	C.Normal = float3(0, 0, 1);
	C.EmissiveColor = float3(0, 0, 0);
	C.BottomNormal = float3(0, 0, 1);
	return C;
}

FShaderLabToon ShaderLabDefaultToon()
{
	FShaderLabToon T;
	T.BaseColor = float3(0.18, 0.18, 0.18);
	T.Metallic = 0;
	T.Specular = 0.5;
	T.Roughness = 0.5;
	T.Normal = float3(0, 0, 1);
	T.EmissiveColor = float3(0, 0, 0);
	T.PatternUVs = float2(0, 0);
	T.Anisotropy = 0;
	T.Tangent = float3(1, 0, 0);
	return T;
}

FShaderLabLightFunction ShaderLabDefaultLightFunction()
{
	FShaderLabLightFunction L;
	L.Color = float3(1, 1, 1);
	return L;
}

FShaderLabSurface ShaderLabDefaultSurface()
{
	FShaderLabSurface S;
	S.DiffuseAlbedo = float3(0.18, 0.18, 0.18);
	S.F0 = float3(0.04, 0.04, 0.04);
	S.F90 = float3(1, 1, 1);
	S.Roughness = 0.5;
	S.Anisotropy = 0;
	S.Normal = float3(0, 0, 1);
	S.Tangent = float3(1, 0, 0);
	S.SSSMFP = float3(0, 0, 0);
	S.SSSMFPScale = 1;
	S.SSSPhaseAnisotropy = 1;
	S.EmissiveColor = float3(0, 0, 0);
	S.SecondRoughness = 0.5;
	S.SecondRoughnessWeight = 0;
	S.FuzzRoughness = 0.5;
	S.FuzzAmount = 0;
	S.FuzzColor = float3(0, 0, 0);
	S.GlintValue = 1;
	S.GlintUV = float2(0, 0);
	S.Opacity = 1;
	S.OpacityMask = 1;
	S.Refraction = 1.0;
	S.PixelDepthOffset = 0.0;
	S.AmbientOcclusion = 1;
	S.SurfaceThickness = 0.01; // SUBSTRATE_LAYER_DEFAULT_THICKNESS_CM
	return S;
}

FShaderLabSlab ShaderLabDefaultSlab()
{
	FShaderLabSlab S;
	S.DiffuseAlbedo = float3(0.18, 0.18, 0.18);
	S.F0 = float3(0.04, 0.04, 0.04);
	S.F90 = float3(1, 1, 1);
	S.Roughness = 0.5;
	S.Anisotropy = 0;
	S.Normal = float3(0, 0, 1);
	S.Tangent = float3(1, 0, 0);
	S.SSSMFP = float3(0, 0, 0);
	S.SSSMFPScale = 1;
	S.SSSPhaseAnisotropy = 1;
	S.EmissiveColor = float3(0, 0, 0);
	S.SecondRoughness = 0.5;
	S.SecondRoughnessWeight = 0;
	S.FuzzRoughness = 0.5;
	S.FuzzAmount = 0;
	S.FuzzColor = float3(0, 0, 0);
	S.GlintValue = 1;
	S.GlintUV = float2(0, 0);
	return S;
}

FShaderLabMaterialOutput ShaderLabDefaultMaterialOutput()
{
	FShaderLabMaterialOutput O;
	O.Opacity = 1;
	O.OpacityMask = 1;
	O.Refraction = 1.0;
	O.PixelDepthOffset = 0.0;
	O.AmbientOcclusion = 1;
	O.SurfaceThickness = 0.01; // SUBSTRATE_LAYER_DEFAULT_THICKNESS_CM
	return O;
}