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359 行
14 KiB
359 行
14 KiB
#ifndef UNITY_IMAGE_BASED_LIGHTING_INCLUDED
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#define UNITY_IMAGE_BASED_LIGHTING_INCLUDED
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#include "CommonLighting.hlsl"
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#include "CommonMaterial.hlsl"
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#include "BSDF.hlsl"
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#include "Sampling.hlsl"
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//-----------------------------------------------------------------------------
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// Util image based lighting
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//-----------------------------------------------------------------------------
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// TODO: We need to change this hard limit!
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#define UNITY_SPECCUBE_LOD_STEPS (6)
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float perceptualRoughnessToMipmapLevel(float perceptualRoughness)
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{
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// TODO: Clean a bit this code
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// CAUTION: remap from Morten may work only with offline convolution, see impact with runtime convolution!
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// For now disabled
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#if 0
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float m = PerceptualRoughnessToRoughness(perceptualRoughness); // m is the real roughness parameter
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float n = (2.0 / max(FLT_EPSILON, m*m)) - 2.0; // remap to spec power. See eq. 21 in --> https://dl.dropboxusercontent.com/u/55891920/papers/mm_brdf.pdf
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n /= 4.0; // remap from n_dot_h formulatino to n_dot_r. See section "Pre-convolved Cube Maps vs Path Tracers" --> https://s3.amazonaws.com/docs.knaldtech.com/knald/1.0.0/lys_power_drops.html
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perceptualRoughness = pow(2.0 / (n + 2.0), 0.25); // remap back to square root of real roughness (0.25 include both the sqrt root of the conversion and sqrt for going from roughness to perceptualRoughness)
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#else
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// MM: came up with a surprisingly close approximation to what the #if 0'ed out code above does.
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perceptualRoughness = perceptualRoughness * (1.7 - 0.7 * perceptualRoughness);
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#endif
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return perceptualRoughness * UNITY_SPECCUBE_LOD_STEPS;
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}
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// Ref: See "Moving Frostbite to PBR" Listing 22
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// This formulation is for GGX only (with smith joint visibility or regular)
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float3 GetSpecularDominantDir(float3 N, float3 R, float roughness)
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{
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float a = 1.0 - roughness;
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float lerpFactor = a * (sqrt(a) + roughness);
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// The result is not normalized as we fetch in a cubemap
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return lerp(N, R, lerpFactor);
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}
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//-----------------------------------------------------------------------------
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// Anisotropic image based lighting
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//-----------------------------------------------------------------------------
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// To simulate the streching of highlight at grazing angle for IBL we shrink the roughness
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// which allow to fake an anisotropic specular lobe.
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// Ref: http://www.frostbite.com/2015/08/stochastic-screen-space-reflections/ - slide 84
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float AnisotropicStrechAtGrazingAngle(float roughness, float perceptualRoughness, float NdotV)
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{
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return roughness * lerp(saturate(NdotV * 2.0), 1.0, perceptualRoughness);
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}
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// ----------------------------------------------------------------------------
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// Importance sampling BSDF functions
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// ----------------------------------------------------------------------------
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void ImportanceSampleCosDir(float2 u,
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float3 N,
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float3 tangentX,
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float3 tangentY,
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out float3 L)
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{
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// Cosine sampling - ref: http://www.rorydriscoll.com/2009/01/07/better-sampling/
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float cosTheta = sqrt(max(0.0, 1.0 - u.x));
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float sinTheta = sqrt(u.x);
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float phi = TWO_PI * u.y;
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// Transform from spherical into cartesian
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L = float3(sinTheta * cos(phi), sinTheta * sin(phi), cosTheta);
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// Local to world
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L = tangentX * L.x + tangentY * L.y + N * L.z;
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}
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void ImportanceSampleGGXDir(float2 u,
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float3 V,
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float3 N,
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float3 tangentX,
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float3 tangentY,
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float roughness,
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out float3 H,
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out float3 L)
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{
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// GGX NDF sampling
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float cosThetaH = sqrt((1.0 - u.x) / (1.0 + (roughness * roughness - 1.0) * u.x));
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float sinThetaH = sqrt(max(0.0, 1.0 - cosThetaH * cosThetaH));
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float phiH = TWO_PI * u.y;
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// Transform from spherical into cartesian
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H = float3(sinThetaH * cos(phiH), sinThetaH * sin(phiH), cosThetaH);
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// Local to world
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H = tangentX * H.x + tangentY * H.y + N * H.z;
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// Convert sample from half angle to incident angle
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L = 2.0 * dot(V, H) * H - V;
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}
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// ref: http://blog.selfshadow.com/publications/s2012-shading-course/burley/s2012_pbs_disney_brdf_notes_v3.pdf p26
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void ImportanceSampleAnisoGGXDir( float2 u,
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float3 V,
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float3 N,
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float3 tangentX,
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float3 tangentY,
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float roughnessT,
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float roughnessB,
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out float3 H,
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out float3 L)
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{
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// AnisoGGX NDF sampling
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H = sqrt(u.x / (1.0 - u.x)) * (roughnessT * cos(TWO_PI * u.y) * tangentX + roughnessB * sin(TWO_PI * u.y) * tangentY) + N;
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H = normalize(H);
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// Local to world
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// H = tangentX * H.x + tangentY * H.y + N * H.z;
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// Convert sample from half angle to incident angle
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L = 2.0 * dot(V, H) * H - V;
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}
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// weightOverPdf return the weight (without the diffuseAlbedo term) over pdf. diffuseAlbedo term must be apply by the caller.
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void ImportanceSampleLambert(
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float2 u,
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float3 N,
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float3 tangentX,
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float3 tangentY,
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out float3 L,
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out float NdotL,
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out float weightOverPdf)
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{
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ImportanceSampleCosDir(u, N, tangentX, tangentY, L);
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NdotL = saturate(dot(N, L));
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// Importance sampling weight for each sample
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// pdf = N.L / PI
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// weight = fr * (N.L) with fr = diffuseAlbedo / PI
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// weight over pdf is:
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// weightOverPdf = (diffuseAlbedo / PI) * (N.L) / (N.L / PI)
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// weightOverPdf = diffuseAlbedo
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// diffuseAlbedo is apply outside the function
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weightOverPdf = 1.0;
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}
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// weightOverPdf return the weight (without the Fresnel term) over pdf. Fresnel term must be apply by the caller.
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void ImportanceSampleGGX(
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float2 u,
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float3 V,
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float3 N,
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float3 tangentX,
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float3 tangentY,
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float roughness,
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float NdotV,
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out float3 L,
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out float VdotH,
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out float NdotL,
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out float weightOverPdf)
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{
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float3 H;
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ImportanceSampleGGXDir(u, V, N, tangentX, tangentY, roughness, H, L);
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float NdotH = saturate(dot(N, H));
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// Note: since L and V are symmetric around H, LdotH == VdotH
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VdotH = saturate(dot(V, H));
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NdotL = saturate(dot(N, L));
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// Importance sampling weight for each sample
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// pdf = D(H) * (N.H) / (4 * (L.H))
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// weight = fr * (N.L) with fr = F(H) * G(V, L) * D(H) / (4 * (N.L) * (N.V))
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// weight over pdf is:
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// weightOverPdf = F(H) * G(V, L) * (L.H) / ((N.H) * (N.V))
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// weightOverPdf = F(H) * 4 * (N.L) * V(V, L) * (L.H) / (N.H) with V(V, L) = G(V, L) / (4 * (N.L) * (N.V))
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// Remind (L.H) == (V.H)
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// F is apply outside the function
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float Vis = V_SmithJointGGX(NdotL, NdotV, roughness);
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weightOverPdf = 4.0 * Vis * NdotL * VdotH / NdotH;
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}
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// weightOverPdf return the weight (without the Fresnel term) over pdf. Fresnel term must be apply by the caller.
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void ImportanceSampleAnisoGGX(
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float2 u,
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float3 V,
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float3 N,
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float3 tangentX,
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float3 tangentY,
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float roughnessT,
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float roughnessB,
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float NdotV,
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out float3 L,
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out float VdotH,
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out float NdotL,
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out float weightOverPdf)
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{
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float3 H;
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ImportanceSampleAnisoGGXDir(u, V, N, tangentX, tangentY, roughnessT, roughnessB, H, L);
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float NdotH = saturate(dot(N, H));
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// Note: since L and V are symmetric around H, LdotH == VdotH
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VdotH = saturate(dot(V, H));
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NdotL = saturate(dot(N, L));
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// Importance sampling weight for each sample
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// pdf = D(H) * (N.H) / (4 * (L.H))
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// weight = fr * (N.L) with fr = F(H) * G(V, L) * D(H) / (4 * (N.L) * (N.V))
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// weight over pdf is:
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// weightOverPdf = F(H) * G(V, L) * (L.H) / ((N.H) * (N.V))
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// weightOverPdf = F(H) * 4 * (N.L) * V(V, L) * (L.H) / (N.H) with V(V, L) = G(V, L) / (4 * (N.L) * (N.V))
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// Remind (L.H) == (V.H)
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// F is apply outside the function
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float TdotV = dot(tangentX, V);
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float BdotV = dot(tangentY, V);
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float TdotL = saturate(dot(tangentX, L));
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float BdotL = saturate(dot(tangentY, L));
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float Vis = V_SmithJointGGXAniso(TdotV, BdotV, NdotV, TdotL, BdotL, NdotL, roughnessT, roughnessB);
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weightOverPdf = 4.0 * Vis * NdotL * VdotH / NdotH;
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}
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// ----------------------------------------------------------------------------
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// Pre-integration
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// ----------------------------------------------------------------------------
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// Ref: Listing 18 in "Moving Frostbite to PBR" + https://knarkowicz.wordpress.com/2014/12/27/analytical-dfg-term-for-ibl/
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float4 IntegrateGGXAndDisneyFGD(float3 V, float3 N, float roughness, uint sampleCount)
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{
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float NdotV = saturate(dot(N, V));
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float4 acc = float4(0.0, 0.0, 0.0, 0.0);
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// Add some jittering on Hammersley2d
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float2 randNum = InitRandom(V.xy * 0.5 + 0.5);
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float3 tangentX, tangentY;
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GetLocalFrame(N, tangentX, tangentY);
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for (uint i = 0; i < sampleCount; ++i)
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{
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float2 u = Hammersley2d(i, sampleCount);
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u = frac(u + randNum + 0.5);
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float VdotH;
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float NdotL;
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float weightOverPdf;
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float3 L; // Unused
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ImportanceSampleGGX(u, V, N, tangentX, tangentY, roughness, NdotV,
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L, VdotH, NdotL, weightOverPdf);
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if (NdotL > 0.0)
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{
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// Integral is
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// 1 / NumSample * \int[ L * fr * (N.L) / pdf ] with pdf = D(H) * (N.H) / (4 * (L.H)) and fr = F(H) * G(V, L) * D(H) / (4 * (N.L) * (N.V))
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// This is split in two part:
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// A) \int[ L * (N.L) ]
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// B) \int[ F(H) * 4 * (N.L) * V(V, L) * (L.H) / (N.H) ] with V(V, L) = G(V, L) / (4 * (N.L) * (N.V))
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// = \int[ F(H) * weightOverPdf ]
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// Recombine at runtime with: ( f0 * weightOverPdf * (1 - Fc) + f90 * weightOverPdf * Fc ) with Fc =(1 - V.H)^5
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float Fc = pow(1.0 - VdotH, 5.0);
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acc.x += (1.0 - Fc) * weightOverPdf;
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acc.y += Fc * weightOverPdf;
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}
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// for Disney we still use a Cosine importance sampling, true Disney importance sampling imply a look up table
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ImportanceSampleLambert(u, N, tangentX, tangentY, L, NdotL, weightOverPdf);
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if (NdotL > 0.0)
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{
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float3 H = normalize(L + V);
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float LdotH = dot(L, H);
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float disneyDiffuse = DisneyDiffuse(NdotV, NdotL, LdotH, RoughnessToPerceptualRoughness(roughness));
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acc.z += disneyDiffuse * weightOverPdf;
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}
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}
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return acc / sampleCount;
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}
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// Ref: Listing 19 in "Moving Frostbite to PBR"
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float4 IntegrateLD(TEXTURECUBE_ARGS(tex, sampl),
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float3 V,
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float3 N,
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float roughness,
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float mipmapcount,
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float invOmegaP,
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uint sampleCount,
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bool prefilter = true) // static bool
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{
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float3 acc = float3(0.0, 0.0, 0.0);
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float accWeight = 0;
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float2 randNum = InitRandom(V.xy * 0.5 + 0.5);
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float3 tangentX, tangentY;
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GetLocalFrame(N, tangentX, tangentY);
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for (uint i = 0; i < sampleCount; ++i)
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{
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float2 u = Hammersley2d(i, sampleCount);
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u = frac(u + randNum + 0.5);
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float3 H;
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float3 L;
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ImportanceSampleGGXDir(u, V, N, tangentX, tangentY, roughness, H, L);
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float NdotL = saturate(dot(N,L));
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float mipLevel;
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if (!prefilter) // BRDF importance sampling
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{
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mipLevel = 0.0;
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}
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else // Prefiltered BRDF importance sampling
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{
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float NdotH = saturate(dot(N, H));
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// Note: since L and V are symmetric around H, LdotH == VdotH
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float LdotH = saturate(dot(L, H));
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// Use pre - filtered importance sampling (i.e use lower mipmap
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// level for fetching sample with low probability in order
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// to reduce the variance ).
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// ( Reference : GPU Gem3: http://http.developer.nvidia.com/GPUGems3/gpugems3_ch20.html)
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//
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// Since we pre - integrate the result for normal direction ,
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// N == V and then NdotH == LdotH . This is why the BRDF pdf
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// can be simplifed from :
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// pdf = D * NdotH /(4* LdotH ) to pdf = D / 4;
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//
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// - OmegaS : Solid angle associated to a sample
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// - OmegaP : Solid angle associated to a pixel of the cubemap
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float pdf = D_GGXNoPI(NdotH, roughness) * NdotH / (4.0 * LdotH); // TODO: Check if divide PI is required here
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float omegaS = 1.0 / (sampleCount * pdf); // Solid angle associated to a sample
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// invOmegaP is precomputed on CPU and provide as a parameter of the function
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// float omegaP = FOUR_PI / (6.0f * cubemapWidth * cubemapWidth); // Solid angle associated to a pixel of the cubemap
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// Clamp is not necessary as the hardware will do it.
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// mipLevel = Clamp(0.5f * log2(omegaS * invOmegaP), 0, mipmapcount);
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mipLevel = 0.5 * log2(omegaS * invOmegaP); // Clamp is not necessary as the hardware will do it.
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}
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if (NdotL > 0.0f)
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{
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float3 val = SAMPLE_TEXTURECUBE_LOD(tex, sampl, L, mipLevel).rgb;
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// See p63 equation (53) of moving Frostbite to PBR v2 for the extra NdotL here (both in weight and value)
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acc += val * NdotL;
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accWeight += NdotL;
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}
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}
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return float4(acc * (1.0 / accWeight), 1.0);
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}
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#endif // UNITY_IMAGE_BASED_LIGHTING_INCLUDED
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