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59 lines
2.2 KiB
59 lines
2.2 KiB
using System;
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using UnityEngine.Rendering;
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namespace UnityEngine.Rendering.HighDefinition.LTC
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{
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/// <summary>
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/// Cook-Torrance implementation of the BRDF interface
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/// </summary>
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struct BRDF_CookTorrance : IBRDF
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{
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public double Eval(ref Vector3 _tsView, ref Vector3 _tsLight, float _alpha, out double _pdf)
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{
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if (_tsView.z <= 0)
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{
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_pdf = 0;
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return 0;
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}
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_alpha = Mathf.Max(0.002f, _alpha);
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Vector3 H = (_tsView + _tsLight).normalized;
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double NdotL = Math.Max(1e-8, _tsLight.z);
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double NdotV = Math.Max(1e-8, _tsView.z);
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double NdotH = H.z;
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double LdotH = Math.Max(1e-8, Vector3.Dot(_tsLight, H));
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// D
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double cosb2 = NdotH * NdotH;
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double m2 = _alpha * _alpha;
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double D = Math.Exp((cosb2 - 1.0) / (cosb2 * m2)) // exp( -tan(a)² / m² )
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/ Math.Max(1e-12, Math.PI * m2 * cosb2 * cosb2); // / (PI * m² * cos(a)^4)
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// masking/shadowing
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double G = Math.Min(1, 2.0 * NdotH * Math.Min(NdotV, NdotL) / LdotH);
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// fr = F(H) * G(V, L) * D(H) / (4 * (N.L) * (N.V))
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double res = D * G / (4.0 * NdotV); // Full specular mico-facet model is F * D * G / (4 * NdotL * NdotV) but since we're fitting with the NdotL included, it gets nicely canceled out!
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// pdf = D(H) * (N.H) / (4 * (L.H))
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_pdf = Math.Abs(D * NdotH / (4.0 * LdotH));
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return res;
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}
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public void GetSamplingDirection(ref Vector3 _tsView, float _alpha, float _U1, float _U2, ref Vector3 _direction)
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{
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float phi = 2.0f * Mathf.PI * _U1;
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float cosTheta = 1.0f / Mathf.Sqrt(1 - _alpha * _alpha * Mathf.Log(Mathf.Max(1e-6f, _U2)));
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float sinTheta = Mathf.Sqrt(1 - cosTheta * cosTheta);
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Vector3 H = new Vector3(sinTheta * Mathf.Cos(phi), sinTheta * Mathf.Sin(phi), cosTheta);
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_direction = 2.0f * Vector3.Dot(H, _tsView) * H - _tsView; // Mirror view direction
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}
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public LTCLightingModel GetLightingModel()
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{
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return LTCLightingModel.CookTorrance;
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}
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}
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}
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