# BRDF

By: a guest on Feb 25th, 2013  |  syntax: C  |  size: 2.83 KB  |  views: 144  |  expires: Never
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1. analytic
2.
3. ::begin parameters
4. color Diffuse 1 0 0
5. color Specular 1 1 1
6. float DiffuseScale 0 1 0.5
7. float SpecularScale 0 1 .028
8. float Roughness 0.00005 2 0.2
9. float Roughness2 0.00005 2 0.2
10. float Retroreflective 0 1 0
11. bool FullFresnel 0 1 0
12. bool isotropic 1
13. ::end parameters
14.
16.
17. //Thanks to Chris_F for starting ideas.
18. // Cook-Torrance, GGX distribution (bastardised with ashikhman shirley), Smith geometry, qualitative Oren-Nayar diffuse.
19.
20. float saturate(float x) { return clamp(x,0,1); }
21.
22. vec3 Fresnel(float CosTheta, vec3 Ks)
23. {
24.         CosTheta = min(CosTheta, 0.99999999999999999);
25.         vec3 n2 = (1.0 + sqrt(Ks)) / (1.0 - sqrt(Ks));
26.         vec3 SinTheta = vec3(sqrt(1 - CosTheta * CosTheta));
27.
28.         vec3 SinThetaT = SinTheta / n2;
29.         vec3 CosThetaT = sqrt(1 - SinThetaT * SinThetaT);
30.
31.         vec3 n2CosThetaT = n2 * CosThetaT;
32.         vec3 n2CosTheta = n2 * CosTheta;
33.
34.         vec3 RsSqrt = (CosTheta - n2CosThetaT) / (CosTheta + n2CosThetaT);
36.
37.         vec3 RpSqrt = (n2CosTheta - CosThetaT) / (n2CosTheta + CosThetaT);
38.         vec3 Rp = RpSqrt * RpSqrt;
39.
40.         return (Rs + Rp) / 2;
41. }
42.
43. vec3 BRDF( vec3 L, vec3 V, vec3 N, vec3 X, vec3 Y )
44. {
45. //vec3 temp = L; L = V; V = temp;
46.         float PI = 3.14159265358979323846;
47.         vec3 Kd = Diffuse * DiffuseScale;
48.         vec3 Ks = Specular * SpecularScale;
49.
50.         vec3 H = normalize(L + V);
51.         float NdotL = clamp(dot(N, L), 0, 1);
52.         float NdotV = dot(N, V);
53.         float NdotH = dot(N, H);
54.         float LdotV = dot(L, V);
55.         float VdotH = dot(V, H);
56.         float LdotH = dot(L, H);
57.         float HdotX = dot(H,X);
58.         float HdotY = dot(H,Y);
59.
60.         float m1 = 1/Roughness;
61.         float m2 = 1/Roughness2;
62.         float M = isotropic ? Roughness : (1-(NdotH*NdotH)) / ( m1*HdotX*HdotX + m2*HdotY*HdotY );
63.         float M_2 = isotropic ? M * M : M* min(Roughness, Roughness2);
64.
65.         NdotH = mix( mix( NdotH, max(NdotH,LdotV), saturate(Retroreflective*2) ), LdotV, saturate(Retroreflective*2-1) );
66.
67.         float NdotL_2 = NdotL * NdotL;
68.         float NdotV_2 = NdotV * NdotV;
69.         float NdotH_2 = NdotH * NdotH;
70.         float OneMinusNdotL_2 = 1.0 - NdotL_2;
71.         float OneMinusNdotV_2 = 1.0 - NdotV_2;
72.
73.         vec3 Fd = 1.0 - Ks;
74.
75.         float gamma = clamp(dot(V - N * NdotV, L - N * NdotL), 0, 1);
76.         float A = 1.0 - 0.5 * (M_2 / (M_2 + 0.33));
77.         float B = 0.45 * (M_2 / (M_2 + 0.09));
78.         float C = sqrt(OneMinusNdotL_2 * OneMinusNdotV_2) / max(NdotL, NdotV);
79.
80.         vec3 Rd = Kd * Fd * (A + B * gamma * C) * 1/PI;
81.
82.         float ggxDenom = NdotH_2 * (M_2 + (1-NdotH_2)/NdotH_2);
83.         float D = M/ggxDenom;
84.         D = D*D/PI;
85.         D *= isotropic ? 1 : min(m1,m2)/max(m1,m2);
86.
87.         vec3 Fs;
88.         if( FullFresnel )
89.                 Fs = Fresnel(NdotV, Ks);
90.         else
91.                 Fs = Ks + Fd * pow(1-LdotH, 5);
92.
93.         float G1_1 = 1.0 + sqrt(1.0 + M_2 * (OneMinusNdotL_2 / NdotL_2));
94.         float G1_2 = 1.0 + sqrt(1.0 + M_2 * (OneMinusNdotV_2 / NdotV_2));
95.         float G = ((2/G1_1) * (2/G1_2))/(4 * NdotV * NdotL);
96.
97.         vec3 Rs = Fs * D * G;
98.
99.         return vec3(Rd + Rs);
100. }
101.