1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
|
/*
* Copyright 2011-2014 Blender Foundation
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#ifndef __BSDF_ASHIKHMIN_SHIRLEY_H__
#define __BSDF_ASHIKHMIN_SHIRLEY_H__
/*
ASHIKHMIN SHIRLEY BSDF
Implementation of
Michael Ashikhmin and Peter Shirley: "An Anisotropic Phong BRDF Model" (2000)
The Fresnel factor is missing to get a separable bsdf (intensity*color), as is
the case with all other microfacet-based BSDF implementations in Cycles.
Other than that, the implementation directly follows the paper.
*/
CCL_NAMESPACE_BEGIN
ccl_device int bsdf_ashikhmin_shirley_setup(ShaderClosure *sc)
{
sc->data0 = clamp(sc->data0, 1e-4f, 1.0f);
sc->data1 = sc->data0;
sc->type = CLOSURE_BSDF_ASHIKHMIN_SHIRLEY_ID;
return SD_BSDF|SD_BSDF_HAS_EVAL;
}
ccl_device int bsdf_ashikhmin_shirley_aniso_setup(ShaderClosure *sc)
{
sc->data0 = clamp(sc->data0, 1e-4f, 1.0f);
sc->data1 = clamp(sc->data1, 1e-4f, 1.0f);
sc->type = CLOSURE_BSDF_ASHIKHMIN_SHIRLEY_ANISO_ID;
return SD_BSDF|SD_BSDF_HAS_EVAL;
}
ccl_device void bsdf_ashikhmin_shirley_blur(ShaderClosure *sc, float roughness)
{
sc->data0 = fmaxf(roughness, sc->data0); /* clamp roughness */
sc->data1 = fmaxf(roughness, sc->data1);
}
ccl_device_inline float bsdf_ashikhmin_shirley_roughness_to_exponent(float roughness)
{
return 2.0f / (roughness*roughness) - 2.0f;
}
ccl_device float3 bsdf_ashikhmin_shirley_eval_reflect(const ShaderClosure *sc, const float3 I, const float3 omega_in, float *pdf)
{
float3 N = sc->N;
float NdotI = dot(N, I); /* in Cycles/OSL convention I is omega_out */
float NdotO = dot(N, omega_in); /* and consequently we use for O omaga_in ;) */
float out = 0.0f;
if(NdotI > 0.0f && NdotO > 0.0f) {
NdotI = fmaxf(NdotI, 1e-6f);
NdotO = fmaxf(NdotO, 1e-6f);
float3 H = normalize(omega_in + I);
float HdotI = fmaxf(fabsf(dot(H, I)), 1e-6f);
float HdotN = fmaxf(dot(H, N), 1e-6f);
float pump = 1.0f / fmaxf(1e-6f, (HdotI*fmaxf(NdotO, NdotI))); /* pump from original paper (first derivative disc., but cancels the HdotI in the pdf nicely) */
/*float pump = 1.0f / fmaxf(1e-4f, ((NdotO + NdotI) * (NdotO*NdotI))); */ /* pump from d-brdf paper */
float n_x = bsdf_ashikhmin_shirley_roughness_to_exponent(sc->data0);
float n_y = bsdf_ashikhmin_shirley_roughness_to_exponent(sc->data1);
if(n_x == n_y) {
/* isotropic */
float e = n_x;
float lobe = powf(HdotN, e);
float norm = (n_x + 1.0f) / (8.0f * M_PI_F);
out = NdotO * norm * lobe * pump;
*pdf = norm * lobe / HdotI; /* this is p_h / 4(H.I) (conversion from 'wh measure' to 'wi measure', eq. 8 in paper) */
}
else {
/* anisotropic */
float3 X, Y;
make_orthonormals_tangent(N, sc->T, &X, &Y);
float HdotX = dot(H, X);
float HdotY = dot(H, Y);
float e = (n_x * HdotX*HdotX + n_y * HdotY*HdotY) / (1.0f - HdotN*HdotN);
float lobe = powf(HdotN, e);
float norm = sqrtf((n_x + 1.0f)*(n_y + 1.0f)) / (8.0f * M_PI_F);
out = NdotO * norm * lobe * pump;
*pdf = norm * lobe / HdotI;
}
}
return make_float3(out, out, out);
}
ccl_device float3 bsdf_ashikhmin_shirley_eval_transmit(const ShaderClosure *sc, const float3 I, const float3 omega_in, float *pdf)
{
return make_float3(0.0f, 0.0f, 0.0f);
}
ccl_device_inline void bsdf_ashikhmin_shirley_sample_first_quadrant(float n_x, float n_y, float randu, float randv, float *phi, float *cos_theta)
{
*phi = atanf(sqrtf((n_x + 1.0f) / (n_y + 1.0f)) * tanf(M_PI_2_F * randu));
float cos_phi = cosf(*phi);
float sin_phi = sinf(*phi);
*cos_theta = powf(randv, 1.0f / (n_x * cos_phi*cos_phi + n_y * sin_phi*sin_phi + 1.0f));
}
ccl_device int bsdf_ashikhmin_shirley_sample(const ShaderClosure *sc, float3 Ng, float3 I, float3 dIdx, float3 dIdy, float randu, float randv, float3 *eval, float3 *omega_in, float3 *domega_in_dx, float3 *domega_in_dy, float *pdf)
{
float3 N = sc->N;
float NdotI = dot(N, I);
if(NdotI > 0.0f) {
float n_x = bsdf_ashikhmin_shirley_roughness_to_exponent(sc->data0);
float n_y = bsdf_ashikhmin_shirley_roughness_to_exponent(sc->data1);
/* get x,y basis on the surface for anisotropy */
float3 X, Y;
if(n_x == n_y)
make_orthonormals(N, &X, &Y);
else
make_orthonormals_tangent(N, sc->T, &X, &Y);
/* sample spherical coords for h in tangent space */
float phi;
float cos_theta;
if(n_x == n_y) {
/* isotropic sampling */
phi = M_2PI_F * randu;
cos_theta = powf(randv, 1.0f / (n_x + 1.0f));
}
else {
/* anisotropic sampling */
if(randu < 0.25f) { /* first quadrant */
float remapped_randu = 4.0f * randu;
bsdf_ashikhmin_shirley_sample_first_quadrant(n_x, n_y, remapped_randu, randv, &phi, &cos_theta);
}
else if(randu < 0.5f) { /* second quadrant */
float remapped_randu = 4.0f * (.5f - randu);
bsdf_ashikhmin_shirley_sample_first_quadrant(n_x, n_y, remapped_randu, randv, &phi, &cos_theta);
phi = M_PI_F - phi;
}
else if(randu < 0.75f) { /* third quadrant */
float remapped_randu = 4.0f * (randu - 0.5f);
bsdf_ashikhmin_shirley_sample_first_quadrant(n_x, n_y, remapped_randu, randv, &phi, &cos_theta);
phi = M_PI_F + phi;
}
else { /* fourth quadrant */
float remapped_randu = 4.0f * (1.0f - randu);
bsdf_ashikhmin_shirley_sample_first_quadrant(n_x, n_y, remapped_randu, randv, &phi, &cos_theta);
phi = 2.0f * M_PI_F - phi;
}
}
/* get half vector in tangent space */
float sin_theta = sqrtf(fmaxf(0.0f, 1.0f - cos_theta*cos_theta));
float cos_phi = cosf(phi);
float sin_phi = sinf(phi); /* no sqrt(1-cos^2) here b/c it causes artifacts */
float3 h = make_float3(
sin_theta * cos_phi,
sin_theta * sin_phi,
cos_theta
);
/* half vector to world space */
float3 H = h.x*X + h.y*Y + h.z*N;
float HdotI = dot(H, I);
if(HdotI < 0.0f) H = -H;
/* reflect I on H to get omega_in */
*omega_in = -I + (2.0f * HdotI) * H;
/* leave the rest to eval_reflect */
*eval = bsdf_ashikhmin_shirley_eval_reflect(sc, I, *omega_in, pdf);
#ifdef __RAY_DIFFERENTIALS__
/* just do the reflection thing for now */
*domega_in_dx = (2.0f * dot(N, dIdx)) * N - dIdx;
*domega_in_dy = (2.0f * dot(N, dIdy)) * N - dIdy;
#endif
}
return LABEL_REFLECT|LABEL_GLOSSY;
}
CCL_NAMESPACE_END
#endif /* __BSDF_ASHIKHMIN_SHIRLEY_H__ */
|
