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
|
/*
* Copyright 2011-2013 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.
*/
#pragma once
CCL_NAMESPACE_BEGIN
typedef ccl_addr_space struct Bssrdf {
SHADER_CLOSURE_BASE;
float3 radius;
float3 albedo;
float roughness;
float anisotropy;
} Bssrdf;
static_assert(sizeof(ShaderClosure) >= sizeof(Bssrdf), "Bssrdf is too large!");
ccl_device float bssrdf_dipole_compute_Rd(float alpha_prime, float fourthirdA)
{
float s = sqrtf(3.0f * (1.0f - alpha_prime));
return 0.5f * alpha_prime * (1.0f + expf(-fourthirdA * s)) * expf(-s);
}
ccl_device float bssrdf_dipole_compute_alpha_prime(float rd, float fourthirdA)
{
/* Little Newton solver. */
if (rd < 1e-4f) {
return 0.0f;
}
if (rd >= 0.995f) {
return 0.999999f;
}
float x0 = 0.0f;
float x1 = 1.0f;
float xmid, fmid;
constexpr const int max_num_iterations = 12;
for (int i = 0; i < max_num_iterations; ++i) {
xmid = 0.5f * (x0 + x1);
fmid = bssrdf_dipole_compute_Rd(xmid, fourthirdA);
if (fmid < rd) {
x0 = xmid;
}
else {
x1 = xmid;
}
}
return xmid;
}
ccl_device void bssrdf_setup_radius(Bssrdf *bssrdf, const ClosureType type, const float eta)
{
if (type == CLOSURE_BSSRDF_RANDOM_WALK_FIXED_RADIUS_ID) {
/* Scale mean free path length so it gives similar looking result to older
* Cubic, Gaussian and Burley models. */
bssrdf->radius *= 0.25f * M_1_PI_F;
}
else {
/* Adjust radius based on IOR and albedo. */
const float inv_eta = 1.0f / eta;
const float F_dr = inv_eta * (-1.440f * inv_eta + 0.710f) + 0.668f + 0.0636f * eta;
const float fourthirdA = (4.0f / 3.0f) * (1.0f + F_dr) /
(1.0f - F_dr); /* From Jensen's Fdr ratio formula. */
const float3 alpha_prime = make_float3(
bssrdf_dipole_compute_alpha_prime(bssrdf->albedo.x, fourthirdA),
bssrdf_dipole_compute_alpha_prime(bssrdf->albedo.y, fourthirdA),
bssrdf_dipole_compute_alpha_prime(bssrdf->albedo.z, fourthirdA));
bssrdf->radius *= sqrt(3.0f * (one_float3() - alpha_prime));
}
}
/* Setup */
ccl_device_inline Bssrdf *bssrdf_alloc(ShaderData *sd, float3 weight)
{
Bssrdf *bssrdf = (Bssrdf *)closure_alloc(sd, sizeof(Bssrdf), CLOSURE_NONE_ID, weight);
if (bssrdf == NULL) {
return NULL;
}
float sample_weight = fabsf(average(weight));
bssrdf->sample_weight = sample_weight;
return (sample_weight >= CLOSURE_WEIGHT_CUTOFF) ? bssrdf : NULL;
}
ccl_device int bssrdf_setup(ShaderData *sd, Bssrdf *bssrdf, ClosureType type, const float ior)
{
int flag = 0;
int bssrdf_channels = 3;
float3 diffuse_weight = make_float3(0.0f, 0.0f, 0.0f);
/* Verify if the radii are large enough to sample without precision issues. */
if (bssrdf->radius.x < BSSRDF_MIN_RADIUS) {
diffuse_weight.x = bssrdf->weight.x;
bssrdf->weight.x = 0.0f;
bssrdf->radius.x = 0.0f;
bssrdf_channels--;
}
if (bssrdf->radius.y < BSSRDF_MIN_RADIUS) {
diffuse_weight.y = bssrdf->weight.y;
bssrdf->weight.y = 0.0f;
bssrdf->radius.y = 0.0f;
bssrdf_channels--;
}
if (bssrdf->radius.z < BSSRDF_MIN_RADIUS) {
diffuse_weight.z = bssrdf->weight.z;
bssrdf->weight.z = 0.0f;
bssrdf->radius.z = 0.0f;
bssrdf_channels--;
}
if (bssrdf_channels < 3) {
/* Add diffuse BSDF if any radius too small. */
#ifdef __PRINCIPLED__
if (bssrdf->roughness != FLT_MAX) {
float roughness = bssrdf->roughness;
float3 N = bssrdf->N;
PrincipledDiffuseBsdf *bsdf = (PrincipledDiffuseBsdf *)bsdf_alloc(
sd, sizeof(PrincipledDiffuseBsdf), diffuse_weight);
if (bsdf) {
bsdf->type = CLOSURE_BSDF_BSSRDF_PRINCIPLED_ID;
bsdf->N = N;
bsdf->roughness = roughness;
flag |= bsdf_principled_diffuse_setup(bsdf);
}
}
else
#endif /* __PRINCIPLED__ */
{
DiffuseBsdf *bsdf = (DiffuseBsdf *)bsdf_alloc(sd, sizeof(DiffuseBsdf), diffuse_weight);
if (bsdf) {
bsdf->type = CLOSURE_BSDF_BSSRDF_ID;
bsdf->N = bssrdf->N;
flag |= bsdf_diffuse_setup(bsdf);
}
}
}
/* Setup BSSRDF if radius is large enough. */
if (bssrdf_channels > 0) {
bssrdf->type = type;
bssrdf->sample_weight = fabsf(average(bssrdf->weight)) * bssrdf_channels;
bssrdf_setup_radius(bssrdf, type, ior);
flag |= SD_BSSRDF;
}
else {
bssrdf->type = type;
bssrdf->sample_weight = 0.0f;
}
return flag;
}
CCL_NAMESPACE_END
|
