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
|
#ifndef __GLITTER_INC
#define __GLITTER_INC
#define PI 3.1415926535897932384626433832795028841971
float gaussian(float3 x, float3 mu, float sigma) {
float3 x_minus_mu = x - mu;
return exp(-dot(x_minus_mu, x_minus_mu) / (2 * sigma * sigma)) / (sigma * sqrt(2 * PI));
}
float det(float2x2 m) {
return m[0][0] * m[1][1] - m[0][1] * m[1][0];
}
float dirac(float3 x) {
// Ternary operator short-circuits in slang >:(
return any(abs(x) < 1e-4) ? 1e4 : 0;
}
// Maps a point on the unit hemisphere to an inscribed circle.
float2 hemisphere_to_inscribed_circle(float3 p) {
// TODO
return 0;
}
float3 rand3_hash(float3 p)
{
// Improved Murmurhash3 by Squirrel Eiserloh (GDC 2017)
p = float3(dot(p, float3(127.1, 311.7, 74.7)),
dot(p, float3(269.5, 183.3, 246.1)),
dot(p, float3(113.5, 271.9, 124.6)));
return -1.0 + 2.0 * frac(sin(p) * 43758.5453123);
}
public float D_Kemppinen(
float3 worldPos,
float3 H_tan, // halfway vector in tangent space
float amount,
float roughness)
{
float2x2 J_T__omega_h = 0; // TODO
float det_J_T__omega_h = det(J_T__omega_h);
float sum = 0;
// x is the current world space position.
float3 x = worldPos;
// omega_h is the halfway vector *in TBN coordinates.*
float3 omega_h = H_tan;
float3 T_omega_h = float3(
hemisphere_to_inscribed_circle(omega_h),
0);
uint K_p = 1; // TODO
for (uint i = 0; i < K_p; ++i) {
// x_i is the position of the facet.
float3 x_i = worldPos; // TODO randomize position
// mu_i is the orientation of the facet.
float3 mu_i = abs(rand3_hash(x_i));
float a_star = roughness;
float cur_gauss = gaussian(
T_omega_h,
mu_i,
a_star * sqrt(det_J_T__omega_h));
sum += cur_gauss * dirac(x_i - x);
}
float scale = det_J_T__omega_h / K_p;
return sum * scale;
}
#endif // __GLITTER_INC
|
