summaryrefslogtreecommitdiff
path: root/indra/newview/app_settings/shaders/class2/interface/irradianceGenF.glsl
blob: 0753e73dc8ac164d71b19a6a23c5df204a1be87d (plain)
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
210
211
212
213
214
/** 
 * @file irradianceGenF.glsl
 *
 * $LicenseInfo:firstyear=2022&license=viewerlgpl$
 * Second Life Viewer Source Code
 * Copyright (C) 2022, Linden Research, Inc.
 * 
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation;
 * version 2.1 of the License only.
 * 
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 * 
 * Linden Research, Inc., 945 Battery Street, San Francisco, CA  94111  USA
 * $/LicenseInfo$
 */
 

/*[EXTRA_CODE_HERE]*/

out vec4 frag_color;

uniform samplerCubeArray   reflectionProbes;
uniform int sourceIdx;

uniform float max_probe_lod;

in vec3 vary_dir;

// Code below is derived from the Khronos GLTF Sample viewer:
// https://github.com/KhronosGroup/glTF-Sample-Viewer/blob/master/source/shaders/ibl_filtering.frag


#define MATH_PI 3.1415926535897932384626433832795

float u_roughness = 1.0;
int u_sampleCount = 32;
float u_lodBias = 2.0;
int u_width = 64;

// Hammersley Points on the Hemisphere
// CC BY 3.0 (Holger Dammertz)
// http://holger.dammertz.org/stuff/notes_HammersleyOnHemisphere.html
// with adapted interface
float radicalInverse_VdC(uint bits)
{
    bits = (bits << 16u) | (bits >> 16u);
    bits = ((bits & 0x55555555u) << 1u) | ((bits & 0xAAAAAAAAu) >> 1u);
    bits = ((bits & 0x33333333u) << 2u) | ((bits & 0xCCCCCCCCu) >> 2u);
    bits = ((bits & 0x0F0F0F0Fu) << 4u) | ((bits & 0xF0F0F0F0u) >> 4u);
    bits = ((bits & 0x00FF00FFu) << 8u) | ((bits & 0xFF00FF00u) >> 8u);
    return float(bits) * 2.3283064365386963e-10; // / 0x100000000
}

// hammersley2d describes a sequence of points in the 2d unit square [0,1)^2
// that can be used for quasi Monte Carlo integration
vec2 hammersley2d(int i, int N) {
    return vec2(float(i)/float(N), radicalInverse_VdC(uint(i)));
}

// Hemisphere Sample

// TBN generates a tangent bitangent normal coordinate frame from the normal
// (the normal must be normalized)
mat3 generateTBN(vec3 normal)
{
    vec3 bitangent = vec3(0.0, 1.0, 0.0);

    float NdotUp = dot(normal, vec3(0.0, 1.0, 0.0));
    float epsilon = 0.0000001;
    /*if (1.0 - abs(NdotUp) <= epsilon)
    {
        // Sampling +Y or -Y, so we need a more robust bitangent.
        if (NdotUp > 0.0)
        {
            bitangent = vec3(0.0, 0.0, 1.0);
        }
        else
        {
            bitangent = vec3(0.0, 0.0, -1.0);
        }
    }*/

    vec3 tangent = normalize(cross(bitangent, normal));
    bitangent = cross(normal, tangent);

    return mat3(tangent, bitangent, normal);
}

struct MicrofacetDistributionSample
{
    float pdf;
    float cosTheta;
    float sinTheta;
    float phi;
};

MicrofacetDistributionSample Lambertian(vec2 xi, float roughness)
{
    MicrofacetDistributionSample lambertian;

    // Cosine weighted hemisphere sampling
    // http://www.pbr-book.org/3ed-2018/Monte_Carlo_Integration/2D_Sampling_with_Multidimensional_Transformations.html#Cosine-WeightedHemisphereSampling
    lambertian.cosTheta = sqrt(1.0 - xi.y);
    lambertian.sinTheta = sqrt(xi.y); // equivalent to `sqrt(1.0 - cosTheta*cosTheta)`;
    lambertian.phi = 2.0 * MATH_PI * xi.x;

    lambertian.pdf = lambertian.cosTheta / MATH_PI; // evaluation for solid angle, therefore drop the sinTheta

    return lambertian;
}


// getImportanceSample returns an importance sample direction with pdf in the .w component
vec4 getImportanceSample(int sampleIndex, vec3 N, float roughness)
{
    // generate a quasi monte carlo point in the unit square [0.1)^2
    vec2 xi = hammersley2d(sampleIndex, u_sampleCount);

    MicrofacetDistributionSample importanceSample;

    // generate the points on the hemisphere with a fitting mapping for
    // the distribution (e.g. lambertian uses a cosine importance)
    importanceSample = Lambertian(xi, roughness);
    
    // transform the hemisphere sample to the normal coordinate frame
    // i.e. rotate the hemisphere to the normal direction
    vec3 localSpaceDirection = normalize(vec3(
        importanceSample.sinTheta * cos(importanceSample.phi), 
        importanceSample.sinTheta * sin(importanceSample.phi), 
        importanceSample.cosTheta
    ));
    mat3 TBN = generateTBN(N);
    vec3 direction = TBN * localSpaceDirection;

    return vec4(direction, importanceSample.pdf);
}

// Mipmap Filtered Samples (GPU Gems 3, 20.4)
// https://developer.nvidia.com/gpugems/gpugems3/part-iii-rendering/chapter-20-gpu-based-importance-sampling
// https://cgg.mff.cuni.cz/~jaroslav/papers/2007-sketch-fis/Final_sap_0073.pdf
float computeLod(float pdf)
{
    // // Solid angle of current sample -- bigger for less likely samples
    // float omegaS = 1.0 / (float(u_sampleCount) * pdf);
    // // Solid angle of texel
    // // note: the factor of 4.0 * MATH_PI 
    // float omegaP = 4.0 * MATH_PI / (6.0 * float(u_width) * float(u_width));
    // // Mip level is determined by the ratio of our sample's solid angle to a texel's solid angle 
    // // note that 0.5 * log2 is equivalent to log4
    // float lod = 0.5 * log2(omegaS / omegaP);

    // babylon introduces a factor of K (=4) to the solid angle ratio
    // this helps to avoid undersampling the environment map
    // this does not appear in the original formulation by Jaroslav Krivanek and Mark Colbert
    // log4(4) == 1
    // lod += 1.0;

    // We achieved good results by using the original formulation from Krivanek & Colbert adapted to cubemaps

    // https://cgg.mff.cuni.cz/~jaroslav/papers/2007-sketch-fis/Final_sap_0073.pdf
    float lod = 0.5 * log2( 6.0 * float(u_width) * float(u_width) / (float(u_sampleCount) * pdf));


    return lod;
}

vec4 filterColor(vec3 N)
{
    vec4 color = vec4(0.f);
    
    for(int i = 0; i < u_sampleCount; ++i)
    {
        vec4 importanceSample = getImportanceSample(i, N, 1.0);

        vec3 H = vec3(importanceSample.xyz);
        float pdf = importanceSample.w;

        // mipmap filtered samples (GPU Gems 3, 20.4)
        float lod = computeLod(pdf);

        // apply the bias to the lod
        lod += u_lodBias;

        lod = clamp(lod, 0, max_probe_lod);
        // sample lambertian at a lower resolution to avoid fireflies
        vec4 lambertian = textureLod(reflectionProbes, vec4(H, sourceIdx), lod);

        color += lambertian;
    }

    color /= float(u_sampleCount);

    return color;
}

// entry point
void main()
{
    vec4 color = vec4(0);

    color = filterColor(vary_dir);
    
    frag_color = max(color, vec4(0));
}