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precision highp float;
#define PI 3.1415926535897932384626433832795
#define EPS 0.001
#define NUM_SAMPLES_AZIMUTH 250
#define NUM_SAMPLES_ZENITH 50
#define MAX_AZIMUTH (2*PI)
#define MAX_ZENITH (PI/2.0)
#define AZIMUTH_DELTA (MAX_AZIMUTH / float(NUM_SAMPLES_AZIMUTH))
#define ZENITH_DELTA (MAX_ZENITH / float(NUM_SAMPLES_ZENITH))
uniform samplerCube Sky;
in vec3 Ray;
// DEBUG
// in vec2 Texcoord;
layout (location = 0) out vec4 Color;
void main()
{
// Tangent space:
//
// N
// |
// |
// |
// |_ _ _ _ _ B
// /
// /
// T
vec3 N = normalize(Ray);
vec3 B = (abs(N.x) - 1.0 <= EPS) ? vec3(0.0, 0.0, 1.0) : vec3(1.0, 0.0, 0.0);
vec3 T = normalize(cross(B, N));
B = normalize(cross(N, T));
int num_samples = 0;
vec3 irradiance = vec3(0.0);
for (float theta = 0.0; theta < MAX_AZIMUTH; theta += AZIMUTH_DELTA) {
for (float phi = 0.0; phi < MAX_ZENITH; phi += ZENITH_DELTA) {
// Spherical to Cartesian.
vec3 sample_tangent_space = vec3(
sin(phi) * cos(theta),
sin(phi) * sin(theta),
cos(phi));
// Tangent space to world space.
vec3 sample_world_space =
sample_tangent_space.x * B +
sample_tangent_space.y * T +
sample_tangent_space.z * N;
irradiance += texture(Sky, sample_world_space).rgb * sin(phi) * cos(phi);
num_samples += 1;
}
}
irradiance = PI * irradiance / float(num_samples);
// For debugging in trace.
//irradiance = texture(Sky, Ray).rgb;
// irradiance = vec3(Texcoord, 0.0);
//irradiance = pow(irradiance, vec3(1.0/2.2));
Color = vec4(irradiance, 1.0);
}
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