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/**
* Random numbers and low discrepency sequences utilities.
**/
#pragma BLENDER_REQUIRE(common_math_lib.glsl)
/* From: http://holger.dammertz.org/stuff/notes_HammersleyOnHemisphere.html */
float van_der_corput_radical_inverse(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);
/* Same as dividing by 0x100000000. */
return float(bits) * 2.3283064365386963e-10;
}
vec2 hammersley_2d(float i, float sample_count)
{
vec2 rand;
rand.x = i / sample_count;
rand.y = van_der_corput_radical_inverse(uint(i));
return rand;
}
/* This transform a 2d random sample (in [0..1] range) to a sample located on a cylinder of the
* same range. This is because the sampling functions expect such a random sample which is
* normally precomputed. */
vec3 rand2d_to_cylinder(vec2 rand)
{
float theta = rand.x;
float phi = (rand.y - 0.5) * M_2PI;
float cos_phi = cos(phi);
float sin_phi = sqrt(1.0 - sqr(cos_phi)) * sign(phi);
return vec3(theta, cos_phi, sin_phi);
}
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