Modified source engine (2017) developed by valve and leaked in 2020. Not for commercial purporses
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//========= Copyright Valve Corporation, All rights reserved. ============//
// $Id$
// halton.h - classes, etc for generating numbers using the Halton pseudo-random sequence. See
// http://halton-sequences.wikiverse.org/.
//
// what this function is useful for is any sort of sampling/integration problem where
// you want to solve it by random sampling. Each call the NextValue() generates
// a random number between 0 and 1, in an unclumped manner, so that the space can be more
// or less evenly sampled with a minimum number of samples.
//
// It is NOT useful for generating random numbers dynamically, since the outputs aren't
// particularly random.
//
// To generate multidimensional sample values (points in a plane, etc), use two
// HaltonSequenceGenerator_t's, with different (primes) bases.
#ifndef HALTON_H
#define HALTON_H
#include <tier0/platform.h>
#include <mathlib/vector.h>
class HaltonSequenceGenerator_t
{
int seed;
int base;
float fbase; //< base as a float
public:
HaltonSequenceGenerator_t(int base); //< base MUST be prime, >=2
float GetElement(int element);
inline float NextValue(void)
{
return GetElement(seed++);
}
};
class DirectionalSampler_t //< pseudo-random sphere sampling
{
HaltonSequenceGenerator_t zdot;
HaltonSequenceGenerator_t vrot;
public:
DirectionalSampler_t(void)
: zdot(2),vrot(3)
{
}
Vector NextValue(void)
{
float zvalue=zdot.NextValue();
zvalue=2*zvalue-1.0; // map from 0..1 to -1..1
float phi=acos(zvalue);
// now, generate a random rotation angle for x/y
float theta=2.0*M_PI*vrot.NextValue();
float sin_p=sin(phi);
return Vector(cos(theta)*sin_p,
sin(theta)*sin_p,
zvalue);
}
};
#endif // halton_h