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