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public/mathlib/halton.h

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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