box_muller_transform.hlsl

// Copyright (C) 2018-2023 - DevSH Graphics Programming Sp. z O.O.
// This file is part of the "Nabla Engine".
// For conditions of distribution and use, see copyright notice in nabla.h

#ifndef _NBL_BUILTIN_HLSL_SAMPLING_BOX_MULLER_TRANSFORM_INCLUDED_
#define _NBL_BUILTIN_HLSL_SAMPLING_BOX_MULLER_TRANSFORM_INCLUDED_

#include "nbl/builtin/hlsl/math/functions.hlsl"
#include "nbl/builtin/hlsl/numbers.hlsl"
#include "nbl/builtin/hlsl/sampling/warp_and_pdf.hlsl"

namespace nbl
{
namespace hlsl
{
namespace sampling
{

template<typename T NBL_PRIMARY_REQUIRES(concepts::FloatingPointLikeScalar<T>)
struct BoxMullerTransform
{
	using scalar_type = T;
	using vector2_type = vector<T, 2>;

	// ResamplableSampler concept types
	using domain_type = vector2_type;
	using codomain_type = vector2_type;
	using density_type = scalar_type;
	using sample_type = codomain_and_rcpPdf<codomain_type, density_type>;

	vector2_type operator()(const vector2_type xi)
	{
		scalar_type sinPhi, cosPhi;
		math::sincos<scalar_type>(2.0 * numbers::pi<scalar_type> * xi.y - numbers::pi<scalar_type>, sinPhi, cosPhi);
		return vector2_type(cosPhi, sinPhi) * nbl::hlsl::sqrt(-2.0 * nbl::hlsl::log(xi.x)) * stddev;
	}

	T stddev;
};

} // namespace sampling
} // namespace hlsl
} // namespace nbl

#endif