splines.cpp

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/*
    This file is part of darktable,
    Copyright (C) 2019 Heiko Bauke.
    Copyright (C) 2019-2020 Pascal Obry.
    
    darktable is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.
    
    darktable is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.
    
    You should have received a copy of the GNU General Public License
    along with darktable.  If not, see <http://www.gnu.org/licenses/>.
*/
 
#include "common/darktable.h"
#include "splines.h"
#include <algorithm>
#include <cmath>
#include <limits>
#include <stdexcept>
#include <tuple>
#include <vector>
 
namespace interpol
{
 
template <typename T> struct point
{
  T x{ 0 }; // knot x position
  T y{ 0 }; // function value at x
  point() = default;
  point(T x_, T y_) : x{ x_ }, y{ y_ }
  {
  }
};
 
template <typename T> struct base_point
{
  T x{ 0 };  // knot x position
  T y{ 0 };  // function value at x
  T dy{ 0 }; // 1st derivative of interpolating spline at x
};
 
template <typename T> struct limits
{
  T min{ -std::numeric_limits<T>::infinity() };
  T max{ +std::numeric_limits<T>::infinity() };
  limits() = default;
  limits(T min_, T max_) : min{ std::min(min_, max_) }, max{ std::max(min_, max_) }
  {
  }
};
 
template <typename T> constexpr limits<T> infinity()
{
  return limits<T>{};
}
 
template <typename T> class spline_base
{
protected:
  using size_type = typename std::vector<base_point<T> >::size_type;
  std::vector<base_point<T> > points;
  limits<T> x_lim;
  limits<T> y_lim;
  bool periodic{ false };
 
  template <typename iter> spline_base(iter i_begin, iter i_end)
  {
    for(iter i{ i_begin }; i != i_end; ++i) points.push_back({ i->x, i->y, 0 });
    if(points.empty()) throw std::invalid_argument("empty set of interpolation points");
    std::sort(points.begin(), points.end(),
              [](const base_point<T> &a, const base_point<T> &b) { return a.x < b.x; });
    x_lim = { points.front().x, points.back().x };
  }
 
  template <typename iter>
  spline_base(iter i_begin, iter i_end, const limits<T> &x_lim_, const limits<T> &y_lim_, bool periodic_ = false)
    : x_lim{ x_lim_ }, y_lim{ y_lim_ }, periodic{ periodic_ }
  {
    if(periodic)
    {
      const T period{ x_lim.max - x_lim.min };
      for(iter i{ i_begin }; i != i_end; ++i)
      {
        T x{ std::fmod(i->x, period) };
        if(x < 0) x += period;
        points.push_back({ x, i->y, 0 });
      }
    }
    else
    {
      for(iter i{ i_begin }; i != i_end; ++i)
      {
        if(x_lim.min <= i->x and i->x <= x_lim.max) points.push_back({ i->x, i->y, 0 });
      }
    }
    if(points.empty()) throw std::invalid_argument("empty set of interpolation points");
    std::sort(points.begin(), points.end(),
              [](const base_point<T> &a, const base_point<T> &b) { return a.x < b.x; });
  }
 
  spline_base(const std::initializer_list<point<T> > &I) : spline_base(I.begin(), I.end())
  {
  }
 
  spline_base(const std::initializer_list<point<T> > &I, const limits<T> &x_lim_, const limits<T> &y_lim_,
              bool periodic_ = false)
    : spline_base(I.begin(), I.end(), x_lim_, y_lim_, periodic_)
  {
  }
 
public:
  T operator()(T x) const
  {
    if(points.size() == 1) return points[0].y;
    size_type n0{ 0 };
    size_type n1{ 0 };
    T h{ 0 };
    // find the knot indices n0 and n1 for value x
    if(periodic)
    {
      const T period{ x_lim.max - x_lim.min };
      x = std::fmod(x, period);
      if(x < points.front().x) x += period;
      n0 = std::upper_bound(points.begin(), points.end(), base_point<T>{ x, 0, 0 },
                            [](const base_point<T> &a, const base_point<T> &b) { return a.x < b.x; })
           - points.begin();
      n0 = n0 > 0 ? n0 - 1 : points.size() - 1;
      n1 = n0 + 1 < points.size() ? n0 + 1 : 0;
      if(n1 > n0)
        h = points[n1].x - points[n0].x;
      else
        h = points[n1].x - (points[n0].x - period);
    }
    else
    {
      x = std::max(x, x_lim.min);
      x = std::min(x, x_lim.max);
      if(x >= points.front().x)
      {
        n0 = std::upper_bound(points.begin(), points.end(), base_point<T>{ x, 0, 0 },
                              [](const base_point<T> &a, const base_point<T> &b) { return a.x < b.x; })
             - points.begin();
        if(n0 > 0) n0 = std::min(n0 - 1, points.size() - 2);
      }
      n1 = n0 + 1;
      h = points[n1].x - points[n0].x;
    }
    T y;
    if((not periodic) and (x <= points.front().x or x >= points.back().x))
    {
      // use linear extrapolation for off-grid points
      const base_point<T> &P{ x <= points.front().x ? points.front() : points.back() };
      y = P.y + (x - P.x) * P.dy;
    }
    else
    {
      const T dx{ (x - points[n0].x) / h };
      const T dx2{ dx * dx };
      const T dx3{ dx2 * dx };
      // calculate the 4 cubic Hermite splines, see
      // https://en.wikipedia.org/wiki/Cubic_Hermite_spline
      const T h00{ 2 * dx3 - 3 * dx2 + 1 };
      const T h10{ dx3 - 2 * dx2 + dx };
      const T h01{ -2 * dx3 + 3 * dx2 };
      const T h11{ dx3 - dx2 };
      // finally get the interpolation value as a weighted sum of h00, h10, h01 and h11
      y = h00 * points[n0].y + h10 * h * points[n0].dy + h01 * points[n1].y + h11 * h * points[n1].dy;
    }
    y = std::max(y, y_lim.min);
    y = std::min(y, y_lim.max);
    return y;
  }
};
 
// cubic hermite spline interpolation
// tangents at the interpolation points given by with central difference formula,
// see https://en.wikipedia.org/wiki/Cubic_Hermite_spline
// https://de.wikipedia.org/wiki/Kubisch_Hermitescher_Spline
template <typename T> class Catmull_Rom_spline : public spline_base<T>
{
  using base = spline_base<T>;
  using base::periodic;
  using base::points;
  using base::x_lim;
  using base::y_lim;
  using typename base::size_type;
 
  void init()
  {
    if(points.size() == 1)
      points[0].dy = 0;
    else
    {
      const size_type N{ points.size() };
      if(periodic)
      {
        const T period{ x_lim.max - x_lim.min };
        points[0].dy = (points[1].y - points[N - 1].y) / (points[1].x - points[N - 1].x + period);
        for(size_type i{ 1 }; i < N - 1; ++i)
          points[i].dy = (points[i + 1].y - points[i - 1].y) / (points[i + 1].x - points[i - 1].x);
        points[N - 1].dy = (points[0].y - points[N - 2].y) / (points[0].x - points[N - 2].x + period);
      }
      else
      {
        points[0].dy = (points[1].y - points[0].y) / (points[1].x - points[0].x);
        for(size_type i{ 1 }; i < N - 1; ++i)
          points[i].dy = (points[i + 1].y - points[i - 1].y) / (points[i + 1].x - points[i - 1].x);
        points[N - 1].dy = (points[N - 1].y - points[N - 2].y) / (points[N - 1].x - points[N - 2].x);
      }
    }
  }
 
public:
  template <typename iter>
  Catmull_Rom_spline(iter i_begin, iter i_end) : spline_base<T>::spline_base(i_begin, i_end)
  {
    init();
  }
 
  template <typename iter>
  Catmull_Rom_spline(iter i_begin, iter i_end, const limits<T> &x_lim_, const limits<T> &y_lim_,
                     bool periodic_ = false)
    : spline_base<T>::spline_base(i_begin, i_end, x_lim_, y_lim_, periodic_)
  {
    init();
  }
 
  Catmull_Rom_spline(const std::initializer_list<point<T> > &I) : spline_base<T>::spline_base(I)
  {
    init();
  }
 
  Catmull_Rom_spline(const std::initializer_list<point<T> > &I, const limits<T> &x_lim_, const limits<T> &y_lim_,
                     bool periodic_ = false)
    : spline_base<T>::spline_base(I, x_lim_, y_lim_, periodic_)
  {
    init();
  }
};
 
// cubic hermite spline interpolation
// tangents at the interpolation points are determined such that the resulting
// interpolating function is monotonous between successive interpolation points,
// see https://en.wikipedia.org/wiki/Monotone_cubic_interpolation
template <typename T> class monotone_hermite_spline : public spline_base<T>
{
  using base = spline_base<T>;
  using base::periodic;
  using base::points;
  using base::x_lim;
  using base::y_lim;
  using typename base::size_type;
 
  void init()
  {
    if(points.size() == 1)
      points[0].dy = 0;
    else
    {
      const size_type N{ points.size() };
      if(periodic)
      {
        const T period{ x_lim.max - x_lim.min };
        std::vector<T> Delta;
        Delta.reserve(N);
        for(size_type i{ 0 }; i < N - 1; ++i)
          Delta.push_back((points[i + 1].y - points[i].y) / (points[i + 1].x - points[i].x));
        Delta.push_back((points[0].y - points[N - 1].y) / (points[0].x - points[N - 1].x + period));
        if(Delta[N - 1] * Delta[0] <= 0)
          points[0].dy = 0;
        else
          points[0].dy = (Delta[N - 1] + Delta[0]) / 2;
        for(size_type i{ 1 }; i < N; ++i)
          if(Delta[i - 1] * Delta[i] <= 0)
            points[i].dy = 0;
          else
            points[i].dy = (Delta[i - 1] + Delta[i]) / 2;
        for(size_type i{ 0 }; i < N; ++i)
        {
          const size_type i_1{ i + 1 < N ? i + 1 : 0 };
          if(std::abs(Delta[i]) < std::numeric_limits<T>::epsilon())
            points[i].dy = points[i_1].dy = 0;
          else
          {
            const T alpha{ points[i].dy / Delta[i] };
            const T beta{ points[i_1].dy / Delta[i] };
            const T tau{ alpha * alpha + beta * beta };
            if(tau > 9)
            {
              points[i].dy = 3 * alpha * Delta[i] / std::sqrt(tau);
              points[i_1].dy = 3 * beta * Delta[i] / std::sqrt(tau);
            }
          }
        }
      }
      else
      {
        std::vector<T> Delta;
        Delta.reserve(N - 1);
        for(size_type i{ 0 }; i < N - 1; ++i)
          Delta.push_back((points[i + 1].y - points[i].y) / (points[i + 1].x - points[i].x));
        points[0].dy = Delta[0];
        for(size_type i{ 1 }; i < N - 1; ++i)
          if(Delta[i - 1] * Delta[i] <= 0)
            points[i].dy = 0;
          else
            points[i].dy = (Delta[i - 1] + Delta[i]) / 2;
        if(N >= 2) points[N - 1].dy = Delta[N - 2];
        for(size_type i{ 0 }; i < N - 1; ++i)
          if(std::abs(Delta[i]) < std::numeric_limits<T>::epsilon())
            points[i].dy = points[i + 1].dy = 0;
          else
          {
            const T alpha{ points[i].dy / Delta[i] };
            const T beta{ points[i + 1].dy / Delta[i] };
            const T tau{ alpha * alpha + beta * beta };
            if(tau > 9)
            {
              points[i].dy = 3 * alpha * Delta[i] / std::sqrt(tau);
              points[i + 1].dy = 3 * beta * Delta[i] / std::sqrt(tau);
            }
          }
      }
    }
  }
 
public:
  template <typename iter>
  monotone_hermite_spline(iter i_begin, iter i_end) : spline_base<T>::spline_base(i_begin, i_end)
  {
    init();
  }
 
  template <typename iter>
  monotone_hermite_spline(iter i_begin, iter i_end, const limits<T> &x_lim_, const limits<T> &y_lim_,
                          bool periodic_ = false)
    : spline_base<T>::spline_base(i_begin, i_end, x_lim_, y_lim_, periodic_)
  {
    init();
  }
 
  monotone_hermite_spline(const std::initializer_list<point<T> > &I) : spline_base<T>::spline_base(I)
  {
    init();
  }
 
  monotone_hermite_spline(const std::initializer_list<point<T> > &I, const limits<T> &x_lim_,
                          const limits<T> &y_lim_, bool periodic_ = false)
    : spline_base<T>::spline_base(I, x_lim_, y_lim_, periodic_)
  {
    init();
  }
};
 
// cubic hermite spline interpolation
// tangents at the interpolation points are determined such that the resulting
// interpolating function is monotonous between successive interpolation points,
// see SIAM J. Sci. Stat. Comput., Vol. 5, pp. 300-304 (1984)
// https://doi.org/10.1137/0905021
// gives similar but sometimes more pleasing results than
// monotone_hermite_spline above
template <typename T> class monotone_hermite_spline_variant : public spline_base<T>
{
  using base = spline_base<T>;
  using base::periodic;
  using base::points;
  using base::x_lim;
  using base::y_lim;
  using typename base::size_type;
 
  static T G(const T S1, const T S2, const T h1, const T h2)
  {
    if(S1 * S2 > 0)
    {
      const T alpha{ (h1 + 2 * h2) / (3 * (h1 + h2)) };
      return S1 * S2 / (alpha * S2 + (1 - alpha) * S1);
    }
    return 0;
  }
  void init()
  {
    if(points.size() == 1)
      points[0].dy = 0;
    else
    {
      const size_type N{ points.size() };
      if(periodic)
      {
        const T period{ x_lim.max - x_lim.min };
        std::vector<T> h, Delta;
        h.reserve(N);
        Delta.reserve(N);
        for(size_type i{ 0 }; i < N - 1; ++i)
        {
          h.push_back(points[i + 1].x - points[i].x);
          Delta.push_back((points[i + 1].y - points[i].y) / (points[i + 1].x - points[i].x));
        }
        h.push_back(points[0].x - points[N - 1].x + period);
        Delta.push_back((points[0].y - points[N - 1].y) / (points[0].x - points[N - 1].x + period));
        points[0].dy = G(Delta[N - 1], Delta[0], h[N - 1], h[0]);
        for(size_type i{ 1 }; i < N; ++i) points[i].dy = G(Delta[i - 1], Delta[i], h[i - 1], h[i]);
      }
      else
      {
        std::vector<T> h, Delta;
        h.reserve(N - 1);
        Delta.reserve(N - 1);
        for(size_type i{ 0 }; i < N - 1; ++i)
        {
          h.push_back(points[i + 1].x - points[i].x);
          Delta.push_back((points[i + 1].y - points[i].y) / (points[i + 1].x - points[i].x));
        }
        points[0].dy = Delta[0];
        for(size_type i{ 1 }; i < N - 1; ++i) points[i].dy = G(Delta[i - 1], Delta[i], h[i - 1], h[i]);
        if(N >= 2) points[N - 1].dy = Delta[N - 2];
      }
    }
  }
 
public:
  template <typename iter>
  monotone_hermite_spline_variant(iter i_begin, iter i_end) : spline_base<T>::spline_base(i_begin, i_end)
  {
    init();
  }
 
  template <typename iter>
  monotone_hermite_spline_variant(iter i_begin, iter i_end, const limits<T> &x_lim_, const limits<T> &y_lim_,
                                  bool periodic_ = false)
    : spline_base<T>::spline_base(i_begin, i_end, x_lim_, y_lim_, periodic_)
  {
    init();
  }
 
  monotone_hermite_spline_variant(const std::initializer_list<point<T> > &I) : spline_base<T>::spline_base(I)
  {
    init();
  }
 
  monotone_hermite_spline_variant(const std::initializer_list<point<T> > &I, const limits<T> &x_lim_,
                                  const limits<T> &y_lim_, bool periodic_ = false)
    : spline_base<T>::spline_base(I, x_lim_, y_lim_, periodic_)
  {
    init();
  }
};
 
// cubic hermite spline interpolation
// tangents at the interpolation points are determined such that the resulting
// interpolating function has continuous 1st and 2nd derivatives over the whole
// interval, natural boundary conditions are assumed in the non-periodic case
// see https://de.wikipedia.org/wiki/Spline-Interpolation
template <typename T> class smooth_cubic_spline : public spline_base<T>
{
  using base = spline_base<T>;
  using base::periodic;
  using base::points;
  using base::x_lim;
  using base::y_lim;
  using typename base::size_type;
 
  using vector = std::vector<T>;
 
  class matrix
  {
    using size_type = typename std::vector<T>::size_type;
    const size_type N{ 0 };
    const bool is_banded{ false };
    std::vector<T> A;
 
  public:
    explicit matrix(size_type N_, bool is_banded_ = false)
      : N{ N_ }, is_banded{ is_banded_ }, A(is_banded_ ? 3 * N_ : N_ * N_, 0)
    {
    }
 
    T &operator()(size_type i, size_type j)
    {
      if(is_banded)
      {
        if(i == j) return A[i + N];
        if(i + 1 == j) return A[i];
        if(i == j + 1) return A[i + 2 * N];
      }
      return A[i + N * j];
    }
 
    const T &operator()(size_type i, size_type j) const
    {
      if(is_banded)
      {
        if(i == j) return A[i + N];
        if(i + 1 == j) return A[i];
        if(i == j + 1) return A[i + 2 * N];
      }
      return A[i + N * j];
    }
 
    size_type size() const
    {
      return N;
    }
    bool isbanded() const
    {
      return is_banded;
    }
  };
 
  // LU factorization without pivoting
  // returns false if matrix A is singular, see
  // https://de.wikipedia.org/wiki/Gau%C3%9Fsches_Eliminationsverfahren
  static bool LU_factor(matrix &A)
  {
    if(A.size() < 1) return false;
    const size_type n{ A.size() };
    if(A.isbanded())
    {
      for(size_type i{ 0 }; i + 1 < n; ++i)
      {
        const T t1{ A(i, i) };
        if(t1 != 0)
        {
          if(i + 1 < n)
          {
            A(i + 1, i) /= t1;
            A(i + 1, i + 1) -= A(i + 1, i) * A(i, i + 1);
          }
        }
        else
          // the matrix is singular
          return false;
      }
    }
    else
    {
      for(size_type i{ 0 }; i + 1 < n; ++i)
      {
        const T t1{ A(i, i) };
        if(t1 != 0)
        {
          for(size_type k{ i + 1 }; k < n; ++k)
          {
            A(k, i) /= t1;
            for(size_type j{ i + 1 }; j < n; ++j) A(k, j) -= A(k, i) * A(i, j);
          }
        }
        else
          // the matrix is singular
          return false;
      }
    }
    return true;
  }
 
  // substitution after LU factorization
  static void LU_solve(const matrix &A, vector &b)
  {
    const size_type n{ A.size() };
    if(n < 1 or A.size() != b.size()) return;
    if(A.isbanded())
    {
      // forward substitution
      for(size_type i{ 0 }; i < n; ++i)
      {
        if(i > 0) b[i] -= A(i, i - 1) * b[i - 1];
      }
      // backward substitution
      for(size_type i{ n - 1 };; --i)
      {
        if(i + 1 < n) b[i] -= A(i, i + 1) * b[i + 1];
        b[i] /= A(i, i);
        if(i == 0) break;
      }
    }
    else
    {
      // forward substitution
      for(size_type i{ 0 }; i < n; ++i)
        for(size_type k{ 0 }; k < i; ++k) b[i] -= A(i, k) * b[k];
      // backward substitution
      for(size_type i{ n - 1 };; --i)
      {
        for(size_type k{ i + 1 }; k < n; ++k) b[i] -= A(i, k) * b[k];
        b[i] /= A(i, i);
        if(i == 0) break;
      }
    }
  }
 
  // solve linear system
  static bool gauss_solve(matrix &A, vector &b)
  {
    // matrix A is diagonal dominant, thus no pivoting required
    const bool ok{ LU_factor(A) };
    if(ok) LU_solve(A, b);
    return ok;
  }
 
  void init()
  {
    // base constructor ensures that there is a non-empty set of knots
    if(points.size() == 1)
      points[0].dy = 0; // with only one data point assume horizontal line as interpolant
    else
    {
      const size_type N{ points.size() };
      std::vector<T> Delta_x, Delta_y;
      Delta_x.reserve(periodic ? N : N - 1);
      Delta_y.reserve(periodic ? N : N - 1);
      for(size_type i{ 0 }; i < N - 1; ++i)
      {
        Delta_x.push_back(points[i + 1].x - points[i].x);
        Delta_y.push_back(points[i + 1].y - points[i].y);
      }
      if(periodic)
      {
        const T period{ x_lim.max - x_lim.min };
        Delta_x.push_back(points[0].x - points[N - 1].x + period);
        Delta_y.push_back(points[0].y - points[N - 1].y);
      }
      // set up and solve the set of linear equations to determine the 2nd derivative of the
      // interpolating function at the knots
      matrix A(N, not periodic);
      std::vector<T> b(N);
      for(size_type i{ 1 }; i < N - 1; ++i)
      {
        A(i, i - 1) = Delta_x[i - 1] / 6;
        A(i, i) = (Delta_x[i - 1] + Delta_x[i]) / 3;
        A(i, i + 1) = Delta_x[i] / 6;
        b[i] = Delta_y[i] / Delta_x[i] - Delta_y[i - 1] / Delta_x[i - 1];
      }
      if(periodic)
      {
        A(0, 0) = (Delta_x[N - 1] + Delta_x[0]) / 3;
        A(N - 1, N - 1) = (Delta_x[N - 2] + Delta_x[N - 1]) / 3;
        b[0] = Delta_y[0] / Delta_x[0] - Delta_y[N - 1] / Delta_x[N - 1];
        b[N - 1] = Delta_y[N - 1] / Delta_x[N - 1] - Delta_y[N - 2] / Delta_x[N - 2];
        if(N > 2)
        {
          A(0, 1) = Delta_x[0] / 6;
          A(N - 1, N - 2) = Delta_x[N - 2] / 6;
          A(0, N - 1) = A(N - 1, 0) = Delta_x[N - 1] / 6;
        }
        else
        {
          A(0, 1) = A(1, 0) = (Delta_x[0] + Delta_x[1]) / 6;
        }
      }
      else
      {
        A(0, 0) = 1;
        A(N - 1, N - 1) = 1;
        b[0] = 0;
        b[N - 1] = 0;
      }
      gauss_solve(A, b);
      // calculate the 1st derivative of the interpolating function at the knots
      T c_i{ 0 };
      for(size_type i{ 0 }; i < N - 1; ++i)
      {
        c_i = Delta_y[i] / Delta_x[i] - Delta_x[i] / 6 * (b[i + 1] - b[i]);
        points[i].dy = -Delta_x[i] * b[i] / 2 + c_i;
      }
      if(periodic)
        points[N - 1].dy = Delta_x[N - 2] * b[N - 1] / 2 + c_i;
      else
        points[N - 1].dy = c_i;
    }
  }
 
public:
  template <typename iter>
  smooth_cubic_spline(iter i_begin, iter i_end) : spline_base<T>::spline_base(i_begin, i_end)
  {
    init();
  }
 
  template <typename iter>
  smooth_cubic_spline(iter i_begin, iter i_end, const limits<T> &x_lim_, const limits<T> &y_lim_,
                      bool periodic_ = false)
    : spline_base<T>::spline_base(i_begin, i_end, x_lim_, y_lim_, periodic_)
  {
    init();
  }
 
  smooth_cubic_spline(const std::initializer_list<point<T> > &I) : spline_base<T>::spline_base(I)
  {
    init();
  }
 
  smooth_cubic_spline(const std::initializer_list<point<T> > &I, const limits<T> &x_lim_, const limits<T> &y_lim_,
                      bool periodic_ = false)
    : spline_base<T>::spline_base(I, x_lim_, y_lim_, periodic_)
  {
    init();
  }
};
 
} // namespace interpol
 
 
float interpolate_val_V2(int n, CurveAnchorPoint Points[], float x, unsigned int type)
{
  if(type == CUBIC_SPLINE)
  {
    interpol::smooth_cubic_spline<float> s(Points, Points + n);
    return s(x);
  }
  else if(type == CATMULL_ROM)
  {
    interpol::Catmull_Rom_spline<float> s(Points, Points + n);
    return s(x);
  }
  else if(type == MONOTONE_HERMITE)
  {
    interpol::monotone_hermite_spline<float> s(Points, Points + n);
    return s(x);
  }
  return NAN;
}
 
 
float interpolate_val_V2_periodic(int n, CurveAnchorPoint Points[], float x, unsigned int type, float period)
{
  if(type == CUBIC_SPLINE)
  {
    interpol::smooth_cubic_spline<float> s(Points, Points + n, { 0.f, period }, interpol::infinity<float>(), true);
    return s(x);
  }
  else if(type == CATMULL_ROM)
  {
    interpol::Catmull_Rom_spline<float> s(Points, Points + n, { 0.f, period }, interpol::infinity<float>(), true);
    return s(x);
  }
  else if(type == MONOTONE_HERMITE)
  {
    interpol::monotone_hermite_spline<float> s(Points, Points + n, { 0.f, period }, interpol::infinity<float>(),
                                               true);
    return s(x);
  }
  return NAN;
}
 
 
int CurveDataSampleV2(CurveData *curve, CurveSample *sample)
{
  try
  {
    const float box_width = curve->m_max_x - curve->m_min_x;
    const float box_height = curve->m_max_y - curve->m_min_y;
 
    std::vector<interpol::point<float> > v;
    // build arrays for processing
    if(curve->m_numAnchors == 0)
    {
      // just a straight line using box coordinates
      v.push_back({ curve->m_min_x, curve->m_min_y });
      v.push_back({ curve->m_max_x, curve->m_max_y });
    }
    else
    {
      for(int i = 0; i < curve->m_numAnchors; i++)
        v.push_back({ curve->m_anchors[i].x * box_width + curve->m_min_x,
                      curve->m_anchors[i].y * box_height + curve->m_min_y });
    }
 
    const float res = 1.0f / (sample->m_samplingRes - 1);
    const int firstPointX = v.front().x * (sample->m_samplingRes - 1);
    const int firstPointY = v.front().y * (sample->m_outputRes - 1);
    const int lastPointX = v.back().x * (sample->m_samplingRes - 1);
    const int lastPointY = v.back().y * (sample->m_outputRes - 1);
    const int maxY = curve->m_max_y * (sample->m_outputRes - 1);
    const int minY = curve->m_min_y * (sample->m_outputRes - 1);
    const int n = sample->m_samplingRes;
    if(curve->m_spline_type == CUBIC_SPLINE)
    {
      interpol::smooth_cubic_spline<float> s(v.begin(), v.end(), { v.front().x, v.back().x },
                                             { curve->m_min_y, curve->m_max_y }, false);
      for(int i = 0; i < n; ++i)
      {
        if(i < firstPointX)
          sample->m_Samples[i] = firstPointY;
        else if(i > lastPointX)
          sample->m_Samples[i] = lastPointY;
        else
        {
          int val = static_cast<int>(std::round(s(i * res) * (sample->m_outputRes - 1)));
          if(val > maxY) val = maxY;
          if(val < minY) val = minY;
          sample->m_Samples[i] = val;
        }
      }
    }
    else if(curve->m_spline_type == CATMULL_ROM)
    {
      interpol::Catmull_Rom_spline<float> s(v.begin(), v.end(), { v.front().x, v.back().x },
                                            { curve->m_min_y, curve->m_max_y }, false);
      for(int i = 0; i < n; ++i)
      {
        if(i < firstPointX)
          sample->m_Samples[i] = firstPointY;
        else if(i > lastPointX)
          sample->m_Samples[i] = lastPointY;
        else
        {
          int val = static_cast<int>(std::round(s(i * res) * (sample->m_outputRes - 1)));
          if(val > maxY) val = maxY;
          if(val < minY) val = minY;
          sample->m_Samples[i] = val;
        }
      }
    }
    else if(curve->m_spline_type == MONOTONE_HERMITE)
    {
      interpol::monotone_hermite_spline<float> s(v.begin(), v.end(), { v.front().x, v.back().x },
                                                 { curve->m_min_y, curve->m_max_y }, false);
      for(int i = 0; i < n; ++i)
      {
        if(i < firstPointX)
          sample->m_Samples[i] = firstPointY;
        else if(i > lastPointX)
          sample->m_Samples[i] = lastPointY;
        else
        {
          int val = std::round(s(i * res) * (sample->m_outputRes - 1));
          if(val > maxY) val = maxY;
          if(val < minY) val = minY;
          sample->m_Samples[i] = val;
        }
      }
    }
    return CT_SUCCESS;
  }
  catch(...)
  {
    return CT_ERROR;
  }
}
 
 
int CurveDataSampleV2Periodic(CurveData *curve, CurveSample *sample)
{
  try
  {
    const float box_width = curve->m_max_x - curve->m_min_x;
    const float box_height = curve->m_max_y - curve->m_min_y;
 
    std::vector<interpol::point<float> > v;
    // build arrays for processing
    if(curve->m_numAnchors == 0)
    {
      // just a straight line using box coordinates
      v.push_back({ curve->m_min_x, curve->m_min_y });
      v.push_back({ curve->m_max_x, curve->m_max_y });
    }
    else
    {
      for(int i = 0; i < curve->m_numAnchors; i++)
        v.push_back({ curve->m_anchors[i].x * box_width + curve->m_min_x,
                      curve->m_anchors[i].y * box_height + curve->m_min_y });
    }
 
    const float res = 1.0f / (sample->m_samplingRes - 1);
    if(curve->m_spline_type == CUBIC_SPLINE)
    {
      interpol::smooth_cubic_spline<float> s(v.begin(), v.end(), { curve->m_min_x, curve->m_max_x },
                                             { curve->m_min_y, curve->m_max_y }, true);
      for(unsigned int i = 0; i < sample->m_samplingRes; ++i)
        sample->m_Samples[i] = static_cast<unsigned short int>(std::round(s(i * res) * (sample->m_outputRes - 1)));
    }
    else if(curve->m_spline_type == CATMULL_ROM)
    {
      interpol::Catmull_Rom_spline<float> s(v.begin(), v.end(), { curve->m_min_x, curve->m_max_x },
                                            { curve->m_min_y, curve->m_max_y }, true);
      for(unsigned int i = 0; i < sample->m_samplingRes; ++i)
        sample->m_Samples[i] = static_cast<unsigned short int>(std::round(s(i * res) * (sample->m_outputRes - 1)));
    }
    else if(curve->m_spline_type == MONOTONE_HERMITE)
    {
      interpol::monotone_hermite_spline_variant<float> s(v.begin(), v.end(), { curve->m_min_x, curve->m_max_x },
                                                         { curve->m_min_y, curve->m_max_y }, true);
      for(unsigned int i = 0; i < sample->m_samplingRes; ++i)
        sample->m_Samples[i] = static_cast<unsigned short int>(std::round(s(i * res) * (sample->m_outputRes - 1)));
    }
    return CT_SUCCESS;
  }
  catch(...)
  {
    return CT_ERROR;
  }
}