Spline.h

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/******************************************************************************************************
 * (C) 2014 markummitchell@github.com. This file is part of Engauge Digitizer, which is released      *
 * under GNU General Public License version 2 (GPLv2) or (at your option) any later version. See file *
 * LICENSE or go to gnu.org/licenses for details. Distribution requires prior written permission.     *
 ******************************************************************************************************/
 
#ifndef SPLINE_H
#define SPLINE_H
 
#include "SplineCoeff.h"
#include "SplinePair.h"
#include <vector>
 
enum SplineTCheck {
  SPLINE_ENABLE_T_CHECK,
  SPLINE_DISABLE_T_CHECK
};

class Spline 
{
  friend class TestSpline;
 
 public:
  Spline(const std::vector<double> &t,
         const std::vector<SplinePair> &xy,
         SplineTCheck splineTCheck = SPLINE_ENABLE_T_CHECK);
 
  virtual ~Spline();

  void computeUntranslatedCoefficients (double aTranslated,
                                        double bTranslated,
                                        double cTranslated,
                                        double dTranslated,
                                        double tI,
                                        double &aUntranslated,
                                        double &bUntranslated,
                                        double &cUntranslated,
                                        double &dUntranslated) const;

  SplinePair findSplinePairForFunctionX (double x,
                                         int numIterations) const;

  SplinePair interpolateCoeff (double t) const;

  SplinePair interpolateControlPoints (double t) const;

  SplinePair p1 (unsigned int i) const;

  SplinePair p2 (unsigned int i) const;
 
private:
  Spline();
 
  // Although coefficient interpolation works for successive t values not 1.0 apart, the control point interpolation
  // does not so we check the increments. Note that the starting value is arbitrary. Removing this restriction will
  // mean upgrading the code to allow arbitrary t increments
  void checkTIncrements (const std::vector<double> &t) const;
 
  void computeCoefficientsForIntervals (const std::vector<double> &t,
                                        const std::vector<SplinePair> &xy);
  void computeControlPointsForIntervals ();
 
  // Coefficients a,b,c,d
  std::vector<SplineCoeff> m_elements;
 
  // Input times
  std::vector<double> m_t;
 
  // Input points
  std::vector<SplinePair> m_xy;
 
  // Control points for each interval
  std::vector<SplinePair> m_p1;
  std::vector<SplinePair> m_p2;
};
 
#endif // SPLINE_H