#ifndef _gp_QuaternionSLerp_HeaderFile
#define _gp_QuaternionSLerp_HeaderFile

#include <gp_Quaternion.hxx>

/**
 * Perform Spherical Linear Interpolation of the quaternions,
 * return unit length quaternion.
 */
class gp_QuaternionSLerp
{

public:

  gp_QuaternionSLerp() {}

  gp_QuaternionSLerp (const gp_Quaternion& theQStart, const gp_Quaternion& theQEnd)
  {
    Init (theQStart, theQEnd);
  }

  void Init (const gp_Quaternion& theQStart, const gp_Quaternion& theQEnd)
  {
    InitFromUnit (theQStart.Normalized(), theQEnd.Normalized());
  }

  void InitFromUnit (const gp_Quaternion& theQStart, const gp_Quaternion& theQEnd)
  {
    myQStart = theQStart;
    myQEnd   = theQEnd;
    Standard_Real cosOmega = myQStart.Dot (myQEnd);
    if (cosOmega < 0.0)
    {
      cosOmega = -cosOmega;
      myQEnd = -myQEnd;
    }
    if (cosOmega > 0.9999)
    {
      cosOmega = 0.9999;
    }
    myOmega = ACos (cosOmega);
    Standard_Real invSinOmega = (1.0 / Sin (myOmega));
    myQStart.Scale (invSinOmega);
    myQEnd.Scale (invSinOmega);
  }

  //! Set interpolated quaternion for theT position (from 0.0 to 1.0)
  void Interpolate (Standard_Real theT, gp_Quaternion& theResultQ) const
  {
    theResultQ = myQStart * Sin((1.0 - theT) * myOmega) + myQEnd * Sin (theT * myOmega);
  }

private:

  gp_Quaternion myQStart;
  gp_Quaternion myQEnd;
  Standard_Real myOmega;

};

#endif //_gp_QuaternionSLerp_HeaderFile