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#ifndef __CGLA_ARITHQUAT_H__

#define __CGLA_ARITHQUAT_H__

#include "CGLA.h"

#include <cmath>

namespace CGLA {

  /** \brief A T based Quaterinion class. 

	Quaternions are algebraic entities useful for rotation. */

	template<class T, class V, class Q>

  class ArithQuat

  {

  public:

    /// Vector part of quaternion

    V qv;

    /// Scalar part of quaternion

    T qw;

    /// Construct undefined quaternion

#ifndef NDEBUG

    ArithQuat() : qw(CGLA_INIT_VALUE) {}

#else

    ArithQuat() {}

#endif

    /// Construct quaternion from vector and scalar

    ArithQuat(const V& imaginary, T real = 1.0f) : qv(imaginary) , qw(real) {}

    /// Construct quaternion from four scalars

    ArithQuat(T x, T y, T z, T _qw) : qv(x,y,z), qw(_qw) {}

    /// Assign values to a quaternion

    void set(const V& imaginary, T real=1.0f)

    {

      qv = imaginary;

      qw = real;

    }

    void set(T x, T y, T z, T _qw) 

    {

      qv.set(x,y,z);

      qw = _qw;

    }

    /*void set(const Vec4f& v)

    {

      qv.set(v[0], v[1], v[2]);

      qw = v[3];		  

    }*/

    /// Get values from a quaternion

    void get(T& x, T& y, T& z, T& _qw) const

    {

      x  = qv[0];

      y  = qv[1];

      z  = qv[2];

      _qw = qw;

    }

    /// Get imaginary part of a quaternion

    V get_imaginary_part() const { return qv; }

    /// Get real part of a quaternion

    T get_real_part() const { return qw; }

    /// Obtain angle of rotation and axis

    void get_rot(T& angle, V& v)

    {

      angle = 2*std::acos(qw);

      if(angle < TINY) 

				v = V(static_cast<T>(1.0), static_cast<T>(0.0), static_cast<T>(0.0));

      else 

				v = qv*(static_cast<T>(1.0)/std::sin(angle));

      if(angle > M_PI)

				v = -v;

      v.normalize();      

    }

    /// Construct a Quaternion from an angle and axis of rotation.

    void make_rot(T angle, const V& v)

    {

      angle /= static_cast<T>(2.0);

      qv = CGLA::normalize(v)*std::sin(angle);

      qw = std::cos(angle);

    }

    /** Construct a Quaternion rotating from the direction given

	by the first argument to the direction given by the second.*/

    void make_rot(const V& s,const V& t)

    {

      T tmp = std::sqrt(2*(1 + dot(s, t)));

      qv = cross(s, t)*(1.0/tmp);

      qw = tmp/2.0;    

    }

    //----------------------------------------------------------------------

    // Binary operators

    //----------------------------------------------------------------------

    bool operator==(const ArithQuat<T,V,Q>& q) const

    {

      return qw == q.qw && qv == q.qv;

    }

    bool operator!=(const ArithQuat<T,V,Q>& q) const

    {

      return qw != q.qw || qv != q.qv;

    }

    /// Multiply two quaternions. (Combine their rotation)

    Q operator*(const ArithQuat<T,V,Q>& q) const

    {

      return Q(cross(qv, q.qv) + qv*q.qw + q.qv*qw, 

		         qw*q.qw - dot(qv, q.qv));      

    }

    /// Multiply scalar onto quaternion.

    Q operator*(T scalar) const

    {

      return Q(qv*scalar, qw*scalar);

    }

    /// Add two quaternions.

    Q operator+(const ArithQuat<T,V,Q>& q) const

    {

      return Q(qv + q.qv, qw + q.qw);

    }

    //----------------------------------------------------------------------

    // Unary operators

    //----------------------------------------------------------------------

    /// Compute the additive inverse of the quaternion

    Q operator-() const { return Q(-qv, -qw); }

    /// Compute norm of quaternion

    T norm() const { return dot(qv, qv) + qw*qw; }

    /// Return conjugate quaternion

    Q conjugate() const { return Q(-qv, qw); }

    /// Compute the multiplicative inverse of the quaternion

    Q inverse() const { return Q(conjugate()*(1/norm())); }

    /// Normalize quaternion.

    Q normalize() { return Q((*this)*(1/norm())); }

    //----------------------------------------------------------------------

    // Application

    //----------------------------------------------------------------------

    /// Rotate vector according to quaternion

    V apply(const V& vec) const 

    {

      return ((*this)*Q(vec)*inverse()).qv;

    }

    /// Rotate vector according to unit quaternion

    V apply_unit(const V& vec) const

    {

      return ((*this)*Q(vec)*conjugate()).qv;

    }

  };

  template<class T, class V, class Q>

  inline Q operator*(T scalar, const ArithQuat<T,V,Q>& q)

  {

    return q*scalar;

  }

  /** Perform linear interpolation of two quaternions. 

      The last argument is the parameter used to interpolate

      between the two first. SLERP - invented by Shoemake -

      is a good way to interpolate because the interpolation

      is performed on the unit sphere. 	

  */

	template<class T, class V, class Q>

  inline Q slerp(const ArithQuat<T,V,Q>& q0, const ArithQuat<T,V,Q>& q1, T t)

  {

    T angle = std::acos(q0.qv[0]*q1.qv[0] + q0.qv[1]*q1.qv[1] 

			    + q0.qv[2]*q1.qv[2] + q0.qw*q1.qw);

    return (q0*std::sin((1 - t)*angle) + q1*std::sin(t*angle))*(1/std::sin(angle));

  }

  /// Print quaternion to stream.

  template<class T, class V, class Q>

  inline std::ostream& operator<<(std::ostream&os, const ArithQuat<T,V,Q>& v)

  {

    os << "[ ";

    for(unsigned int i=0;i<3;i++) os << v.qv[i] << " ";

    os << "~ " << v.qw << " ";

    os << "]";

    return os;

  }

}

#endif // __CGLA_ARITHQUAT_H__