quaternion_ref.h

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#ifndef OPEN_WALKER_CORE_EIGEN_QUATERNION_REF_H
#define OPEN_WALKER_CORE_EIGEN_QUATERNION_REF_H

#include <Eigen/Geometry>

// has to be in eigen namespace for QuaternionBase<...> to work with custom type QuaternionRef
namespace Eigen
{
// forward declaration
template <typename _Derived>
class QuaternionRef;

namespace internal
{
template <typename _Derived>
struct traits<QuaternionRef<_Derived> >
{
  typedef QuaternionRef<_Derived> PlainObject;
  typedef typename _Derived::Scalar Scalar;
  typedef Eigen::Block<_Derived, 4, 1> Coefficients;

  enum
  {
    Alignment = internal::traits<Coefficients>::Alignment,
    Flags = LvalueBit
  };
};

}  // namespace internal

template <typename _Derived>
class QuaternionRef : public Eigen::QuaternionBase<QuaternionRef<_Derived> >
{
public:
  typedef _Derived Derived;
  typedef Eigen::QuaternionBase<QuaternionRef<_Derived> > Base;
  typedef typename Eigen::internal::traits<QuaternionRef>::Coefficients Coefficients;

protected:
  Coefficients coeffs_;  

public:
  QuaternionRef(Derived& ref, int startRow = 0, int startCol = 0) :
    coeffs_(ref, startRow, startCol)
  {
  }

  //    /*!
  //     *  \brief Copy constructor.
  //     */
  //    QuaternionRef(const QuaternionRef& other) :
  //        m_coeffs(other.coeffs())
  //    {}

  using Base::operator=;

  using Base::operator*=;

  Coefficients& coeffs()
  {
    return coeffs_;
  }

  const Coefficients& coeffs() const
  {
    return coeffs_;
  }

  std::string toString() const
  {
    std::ostringstream out;
    out << coeffs_.transpose();
    return out.str();
  }

private:
  QuaternionRef();
};

}  // namespace Eigen

#endif  // OPEN_WALKER_CORE_EIGEN_QUATERNION_REF_H