gls_quaternion.h

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/*! \file
  \brief  The disti::GlsQuaternion class.

  \par Copyright Information

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*/

#ifndef GLS_QUATERNION_H
#define GLS_QUATERNION_H

#include "vertex.h"

namespace disti
{
namespace
{
    // Circular dependancies prevent us from using VeryCloseToZero in util.h
    bool IsVeryCloseToZero( double value ) { return fabs( value ) < 0.0001; }
} // namespace

template<class Type>
class GlsMatrixAffine;

/** The GlsQuaternion class */
template<class Type>
class GlsQuaternion
{
public:
    //------------------------------------------------------------------------
    /** 
    * Default constructor. This will initialize the quaternion to zero.
    */
    //------------------------------------------------------------------------
    inline GlsQuaternion()
    {
        _v[ 0 ] = 0;
        _v[ 1 ] = 0;
        _v[ 2 ] = 0;
        _v[ 3 ] = 0;
    }

    //------------------------------------------------------------------------
    /** 
    * Constructor.  Sets quaternion from 4 constants.
    * \param x  Initial X value
    * \param y  Initial Y value
    * \param z  Initial Z value
    * \param w  Initial W value
    */
    //------------------------------------------------------------------------
    inline GlsQuaternion( Type x, Type y, Type z, Type w )
    {
        _v[ 0 ] = x;
        _v[ 1 ] = y;
        _v[ 2 ] = z;
        _v[ 3 ] = w;
    }

    //------------------------------------------------------------------------
    /** 
    * Constructor.  Sets quaternion from angle about an arbitrary axis
    * \param angle  Rotation angle in radians
    * \param axis   Unit vector representing arbitrary axis 
    */
    //------------------------------------------------------------------------
    inline GlsQuaternion( Type angle, const Vector& axis )
    {
        SetFromAngleAxis( angle, axis );
    }

    //------------------------------------------------------------------------
    /** 
    * Constructor.  Sets quaternion from 3 angles about 3 axes
    * \param angle1  Rotation angle about first axis in radians
    * \param axis1   Unit vector representing first arbitrary axis 
    * \param angle2  Rotation angle about second axis in radians
    * \param axis2   Unit vector representing second arbitrary axis 
    * \param angle3  Rotation angle about third axis in radians
    * \param axis3   Unit vector representing third arbitrary axis 
    */
    //------------------------------------------------------------------------
    inline GlsQuaternion( Type angle1, const Vector& axis1,
        Type angle2, const Vector& axis2,
        Type angle3, const Vector& axis3 )
    {
        SetFromAngleAxis( angle1, axis1, angle2, axis2, angle3, axis3 );
    }

    //------------------------------------------------------------------------
    /** 
    * Constructor.  Sets quaternion from 3 angles (Euler Angles)
    * \param angleX  Rotation angle about X axis in radians
    * \param angleY  Rotation angle about Y axis in radians
    * \param angleZ  Rotation angle about Z axis in radians
    */
    //------------------------------------------------------------------------
    inline GlsQuaternion( Type angleX, Type angleY, Type angleZ )
    {
        SetFromEulerAngles( angleX, angleY, angleZ );
    }

    //------------------------------------------------------------------------
    /** 
    * Constructor.  Sets quaternion from 3 angles (Euler Angles)
    * \param anglesVec  A vector where each component of the vector is an
    *                   Euler angle component in radians.
    */
    //------------------------------------------------------------------------
    inline GlsQuaternion( const Vector& anglesVec )
    {
        SetFromEulerAngles( anglesVec.x, anglesVec.y, anglesVec.z );
    }

    //------------------------------------------------------------------------
    /** 
    * Constructor.  Sets quaternion from a rotation matrix
    * \param matrix  An affine matrix representing a rotation matrix
    */
    //------------------------------------------------------------------------
    inline GlsQuaternion( const GlsMatrixAffine<Type>& matrix )
    {
        SetFromRotationMatrix( matrix );
    }

    //------------------------------------------------------------------------
    /** 
    * Accessor method providing access to quaternion data.
    * \return  A pointer to the quaternion data.
    */
    //------------------------------------------------------------------------
    inline Type* Data()
    {
        return _v;
    }

    //------------------------------------------------------------------------
    /** 
    * Accessor method providing access to quaternion data.
    * \return  A pointer to the quaternion data.
    */
    //------------------------------------------------------------------------
    inline const Type* Data() const
    {
        return _v;
    }

    //------------------------------------------------------------------------
    /** 
    * Boolean equivalence operator
    * \param  q  Quaternion to compare against
    * \return  True if the two quaternions are exactly equal
    */
    //------------------------------------------------------------------------
    inline bool operator==( const GlsQuaternion& q ) const
    {
        return _v[ 0 ] == q._v[ 0 ] && _v[ 1 ] == q._v[ 1 ] && _v[ 2 ] == q._v[ 2 ] && _v[ 3 ] == q._v[ 3 ];
    }

    //------------------------------------------------------------------------
    /** 
    * Boolean non-equivalence operator
    * \param  q  Quaternion to compare against
    * \return  True if the two quaternions are not exactly equal
    */
    //------------------------------------------------------------------------
    inline bool operator!=( const GlsQuaternion& q ) const
    {
        return _v[ 0 ] != q._v[ 0 ] || _v[ 1 ] != q._v[ 1 ] || _v[ 2 ] != q._v[ 2 ] || _v[ 3 ] != q._v[ 3 ];
    }

    //------------------------------------------------------------------------
    /** 
    * Boolean less than operator
    * \param  q  Quaternion to compare against
    * \return  True if the this quaternion is less than the provided one
    */
    //------------------------------------------------------------------------
    inline bool operator<( const GlsQuaternion& q ) const
    {
        if( _v[ 0 ] < q._v[ 0 ] )
            return true;
        else if( _v[ 0 ] > q._v[ 0 ] )
            return false;
        else if( _v[ 1 ] < q._v[ 1 ] )
            return true;
        else if( _v[ 1 ] > q._v[ 1 ] )
            return false;
        else if( _v[ 2 ] < q._v[ 2 ] )
            return true;
        else if( _v[ 2 ] > q._v[ 2 ] )
            return false;
        else
            return ( _v[ 3 ] < q._v[ 3 ] );
    }

    //------------------------------------------------------------------------
    /** 
    * Scalar multiplication operator
    * \param  s  A scalar to multiply against
    * \return  This quaternion multiplied by the scalar
    */
    //------------------------------------------------------------------------
    inline const GlsQuaternion operator*( Type s ) const
    {
        return GlsQuaternion( _v[ 0 ] * s, _v[ 1 ] * s, _v[ 2 ] * s, _v[ 3 ] * s );
    }

    //------------------------------------------------------------------------
    /** 
    * Scalar multiplication operator and assignment operator
    * \param  s  A scalar to multiply against
    * \return  This quaternion multiplied by the scalar
    */
    //------------------------------------------------------------------------
    inline GlsQuaternion& operator*=( Type s )
    {
        _v[ 0 ] *= s;
        _v[ 1 ] *= s;
        _v[ 2 ] *= s;
        _v[ 3 ] *= s;
        return *this; // enable nesting
    }

    //------------------------------------------------------------------------
    /** 
    * Quaternion multiplication operator  
    * \param q  A quaternion to multiply against
    * \return  This quaternion multiplied by the quaternion
    */
    //------------------------------------------------------------------------
    inline const GlsQuaternion operator*( const GlsQuaternion& q ) const
    {
        return GlsQuaternion( q._v[ 3 ] * _v[ 0 ] + q._v[ 0 ] * _v[ 3 ] + q._v[ 1 ] * _v[ 2 ] - q._v[ 2 ] * _v[ 1 ],
            q._v[ 3 ] * _v[ 1 ] - q._v[ 0 ] * _v[ 2 ] + q._v[ 1 ] * _v[ 3 ] + q._v[ 2 ] * _v[ 0 ],
            q._v[ 3 ] * _v[ 2 ] + q._v[ 0 ] * _v[ 1 ] - q._v[ 1 ] * _v[ 0 ] + q._v[ 2 ] * _v[ 3 ],
            q._v[ 3 ] * _v[ 3 ] - q._v[ 0 ] * _v[ 0 ] - q._v[ 1 ] * _v[ 1 ] - q._v[ 2 ] * _v[ 2 ] );
    }

    //------------------------------------------------------------------------
    /** 
    * Quaternion multiplication operator  
    * \param q  A quaternion to multiply against
    * \return  This quaternion multiplied by the quaternion
    */
    //------------------------------------------------------------------------
    inline GlsQuaternion& operator*=( const GlsQuaternion& q )
    {
        Type x  = q._v[ 3 ] * _v[ 0 ] + q._v[ 0 ] * _v[ 3 ] + q._v[ 1 ] * _v[ 2 ] - q._v[ 2 ] * _v[ 1 ];
        Type y  = q._v[ 3 ] * _v[ 1 ] - q._v[ 0 ] * _v[ 2 ] + q._v[ 1 ] * _v[ 3 ] + q._v[ 2 ] * _v[ 0 ];
        Type z  = q._v[ 3 ] * _v[ 2 ] + q._v[ 0 ] * _v[ 1 ] - q._v[ 1 ] * _v[ 0 ] + q._v[ 2 ] * _v[ 3 ];
        _v[ 3 ] = q._v[ 3 ] * _v[ 3 ] - q._v[ 0 ] * _v[ 0 ] - q._v[ 1 ] * _v[ 1 ] - q._v[ 2 ] * _v[ 2 ];

        _v[ 2 ] = z;
        _v[ 1 ] = y;
        _v[ 0 ] = x;

        return ( *this ); // enable nesting
    }

    //------------------------------------------------------------------------
    /** 
    * Scalar division operator
    * \param  s  A scalar to divide
    * \return  This quaternion divided by the scalar
    */
    //------------------------------------------------------------------------
    inline GlsQuaternion operator/( Type s ) const
    {
        Type div = 1.0 / s;
        return GlsQuaternion( _v[ 0 ] * div, _v[ 1 ] * div, _v[ 2 ] * div, _v[ 3 ] * div );
    }

    //------------------------------------------------------------------------
    /** 
    * Scalar division and assignment operator
    * \param  s  A scalar to divide
    * \return  This quaternion divided by the scalar
    */
    //------------------------------------------------------------------------
    inline GlsQuaternion& operator/=( Type s )
    {
        Type div = 1 / s;
        _v[ 0 ] *= div;
        _v[ 1 ] *= div;
        _v[ 2 ] *= div;
        _v[ 3 ] *= div;
        return *this;
    }

    //------------------------------------------------------------------------
    /** 
    * Quaternion division operator  
    * \param q  A quaternion to division by
    * \return  This quaternion divided by the quaternion
    */
    //------------------------------------------------------------------------
    inline const GlsQuaternion operator/( const GlsQuaternion& q ) const
    {
        return ( ( *this ) * q.Inverse() );
    }

    //------------------------------------------------------------------------
    /** 
    * Quaternion division operator  
    * \param q  A quaternion to division by
    * \return  This quaternion divided by the quaternion
    */
    //------------------------------------------------------------------------
    inline GlsQuaternion& operator/=( const GlsQuaternion& q )
    {
        ( *this ) = ( *this ) * q.Inverse();
        return ( *this ); // enable nesting
    }

    //------------------------------------------------------------------------
    /** 
    * Quaternion addition operator  
    * \param q  A quaternion to add
    * \return  This quaternion plus the supplied quaternion
    */
    //------------------------------------------------------------------------
    inline const GlsQuaternion operator+( const GlsQuaternion& q ) const
    {
        return GlsQuaternion( _v[ 0 ] + q._v[ 0 ], _v[ 1 ] + q._v[ 1 ],
            _v[ 2 ] + q._v[ 2 ], _v[ 3 ] + q._v[ 3 ] );
    }

    //------------------------------------------------------------------------
    /** 
    * Quaternion addition and assignment operator  
    * \param q  A quaternion to add
    * \return  This quaternion plus the supplied quaternion
    */
    //------------------------------------------------------------------------
    inline GlsQuaternion& operator+=( const GlsQuaternion& q )
    {
        _v[ 0 ] += q._v[ 0 ];
        _v[ 1 ] += q._v[ 1 ];
        _v[ 2 ] += q._v[ 2 ];
        _v[ 3 ] += q._v[ 3 ];
        return *this; // enable nesting
    }

    //------------------------------------------------------------------------
    /** 
    * Quaternion subtrtaction operator  
    * \param q  A quaternion to subtract
    * \return  This quaternion minus the supplied quaternion
    */
    //------------------------------------------------------------------------
    inline const GlsQuaternion operator-( const GlsQuaternion& q ) const
    {
        return GlsQuaternion( _v[ 0 ] - q._v[ 0 ], _v[ 1 ] - q._v[ 1 ],
            _v[ 2 ] - q._v[ 2 ], _v[ 3 ] - q._v[ 3 ] );
    }

    //------------------------------------------------------------------------
    /** 
    * Quaternion subtraction and assignment operator  
    * \param q  A quaternion to subtract
    * \return  This quaternion minus the supplied quaternion
    */
    //------------------------------------------------------------------------
    inline GlsQuaternion& operator-=( const GlsQuaternion& q )
    {
        _v[ 0 ] -= q._v[ 0 ];
        _v[ 1 ] -= q._v[ 1 ];
        _v[ 2 ] -= q._v[ 2 ];
        _v[ 3 ] -= q._v[ 3 ];
        return *this; // enable nesting
    }

    /** Negation operator - returns the negative of the quaternion.
    Basically just calls operator - () on the Vec4 */
    inline const GlsQuaternion operator-() const
    {
        return GlsQuaternion( -_v[ 0 ], -_v[ 1 ], -_v[ 2 ], -_v[ 3 ] );
    }

    //------------------------------------------------------------------------
    /** 
    * Returns the magnitude of the quaternion
    * \return  The magnitude of the quaternion
    */
    //------------------------------------------------------------------------
    inline Type Magnitude() const
    {
        return sqrt( _v[ 0 ] * _v[ 0 ] + _v[ 1 ] * _v[ 1 ] + _v[ 2 ] * _v[ 2 ] + _v[ 3 ] * _v[ 3 ] );
    }

    //------------------------------------------------------------------------
    /** 
    * Returns the magnitude squared of the quaternion
    * \return  The magnitude squared of the quaternion
    */
    //------------------------------------------------------------------------
    inline Type MagnitudeSquared() const
    {
        return _v[ 0 ] * _v[ 0 ] + _v[ 1 ] * _v[ 1 ] + _v[ 2 ] * _v[ 2 ] + _v[ 3 ] * _v[ 3 ];
    }

    //------------------------------------------------------------------------
    /** 
    * Returns the conjugate of the quaternion
    * \return  The conjugate of the quaternion
    */
    //------------------------------------------------------------------------
    inline GlsQuaternion Conjugate() const
    {
        return GlsQuaternion( -_v[ 0 ], -_v[ 1 ], -_v[ 2 ], _v[ 3 ] );
    }

    //------------------------------------------------------------------------
    /** 
    * Returns the inverse of the quaternion
    * \return  The inverse of the quaternion
    */
    //------------------------------------------------------------------------
    inline const GlsQuaternion Inverse() const
    {
        return Conjugate() / MagnitudeSquared();
    }

    //------------------------------------------------------------------------
    /** 
    * Returns the dot product of the quaternion and a supplied quaternion
    * \param q  A quaternion to multiply against this quaternion
    * \return The dot product of the quaternion and a supplied quaternion
    */
    //------------------------------------------------------------------------
    inline Type DotProduct( const GlsQuaternion& q ) const
    {
        return ( ( _v[ 0 ] * q._v[ 0 ] ) + ( _v[ 1 ] * q._v[ 1 ] ) + ( _v[ 2 ] * q._v[ 2 ] ) + ( _v[ 3 ] * q._v[ 3 ] ) );
    }

    //------------------------------------------------------------------------
    /** 
    * Normalizes this quaternion
    */
    //------------------------------------------------------------------------
    inline void Normalize()
    {
        *this /= Magnitude();
    }

    //------------------------------------------------------------------------
    /** 
    * Sets the component values for this quaternion
    * \param x  The X value
    * \param y  The Y value
    * \param z  The Z value
    * \param w  The W value
    */
    //------------------------------------------------------------------------
    inline void Set( Type x, Type y, Type z, Type w )
    {
        _v[ 0 ] = x;
        _v[ 1 ] = y;
        _v[ 2 ] = z;
        _v[ 3 ] = w;
    }

    //------------------------------------------------------------------------
    /** 
    * Sets quaternion from angle about an arbitrary axis
    * \param angle  Rotation angle in radians
    * \param axis   Unit vector representing arbitrary axis 
    */
    //------------------------------------------------------------------------
    void SetFromAngleAxis( Type angle, const Vector& axis )
    {
        Type half_angle     = angle * (Type)0.5;
        Type sin_half_angle = sin( half_angle );

        _v[ 0 ] = sin_half_angle * axis.x;
        _v[ 1 ] = sin_half_angle * axis.y;
        _v[ 2 ] = sin_half_angle * axis.z;
        _v[ 3 ] = cos( half_angle );
    }

    //------------------------------------------------------------------------
    /** 
    * Sets quaternion from three angle-axis pairs.
    * \param angle1  Rotation angle in radians
    * \param axis1   Unit vector representing arbitrary axis 
    * \param angle2  Rotation angle in radians
    * \param axis2   Unit vector representing arbitrary axis 
    * \param angle3  Rotation angle in radians
    * \param axis3   Unit vector representing arbitrary axis 
    */
    //------------------------------------------------------------------------
    void SetFromAngleAxis( Type angle1, const Vector& axis1,
        Type angle2, const Vector& axis2,
        Type angle3, const Vector& axis3 )
    {
        GlsQuaternion q1( angle1, axis1 );
        GlsQuaternion q2( angle2, axis2 );
        SetFromAngleAxis( angle3, axis3 );

        *this = q1 * q2 * *this;
    }

    //------------------------------------------------------------------------
    /** 
    * Sets quaternion from the Euler angles.
    * \param angleX The X Euler angle in radians
    * \param angleY The Y Euler angle in radians
    * \param angleZ The Z Euler angle in radians
    */
    //------------------------------------------------------------------------
    void SetFromEulerAngles( Type angleX, Type angleY, Type angleZ )
    {
        GlsQuaternion<Type> qx, qy, qz;

        // precompute half angles
        Type xOver2 = angleX * (Type)0.5;
        Type yOver2 = angleY * (Type)0.5;
        Type zOver2 = angleZ * (Type)0.5;

        // set the pitch quat
        qx._v[ 0 ] = sin( xOver2 );
        qx._v[ 1 ] = (Type)0.0;
        qx._v[ 2 ] = (Type)0.0;
        qx._v[ 3 ] = cos( xOver2 );

        // set the yaw quat
        qy._v[ 0 ] = (Type)0.0;
        qy._v[ 1 ] = sin( yOver2 );
        qy._v[ 2 ] = (Type)0.0;
        qy._v[ 3 ] = cos( yOver2 );

        // set the roll quat
        qz._v[ 0 ] = (Type)0.0;
        qz._v[ 1 ] = (Type)0.0;
        qz._v[ 2 ] = sin( zOver2 );
        qz._v[ 3 ] = cos( zOver2 );

        // compose the three in x y z order...
        *this = qx * qy * qz;

        this->Normalize();
    }

    //------------------------------------------------------------------------
    /** 
    * Sets this quaternion to a rotation that rotates 'to' into 'from'.
    * \param to The rotation destination
    * \param from The rotation start point
    */
    //------------------------------------------------------------------------
    void SetFromVectors( const Vector& to, const Vector& from )
    {
        // dot product vec1*vec2
        Type cosangle = from.DotProduct( to ) / ( from.Magnitude() * to.Magnitude() );

        if( IsVeryCloseToZero( cosangle - 1 ) )
        {
            // cosangle is close to 1, so the vectors are close to being coincident
            // Need to generate an angle of zero with any vector we like
            // We'll choose (1,0,0)
            SetFromAngleAxis( 0.0, Vector( 1.0, 0.0, 0.0 ) );
        }
        else if( IsVeryCloseToZero( cosangle + 1.0 ) )
        {
            // vectors are close to being opposite, so will need to find a
            // vector orthongonal to from to rotate about.
            Vector tmp;
            if( fabs( from.x ) < fabs( from.y ) )
                if( fabs( from.x ) < fabs( from.z ) )
                    tmp = Vector( 1.0, 0.0, 0.0 ); // use x axis.
                else
                    tmp = Vector( 0.0, 0.0, 1.0 );
            else if( fabs( from.y ) < fabs( from.z ) )
                tmp = Vector( 0.0, 1.0, 0.0 );
            else
                tmp = Vector( 0.0, 0.0, 1.0 );

            // find orthogonal axis.
            Vector axis( from.CrossProduct( tmp ) );
            axis.Normalize();

            _v[ 0 ] = axis.x; // sin of half angle of PI is 1.0.
            _v[ 1 ] = axis.y; // sin of half angle of PI is 1.0.
            _v[ 2 ] = axis.z; // sin of half angle of PI is 1.0.
            _v[ 3 ] = 0;      // cos of half angle of PI is zero.
        }
        else
        {
            // This is the usual situation - take a cross-product of vec1 and vec2
            // and that is the axis around which to rotate.
            Vector axis( from.CrossProduct( to ) );
            axis.Normalize();
            Type angle = acos( cosangle );
            SetFromAngleAxis( angle, axis );
        }
    }

    //------------------------------------------------------------------------
    /** 
    * Sets this quaternion from the specified rotation matrix.
    * \param matrix The rotation matrix
    */
    //------------------------------------------------------------------------
    void SetFromRotationMatrix( const GlsMatrixAffine<Type>& matrix )
    {
        Type        tr, s;
        Type        tq[ 4 ];
        int         i, j, k;
        const Type* mat = const_cast<GlsMatrixAffine<Type>&>( matrix ).Data();

        int nxt[ 3 ] = { 1, 2, 0 };

        tr = mat[ 0 * 4 + 0 ] + mat[ 1 * 4 + 1 ] + mat[ 2 * 4 + 2 ];

        // check the diagonal
        if( tr > 0.0 )
        {
            s       = (Type)sqrt( tr + 1.0 );
            _v[ 3 ] = s / 2.0f;
            s       = 0.5f / s;
            _v[ 0 ] = ( mat[ 1 * 4 + 2 ] - mat[ 2 * 4 + 1 ] ) * s;
            _v[ 1 ] = ( mat[ 2 * 4 + 0 ] - mat[ 0 * 4 + 2 ] ) * s;
            _v[ 2 ] = ( mat[ 0 * 4 + 1 ] - mat[ 1 * 4 + 0 ] ) * s;
        }
        else
        {
            // diagonal is negative
            i = 0;
            if( mat[ 1 * 4 + 1 ] > mat[ 0 * 4 + 0 ] )
                i = 1;
            if( mat[ 2 * 4 + 2 ] > mat[ i * 4 + i ] )
                i = 2;
            j = nxt[ i ];
            k = nxt[ j ];

            s = (Type)sqrt( ( mat[ i * 4 + i ] - ( mat[ j * 4 + j ] + mat[ k * 4 + k ] ) ) + 1.0 );

            tq[ i ] = s * 0.5f;

            if( s != 0.0f )
                s = 0.5f / s;

            tq[ 3 ] = ( mat[ j * 4 + k ] - mat[ k * 4 + j ] ) * s;
            tq[ j ] = ( mat[ i * 4 + j ] + mat[ j * 4 + i ] ) * s;
            tq[ k ] = ( mat[ i * 4 + k ] + mat[ k * 4 + i ] ) * s;

            _v[ 0 ] = tq[ 0 ];
            _v[ 1 ] = tq[ 1 ];
            _v[ 2 ] = tq[ 2 ];
            _v[ 3 ] = tq[ 3 ];
        }
    }

    /** Returns the rotation about the X axis
      * \return The rotation about the X axis
      */
    Type GetRoll( void ) const
    {
        return atan2( 2 * ( _v[ 1 ] * _v[ 2 ] + _v[ 3 ] * _v[ 0 ] ), _v[ 3 ] * _v[ 3 ] - _v[ 0 ] * _v[ 0 ] - _v[ 1 ] * _v[ 1 ] + _v[ 2 ] * _v[ 2 ] );
    }

    /** Returns the rotation about the Y axis
      * \return The rotation about the Y axis
      */
    Type GetPitch( void ) const
    {
        Type tmp = -2 * ( _v[ 0 ] * _v[ 2 ] - _v[ 3 ] * _v[ 1 ] );

        if( tmp > 1.0 )
        {
            tmp = 1.0;
        }
        else if( tmp < -1.0 )
        {
            tmp = -1.0;
        }

        return asin( tmp );
    }
    /** Returns the rotation about the Z axis
      * \return The rotation about the Z axis
      */
    Type GetYaw( void ) const
    {
        return atan2( 2 * ( _v[ 0 ] * _v[ 1 ] + _v[ 3 ] * _v[ 2 ] ), _v[ 3 ] * _v[ 3 ] + _v[ 0 ] * _v[ 0 ] - _v[ 1 ] * _v[ 1 ] - _v[ 2 ] * _v[ 2 ] );
    }

    /** Returns the Euler Angles as a Vector (Warning: SLOW)
      * \return The Euler Angles as a Vector
      */
    Vector GetEulerAngles()
    {
        // This is slow
        return Vector( float( GetRoll() ), float( GetPitch() ), float( GetYaw() ) );
    }

    /** Gets the rotation angle (radians) and the axis about which the angle is rotated.
      * \param angle  Returns the angle of rotation of the quaternion
      * \param axis   Returns the axis of rotation of the quaternion
      */
    void GetAngleAxis( Type* angle, Vector* axis )
    {
// set sure we don't get a NaN result from acos...
#ifdef _WIN32
        if( abs( _v[ 3 ] ) > (Type)1.0 )
#else
        if( fabs( (double)_v[ 3 ] ) > 1.0 )
#endif
        {
            this->Normalize();
        }

        // set the angle - aCos is mathematically defined to be between 0 and PI
        Type rad = acos( _v[ 3 ] ) * (Type)2.0;

        if( angle )
        {
            *angle = rad;
        }

        // set the axis: (use sin(rad) instead of asin(w))
        if( axis )
        {
            Type sin_half_angle = sin( rad * (Type)0.5 );
            if( sin_half_angle >= (Type)0.0001 ) // because (PI >= rad >= 0)
            {
                Type sin_half_angle_inv = Type( 1.0 ) / sin_half_angle;
                axis->x                 = float( _v[ 0 ] * sin_half_angle_inv );
                axis->y                 = float( _v[ 1 ] * sin_half_angle_inv );
                axis->z                 = float( _v[ 2 ] * sin_half_angle_inv );
                axis->Normalize();
            }

            // avoid NAN
            else
            {
                // one of the terms should be a 1,
                // so we can maintain unit-ness
                // in case w is 0 (which here w is 0)
                axis->x = (float)1.0;
                axis->y = (float)0.0;
                axis->z = (float)0.0;
            }
        }
    }

    /** Returns a rotation matrix representation of the quaternion.
      * \return The rotation matrix computed from the quaternion 
      */
    GlsMatrixAffine<Type> GetRotationMatrix()
    {
        Type wx, wy, wz, xx, yy, yz, xy, xz, zz, x2, y2, z2;
        Type mat[ 4 ][ 4 ];

        x2 = _v[ 0 ] + _v[ 0 ];
        y2 = _v[ 1 ] + _v[ 1 ];
        z2 = _v[ 2 ] + _v[ 2 ];

        xx = _v[ 0 ] * x2;
        xy = _v[ 0 ] * y2;
        xz = _v[ 0 ] * z2;

        yy = _v[ 1 ] * y2;
        yz = _v[ 1 ] * z2;
        zz = _v[ 2 ] * z2;

        wx = _v[ 3 ] * x2;
        wy = _v[ 3 ] * y2;
        wz = _v[ 3 ] * z2;

        mat[ 0 ][ 0 ] = 1.0f - ( yy + zz );
        mat[ 0 ][ 1 ] = xy - wz;
        mat[ 0 ][ 2 ] = xz + wy;
        mat[ 0 ][ 3 ] = 0.0f;

        mat[ 1 ][ 0 ] = xy + wz;
        mat[ 1 ][ 1 ] = 1.0f - ( xx + zz );
        mat[ 1 ][ 2 ] = yz - wx;
        mat[ 1 ][ 3 ] = 0.0f;

        mat[ 2 ][ 0 ] = xz - wy;
        mat[ 2 ][ 1 ] = yz + wx;
        mat[ 2 ][ 2 ] = 1.0f - ( xx + yy );
        mat[ 2 ][ 3 ] = 0.0f;

        mat[ 3 ][ 0 ] = 0;
        mat[ 3 ][ 1 ] = 0;
        mat[ 3 ][ 2 ] = 0;
        mat[ 3 ][ 3 ] = 1;

        return GlsMatrixAffine<Type>( mat );
    }

    /** Sets this quaternion to an interpolated rotation between the
      * from and to vectors using spherical linear interpolation (slerp).
       * \param t     Percent of interpelation (0.0 -> 1.0)
       * \param from  The starting quaternion
       * \param to    The ending quaternion
       * \param adjustSign  Whether or not to negate the sign of the to quaternion
       */
    void SetFromSlerp( float t, const GlsQuaternion& from, const GlsQuaternion& to, bool adjustSign = true )
    {
        const GlsQuaternion& p = from;

        // calc cosine theta
        Type cosom = from.DotProduct( to );

        // adjust signs (if necessary)
        GlsQuaternion<Type> q;
        if( adjustSign && ( cosom < (Type)0.0 ) )
        {
            cosom     = -cosom;
            q._v[ 0 ] = -to._v[ 0 ]; // Reverse all signs
            q._v[ 1 ] = -to._v[ 1 ];
            q._v[ 2 ] = -to._v[ 2 ];
            q._v[ 3 ] = -to._v[ 3 ];
        }
        else
        {
            q = to;
        }

        // Calculate coefficients
        Type sclp, sclq;
        if( ( (Type)1.0 - cosom ) > (Type)0.0001 ) // 0.0001 -> some epsillon
        {
            // Standard case (slerp)
            Type omega, sinom;
            omega = acos( cosom ); // extract theta from dot product's cos theta
            sinom = sin( omega );
            sclp  = sin( ( (Type)1.0 - t ) * omega ) / sinom;
            sclq  = sin( t * omega ) / sinom;
        }
        else
        {
            // Very close, do linear interp (because it's faster)
            sclp = (Type)1.0 - t;
            sclq = t;
        }

        _v[ 0 ] = sclp * p._v[ 0 ] + sclq * q._v[ 0 ];
        _v[ 1 ] = sclp * p._v[ 1 ] + sclq * q._v[ 1 ];
        _v[ 2 ] = sclp * p._v[ 2 ] + sclq * q._v[ 2 ];
        _v[ 3 ] = sclp * p._v[ 3 ] + sclq * q._v[ 3 ];
    }

protected:
    Type _v[ 4 ];
};

typedef GlsQuaternion<float>  GlsQuaternionF;
typedef GlsQuaternion<double> GlsQuaternionD;

template<class Type>
inline std::ostream& operator<<( std::ostream& outstr, const GlsQuaternion<Type>& quat )
{
    outstr.precision( 10 );

    outstr.width( 1 );
    outstr << quat.Data()[ 0 ] << " ";
    outstr.width( 8 );
    outstr << quat.Data()[ 1 ] << " ";
    outstr.width( 8 );
    outstr << quat.Data()[ 2 ] << " ";
    outstr.width( 8 );
    outstr << quat.Data()[ 3 ];

    return outstr;
}

template<class Type>
inline std::istream& operator>>( std::istream& instr, GlsQuaternion<Type>& quat )
{
    instr >> quat.Data()[ 0 ] >> quat.Data()[ 1 ] >> quat.Data()[ 2 ] >> quat.Data()[ 3 ];
    return instr;
}

} // end namespace disti

#endif