/****************************************************************************

 Copyright (C) 2002-2014 Gilles Debunne. All rights reserved.

 This file is part of the QGLViewer library version 2.6.3.

 http://www.libqglviewer.com - contact@libqglviewer.com

 This file may be used under the terms of the GNU General Public License 
 versions 2.0 or 3.0 as published by the Free Software Foundation and
 appearing in the LICENSE file included in the packaging of this file.
 In addition, as a special exception, Gilles Debunne gives you certain 
 additional rights, described in the file GPL_EXCEPTION in this package.

 libQGLViewer uses dual licensing. Commercial/proprietary software must
 purchase a libQGLViewer Commercial License.

 This file is provided AS IS with NO WARRANTY OF ANY KIND, INCLUDING THE
 WARRANTY OF DESIGN, MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.

*****************************************************************************/

#ifndef QGLVIEWER_QUATERNION_H
#define QGLVIEWER_QUATERNION_H

#include "vec.h"
#include <math.h>
#include <iostream>

namespace qglviewer {
/*! \brief The Quaternion class represents 3D rotations and orientations.
	\class Quaternion quaternion.h QGLViewer/quaternion.h

	The Quaternion is an appropriate (although not very intuitive) representation for 3D rotations and
	orientations. Many tools are provided to ease the definition of a Quaternion: see constructors,
	setAxisAngle(), setFromRotationMatrix(), setFromRotatedBasis().

	You can apply the rotation represented by the Quaternion to 3D points using rotate() and
	inverseRotate(). See also the Frame class that represents a coordinate system and provides other
	conversion functions like Frame::coordinatesOf() and Frame::transformOf().

	You can apply the Quaternion \c q rotation to the OpenGL matrices using:
	\code
	glMultMatrixd(q.matrix());
	// equvalent to glRotate(q.angle()*180.0/M_PI, q.axis().x, q.axis().y, q.axis().z);
	\endcode

	Quaternion is part of the \c qglviewer namespace, specify \c qglviewer::Quaternion or use the qglviewer
	namespace: \code using namespace qglviewer; \endcode

	<h3>Internal representation</h3>

	The internal representation of a Quaternion corresponding to a rotation around axis \c axis, with an angle
	\c alpha is made of four qreals (i.e. doubles) q[i]:
	\code
	{q[0],q[1],q[2]} = sin(alpha/2) * {axis[0],axis[1],axis[2]}
	q[3] = cos(alpha/2)
	\endcode

	Note that certain implementations place the cosine term in first position (instead of last here).

	The Quaternion is always normalized, so that its inverse() is actually its conjugate.

	See also the Vec and Frame classes' documentations.
	\nosubgrouping */
class QGLVIEWER_EXPORT Quaternion
{
public:
	/*! @name Defining a Quaternion */
	//@{
	/*! Default constructor, builds an identity rotation. */
	Quaternion()
	{ q[0]=q[1]=q[2]=0.0;  q[3]=1.0; }

	/*! Constructor from rotation axis (non null) and angle (in radians). See also setAxisAngle(). */
	Quaternion(const Vec& axis, qreal angle)
	{
		setAxisAngle(axis, angle);
	}

	Quaternion(const Vec& from, const Vec& to);

	/*! Constructor from the four values of a Quaternion. First three values are axis*sin(angle/2) and
		last one is cos(angle/2).

		\attention The identity Quaternion is Quaternion(0,0,0,1) and \e not Quaternion(0,0,0,0) (which is
		not unitary). The default Quaternion() creates such identity Quaternion. */
	Quaternion(qreal q0, qreal q1, qreal q2, qreal q3)
	{ q[0]=q0;    q[1]=q1;    q[2]=q2;    q[3]=q3; }

	/*! Copy constructor. */
	Quaternion(const Quaternion& Q)
	{ for (int i=0; i<4; ++i) q[i] = Q.q[i]; }

	/*! Equal operator. */
	Quaternion& operator=(const Quaternion& Q)
	{
		for (int i=0; i<4; ++i)
			q[i] = Q.q[i];
		return (*this);
	}

	/*! Sets the Quaternion as a rotation of axis \p axis and angle \p angle (in radians).

		\p axis does not need to be normalized. A null \p axis will result in an identity Quaternion. */
	void setAxisAngle(const Vec& axis, qreal angle)
	{
		const qreal norm = axis.norm();
		if (norm < 1E-8)
		{
			// Null rotation
			q[0] = 0.0;      q[1] = 0.0;      q[2] = 0.0;      q[3] = 1.0;
		}
		else
		{
			const qreal sin_half_angle = sin(angle / 2.0);
			q[0] = sin_half_angle*axis[0]/norm;
			q[1] = sin_half_angle*axis[1]/norm;
			q[2] = sin_half_angle*axis[2]/norm;
			q[3] = cos(angle / 2.0);
		}
	}

	/*! Sets the Quaternion value. See the Quaternion(qreal, qreal, qreal, qreal) constructor documentation. */
	void setValue(qreal q0, qreal q1, qreal q2, qreal q3)
	{ q[0]=q0;    q[1]=q1;    q[2]=q2;    q[3]=q3; }

#ifndef DOXYGEN
	void setFromRotationMatrix(const float m[3][3]);
	void setFromRotatedBase(const Vec& X, const Vec& Y, const Vec& Z);
#endif
	void setFromRotationMatrix(const qreal m[3][3]);
	void setFromRotatedBasis(const Vec& X, const Vec& Y, const Vec& Z);
	//@}


	/*! @name Accessing values */
	//@{
	Vec axis() const;
	qreal angle() const;
	void getAxisAngle(Vec& axis, qreal& angle) const;

	/*! Bracket operator, with a constant return value. \p i must range in [0..3]. See the Quaternion(qreal, qreal, qreal, qreal) documentation. */
	qreal operator[](int i) const { return q[i]; }

	/*! Bracket operator returning an l-value. \p i must range in [0..3]. See the Quaternion(qreal, qreal, qreal, qreal) documentation. */
	qreal& operator[](int i) { return q[i]; }
	//@}


	/*! @name Rotation computations */
	//@{
	/*! Returns the composition of the \p a and \p b rotations.

		The order is important. When applied to a Vec \c v (see operator*(const Quaternion&, const Vec&)
		and rotate()) the resulting Quaternion acts as if \p b was applied first and then \p a was
		applied. This is obvious since the image \c v' of \p v by the composited rotation satisfies: \code
		v'= (a*b) * v = a * (b*v) \endcode

		Note that a*b usually differs from b*a.

		\attention For efficiency reasons, the resulting Quaternion is not normalized. Use normalize() in
		case of numerical drift with small rotation composition. */
	friend Quaternion operator*(const Quaternion& a, const Quaternion& b)
	{
		return Quaternion(a.q[3]*b.q[0] + b.q[3]*a.q[0] + a.q[1]*b.q[2] - a.q[2]*b.q[1],
				a.q[3]*b.q[1] + b.q[3]*a.q[1] + a.q[2]*b.q[0] - a.q[0]*b.q[2],
				a.q[3]*b.q[2] + b.q[3]*a.q[2] + a.q[0]*b.q[1] - a.q[1]*b.q[0],
				a.q[3]*b.q[3] - b.q[0]*a.q[0] - a.q[1]*b.q[1] - a.q[2]*b.q[2]);
	}

	/*! Quaternion rotation is composed with \p q.

		See operator*(), since this is equivalent to \c this = \c this * \p q.

		\note For efficiency reasons, the resulting Quaternion is not normalized.
		You may normalize() it after each application in case of numerical drift. */
	Quaternion& operator*=(const Quaternion &q)
	{
		*this = (*this)*q;
		return *this;
	}

	/*! Returns the image of \p v by the rotation \p q.

		Same as q.rotate(v). See rotate() and inverseRotate(). */
	friend Vec operator*(const Quaternion& q, const Vec& v)
	{
		return q.rotate(v);
	}

	Vec rotate(const Vec& v) const;
	Vec inverseRotate(const Vec& v) const;
	//@}


	/*! @name Inversion */
	//@{
	/*! Returns the inverse Quaternion (inverse rotation).

		Result has a negated axis() direction and the same angle(). A composition (see operator*()) of a
		Quaternion and its inverse() results in an identity function.

		Use invert() to actually modify the Quaternion. */
	Quaternion inverse() const { return Quaternion(-q[0], -q[1], -q[2], q[3]); }

	/*! Inverses the Quaternion (same rotation angle(), but negated axis()).

		See also inverse(). */
	void invert() { q[0] = -q[0]; q[1] = -q[1]; q[2] = -q[2]; }

	/*! Negates all the coefficients of the Quaternion.

		This results in an other representation of the \e same rotation (opposite rotation angle, but with
		a negated axis direction: the two cancel out). However, note that the results of axis() and
		angle() are unchanged after a call to this method since angle() always returns a value in [0,pi].

		This method is mainly useful for Quaternion interpolation, so that the spherical
		interpolation takes the shortest path on the unit sphere. See slerp() for details. */
	void negate() { invert(); q[3] = -q[3]; }

	/*! Normalizes the Quaternion coefficients.

		This method should not need to be called since we only deal with unit Quaternions. This is however
		useful to prevent numerical drifts, especially with small rotational increments. See also
		normalized(). */
	qreal normalize()
	{
		const qreal norm = sqrt(q[0]*q[0] + q[1]*q[1] + q[2]*q[2] + q[3]*q[3]);
		for (int i=0; i<4; ++i)
			q[i] /= norm;
		return norm;
	}

	/*! Returns a normalized version of the Quaternion.

		See also normalize(). */
	Quaternion normalized() const
	{
		qreal Q[4];
		const qreal norm = sqrt(q[0]*q[0] + q[1]*q[1] + q[2]*q[2] + q[3]*q[3]);
		for (int i=0; i<4; ++i)
			Q[i] = q[i] / norm;
		return Quaternion(Q[0], Q[1], Q[2], Q[3]);
	}
	//@}


	/*! @name Associated matrix */
	//@{
	const GLdouble* matrix() const;
	void getMatrix(GLdouble m[4][4]) const;
	void getMatrix(GLdouble m[16]) const;

	void getRotationMatrix(qreal m[3][3]) const;

	const GLdouble* inverseMatrix() const;
	void getInverseMatrix(GLdouble m[4][4]) const;
	void getInverseMatrix(GLdouble m[16]) const;

	void getInverseRotationMatrix(qreal m[3][3]) const;
	//@}


	/*! @name Slerp interpolation */
	//@{
	static Quaternion slerp(const Quaternion& a, const Quaternion& b, qreal t, bool allowFlip=true);
	static Quaternion squad(const Quaternion& a, const Quaternion& tgA, const Quaternion& tgB, const Quaternion& b, qreal t);
	/*! Returns the "dot" product of \p a and \p b: a[0]*b[0] + a[1]*b[1] + a[2]*b[2] + a[3]*b[3]. */
	static qreal dot(const Quaternion& a, const Quaternion& b) { return a[0]*b[0] + a[1]*b[1] + a[2]*b[2] + a[3]*b[3]; }

	Quaternion log();
	Quaternion exp();
	static Quaternion lnDif(const Quaternion& a, const Quaternion& b);
	static Quaternion squadTangent(const Quaternion& before, const Quaternion& center, const Quaternion& after);
	//@}

	/*! @name Random Quaternion */
	//@{
	static Quaternion randomQuaternion();
	//@}

	/*! @name XML representation */
	//@{
	explicit Quaternion(const QDomElement& element);
	QDomElement domElement(const QString& name, QDomDocument& document) const;
	void initFromDOMElement(const QDomElement& element);
	//@}

#ifdef DOXYGEN
	/*! @name Output stream */
	//@{
	/*! Output stream operator. Enables debugging code like:
		\code
		Quaternion rot(...);
		cout << "Rotation=" << rot << endl;
		\endcode */
	std::ostream& operator<<(std::ostream& o, const qglviewer::Vec&);
	//@}
#endif

private:
	/*! The internal data representation is private, use operator[] to access values. */
	qreal q[4];
};

} // namespace

std::ostream& operator<<(std::ostream& o, const qglviewer::Quaternion&);

#endif // QGLVIEWER_QUATERNION_H
