quaternion_spline.cpp

friend void squad(quaternion& qR, const quaternion& q1, const quaternion& qA, 
				  const quaternion& qB, const quaternion& q2,
				  float t)
	quaternion r1, r2;
{
	slerp(r1, q1, q2, t);
	slerp(r2, qA, qB, t);
	slerp(qR, r1, r2, 2.0f * t * (1.0f - t));
}

friend void spline(quaternion& qR,  const quaternion& q0, const quaternion& q1, 
				   const quaternion& q2, const quaternion& q3, float t)
{
	quaternion a1, a2, qinv, qa, qb;
	
	invert(qinv, q1);
	log(qa, qinv*q2);
	log(qb, qinv*q0);
	qa += qb;
	qa /= -4.0;
	exp(qb, qa);
	a1 = q1 * qb;
	
	invert(qinv, q2);
	log(qa, qinv*q3);
	log(qb, qinv*q1);
	qa += qb;
	qa /= -4.0;
	exp(qb, qa);
	a2 = q2 * qb;

	squad(qR, q1, a1, a2, q2, t);
}