/*@brief Return the result of spherical linear interpolation betwen two quaternions
@param q1 The first quaternion
@param q2 The second quaternion
@param t The ration between q1 and q2. t = 0 return q1, t=1 returns q2
Slerp assumes constant velocity between positions. */
public void slerp( ref btQuaternion q1, ref btQuaternion q2, double t, out btQuaternion result )
{
q1.slerp( ref q2, t, out result );
}