rotateInto method

Implementation

Quaternion rotateInto(Vector3 from, Vector3 to) {
  double kTolerance = MathUtils.epsilon * 100;

  // Directly build the quaternion using the following technique:
  // http://lolengine.net/blog/2014/02/24/quaternion-from-two-vectors-final
  double norm_u_norm_v = math.sqrt(from.length2 * to.length2);
  double real_part = norm_u_norm_v + from.clone().dot(to);
  Vector3 n;
  if (real_part < kTolerance * norm_u_norm_v) {
    // If |from| and |to| are exactly opposite, rotate 180 degrees around an
    // arbitrary orthogonal axis. Axis normalization can happen later, when we
    // normalize the quaternion.
    real_part = 0.0;
    n = (from.x.abs() > from.z.abs()) ? Vector3(-from[1], from[0], 0) : Vector3(0, -from[2], from[1]);
  } else {
    // Otherwise, build the quaternion the standard way.
    n = from.clone().cross(to);
  }

  x = n.x;
  y = n.y;
  z = n.z;
  w = real_part;

  // Build and return a normalized quaternion.
  // Note that Rotation::FromQuaternion automatically performs normalization.
  return this;
}