sLerp method

Q sLerp(Q o, double amount)

Implementation

Q sLerp(Q o, double amount) {
  double cosHalfTheta = x*o.x + y*o.y + z*o.z + w*o.w;

  if (cosHalfTheta < 0)
  {
    o = _q(-o.x, -o.y, -o.z, -o.w);
    cosHalfTheta = -cosHalfTheta;
  }

  if (cosHalfTheta.abs() >= 1.0) return _this;
  else if (cosHalfTheta > 0.95) return nLerp(o, amount);
  else
  {
    final halfTheta = math.acos(cosHalfTheta);
    final sinHalfTheta = math.sqrt(1.0 - cosHalfTheta*cosHalfTheta);

    if (sinHalfTheta.abs() < RaylibConstants.EPSILON)
    {
      return _q(
        x*0.5 + o.x*0.5,
        y*0.5 + o.y*0.5,
        z*0.5 + o.z*0.5,
        w*0.5 + o.w*0.5,
      );
    }
    else
    {
      final ratioA = math.sin((1 - amount)*halfTheta)/sinHalfTheta;
      final ratioB = math.sin(amount*halfTheta)/sinHalfTheta;

      return _q(
        x*ratioA + o.x*ratioB,
        y*ratioA + o.y*ratioB,
        z*ratioA + o.z*ratioB,
        w*ratioA + o.w*ratioB,
      );
    }
  }
}