def easeInOutQuart(n):
    """A quartic tween function that accelerates, reaches the midpoint, and then decelerates.

    Args:
      n (float): The time progress, starting at 0.0 and ending at 1.0.

    Returns:
      (float) The line progress, starting at 0.0 and ending at 1.0. Suitable for passing to getPointOnLine().
    """
    _checkRange(n)
    n = 2 * n
    if n < 1:
        return 0.5 * n**4
    else:
        n = n - 2
        return -0.5 * (n**4 - 2)