def getPointOnLine(x1, y1, x2, y2, n):
x = ((x2 - x1) * n) + x1<EOL>y = ((y2 - y1) * n) + y1<EOL>return (x, y)<EOL>
Returns the (x, y) tuple of the point that has progressed a proportion
    n along the line defined by the two x, y coordinates.

    Copied from pytweening module.