Distance from a point p in 2d to a line defined by two points a and b.
public static float DistancePointToLine(Vector2 p, Vector2 a, Vector2 b) { Vector2 vector = b - a; return (Mathf.Abs((float) (((b.x - a.x) * (a.y - p.y)) - ((a.x - p.x) * (b.y - a.y)))) / vector.magnitude); }