code: public static int dot (int v1sx, int v1sy, int v1ex, int v1ey,
                             int v2sx, int v2sy, int v2ex, int v2ey)
      {
          return ((v1ex - v1sx) * (v2ex - v2sx) + (v1ey - v1sy) * (v2ey - v2sy));
      }
docs: Computes and returns the dot product of the two vectors.  See {@link
  #dot(Point,Point,Point,Point)} for an explanation of the arguments