public static int dot (Point vs, Point v1e, Point v2e)
    {
        return ((v1e.x - vs.x) * (v2e.x - vs.x) + (v1e.y - vs.y) * (v2e.y - vs.y));
    }
public static int dot ( Point vs , Point v1e , Point v2e ) { return ( ( v1e . x - vs . x ) * ( v2e . x - vs . x ) + ( v1e . y - vs . y ) * ( v2e . y - vs . y ) ) ; }
Computes and returns the dot product of the two vectors. The vectors are assumed to start
with the same coordinate and end with different coordinates.

@param vs the starting point of both vectors.
@param v1e the ending point of the first vector.
@param v2e the ending point of the second vector.