如何找到两个精灵之间接触点的法向量?

I am creating a game where the character can jump in the direction opposite of the surface he lands on. For example if he is on the ground he can only jump up. If he is on a right edge he can only jump left...etc etc.. Currently I have set up my SKNodes into leftWall, rightWall, bottomSurface, topSurface and have a huge if/else... this works but will become way more complicated as I add different surfaces with different angles etc...I am creating a game where the character can ju