Guarantee outward direction of polygon normals
===

I'm trying to write a 2D game in Java that uses the Separating Axis Theorem for collision detection. In order to resolve collisions between two polygons, I need to know the Minimum Translation Vector of the collision, and I need to know which direction it points relative to the polygons (so that I can give one polygon a penalty force along that direction and the other a penalty force in the opposite direction). For reference, I'm trying to implement the algorithm [here](http://www.codezealot.org/archives/55#sat-mtv).

I'd like to guarantee that if I call my collision detection function `collide(Polygon polygon1, Polygon polygon2)` and it detects a collision, the returned MTV will always point *away* from polygon1, *toward* polygon2. In order to do this, I need to guarantee that the separating axes that I generate, which are the normals of the polygon edges, always point away from the polygon that generated them. (That way, I know to negate any axis from polygon2 before using it as the MTV). 

Unfortunately, it seems that whether or not the normal I generate for a polygon edge points towards the interior of the polygon or the exterior depends on whether the polygon's points are declared in clockwise or counterclockwise order. I'm using the algorithm described [here](http://www.codezealot.org/archives/55#sat-axes) to generate normals, and assuming that I pick `(x, y) => (y, -x)` for the "perpendicular" method, the resulting normals will only point away from the polygon if I iterate over the vertices in clockwise order.

Given that I can't force the client to declare the points of the polygon in clockwise order (I'm using java.awt.Polygon, which just exposes two arrays for x and y coordinates), is there a mathematical way to guarantee that the direction of the normal vectors I generate is toward the exterior of the polygon? I'm not very good at vector math, so there may be an obvious solution to this that I'm missing. Most Internet resources about the SAT just assume that you can always iterate over the vertices of a polygon in clockwise order.