choosing proper hull axes for SAT

[vicviper]

SAT requires to test a set of axes given by both convex hulls.

As far as I know, to compute a SAT, the axes to be chosen from a convex hull are those that correspond to the edges of the convex hull.

It happens that, for a box hull, the edge axes are the same as if we choose the face normals as axes, so I'm really not sure if the first statement of choosing the edges is ok, to me, it would be more correct to choose the face normals.

So which is the correct set of axes? edges, or face normals? (or both?)

thanks

Vic

[Erin Catto]

You have to use the face normals for both hulls and the edge-edge cross products, where the edge pairs are all the combinations of edges between the two hulls. No edge pairs are taken from a single hull.