Inputs for collision detection between convex meshes (function of sat_hull_hull)

[Jichen66]

Hi all,

I have been studied and tested the function of sat_hull_hull in _convex_convex (https://github.com/google/brax/blob/a89322496dcb07ac5a7e002c2e1d287c8c64b7dd/brax/geometry/contact.py, https://github.com/google/brax/blob/a89322496dcb07ac5a7e002c2e1d287c8c64b7dd/brax/geometry/math.py) recently and have a few questions about the proper input (i.e. vertices, faces, unique edges of the object) to this function.
c = geom_math.sat_hull_hull( faces_a, faces_b, vertices_a, vertices_b, normals_a, normals_b, unique_edges_a, unique_edges_b)

I have used the trimesh to create regular boxes and use trimesh object's default properties to extract faces and unique_edges from the boxes directly, i.e. via box.faces & box.edges_unique, and then fed into this sat_hull_hull method. However, the collision detection doesn't work as expected. It works when I did the further steps to deal with the faces & unique_edges, e.g. merge coplanar facets and then get unique edges from the new faces. I was wondering the reason for merging the coplanar facets and why cannot just use the trimesh's default property to obtain the faces and unique edges directly for regular convex meshes?

Thank you very much in advance!