  Continuous collision detection (CCD) and response methods are widely adopted
in dynamics simulation of deformable models. They are history-based, as their
success is strictly based on an assumption of a collision-free state at the
start of each time interval. On the other hand, in many applications surfaces
have normals defined to designate their orientation (i.e. front- and
back-face), yet CCD methods are totally blind to such orientation
identification (thus are orientation-free). We notice that if such information
is utilized, many penetrations can be untangled. In this paper we present a
history-free method for separation of two penetrating meshes, where at least
one of them has clarified surface orientation. This method first computes all
edge-face (E-F) intersections with discrete collision detection (DCD), and then
builds a number of penetration stencils. On response, the stencil vertices are
relocated into a penetration-free state, via a global displacement minimizer.
Our method is very effective for handling penetration between two meshes, being
it an initial configuration or in the middle of physics simulation. The major
limitation is that it is not applicable to self-collision within one mesh at
the time being.
