internal void advance( float alpha )
{
// Advance to the new safe time. This doesn't sync the broad-phase.
_sweep.Advance( alpha );
_sweep.C = _sweep.C0;
_sweep.A = _sweep.A0;
_xf.q.Set( _sweep.A );
_xf.p = _sweep.C - MathUtils.mul( _xf.q, _sweep.LocalCenter );
}