private void AddSentinel(float smin, float smax, float t)
{
MeshUtils.Edge edge = _mesh.MakeEdge();
edge._Org._s = smax;
edge._Org._t = t;
edge._Dst._s = smin;
edge._Dst._t = t;
_event = edge._Dst;
ActiveRegion activeRegion = new ActiveRegion();
activeRegion._eUp = edge;
activeRegion._windingNumber = 0;
activeRegion._inside = false;
activeRegion._fixUpperEdge = false;
activeRegion._sentinel = true;
activeRegion._dirty = false;
activeRegion._nodeUp = _dict.Insert(activeRegion);
}