// Figure out if we can collapse edge eid=[a,b] under current constraint set.
// First we resolve vertex constraints using can_collapse_vtx(). However this
// does not catch some topological cases at the edge-constraint level, which
// which we will only be able to detect once we know if we are losing a or b.
// See comments on can_collapse_vtx() for what collapse_to is for.
protected bool can_collapse_constraints(int eid, int a, int b, int c, int d, int tc, int td, out int collapse_to)
{
collapse_to = -1;
if (constraints == null)
{
return(true);
}
bool bVtx = can_collapse_vtx(eid, a, b, out collapse_to);
if (bVtx == false)
{
return(false);
}
// when we lose a vtx in a collapse, we also lose two edges [iCollapse,c] and [iCollapse,d].
// If either of those edges is constrained, we would lose that constraint.
// This would be bad.
int iCollapse = (collapse_to == a) ? b : a;
if (c != DMesh3.InvalidID)
{
int ec = mesh.FindEdgeFromTri(iCollapse, c, tc);
if (constraints.GetEdgeConstraint(ec).IsUnconstrained == false)
{
return(false);
}
}
if (d != DMesh3.InvalidID)
{
int ed = mesh.FindEdgeFromTri(iCollapse, d, td);
if (constraints.GetEdgeConstraint(ed).IsUnconstrained == false)
{
return(false);
}
}
return(true);
}