/// <summary>
/// Removes the edge eDel. There are several cases:
/// if (eDel->Lface != eDel->Rface), we join two loops into one; the loop
/// eDel->Lface is deleted. Otherwise, we are splitting one loop into two;
/// the newly created loop will contain eDel->Dst. If the deletion of eDel
/// would create isolated vertices, those are deleted as well.
/// </summary>
public void Delete(MeshUtils.Edge eDel)
{
var eDelSym = eDel._Sym;
// First step: disconnect the origin vertex eDel->Org. We make all
// changes to get a consistent mesh in this "intermediate" state.
bool joiningLoops = false;
if (eDel._Lface != eDel._Rface)
{
// We are joining two loops into one -- remove the left face
joiningLoops = true;
MeshUtils.KillFace(eDel._Lface, eDel._Rface);
}
if (eDel._Onext == eDel)
{
MeshUtils.KillVertex(eDel._Org, null);
}
else
{
// Make sure that eDel->Org and eDel->Rface point to valid half-edges
eDel._Rface._anEdge = eDel._Oprev;
eDel._Org._anEdge = eDel._Onext;
MeshUtils.Splice(eDel, eDel._Oprev);
if (!joiningLoops)
{
// We are splitting one loop into two -- create a new loop for eDel.
MeshUtils.MakeFace(new MeshUtils.Face(), eDel, eDel._Lface);
}
}
// Claim: the mesh is now in a consistent state, except that eDel->Org
// may have been deleted. Now we disconnect eDel->Dst.
if (eDelSym._Onext == eDelSym)
{
MeshUtils.KillVertex(eDelSym._Org, null);
MeshUtils.KillFace(eDelSym._Lface, null);
}
else
{
// Make sure that eDel->Dst and eDel->Lface point to valid half-edges
eDel._Lface._anEdge = eDelSym._Oprev;
eDelSym._Org._anEdge = eDelSym._Onext;
MeshUtils.Splice(eDelSym, eDelSym._Oprev);
}
// Any isolated vertices or faces have already been freed.
MeshUtils.KillEdge(eDel);
}
/// <summary>
/// Splice is the basic operation for changing the
/// mesh connectivity and topology. It changes the mesh so that
/// eOrg->Onext = OLD( eDst->Onext )
/// eDst->Onext = OLD( eOrg->Onext )
/// where OLD(...) means the value before the meshSplice operation.
///
/// This can have two effects on the vertex structure:
/// - if eOrg->Org != eDst->Org, the two vertices are merged together
/// - if eOrg->Org == eDst->Org, the origin is split into two vertices
/// In both cases, eDst->Org is changed and eOrg->Org is untouched.
///
/// Similarly (and independently) for the face structure,
/// - if eOrg->Lface == eDst->Lface, one loop is split into two
/// - if eOrg->Lface != eDst->Lface, two distinct loops are joined into one
/// In both cases, eDst->Lface is changed and eOrg->Lface is unaffected.
///
/// Some special cases:
/// If eDst == eOrg, the operation has no effect.
/// If eDst == eOrg->Lnext, the new face will have a single edge.
/// If eDst == eOrg->Lprev, the old face will have a single edge.
/// If eDst == eOrg->Onext, the new vertex will have a single edge.
/// If eDst == eOrg->Oprev, the old vertex will have a single edge.
/// </summary>
public void Splice(MeshUtils.Edge eOrg, MeshUtils.Edge eDst)
{
if (eOrg == eDst)
{
return;
}
bool joiningVertices = false;
if (eDst._Org != eOrg._Org)
{
// We are merging two disjoint vertices -- destroy eDst->Org
joiningVertices = true;
MeshUtils.KillVertex(eDst._Org, eOrg._Org);
}
bool joiningLoops = false;
if (eDst._Lface != eOrg._Lface)
{
// We are connecting two disjoint loops -- destroy eDst->Lface
joiningLoops = true;
MeshUtils.KillFace(eDst._Lface, eOrg._Lface);
}
// Change the edge structure
MeshUtils.Splice(eDst, eOrg);
if (!joiningVertices)
{
// We split one vertex into two -- the new vertex is eDst->Org.
// Make sure the old vertex points to a valid half-edge.
MeshUtils.MakeVertex(new MeshUtils.Vertex(), eDst, eOrg._Org);
eOrg._Org._anEdge = eOrg;
}
if (!joiningLoops)
{
// We split one loop into two -- the new loop is eDst->Lface.
// Make sure the old face points to a valid half-edge.
MeshUtils.MakeFace(new MeshUtils.Face(), eDst, eOrg._Lface);
eOrg._Lface._anEdge = eOrg;
}
}