/// <summary>
/// Find and remove any junction (ie valence>2) vertices of the graph.
/// At a junction, the pair of best-aligned (ie straightest) edges are left
/// connected, and all the other edges are disconnected
///
/// [TODO] currently there is no DGraph2.SetEdge(), so the 'other' edges
/// are deleted and new edges inserted. Hence, edge IDs are not preserved.
/// </summary>
public static int DisconnectJunctions(DGraph2 graph)
{
var junctions = new List <int>();
// find all junctions
foreach (int vid in graph.VertexIndices())
{
if (graph.IsJunctionVertex(vid))
{
junctions.Add(vid);
}
}
foreach (int vid in junctions)
{
Vector2d v = graph.GetVertex(vid);
int[] nbr_verts = graph.VtxVerticesItr(vid).ToArray();
// find best-aligned pair of edges connected to vid
Index2i best_aligned = Index2i.Max; double max_angle = 0;
for (int i = 0; i < nbr_verts.Length; ++i)
{
for (int j = i + 1; j < nbr_verts.Length; ++j)
{
double angle = Vector2d.AngleD(
(graph.GetVertex(nbr_verts[i]) - v).Normalized,
(graph.GetVertex(nbr_verts[j]) - v).Normalized);
angle = Math.Abs(angle);
if (angle > max_angle)
{
max_angle = angle;
best_aligned = new Index2i(nbr_verts[i], nbr_verts[j]);
}
}
}
// for nbr verts that are not part of the best_aligned edges,
// we remove those edges and add a new one connected to a new vertex
for (int k = 0; k < nbr_verts.Length; ++k)
{
if (nbr_verts[k] == best_aligned.a || nbr_verts[k] == best_aligned.b)
{
continue;
}
int eid = graph.FindEdge(vid, nbr_verts[k]);
graph.RemoveEdge(eid, true);
if (graph.IsVertex(nbr_verts[k]))
{
var newpos = Vector2d.Lerp(graph.GetVertex(nbr_verts[k]), v, 0.99);
int newv = graph.AppendVertex(newpos);
graph.AppendEdge(nbr_verts[k], newv);
}
}
}
return(junctions.Count);
}
/// <summary>
/// foreach edge [vid,b] connected to junction vertex vid, remove, add new vertex c,
/// and then add new edge [b,c]. Optionally move c a bit back along edge from vid.
/// </summary>
public static void DisconnectJunction(DGraph2 graph, int vid, double shrinkFactor = 1.0)
{
Vector2d v = graph.GetVertex(vid);
int[] nbr_verts = graph.VtxVerticesItr(vid).ToArray();
for (int k = 0; k < nbr_verts.Length; ++k)
{
int eid = graph.FindEdge(vid, nbr_verts[k]);
graph.RemoveEdge(eid, true);
if (graph.IsVertex(nbr_verts[k]))
{
Vector2d newpos = Vector2d.Lerp(graph.GetVertex(nbr_verts[k]), v, shrinkFactor);
int newv = graph.AppendVertex(newpos);
graph.AppendEdge(nbr_verts[k], newv);
}
}
}
/// <summary>
/// If vid has two or more neighbours, returns uniform laplacian, otherwise returns vid position
/// </summary>
public static Vector2d VertexLaplacian(DGraph2 graph, int vid, out bool isValid)
{
Vector2d v = graph.GetVertex(vid);
Vector2d centroid = Vector2d.Zero;
int n = 0;
foreach (int vnbr in graph.VtxVerticesItr(vid))
{
centroid += graph.GetVertex(vnbr);
n++;
}
if (n == 2)
{
centroid /= n;
isValid = true;
return(centroid - v);
}
isValid = false;
return(v);
}
