// The old version of this was recursing directly and deeply, leading to stack
// overflows in stack restricted environments (e.g. multithreading). The
// current version is a fairly direct iteratization of the old, directly
// recursive version.
void
Skeletonize::traverse(const GraphVolume::Node& root, Skeleton& skeleton) {
// DFS of nodes from root. Data-wise, Nodes are just integer values.
std::stack<GraphVolume::Node> traversal;
traversal.push(root);
while (!traversal.empty()) {
const GraphVolume::Node n = traversal.top();
const int nNeighbors = numNeighbors(n);
// Special nodes that open new segments.
const bool isOpeningNode = n == _root || nNeighbors != 2;
// The second time we see a node, we are in back-traversal, popping from
// traversal stack and potentially closing segments.
if (_nodeLabels[n] == Visited) {
if (isOpeningNode) skeleton.closeSegment();
traversal.pop();
continue;
}
// Otherwise, we're seeing the node for the first time, so opening /
// extending segment.
_nodeLabels[n] = Visited;
const Position pos = _graphVolume.positions()[n];
const float boundDist = sqrt(boundaryDistance(pos));
if (isOpeningNode) {
skeleton.openSegment(pos, 2*boundDist);
} else {
skeleton.extendSegment(pos, 2*boundDist);
}
// Iterate through neighbors and put unseen ones onto traversal stack. The
// loop checks against nNeighbors to allow early termination.
GraphVolume::IncEdgeIt e(_graphVolume.graph(), n);
for (int i = 0; i < nNeighbors; ++e /* increment e, not i */) {
assert(e != lemon::INVALID); // Should never occur.
// Only increment i if we are using this edge.
if (_distanceMap[e] != 0.0) continue;
++i;
const GraphVolume::Node neighbor = (_graphVolume.graph().u(e) == n ? _graphVolume.graph().v(e) : _graphVolume.graph().u(e));
if (_nodeLabels[neighbor] != Visited) traversal.push(neighbor);
}
}
}
