separate Voronoi graf and searching longest path into own files

src/libslic3r/CMakeLists.txt

@@ -1,4 +1,4 @@
-#/|/ Copyright (c) Prusa Research 2018 - 2023 Tomáš Mészáros @tamasmeszaros, Oleksandra Iushchenko @YuSanka, Enrico Turri @enricoturri1966, Vojtěch Bubník @bubnikv, Pavel Mikuš @Godrak, Lukáš Hejl @hejllukas, Lukáš Matěna @lukasmatena, Filip Sykala @Jony01, David Kocík @kocikdav, Vojtěch Král @vojtechkral
+#/|/ Copyright (c) Prusa Research 2018 - 2023 Tom<EFBFBD> M<EFBFBD>sz<EFBFBD>ros @tamasmeszaros, Oleksandra Iushchenko @YuSanka, Enrico Turri @enricoturri1966, Vojt<EFBFBD>ch Bubn<EFBFBD>k @bubnikv, Pavel Miku<EFBFBD> @Godrak, Luk<EFBFBD> Hejl @hejllukas, Luk<EFBFBD> Mat<EFBFBD>na @lukasmatena, Filip Sykala @Jony01, David Koc<EFBFBD>k @kocikdav, Vojt<EFBFBD>ch Kr<EFBFBD>l @vojtechkral
 #/|/ Copyright (c) BambuStudio 2023 manch1n @manch1n
 #/|/ Copyright (c) 2023 Mimoja @Mimoja
 #/|/ Copyright (c) 2022 ole00 @ole00
@@ -452,7 +452,21 @@ set(SLIC3R_SOURCES
     SLA/BranchingTreeSLA.hpp
     SLA/BranchingTreeSLA.cpp
     SLA/ZCorrection.hpp
-    SLA/ZCorrection.cpp
+    SLA/ZCorrection.cpp    
+    SLA/SupportIslands/EvaluateNeighbor.cpp
+    SLA/SupportIslands/EvaluateNeighbor.hpp
+    SLA/SupportIslands/ExpandNeighbor.cpp
+    SLA/SupportIslands/ExpandNeighbor.hpp
+    SLA/SupportIslands/IStackFunction.hpp
+    SLA/SupportIslands/NodeDataWithResult.hpp
+    SLA/SupportIslands/PostProcessNeighbor.cpp
+    SLA/SupportIslands/PostProcessNeighbor.hpp
+    SLA/SupportIslands/PostProcessNeighbors.cpp
+    SLA/SupportIslands/PostProcessNeighbors.hpp
+    SLA/SupportIslands/SampleConfig.hpp
+    SLA/SupportIslands/VoronoiGraph.hpp
+    SLA/SupportIslands/VoronoiGraphUtils.cpp
+    SLA/SupportIslands/VoronoiGraphUtils.hpp
     BranchingTree/BranchingTree.cpp
     BranchingTree/BranchingTree.hpp
     BranchingTree/PointCloud.cpp
@@ -524,6 +538,9 @@ foreach(_source IN ITEMS ${SLIC3R_SOURCES})
     source_group("${_group_path}" FILES "${_source}")
 endforeach()
 
+# Create the source groups for source tree with root at CMAKE_CURRENT_SOURCE_DIR.
+source_group(TREE ${CMAKE_CURRENT_SOURCE_DIR} FILES ${SOURCE_LIST_SLA})
+
 if (SLIC3R_STATIC)
     set(CGAL_Boost_USE_STATIC_LIBS ON CACHE BOOL "" FORCE)
 endif ()

src/libslic3r/SLA/SupportIslands/EvaluateNeighbor.cpp

@@ -0,0 +1,23 @@
+#include "EvaluateNeighbor.hpp"
+#include "ExpandNeighbor.hpp"
+
+using namespace Slic3r::sla;
+    
+EvaluateNeighbor::EvaluateNeighbor(VoronoiGraph::ExPath &    result,
+                                   const VoronoiGraph::Node *node,
+                                   double                    distance_to_node,
+                                   const VoronoiGraph::Path &prev_path)
+    : post_process_neighbor(
+          std::make_unique<PostProcessNeighbors>(result,
+                                                 node,
+                                                 distance_to_node,
+                                                 prev_path))
+{}
+
+void EvaluateNeighbor::process(CallStack &call_stack)
+{
+    NodeDataWithResult &data = *post_process_neighbor;
+    call_stack.emplace(std::move(post_process_neighbor));
+    for (const VoronoiGraph::Node::Neighbor &neighbor : data.node->neighbors)
+        call_stack.emplace(std::make_unique<ExpandNeighbor>(data, neighbor));
+}

src/libslic3r/SLA/SupportIslands/EvaluateNeighbor.hpp

@@ -0,0 +1,36 @@
+#ifndef slic3r_SLA_SuppotstIslands_EvaluateNeighbor_hpp_
+#define slic3r_SLA_SuppotstIslands_EvaluateNeighbor_hpp_
+
+#include <memory>
+
+#include "IStackFunction.hpp"
+#include "PostProcessNeighbors.hpp"
+#include "VoronoiGraph.hpp"
+
+namespace Slic3r::sla {
+
+/// <summary>
+/// create on stack
+///  1 * PostProcessNeighbors
+///  N * ExpandNode
+/// </summary>
+class EvaluateNeighbor : public IStackFunction
+{
+    std::unique_ptr<PostProcessNeighbors> post_process_neighbor;
+public:
+    EvaluateNeighbor(
+        VoronoiGraph::ExPath &    result,
+        const VoronoiGraph::Node *node,
+        double                    distance_to_node = 0.,
+        const VoronoiGraph::Path &prev_path = VoronoiGraph::Path({}, 0.));
+
+    /// <summary>
+    /// create on stack
+    ///  1 * PostProcessNeighbors
+    ///  N * ExpandNode
+    /// </summary>
+    virtual void process(CallStack &call_stack);
+};
+
+} // namespace Slic3r::sla
+#endif // slic3r_SLA_SuppotstIslands_EvaluateNeighbor_hpp_

src/libslic3r/SLA/SupportIslands/ExpandNeighbor.cpp

@@ -0,0 +1,44 @@
+#include "ExpandNeighbor.hpp"
+#include "VoronoiGraphUtils.hpp"
+
+using namespace Slic3r::sla;
+
+ExpandNeighbor::ExpandNeighbor(
+    NodeDataWithResult &                data,
+    const VoronoiGraph::Node::Neighbor &neighbor)
+    : data(data)
+    , neighbor(neighbor)
+{}
+
+void ExpandNeighbor::process(CallStack &call_stack)
+{
+    if (data.skip_nodes.find(neighbor.node) != data.skip_nodes.end()) return;
+
+    // detection of circle
+    auto circle_opt = VoronoiGraphUtils::create_circle(data.act_path,
+                                                       neighbor);
+    if (circle_opt.has_value()) {
+        size_t circle_index = data.result.circles.size();
+        data.circle_indexes.push_back(circle_index);
+        data.result.circles.emplace_back(std::move(circle_opt.value()));
+        return;
+    }
+
+    // create copy of path(not circles, not side_branches)
+    const VoronoiGraph::Node &next_node = *neighbor.node;
+    // is next node leaf ?
+    if (next_node.neighbors.size() == 1) {
+        VoronoiGraph::Path side_branch({&next_node}, neighbor.edge_length);
+        data.side_branches.push(std::move(side_branch));
+        return;
+    }
+
+    auto post_process_neighbor = std::make_unique<PostProcessNeighbor>(data);
+    VoronoiGraph::ExPath &neighbor_path = post_process_neighbor->neighbor_path;
+
+    call_stack.emplace(std::move(post_process_neighbor));
+    call_stack.emplace(
+        std::make_unique<EvaluateNeighbor>(neighbor_path, neighbor.node,
+                                           neighbor.edge_length,
+                                           data.act_path));
+}

src/libslic3r/SLA/SupportIslands/ExpandNeighbor.hpp

@@ -0,0 +1,35 @@
+#ifndef slic3r_SLA_SuppotstIslands_ExpandNeighbor_hpp_
+#define slic3r_SLA_SuppotstIslands_ExpandNeighbor_hpp_
+
+#include "IStackFunction.hpp"
+#include "VoronoiGraph.hpp"
+#include "PostProcessNeighbor.hpp"
+#include "EvaluateNeighbor.hpp"
+
+namespace Slic3r::sla {
+
+/// <summary>
+/// Expand neighbor to
+///  - PostProcessNeighbor
+///  - EvaluateNeighbor
+/// </summary>
+class ExpandNeighbor : public IStackFunction
+{
+    NodeDataWithResult &                data;
+    const VoronoiGraph::Node::Neighbor &neighbor;
+
+public:
+    ExpandNeighbor(NodeDataWithResult &                data,
+                   const VoronoiGraph::Node::Neighbor &neighbor);
+
+    /// <summary>
+    /// Expand neighbor to
+    ///  - PostProcessNeighbor
+    ///  - EvaluateNeighbor
+    /// </summary>
+    /// <param name="call_stack">Output callStack</param>
+    virtual void process(CallStack &call_stack);
+};
+
+} // namespace Slic3r::sla
+#endif // slic3r_SLA_SuppotstIslands_ExpandNeighbor_hpp_

src/libslic3r/SLA/SupportIslands/IStackFunction.hpp

@@ -0,0 +1,23 @@
+#ifndef slic3r_SLA_SuppotstIslands_IStackFunction_hpp_
+#define slic3r_SLA_SuppotstIslands_IStackFunction_hpp_
+
+#include <stack>
+#include <memory> 
+
+namespace Slic3r::sla {
+
+/// <summary>
+/// Interface for objects inside of CallStack.
+/// It is way to prevent stack overflow inside recurrent functions.
+/// </summary>
+class IStackFunction
+{
+public:
+    virtual ~IStackFunction() = default;
+    virtual void process(std::stack<std::unique_ptr<IStackFunction>> &call_stack) = 0;
+};
+
+using CallStack = std::stack<std::unique_ptr<IStackFunction>>;
+
+} // namespace Slic3r::sla
+#endif // slic3r_SLA_SuppotstIslands_IStackFunction_hpp_

src/libslic3r/SLA/SupportIslands/NodeDataWithResult.hpp

@@ -0,0 +1,72 @@
+#ifndef slic3r_SLA_SuppotstIslands_NodeDataWithResult_hpp_
+#define slic3r_SLA_SuppotstIslands_NodeDataWithResult_hpp_
+
+#include <vector>
+#include <set>
+#include "VoronoiGraph.hpp"
+
+namespace Slic3r::sla {
+
+/// <summary>
+/// DTO for process node during depth search
+/// which create longest path in voronoi graph
+/// </summary>
+struct NodeDataWithResult
+{
+    // result for this node
+    VoronoiGraph::ExPath &result;
+
+    // actual proccessed node
+    const VoronoiGraph::Node *node;
+    // distance to this node from input node
+    double distance_to_node;
+
+    // path from start point to this node
+    // last one is actual node
+    VoronoiGraph::Path act_path;
+
+    // skip node when circle start - must end at this node
+    // set --> multiple cirle could start at same node
+    // previous node should be skiped to so it is initialized with it
+    std::set<const VoronoiGraph::Node *> skip_nodes; // circle
+
+    // store all circle indexes this node is lay on
+    // used to create connected circles structure
+    std::vector<size_t> circle_indexes;
+    // When circle_indexes is not empty node lays on circle
+    // and in this node is not searching for longest path only store side
+    // branches(not part of circle)
+
+    // indexes of circle ending in this node(could be more than one)
+    std::vector<size_t> end_circle_indexes;
+    // When end_circle_indexes == circle_indexes
+    // than it is end of circle (multi circle structure) and it is processed
+
+    // contain possible continue path
+    // possible empty
+    VoronoiGraph::ExPath::SideBranches side_branches;
+
+public:
+    // append node to act path
+    NodeDataWithResult(
+        VoronoiGraph::ExPath &    result,
+        const VoronoiGraph::Node *node,
+        double                    distance_to_node,
+        const VoronoiGraph::Path &prev_path)
+        : result(result)
+        , node(node)
+        , distance_to_node(distance_to_node)
+    {
+        // TODO: process it before constructor or in factory
+        const VoronoiGraph::Node *prev_node = (prev_path.path.size() >= 1) ?
+                                                  prev_path.path.back() :
+                                                  nullptr;
+        skip_nodes = {prev_node};
+        // append actual node
+        act_path = prev_path;                    // copy
+        act_path.append(node, distance_to_node); // increase path
+    }
+};
+
+} // namespace Slic3r::sla
+#endif // slic3r_SLA_SuppotstIslands_NodeDataWithResult_hpp_

src/libslic3r/SLA/SupportIslands/PostProcessNeighbor.cpp

@@ -0,0 +1,40 @@
+#include "PostProcessNeighbor.hpp"
+
+#include "VoronoiGraphUtils.hpp"
+
+using namespace Slic3r::sla;
+
+void PostProcessNeighbor::process()
+{
+    bool is_circle_neighbor = false;
+    if (neighbor_path.path.empty()) { // neighbor node is on circle
+        for (VoronoiGraph::Circle &circle : neighbor_path.circles) {
+            const auto &circle_item = std::find(circle.path.begin(),
+                                                circle.path.end(), data.node);
+            if (circle_item == circle.path.end())
+                continue; // node is NOT on circle
+
+            size_t next_circle_index = &circle -
+                                       &neighbor_path.circles.front();
+            size_t circle_index = data.result.circles.size() +
+                                  next_circle_index;
+            data.circle_indexes.push_back(circle_index);
+
+            // check if this node is end of circle
+            if (circle_item == circle.path.begin()) {
+                data.end_circle_indexes.push_back(circle_index);
+
+                // !! this FIX circle lenght because at detection of
+                // circle it will cost time to calculate it
+                circle.length -= data.act_path.length;
+
+                // skip twice checking of circle
+                data.skip_nodes.insert(circle.path.back());
+            }
+            is_circle_neighbor = true;
+        }
+    }
+    VoronoiGraphUtils::append_neighbor_branch(data.result, neighbor_path);
+    if (!is_circle_neighbor)
+        data.side_branches.push(std::move(neighbor_path));
+}

src/libslic3r/SLA/SupportIslands/PostProcessNeighbor.hpp

@@ -0,0 +1,36 @@
+#ifndef slic3r_SLA_SuppotstIslands_PostProcessNeighbor_hpp_
+#define slic3r_SLA_SuppotstIslands_PostProcessNeighbor_hpp_
+
+#include "IStackFunction.hpp"
+#include "NodeDataWithResult.hpp"
+#include "VoronoiGraph.hpp"
+#include "NodeDataWithResult.hpp"
+
+namespace Slic3r::sla {
+
+/// <summary>
+/// Decimate data from Ex path to path
+/// Done after ONE neighbor is procceessed.
+/// Check if node is on circle.
+/// Remember ended circle
+/// Merge side branches and circle information into result
+/// </summary>
+class PostProcessNeighbor : public IStackFunction
+{
+    NodeDataWithResult &data;
+
+public:
+    VoronoiGraph::ExPath neighbor_path; // data filled in EvaluateNeighbor
+    PostProcessNeighbor(NodeDataWithResult &data) : data(data) {}
+
+    virtual void process([[maybe_unused]] CallStack &call_stack)
+    {
+        process();
+    }
+
+private:
+    void process();
+};
+
+} // namespace Slic3r::sla
+#endif // slic3r_SLA_SuppotstIslands_PostProcessNeighbor_hpp_

src/libslic3r/SLA/SupportIslands/PostProcessNeighbors.cpp

@@ -0,0 +1,50 @@
+#include "PostProcessNeighbors.hpp"
+
+#include "VoronoiGraphUtils.hpp"
+
+using namespace Slic3r::sla;
+
+void PostProcessNeighbors::process()
+{
+    // remember connected circle
+    if (circle_indexes.size() > 1) {
+        for (size_t circle_index : circle_indexes) {
+            for (size_t circle_index2 : circle_indexes) {
+                if (circle_index == circle_index2) continue;
+                result.connected_circle[circle_index].insert(circle_index2);
+            }
+        }
+    }
+
+    // detect end of circles in this node
+    if (!end_circle_indexes.empty() &&
+        end_circle_indexes.size() == circle_indexes.size()) {
+        size_t circle_index = circle_indexes.front(); // possible any of them
+        side_branches.push(
+            VoronoiGraphUtils::find_longest_path_on_circles(*node,
+                                                            circle_index,
+                                                            result));
+
+        circle_indexes.clear(); // resolved circles
+    }
+
+    // simple node on circle --> only input and output neighbor
+    if (side_branches.empty()) return;
+
+    // is node on unresolved circle?
+    if (!circle_indexes.empty()) {
+        // not search for longest path, it will eval on end of circle
+        result.side_branches[node] = side_branches;
+        return;
+    }
+
+    // create result longest path from longest side branch
+    VoronoiGraph::Path longest_path(std::move(side_branches.top()));
+    side_branches.pop();
+    if (!side_branches.empty()) {
+        result.side_branches[node] = side_branches;
+    }
+    longest_path.path.insert(longest_path.path.begin(), node);
+    result.path   = std::move(longest_path.path);
+    result.length = distance_to_node + longest_path.length;
+}

src/libslic3r/SLA/SupportIslands/PostProcessNeighbors.hpp

@@ -0,0 +1,35 @@
+#ifndef slic3r_SLA_SuppotstIslands_PostProcessNeighbors_hpp_
+#define slic3r_SLA_SuppotstIslands_PostProcessNeighbors_hpp_
+
+#include "IStackFunction.hpp"
+#include "VoronoiGraph.hpp"
+#include "NodeDataWithResult.hpp"
+
+namespace Slic3r::sla {
+
+/// <summary>
+/// call after all neighbors are processed
+/// </summary>
+class PostProcessNeighbors : public NodeDataWithResult, public IStackFunction
+{
+public:
+    PostProcessNeighbors(VoronoiGraph::ExPath &    result,
+                         const VoronoiGraph::Node *node,
+                         double                    distance_to_node = 0.,
+                         const VoronoiGraph::Path &prev_path =
+                             VoronoiGraph::Path({}, 0.) // make copy
+                         )
+        : NodeDataWithResult(result, node, distance_to_node, prev_path)
+    {}
+
+    virtual void process([[maybe_unused]] CallStack &call_stack)
+    {
+        process();
+    }
+
+private:
+    void process();
+};
+
+} // namespace Slic3r::sla
+#endif // slic3r_SLA_SuppotstIslands_PostProcessNeighbors_hpp_

src/libslic3r/SLA/SupportIslands/SampleConfig.hpp

@@ -0,0 +1,28 @@
+#ifndef slic3r_SLA_SuppotstIslands_SampleConfig_hpp_
+#define slic3r_SLA_SuppotstIslands_SampleConfig_hpp_
+
+namespace Slic3r::sla {
+
+/// <summary>
+/// Configuration fro sampling voronoi diagram for support point generator
+/// </summary>
+struct SampleConfig
+{
+    // Maximal distance from edge
+    double max_distance = 1.; // must be bigger than zero
+    // Maximal distance between samples on skeleton
+    double sample_size = 1.; // must be bigger than zero
+    // distance from edge of skeleton
+    double start_distance = 0; // support head diameter
+
+    // maximal length of longest path in voronoi diagram to be island
+    // supported only by one single support point this point will be in center
+    // of path suggestion: smaller than 2* SampleConfig.start_distance
+    double max_length_for_one_support_point = 1.;
+
+    // each curve is sampled by this value to test distance to edge of island
+    double curve_sample = 1.; // must be bigger than zero
+};
+
+} // namespace Slic3r::sla
+#endif // slic3r_SLA_SuppotstIslands_SampleConfig_hpp_

src/libslic3r/SLA/SupportIslands/VoronoiGraph.hpp

@@ -0,0 +1,144 @@
+#ifndef slic3r_SLA_SuppotstIslands_VoronoiGraph_hpp_
+#define slic3r_SLA_SuppotstIslands_VoronoiGraph_hpp_
+
+#include <map>
+#include <libslic3r/Geometry.hpp>
+#include <numeric>
+
+namespace Slic3r::sla {
+
+/// <summary>
+/// DTO store skeleton With longest path
+/// </summary>
+struct VoronoiGraph
+{
+    using VD = Slic3r::Geometry::VoronoiDiagram;
+    struct Node;
+    using Nodes = std::vector<const Node *>;
+    struct Path;
+    struct ExPath;
+    using Circle = Path;
+    std::map<const VD::vertex_type *, Node> data;
+};
+
+/// <summary>
+/// Node data structure for Voronoi Graph.
+/// Extend information about Voronoi vertex.
+/// </summary>
+struct VoronoiGraph::Node
+{
+    // reference to Voronoi diagram VertexCategory::Inside OR
+    // VertexCategory::OnContour but NOT VertexCategory::Outside
+    const VD::vertex_type *vertex;
+    // longest distance to edge sum of line segment size (no euclid because of shape U)
+    double longestDistance;
+
+    // actual distance to edge
+    double distance;
+
+    struct Neighbor;
+    std::vector<Neighbor> neighbors;
+
+    // constructor
+    Node(const VD::vertex_type *vertex, double distance)
+        : vertex(vertex), longestDistance(0.), distance(distance), neighbors()
+    {}
+};
+
+/// <summary>
+/// Surrond GraphNode data type.
+/// Extend information about voronoi edge.
+/// </summary>
+struct VoronoiGraph::Node::Neighbor
+{
+    const VD::edge_type *edge;
+    // length edge between vertices
+    double edge_length;
+    // pointer on graph node structure
+    Node *node;
+public:
+    Neighbor(const VD::edge_type *edge, double edge_length, Node *node)
+        : edge(edge), edge_length(edge_length), node(node)
+    {}
+};
+
+
+/// <summary>
+/// DTO represents path over nodes of VoronoiGraph
+/// store queue of Nodes
+/// store length of path
+/// </summary>
+struct VoronoiGraph::Path
+{
+    // row of neighbor Nodes
+    VoronoiGraph::Nodes path; // TODO: rename to nodes
+
+    // length of path
+    // when circle contain length from back to front;
+    double length;
+
+public:
+    Path() : path(), length(0.) {}
+    Path(const VoronoiGraph::Node *node) : path({node}), length(0.) {}
+    Path(VoronoiGraph::Nodes nodes, double length)
+        : path(std::move(nodes)), length(length)
+    {}
+
+    void append(const VoronoiGraph::Node *node, double length)
+    {
+        path.push_back(node);
+        this->length += length;
+    }
+    
+    struct OrderLengthFromShortest{
+        bool operator()(const VoronoiGraph::Path &path1,
+                        const VoronoiGraph::Path &path2){
+            return path1.length > path2.length;
+        }
+    };
+
+    struct OrderLengthFromLongest{
+        bool operator()(const VoronoiGraph::Path &path1,
+                        const VoronoiGraph::Path &path2){
+            return path1.length < path2.length;
+        }
+    };
+};
+
+
+/// <summary>
+/// DTO
+/// extends path with side branches and circles(connection of circles)
+/// </summary>
+struct VoronoiGraph::ExPath : public VoronoiGraph::Path
+{
+    // not main path is stored in secondary paths
+    // key is pointer to source node
+    using SideBranches    = std::priority_queue<VoronoiGraph::Path,
+                                             std::vector<VoronoiGraph::Path>,
+                                             OrderLengthFromLongest>;
+    using SideBranchesMap = std::map<const VoronoiGraph::Node *, SideBranches>;
+
+    // All side branches in Graph under node
+    // Map contains only node, which has side branche(s)
+    // There is NOT empty SideBranches in map !!!
+    SideBranchesMap side_branches;
+
+    // All circles in Graph under node
+    std::vector<VoronoiGraph::Circle> circles;
+
+    // alone circle does'n have record in connected_circle
+    // every connected circle have at least two records(firs to second &
+    // second to first) EXAMPLE with 3 circles(index to circles stored in
+    // this->circles are: c1, c2 and c3) connected together
+    // connected_circle[c1] = {c2, c3}; connected_circle[c2] = {c1, c3};
+    // connected_circle[c3] = {c1, c2};
+    using ConnectedCircles = std::map<size_t, std::set<size_t>>;    
+    ConnectedCircles connected_circle;
+
+public:
+    ExPath() = default;
+};
+
+} // namespace Slic3r::sla
+#endif // slic3r_SLA_SuppotstIslands_VoronoiGraph_hpp_

src/libslic3r/SLA/SupportIslands/VoronoiGraphUtils.cpp

@@ -0,0 +1,584 @@
+#include "VoronoiGraphUtils.hpp"
+
+#include <libslic3r/VoronoiOffset.hpp>
+#include "IStackFunction.hpp"
+#include "EvaluateNeighbor.hpp"
+
+using namespace Slic3r::sla;
+
+VoronoiGraph::Node *VoronoiGraphUtils::getNode(VoronoiGraph &         graph,
+                            const VD::vertex_type *vertex,
+                            const VD::edge_type *  edge,
+                            const Lines &          lines)
+{
+    std::map<const VD::vertex_type *, VoronoiGraph::Node> &data = graph.data;
+    auto &mapItem = data.find(vertex);
+    // return when exists
+    if (mapItem != data.end()) return &mapItem->second;
+
+    // is new vertex (first edge to this vertex)
+    // calculate distance to islad border + fill item0
+    const VD::cell_type *cell = edge->cell();
+    // const VD::cell_type *  cell2     = edge.twin()->cell();
+    const Line &line = lines[cell->source_index()];
+    // const Line &           line1     = lines[cell2->source_index()];
+    Point  point(vertex->x(), vertex->y());
+    double distance = line.distance_to(point);
+
+    auto &[iterator,
+           success] = data.emplace(vertex,
+                                   VoronoiGraph::Node(vertex, distance));
+    assert(success);
+    return &iterator->second;
+}
+
+VoronoiGraph VoronoiGraphUtils::getSkeleton(const VD &vd, const Lines &lines)
+{
+    // vd should be annotated.
+    // assert(Voronoi::debug::verify_inside_outside_annotations(vd));
+
+    VoronoiGraph         skeleton;
+    const VD::edge_type *first_edge = &vd.edges().front();
+    for (const VD::edge_type &edge : vd.edges()) {
+        size_t edge_idx = &edge - first_edge;
+        if (
+            // Ignore secondary and unbounded edges, they shall never be part
+            // of the skeleton.
+            edge.is_secondary() || edge.is_infinite() ||
+            // Skip the twin edge of an edge, that has already been processed.
+            &edge > edge.twin() ||
+            // Ignore outer edges.
+            (Voronoi::edge_category(edge) !=
+                 Voronoi::EdgeCategory::PointsInside &&
+             Voronoi::edge_category(edge.twin()) !=
+                 Voronoi::EdgeCategory::PointsInside))
+            continue;
+
+        const VD::vertex_type * v0        = edge.vertex0();
+        const VD::vertex_type * v1        = edge.vertex1();
+        Voronoi::VertexCategory category0 = Voronoi::vertex_category(*v0);
+        Voronoi::VertexCategory category1 = Voronoi::vertex_category(*v1);
+        if (category0 == Voronoi::VertexCategory::Outside ||
+            category1 == Voronoi::VertexCategory::Outside)
+            continue;
+        // only debug check annotation
+        if (category0 == Voronoi::VertexCategory::Unknown ||
+            category1 == Voronoi::VertexCategory::Unknown)
+            return {}; // vd must be annotated
+
+        double length = 0;
+        if (edge.is_linear()) {
+            double diffX = v0->x() - v1->x();
+            double diffY = v0->y() - v1->y();
+            length       = sqrt(diffX * diffX + diffY * diffY);
+        } else { // if (edge.is_curved())
+            // TODO: len of parabola
+            length = 1.0;
+        }
+
+        VoronoiGraph::Node *node0 = getNode(skeleton, v0, &edge, lines);
+        VoronoiGraph::Node *node1 = getNode(skeleton, v1, &edge, lines);
+
+        // add extended Edge to graph, both side
+        VoronoiGraph::Node::Neighbor neighbor0(&edge, length, node1);
+        node0->neighbors.push_back(neighbor0);
+        VoronoiGraph::Node::Neighbor neighbor1(edge.twin(), length, node0);
+        node1->neighbors.push_back(neighbor1);
+    }
+    return skeleton;
+}
+
+Slic3r::Point VoronoiGraphUtils::get_offseted_point(
+    const VoronoiGraph::Node &node,
+                                            double padding)
+{
+    assert(node.neighbors.size() == 1);
+    const VoronoiGraph::Node::Neighbor &neighbor = node.neighbors.front();
+    const VD::edge_type &               edge     = *neighbor.edge;
+    const VD::vertex_type &             v0       = *edge.vertex0();
+    const VD::vertex_type &             v1       = *edge.vertex1();
+    Point                               dir(v0.x() - v1.x(), v0.y() - v1.y());
+    if (node.vertex == &v0)
+        dir *= -1;
+    else
+        assert(node.vertex == &v1);
+
+    double size = neighbor.edge_length / padding;
+    Point  move(dir[0] / size, dir[1] / size);
+    return Point(node.vertex->x() + move[0], node.vertex->y() + move[1]);
+}
+
+const VoronoiGraph::Node::Neighbor *VoronoiGraphUtils::get_neighbor(
+    const VoronoiGraph::Node *from, const VoronoiGraph::Node *to)
+{
+    for (const VoronoiGraph::Node::Neighbor &neighbor : from->neighbors)
+        if (neighbor.node == to) return &neighbor;
+    return nullptr;
+}
+
+double VoronoiGraphUtils::get_neighbor_distance(const VoronoiGraph::Node *from,
+                             const VoronoiGraph::Node *to)
+{
+    const VoronoiGraph::Node::Neighbor *neighbor = get_neighbor(from, to);
+    assert(neighbor != nullptr);
+    return neighbor->edge_length;
+}
+
+VoronoiGraph::Path VoronoiGraphUtils::find_longest_path_on_circle(
+    const VoronoiGraph::Circle &                 circle,
+    const VoronoiGraph::ExPath::SideBranchesMap &side_branches)
+{
+    double half_circle_length = circle.length / 2.;
+    double distance_on_circle = 0;
+
+    bool                      is_longest_revers_direction = false;
+    const VoronoiGraph::Node *longest_circle_node         = nullptr;
+    const VoronoiGraph::Path *longest_circle_branch       = nullptr;
+    double                    longest_branch_length       = 0;
+
+    bool is_short_revers_direction = false;
+    // find longest side branch
+    const VoronoiGraph::Node *prev_circle_node = nullptr;
+    for (const VoronoiGraph::Node *circle_node : circle.path) {
+        if (prev_circle_node != nullptr)
+            distance_on_circle += get_neighbor_distance(circle_node,
+                                                        prev_circle_node);
+        prev_circle_node = circle_node;
+
+        auto side_branches_item = side_branches.find(circle_node);
+        if (side_branches_item != side_branches.end()) {
+            // side_branches should be sorted by length
+            if (distance_on_circle > half_circle_length)
+                is_short_revers_direction = true;
+            const auto &longest_node_branch = side_branches_item->second.top();
+            double      circle_branch_length = longest_node_branch.length +
+                                          ((is_short_revers_direction) ?
+                                               (circle.length -
+                                                distance_on_circle) :
+                                               distance_on_circle);
+            if (longest_branch_length < circle_branch_length) {
+                longest_branch_length       = circle_branch_length;
+                is_longest_revers_direction = is_short_revers_direction;
+                longest_circle_node         = circle_node;
+                longest_circle_branch       = &longest_node_branch;
+            }
+        }
+    }
+    assert(longest_circle_node !=
+           nullptr); // only circle with no side branches
+    assert(longest_circle_branch != nullptr);
+    // almost same - double preccission
+    // distance_on_circle += get_neighbor_distance(circle.path.back(),
+    // circle.path.front()); assert(distance_on_circle == circle.length);
+
+    // circlePath
+    auto circle_iterator = std::find(circle.path.begin(), circle.path.end(),
+                                     longest_circle_node);
+    VoronoiGraph::Nodes circle_path;
+    if (is_longest_revers_direction) {
+        circle_path = VoronoiGraph::Nodes(circle_iterator, circle.path.end());
+        std::reverse(circle_path.begin(), circle_path.end());
+    } else {
+        if (longest_circle_node != circle.path.front())
+            circle_path = VoronoiGraph::Nodes(circle.path.begin() + 1,
+                                              circle_iterator + 1);
+    }
+    // append longest side branch
+    circle_path.insert(circle_path.end(), longest_circle_branch->path.begin(),
+                       longest_circle_branch->path.end());
+    return {circle_path, longest_branch_length};
+}
+
+VoronoiGraph::Path VoronoiGraphUtils::find_longest_path_on_circles(
+    const VoronoiGraph::Node &  input_node,
+    size_t                      finished_circle_index,
+    const VoronoiGraph::ExPath &ex_path)
+{
+    const std::vector<VoronoiGraph::Circle> &circles = ex_path.circles;
+    const auto &circle                = circles[finished_circle_index];
+    auto        connected_circle_item = ex_path.connected_circle.find(
+        finished_circle_index);
+    // is only one circle
+    if (connected_circle_item == ex_path.connected_circle.end()) {
+        // find longest path over circle and store it into next_path
+        return find_longest_path_on_circle(circle, ex_path.side_branches);
+    }
+
+    // multi circle
+    // find longest path over circles
+    const std::set<size_t> &connected_circles = connected_circle_item->second;
+
+    // collect all circle ndoes
+    std::set<const VoronoiGraph::Node *> nodes;
+    nodes.insert(circle.path.begin(), circle.path.end());
+    for (size_t circle_index : connected_circles) {
+        const auto &circle = circles[circle_index];
+        nodes.insert(circle.path.begin(), circle.path.end());
+    }
+
+    // nodes are path throw circles
+    // length is sum path throw circles PLUS length of longest side_branch
+    VoronoiGraph::Path longest_path;
+
+    // wide search by shortest distance for path over circle's node
+    // !! Do NOT use recursion, may cause stack overflow
+    std::set<const VoronoiGraph::Node *> done; // all ready checked
+    // on top is shortest path
+    std::priority_queue<VoronoiGraph::Path, std::vector<VoronoiGraph::Path>,
+                        VoronoiGraph::Path::OrderLengthFromShortest>
+                       search_queue;
+    VoronoiGraph::Path start_path({&input_node}, 0.);
+    search_queue.emplace(start_path);
+    while (!search_queue.empty()) {
+        // shortest path from input_node
+        VoronoiGraph::Path path(std::move(search_queue.top()));
+        search_queue.pop();
+        const VoronoiGraph::Node &node = *path.path.back();
+        if (done.find(&node) != done.end()) { // already checked
+            continue;
+        }
+        done.insert(&node);
+        for (const VoronoiGraph::Node::Neighbor &neighbor : node.neighbors) {
+            if (nodes.find(neighbor.node) == nodes.end())
+                continue; // out of circles
+            if (done.find(neighbor.node) != done.end()) continue;
+            VoronoiGraph::Path neighbor_path = path; // make copy
+            neighbor_path.append(neighbor.node, neighbor.edge_length);
+            search_queue.push(neighbor_path);
+
+            auto branches_item = ex_path.side_branches.find(neighbor.node);
+            // exist side from this neighbor node ?
+            if (branches_item == ex_path.side_branches.end()) continue;
+            const VoronoiGraph::Path &longest_branch = branches_item->second
+                                                           .top();
+            double length = longest_branch.length + neighbor_path.length;
+            if (longest_path.length < length) {
+                longest_path.length = length;
+                longest_path.path   = neighbor_path.path; // copy path
+            }
+        }
+    }
+
+    // create result path
+    assert(!longest_path.path.empty());
+    longest_path.path.erase(longest_path.path.begin()); // remove input_node
+    assert(!longest_path.path.empty());
+    auto branches_item = ex_path.side_branches.find(longest_path.path.back());
+    if (branches_item == ex_path.side_branches.end()) {
+        // longest path ends on circle
+        return longest_path;
+    }
+    const VoronoiGraph::Path &longest_branch = branches_item->second.top();
+    longest_path.path.insert(longest_path.path.end(),
+                             longest_branch.path.begin(),
+                             longest_branch.path.end());
+    return longest_path;
+}
+
+std::optional<VoronoiGraph::Circle> VoronoiGraphUtils::create_circle(
+    const VoronoiGraph::Path &          path,
+    const VoronoiGraph::Node::Neighbor &neighbor)
+{
+    VoronoiGraph::Nodes passed_nodes = path.path;
+    // detection of circle
+    // not neccesary to check last one in path
+    auto        end_find  = passed_nodes.end() - 1;
+    const auto &path_item = std::find(passed_nodes.begin(), end_find,
+                                      neighbor.node);
+    if (path_item == end_find) return {}; // circle not detected
+    // separate Circle:
+    VoronoiGraph::Nodes circle_path(path_item, passed_nodes.end());
+    // !!! Real circle lenght is calculated on detection of end circle
+    // now circle_length contain also lenght of path before circle
+    double circle_length = path.length + neighbor.edge_length;
+    // solve of branch length will be at begin of cirlce
+    return VoronoiGraph::Circle(std::move(circle_path), circle_length);
+};
+
+void VoronoiGraphUtils::merge_connected_circle(
+    VoronoiGraph::ExPath::ConnectedCircles &dst,
+    VoronoiGraph::ExPath::ConnectedCircles &src,
+    size_t dst_circle_count)
+{
+    std::set<size_t> done;
+    for (const auto &item : src) {
+        size_t dst_index = dst_circle_count + item.first;
+        if (done.find(dst_index) != done.end()) continue;
+        done.insert(dst_index);
+
+        std::set<size_t> connected_circle;
+        for (const size_t &src_index : item.second)
+            connected_circle.insert(dst_circle_count + src_index);
+
+        auto &dst_set = dst[dst_index];
+        dst_set.merge(connected_circle);
+
+        // write same information into connected circles
+        connected_circle = dst_set; // copy
+        connected_circle.insert(dst_index);
+        for (size_t prev_connection_idx : dst_set) {
+            done.insert(prev_connection_idx);
+            for (size_t connected_circle_idx : connected_circle) {
+                if (connected_circle_idx == prev_connection_idx) continue;
+                dst[prev_connection_idx].insert(connected_circle_idx);
+            }
+        }
+    }
+}
+
+void VoronoiGraphUtils::append_neighbor_branch(
+    VoronoiGraph::ExPath &dst, VoronoiGraph::ExPath &src)
+{
+    // move side branches
+    if (!src.side_branches.empty())
+        dst.side_branches
+            .insert(std::make_move_iterator(src.side_branches.begin()),
+                    std::make_move_iterator(src.side_branches.end()));
+
+    // move circles
+    if (!src.circles.empty()) {
+        // copy connected circles indexes
+        if (!src.connected_circle.empty()) {
+            merge_connected_circle(dst.connected_circle, src.connected_circle,
+                                   dst.circles.size());
+        }
+        dst.circles.insert(dst.circles.end(),
+                           std::make_move_iterator(src.circles.begin()),
+                           std::make_move_iterator(src.circles.end()));
+    }
+}
+
+void VoronoiGraphUtils::reshape_longest_path(VoronoiGraph::ExPath &path)
+{
+    assert(path.path.size() >= 1);
+
+    double                    actual_length = 0.;
+    const VoronoiGraph::Node *prev_node     = nullptr;
+    VoronoiGraph::Nodes       origin_path   = path.path; // make copy
+    // index to path
+    size_t path_index = 0;
+    for (const VoronoiGraph::Node *node : origin_path) {
+        if (prev_node != nullptr) {
+            ++path_index;
+            actual_length += get_neighbor_distance(prev_node, node);
+        }
+        prev_node = node;
+        // increase actual length
+
+        auto side_branches_item = path.side_branches.find(node);
+        if (side_branches_item == path.side_branches.end())
+            continue; // no side branches
+        VoronoiGraph::ExPath::SideBranches &branches = side_branches_item
+                                                           ->second;
+        if (actual_length >= branches.top().length)
+            continue; // no longer branch
+
+        auto               end_path = path.path.begin() + path_index;
+        VoronoiGraph::Path side_branch({path.path.begin(), end_path},
+                                       actual_length);
+        std::reverse(side_branch.path.begin(), side_branch.path.end());
+        VoronoiGraph::Path new_main_branch(std::move(branches.top()));
+        branches.pop();
+        std::reverse(new_main_branch.path.begin(), new_main_branch.path.end());
+        // add old main path store into side branches - may be it is not neccessary
+        branches.push(std::move(side_branch));
+
+        // swap side branch with main branch
+        path.path.erase(path.path.begin(), end_path);
+        path.path.insert(path.path.begin(), new_main_branch.path.begin(),
+                         new_main_branch.path.end());
+
+        path.length += new_main_branch.length;
+        path.length -= actual_length;
+        path_index    = new_main_branch.path.size();
+        actual_length = new_main_branch.length;
+    }
+}
+
+VoronoiGraph::ExPath VoronoiGraphUtils::create_longest_path(
+    const VoronoiGraph::Node *start_node)
+{
+    VoronoiGraph::ExPath      longest_path;
+    CallStack call_stack;
+    call_stack.emplace(
+        std::make_unique<EvaluateNeighbor>(longest_path, start_node));
+
+    // depth search for longest path in graph
+    while (!call_stack.empty()) {
+        std::unique_ptr<IStackFunction> stack_function = std::move(
+            call_stack.top());
+        call_stack.pop();
+        stack_function->process(call_stack);
+        // stack function deleted
+    }
+
+    reshape_longest_path(longest_path);
+    // after reshape it shoud be longest path for whole Voronoi Graph
+    return longest_path;
+}
+
+Slic3r::Point VoronoiGraphUtils::get_edge_point(const VD::edge_type *edge,
+                                                double               ratio)
+{
+    const VD::vertex_type *v0 = edge->vertex0();
+    const VD::vertex_type *v1 = edge->vertex1();
+    if (ratio <= std::numeric_limits<double>::epsilon())
+        return Point(v0->x(), v0->y());
+    if (ratio >= 1. - std::numeric_limits<double>::epsilon())
+        return Point(v1->x(), v1->y());
+
+    if (edge->is_linear()) {
+        Point dir(v1->x() - v0->x(), v1->y() - v0->y());
+        // normalize
+        dir *= ratio;
+        return Point(v0->x() + dir.x(), v0->y() + dir.y());
+    }
+
+    assert(edge->is_curved());
+    // TODO: distance on curve
+    return Point(v0->x(), v0->y());
+}
+
+Slic3r::Point VoronoiGraphUtils::get_center_of_path(
+    const VoronoiGraph::Nodes &path,
+                                            double path_length)
+{
+    const VoronoiGraph::Node *prev_node        = nullptr;
+    double                    half_path_length = path_length / 2.;
+    double                    distance         = 0.;
+    for (const VoronoiGraph::Node *node : path) {
+        if (prev_node == nullptr) { // first call
+            prev_node = node;
+            continue;
+        }
+        const VoronoiGraph::Node::Neighbor *neighbor = get_neighbor(prev_node,
+                                                                    node);
+        distance += neighbor->edge_length;
+        if (distance >= half_path_length) {
+            // over half point is on
+            double ratio = 1. - (distance - half_path_length) /
+                                    neighbor->edge_length;
+            return get_edge_point(neighbor->edge, ratio);
+        }
+        prev_node = node;
+    }
+    // half_path_length must be inside path
+    // this means bad input params
+    assert(false);
+    return Point(0, 0);
+}
+
+std::vector<Slic3r::Point> VoronoiGraphUtils::sample_voronoi_graph(
+    const VoronoiGraph &  graph,
+                                        const SampleConfig &  config,
+                                        VoronoiGraph::ExPath &longest_path)
+{
+    // first vertex on contour:
+    const VoronoiGraph::Node *start_node = nullptr;
+    for (const auto &[key, value] : graph.data) {
+        const VD::vertex_type & vertex   = *key;
+        Voronoi::VertexCategory category = Voronoi::vertex_category(vertex);
+        if (category == Voronoi::VertexCategory::OnContour) {
+            start_node = &value;
+            break;
+        }
+    }
+    // every island has to have a point on contour
+    assert(start_node != nullptr);
+
+    longest_path = create_longest_path(start_node);
+    // longest_path = create_longest_path_recursive(start_node);
+    if (longest_path.length <
+        config.max_length_for_one_support_point) { // create only one
+                                                   // point in center
+        // sample in center of voronoi
+        return {get_center_of_path(longest_path.path, longest_path.length)};
+    }
+
+    std::vector<Point> points;
+    points.push_back(get_offseted_point(*start_node, config.start_distance));
+
+    return points;
+}
+
+void VoronoiGraphUtils::draw(SVG &svg, const VoronoiGraph &graph, coord_t width)
+{
+    for (const auto &[key, value] : graph.data) {
+        svg.draw(Point(key->x(), key->y()), "lightgray", width);
+        for (const auto &n : value.neighbors) {
+            if (n.edge->vertex0() > n.edge->vertex1()) continue;
+            auto  v0 = *n.edge->vertex0();
+            Point from(v0.x(), v0.y());
+            auto  v1 = *n.edge->vertex1();
+            Point to(v1.x(), v1.y());
+            svg.draw(Line(from, to), "gray", width);
+
+            Point center = from + to;
+            center *= .5;
+            // svg.draw_text(center,
+            // (std::to_string(std::round(n.edge_length/3e5)/100.)).c_str(), "gray");
+        }
+    }
+}
+
+void VoronoiGraphUtils::draw(SVG &                      svg,
+                             const VoronoiGraph::Nodes &path,
+                             coord_t                    width,
+                             const char *               color,
+                             bool                       finish)
+{
+    const VoronoiGraph::Node *prev_node = (finish) ? path.back() : nullptr;
+    int                       index     = 0;
+    for (auto &node : path) {
+        ++index;
+        if (prev_node == nullptr) {
+            prev_node = node;
+            continue;
+        }
+        Point from(prev_node->vertex->x(), prev_node->vertex->y());
+        Point to(node->vertex->x(), node->vertex->y());
+        svg.draw(Line(from, to), color, width);
+
+        svg.draw_text(from, std::to_string(index - 1).c_str(), color);
+        svg.draw_text(to, std::to_string(index).c_str(), color);
+        prev_node = node;
+    }
+}
+
+void VoronoiGraphUtils::draw(SVG &                       svg,
+                             const VoronoiGraph::ExPath &path,
+                             coord_t                     width)
+{
+    const char *circlePathColor   = "green";
+    const char *sideBranchesColor = "blue";
+    const char *mainPathColor     = "red";
+
+    for (auto &circle : path.circles) {
+        draw(svg, circle.path, width, circlePathColor, true);
+        Point center(0, 0);
+        for (auto p : circle.path) {
+            center.x() += p->vertex->x();
+            center.y() += p->vertex->y();
+        }
+        center.x() /= circle.path.size();
+        center.y() /= circle.path.size();
+
+        svg.draw_text(center,
+                      ("C" + std::to_string(&circle - &path.circles.front()))
+                          .c_str(),
+                      circlePathColor);
+    }
+
+    for (const auto &branches : path.side_branches) {
+        auto tmp = branches.second; // copy
+        while (!tmp.empty()) {
+            const auto &branch = tmp.top();
+            auto        path   = branch.path;
+            path.insert(path.begin(), branches.first);
+            draw(svg, path, width, sideBranchesColor);
+            tmp.pop();
+        }
+    }
+
+    draw(svg, path.path, width, mainPathColor);
+}

src/libslic3r/SLA/SupportIslands/VoronoiGraphUtils.hpp

@@ -0,0 +1,186 @@
+#ifndef slic3r_SLA_SuppotstIslands_VoronoiGraphUtils_hpp_
+#define slic3r_SLA_SuppotstIslands_VoronoiGraphUtils_hpp_
+
+#include <optional>
+#include <map>
+#include <set>
+#include <libslic3r/Geometry.hpp>
+#include <libslic3r/Point.hpp>
+#include "VoronoiGraph.hpp"
+#include "SampleConfig.hpp"
+
+// for debug draw purpose
+#include "SVG.hpp"
+
+namespace Slic3r::sla {
+
+/// <summary>
+/// Class which contain collection of static function
+/// for work with Voronoi Graph.
+/// </summary>
+class VoronoiGraphUtils {
+    using VD = Slic3r::Geometry::VoronoiDiagram;
+public:
+    VoronoiGraphUtils() = delete;
+
+    // return node from graph by vertex, when no exists create one
+    static VoronoiGraph::Node *getNode(
+        VoronoiGraph &         graph,
+        const VD::vertex_type *vertex,
+        const VD::edge_type *  edge,
+        const Lines &          lines
+    );
+        
+    /// <summary>
+    /// calculate distances to border of island and length on skeleton
+    /// </summary>
+    /// <param name="voronoi_diagram">Input anotated voronoi diagram
+    /// (use function Slic3r::Voronoi::annotate_inside_outside)</param>
+    /// <param name="lines">Source lines for voronoi diagram</param> 
+    /// <returns>Extended voronoi graph by distances and length</returns>
+    static VoronoiGraph getSkeleton(const VD &vd, const Lines &lines);
+
+    /// <summary>
+    /// For generating support point in distance from node
+    /// </summary>
+    /// <param name="node">Node lay on outline with only one neighbor</param>
+    /// <param name="padding">Distance from outline</param>
+    /// <returns></returns>
+    static Slic3r::Point get_offseted_point(const VoronoiGraph::Node &node,
+                                          double                    padding);
+    
+    /// <summary>
+    /// find neighbor and return distance between nodes
+    /// </summary>
+    /// <param name="from">source of neighborse</param>
+    /// <param name="to">neighbor node</param>
+    /// <returns>When neighbor return distance between neighbor Nodes
+    /// otherwise no value</returns>
+    static const VoronoiGraph::Node::Neighbor *get_neighbor(
+        const VoronoiGraph::Node *from, const VoronoiGraph::Node *to);
+
+    /// <summary>
+    /// use function get_neighbor
+    /// when not neighbor assert
+    /// </summary>
+    /// <param name="from">source Node</param>
+    /// <param name="to">destination Node</param>
+    /// <returns>distance between Nodes or Assert when not neighbor</returns>
+    static double get_neighbor_distance(const VoronoiGraph::Node *from,
+                                 const VoronoiGraph::Node *to);
+
+    /// <summary>
+    /// Create longest node path over circle together with side branches
+    /// </summary>
+    /// <param name="circle">Source circle, can't be connected with another circle</param>
+    /// <param name="side_branches">Circle side branches from nodes of circle</param>
+    /// <param name="start_path">Path before circle - defince input point to circle</param>
+    /// <returns>Longest nodes path and its length</returns>
+    static VoronoiGraph::Path find_longest_path_on_circle(
+        const VoronoiGraph::Circle &                 circle,
+        const VoronoiGraph::ExPath::SideBranchesMap &side_branches);
+        
+    /// <summary>
+    /// Serach longest path from input_node throw Nodes in connected circles,
+    /// when circle is alone call find_longest_path_on_circle.
+    /// </summary>
+    /// <param name="input_node">Node on circle</param>
+    /// <param name="finished_circle_index">index of circle with input node</param> 
+    /// <param name="ex_path">Hold Circles, connection of circles and Side branches</param> 
+    /// <returns>Longest path from input node</returns>
+    static VoronoiGraph::Path find_longest_path_on_circles(
+        const VoronoiGraph::Node &  input_node,
+        size_t                      finished_circle_index,
+        const VoronoiGraph::ExPath &ex_path);
+
+    /// <summary>
+    /// Function for detection circle in passed path.
+    /// </summary>
+    /// <param name="path">Already passed path in Graph</param>
+    /// <param name="neighbor">Actual neighbor possible created circle</param>
+    /// <returns>Circle when exists</returns>
+    static std::optional<VoronoiGraph::Circle> create_circle(
+        const VoronoiGraph::Path &          path,
+        const VoronoiGraph::Node::Neighbor &neighbor);
+
+    /// <summary>
+    /// Move source connected circles into destination
+    /// </summary>
+    /// <param name="dst">In/Out param</param>
+    /// <param name="src">Input possible modified, do not use it after this function</param>
+    /// <param name="dst_circle_count">Count of destination circles before
+    /// merge Source circle are append afted destination, therfore all src
+    /// indexes must be increased by destination circle count</param>
+    static void merge_connected_circle(
+        VoronoiGraph::ExPath::ConnectedCircles &dst,
+        VoronoiGraph::ExPath::ConnectedCircles &src,
+        size_t dst_circle_count);
+
+    /// <summary>
+    /// move data from source to destination
+    /// side_branches + circles + connected_circle
+    /// </summary>
+    /// <param name="dst">destination extended path - append data from source</param>
+    /// <param name="src">source extended path - data will be moved to dst</param>
+    static void append_neighbor_branch(VoronoiGraph::ExPath &dst,
+                                       VoronoiGraph::ExPath &src);
+
+    /// <summary>
+    /// Heal starting from random point.
+    /// Compare length of all starting path with side branches
+    /// when side branch is longer than swap with start path
+    /// </summary>
+    /// <param name="path">IN/OUT path to be fixed after creating longest path
+    /// from one point</param>
+    static void reshape_longest_path(VoronoiGraph::ExPath &path);
+
+    /// <summary>
+    /// Extract the longest path from voronoi graph
+    /// by own function call stack(IStackFunction).
+    /// Restructuralize path by branch created from random point.
+    /// </summary>
+    /// <param name="start_node">Random point from outline.</param>
+    static VoronoiGraph::ExPath create_longest_path(
+        const VoronoiGraph::Node *start_node);
+        
+    /// <summary>
+    /// Create point on edge defined by neighbor
+    /// in distance defined by edge length ratio
+    /// </summary>
+    static Point get_edge_point(const VD::edge_type *edge, double ratio);
+
+    /// <summary>
+    /// Find point lay in center of path
+    /// Distance from this point to front of path 
+    /// is same as distance to back of path
+    /// </summary>
+    /// <param name="path">Queue of neighbor nodes.(must be neighbor)</param>
+    /// <param name="path_length">length of path</param>
+    /// <returns>Point laying on voronoi diagram</returns>
+    static Point get_center_of_path(const VoronoiGraph::Nodes &path,
+                             double                     path_length);
+
+    /// <summary>
+    /// Sample voronoi skeleton
+    /// </summary>
+    /// <param name="graph">Inside skeleton of island</param>
+    /// <param name="config">Params for sampling</param>
+    /// <param name="longest_path">OUTPUT: longest path in graph</param>
+    /// <returns>Vector of sampled points or Empty when distance from edge is
+    /// bigger than max_distance</returns>
+    static std::vector<Point> sample_voronoi_graph(const VoronoiGraph &  graph,
+                                            const SampleConfig &  config,
+                                            VoronoiGraph::ExPath &longest_path);
+
+public: //draw function for debug
+    static void draw(SVG &svg, const VoronoiGraph &graph, coord_t width);
+    static void draw(SVG &                      svg,
+                     const VoronoiGraph::Nodes &path,
+                     coord_t                    width,
+                     const char *               color,
+                     bool                       finish = false);
+    static void draw(SVG &svg, const VoronoiGraph::ExPath &path, coord_t width);
+};
+
+} // namespace Slic3r::sla
+#endif // slic3r_SLA_SuppotstIslands_VoronoiGraphUtils_hpp_

tests/libslic3r/test_voronoi.cpp

@@ -2283,3 +2283,4 @@ TEST_CASE("Voronoi cell doesn't contain a source point - SPE-2298", "[VoronoiCel
 
     REQUIRE(vd.is_valid());
 }
+// */

tests/sla_print/sla_supptgen_tests.cpp

@@ -5,6 +5,8 @@
 #include <libslic3r/BoundingBox.hpp>
 #include <libslic3r/SLA/SpatIndex.hpp>
 
+#include <libslic3r/SLA/SupportIslands/SampleConfig.hpp>
+
 #include "sla_test_utils.hpp"
 
 namespace Slic3r { namespace sla {
@@ -132,4 +134,128 @@ TEST_CASE("Two parallel plates should be supported", "[SupGen][Hollowed]")
     REQUIRE(!pts.empty());
 }
 
+ExPolygons createTestIslands(double size)
+{
+    ExPolygon triangle(
+        Polygon{{.0, .0},
+                {size, .0},
+                {size / 2., sqrt(size * size - size * size / 4)}});
+    ExPolygon sharp_triangle(
+        Polygon{{.0, size / 2}, {.0, .0}, {2 * size, .0}});
+    ExPolygon triangle_with_hole({{.0, .0},
+                                  {size, .0},
+                                  {size / 2.,
+                                   sqrt(size * size - size * size / 4)}},
+                                 {{size / 4, size / 4},
+                                  {size / 2, size / 2},
+                                  {size / 2, size / 4}});
+    ExPolygon square(Polygon{{.0, size}, {.0, .0}, {size, .0}, {size, size}});
+    ExPolygon rect(
+        Polygon{{.0, size}, {.0, .0}, {2 * size, .0}, {2 * size, size}});
+    ExPolygon rect_with_hole({{-size, size}, // rect CounterClockWise
+                              {-size, -size},
+                              {size, -size},
+                              {size, size}},
+                             {{0., size / 2}, // inside rect ClockWise
+                              {size / 2, 0.},
+                              {0., -size / 2},
+                              {-size / 2, 0.}});
+    // need post reorganization of longest path
+    ExPolygon mountains({{0., 0.},
+                         {size, 0.},
+                         {5 * size / 6, size},
+                         {4 * size / 6, size / 6},
+                         {3 * size / 7, 2 * size},
+                         {2 * size / 7, size / 6},
+                         {size / 7, size}});
+    ExPolygon rect_with_4_hole(Polygon{{0., size}, // rect CounterClockWise
+                                       {0., 0.},
+                                       {size, 0.},
+                                       {size, size}});
+    // inside rects ClockWise
+    double size5           = size / 5.;
+    rect_with_4_hole.holes = Polygons{{{size5, 4 * size5},
+                                       {2 * size5, 4 * size5},
+                                       {2 * size5, 3 * size5},
+                                       {size5, 3 * size5}},
+                                      {{3 * size5, 4 * size5},
+                                       {4 * size5, 4 * size5},
+                                       {4 * size5, 3 * size5},
+                                       {3 * size5, 3 * size5}},
+                                      {{size5, 2 * size5},
+                                       {2 * size5, 2 * size5},
+                                       {2 * size5, size5},
+                                       {size5, size5}},
+                                      {{3 * size5, 2 * size5},
+                                       {4 * size5, 2 * size5},
+                                       {4 * size5, size5},
+                                       {3 * size5, size5}}};
+
+    size_t count_cirlce_lines = 1000; // test stack overfrow
+    double r_CCW              = size / 2;
+    double r_CW               = r_CCW - size / 6;
+    // CCW: couter clock wise, CW: clock wise
+    Points circle_CCW, circle_CW;
+    circle_CCW.reserve(count_cirlce_lines);
+    circle_CW.reserve(count_cirlce_lines);
+    for (size_t i = 0; i < count_cirlce_lines; ++i) {
+        double alpha = (2 * M_PI * i) / count_cirlce_lines;
+        double sina  = sin(alpha);
+        double cosa  = cos(alpha);
+        circle_CCW.emplace_back(-r_CCW * sina, r_CCW * cosa);
+        circle_CW.emplace_back(r_CW * sina, r_CW * cosa);
+    }
+    ExPolygon double_circle(circle_CCW, circle_CW);
+
+    TriangleMesh            mesh = load_model("frog_legs.obj");
+    TriangleMeshSlicer      slicer{&mesh};
+    std::vector<float>      grid({0.1f});
+    std::vector<ExPolygons> slices;
+    slicer.slice(grid, SlicingMode::Regular, 0.05f, &slices, [] {});
+    ExPolygon frog_leg = slices.front()[1]; //
+
+    return {
+        triangle,         square,
+        sharp_triangle,   rect,
+        rect_with_hole,   triangle_with_hole,
+        rect_with_4_hole, mountains,
+        double_circle
+        //, frog_leg
+    };
+}
+
+std::vector<Point> test_island_sampling(const ExPolygon &   island,
+                                        const SampleConfig &config)
+{
+    auto points = SupportPointGenerator::uniform_cover_island(island, config);
+    CHECK(!points.empty());
+
+    // all points must be inside of island
+    for (const auto &point : points) { CHECK(island.contains(point)); }
+    return points;
+}
+
+TEST_CASE("Small islands should be supported in center", "[SupGen][VoronoiSkeleton]")
+{
+    double size = 3e7;
+    SampleConfig cfg;
+    cfg.max_distance   = size + 0.1;
+    cfg.sample_size    = size / 5;
+    cfg.start_distance = 0.2 * size; // radius of support head
+    cfg.curve_sample   = 0.1 * size;
+    cfg.max_length_for_one_support_point = 3 * size;
+
+    ExPolygons islands = createTestIslands(size);
+    for (auto &island : islands) {
+        auto   points = test_island_sampling(island, cfg);
+        double angle  = 3.14 / 3; // cca 60 degree
+
+        island.rotate(angle);
+        auto pointsR = test_island_sampling(island, cfg);
+        for (Point &p : pointsR) p.rotate(-angle);
+
+        // points should be equal to pointsR
+    }
+}
+
 }} // namespace Slic3r::sla