Graph Class Reference

Collaboration diagram for Graph:

Public Member Functions
	Graph (std::unique_ptr< std::vector< Node_ptr > > &nodes, int width, int height)
bool	add_edge (int32_t node_id1, int32_t node_id2)
bool	merge_nodes (const Node_ptr &node_to_keep, const Node_ptr &node_to_remove)
void	clear_unconnected_nodes ()
const std::vector< Node_ptr > &	get_nodes () const
bool	all_areas_bigger_than (int32_t min_area)
const size_t	size ()
void	discover_edges (const std::vector< int32_t > &region_labels, const int32_t width, const int32_t height)
void	merge_small_area_nodes (const int32_t min_area, const int32_t min_thickness=0)
void	compute_contours ()

Protected Member Functions
void	hash_node_ids (void)
void	process_overlapping_edges ()
uint8_t	getPixel (const std::vector< uint8_t > &img, int w, int h, int x, int y)
std::vector< uint8_t >	analyzeJunctions (const std::vector< uint8_t > &skel, int w, int h)

Protected Attributes
int	m_width
int	m_height
std::unique_ptr< std::vector< Node_ptr > >	m_nodes
std::unordered_map< int32_t, int32_t >	m_node_ids

Detailed Description

Definition at line 33 of file graph.h.

Constructor & Destructor Documentation

Graph()

Graph::Graph ( std::unique_ptr< std::vector< Node_ptr > > &  nodes, int  width, int  height  )

inline

Definition at line 73 of file graph.h.

        : m_nodes(std::move(nodes))
        , m_width(width)
        , m_height(height) {
        hash_node_ids();
    }

~Graph()

Graph::~Graph ( )

inline

Definition at line 80 of file graph.h.

                    {
        // Break the circular references so the shared_ptrs can reach 0
        for (auto& node : *m_nodes) {
            node->clear_all();
        }
    }

Member Function Documentation

add_edge()

bool Graph::add_edge	(	int32_t	node_id1,
		int32_t	node_id2
	)

Definition at line 55 of file graph.cpp.

                                                       {
    auto end_node_ids {m_node_ids.end()};
    auto node1_it {m_node_ids.find(node_id1)};
    auto node2_it {m_node_ids.find(node_id2)};
 
    if (node1_it == end_node_ids || node2_it == end_node_ids) {
        return false;
    }
 
    const int32_t idx1 {node1_it->second};
    const int32_t idx2 {node2_it->second};
 
    m_nodes->at(idx1)->add_edge(m_nodes->at(idx2));
    m_nodes->at(idx2)->add_edge(m_nodes->at(idx1));
    return true;
}

all_areas_bigger_than()

bool Graph::all_areas_bigger_than

(

int32_t

min_area

)

Definition at line 45 of file graph.cpp.

                                                  {
    for (auto& n : *m_nodes) {
        if (n->area() < min_area) {
            return false;
        }
    }
 
    return true;
}

analyzeJunctions()

std::vector< uint8_t > Graph::analyzeJunctions ( const std::vector< uint8_t > &  skel, int  w, int  h  )

protected

@brief Analyzes a skeleton image to detect junction points using 8-neighbor crossing-number.

Scans the skeleton image and marks pixels as junctions where three or more branches meet, using the crossing-number method (counts 0→1 transitions in the 8-neighbor ring).

@param skel Binary skeleton image (nonzero = skeleton pixel) @param w Image width @param h Image height @return Junction mask with nonzero entries marking junction pixels

Definition at line 223 of file graph.cpp.

                                                                                       {
    std::vector<uint8_t> junction_map(static_cast<size_t>(w) * h, 0);
 
    // 8-Neighbor Order (Clockwise)
    // P9 P2 P3
    // P8 P1 P4
    // P7 P6 P5
    int dx[] = {0, 1, 1, 1, 0, -1, -1, -1};
    int dy[] = {-1, -1, 0, 1, 1, 1, 0, -1};
 
    for (int y = 0; y < h; ++y) {
        for (int x = 0; x < w; ++x) {
            if (getPixel(skel, w, h, x, y) == 0)
                continue;
 
            // 1. Get Neighbors in Circular Order
            int p[8];
            for (int k = 0; k < 8; ++k) {
                p[k] = getPixel(skel, w, h, x + dx[k], y + dy[k]) ? 1 : 0;
            }
 
            // 2. Count Transitions (0 -> 1)
            // This is the Crossing Number / 2
            int transitions = 0;
            for (int k = 0; k < 8; ++k) {
                if (p[k] == 0 && p[(k + 1) % 8] == 1)
                    transitions++;
            }
 
            // 3. Count Total Neighbors (for Endpoint check)
            int neighbors = 0;
            for (int k = 0; k < 8; ++k)
                neighbors += p[k];
 
            // 4. Classify
            if (transitions >= 3) {
                junction_map[y * w + x] = 1;
            }
        }
    }
    return junction_map;
}

References getPixel().

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clear_unconnected_nodes()

void Graph::clear_unconnected_nodes

(

)

Definition at line 101 of file graph.cpp.

                                    {
    std::vector<Node_ptr>& nodes {*m_nodes};
 
    nodes.erase(
        std::remove_if(
            nodes.begin(), nodes.end(), [](const Node_ptr& n) { return n->area() == 0; }
        ),
        nodes.end()
    );
 
    hash_node_ids();
}

compute_contours()

void Graph::compute_contours

(

)

Definition at line 266 of file graph.cpp.

                             {
 
    /*
    Shared-edge mode: build region boundaries on the crack grid so
    neighbouring contours are exactly coincident along shared edges -- no
    overlap band, no gaps
    */
 
    float eps = 0.25f;
 
    std::vector<int32_t> labels(static_cast<size_t>(m_width) * m_height, -1);
    for (const Node_ptr& n : get_nodes()) {
        if (n->area() == 0)
            continue;
        for (auto& p : n->get_pixels())
            labels[static_cast<size_t>(p.position.y) * m_width + p.position.x] = n->id();
    }
 
    auto loops = build_shared_loops(labels, m_width, m_height, eps);
 
    for (const Node_ptr& n : get_nodes()) {
        if (n->area() == 0)
            continue;
        n->clear_contour();
        auto it = loops.find(n->id());
        if (it == loops.end())
            continue;
        ImageLib::RGBPixel<uint8_t> c = n->color();
        ImageLib::RGBAPixel<uint8_t> col {c.red, c.green, c.blue, 255};
        for (std::vector<QuadBezier>& curve : it->second) {
            std::vector<Point> anchors; // keep contours[] parallel to curves[]
            anchors.reserve(curve.size() + 1);
            for (const QuadBezier& q : curve)
                anchors.push_back(q.p0);
            if (!curve.empty())
                anchors.push_back(curve.back().p2);
            n->m_contours.contours.push_back(std::move(anchors));
            n->m_contours.curves.push_back(std::move(curve));
            n->m_contours.colors.push_back(col);
            n->m_contours.hierarchy.push_back({-1, -1, -1, -1});
            n->m_contours.is_hole.push_back(false);
        }
    }
}

discover_edges()

void Graph::discover_edges	(	const std::vector< int32_t > &	region_labels,
		const int32_t	width,
		const int32_t	height
	)

Definition at line 114 of file graph.cpp.

  {
    // Moore 8-connected neighbourhood
    constexpr int8_t dirs[8][2] {{1, 0}, {-1, 0},  {0, 1},  {0, -1},
                                 {1, 1}, {-1, -1}, {-1, 1}, {1, -1}};
 
    int32_t rneigh[8];
 
    for (int32_t y {0}; y < height; ++y) {
        for (int32_t x {0}; x < width; ++x) {
            const int32_t idx {y * width + x};
            const int32_t rid {region_labels[idx]};
 
            for (int32_t k {0}; k < 8; ++k) {
                const int32_t nx {x + dirs[k][0]};
                const int32_t ny {y + dirs[k][1]};
 
                if (nx >= 0 && nx < width && ny >= 0 && ny < height) {
                    rneigh[k] = region_labels[ny * width + nx];
                } else {
                    rneigh[k] = rid; // ignore out-of-bounds
                }
            }
 
            for (int32_t r : rneigh) {
                if (r != rid) {
                    add_edge(rid, r);
                }
            }
        }
    }
}

get_nodes()

const std::vector< Node_ptr > & Graph::get_nodes ( ) const

inline

Definition at line 92 of file graph.h.

                                                        {
        return *m_nodes;
    }

getPixel()

uint8_t Graph::getPixel ( const std::vector< uint8_t > &  img, int  w, int  h, int  x, int  y  )

inlineprotected

@brief Safely retrieves a pixel value from a binary image with bounds checking.

@param img Binary image buffer @param w Image width @param h Image height @param x Pixel x-coordinate @param y Pixel y-coordinate @return Pixel value at (x, y), or 0 if out of bounds

Definition at line 52 of file graph.h.

                                                                                       {
        if (x < 0 || x >= w || y < 0 || y >= h)
            return 0; // Boundary check
        return img[y * w + x];
    }

Referenced by analyzeJunctions().

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hash_node_ids()

void Graph::hash_node_ids ( void  )

protected

Definition at line 38 of file graph.cpp.

                          {
    for (int32_t i {0}; i < m_nodes->size(); i++) {
        const int32_t key {m_nodes->at(i)->id()};
        m_node_ids[key] = i;
    }
}

merge_nodes()

bool Graph::merge_nodes	(	const Node_ptr &	node_to_keep,
		const Node_ptr &	node_to_remove
	)

Definition at line 72 of file graph.cpp.

                                                                                    {
    auto end_node_ids {m_node_ids.end()};
    auto node1_it {m_node_ids.find(node_to_keep->id())};
    auto node2_it {m_node_ids.find(node_to_remove->id())};
 
    if (node1_it == end_node_ids || node2_it == end_node_ids) {
        return false;
    }
 
    const int32_t idx_k {node1_it->second};
    const int32_t idx_r {node2_it->second};
 
    // transfer edges from node_to_remove to node_to_keep
    for (Node_ptr n : m_nodes->at(idx_r)->edges()) {
        if (n->id() != node_to_keep->id()) {
            // prevents self referencing
            n->remove_edge(node_to_remove);
            n->add_edge(node_to_keep);
            node_to_keep->add_edge(n);
        }
    }
 
    node_to_keep->add_pixels(node_to_remove->get_pixels());
 
    node_to_remove->clear_all();
 
    return true;
}

merge_small_area_nodes()

void Graph::merge_small_area_nodes	(	const int32_t	min_area,
		const int32_t	min_thickness = 0
	)

Definition at line 401 of file graph.cpp.

                                                                                      {
    // Keep merging while any pass still makes progress. Using "did this pass
    // merge anything?" as the loop guard (instead of re-testing every node)
    // also avoids spinning forever on a node that is too small/thin but has no
    // valid neighbour to merge into.
    bool merged_any = true;
    while (merged_any) {
        merged_any = false;
 
        for (const Node_ptr& n : get_nodes()) {
            if (n->area() == 0)
                continue;
 
            bool needs_merge = n->area() < static_cast<size_t>(min_area);
            if (!needs_merge && min_thickness > 0) {
                // too thin == no inscribed disk of radius min_thickness/2 fits.
                needs_merge = 2.0f * max_inscribed_radius(n) < static_cast<float>(min_thickness);
            }
            if (!needs_merge)
                continue;
 
            ImageLib::RGBPixel<uint8_t> col = n->color();
 
            Node_ptr best_neighbor = nullptr;
            float best_score = std::numeric_limits<float>::max();
            for (const Node_ptr& ne : n->edges()) {
                if (ne->area() > 0) {
                    float cdist = ImageLib::RGBPixel<uint8_t>::colorDistance(ne->color(), col);
                    float score = static_cast<float>(ne->area()) + 10.f * cdist;
                    if (score < best_score) {
                        best_score = score;
                        best_neighbor = ne;
                    }
                }
            }
 
            // no valid neighbor found, skip this node
            if (!best_neighbor) {
                continue;
            }
 
            if (best_neighbor->area() >= n->area()) {
                merge_nodes(best_neighbor, n);
            } else {
                merge_nodes(n, best_neighbor);
            }
            merged_any = true;
        }
 
        clear_unconnected_nodes();
    }
}

process_overlapping_edges()

void Graph::process_overlapping_edges ( )

protected

Definition at line 148 of file graph.cpp.

                                      {
    // 1. Build the Global Label Map ONCE (0 = background, else = node->id())
    std::vector<int32_t> label_map(static_cast<size_t>(m_width) * static_cast<size_t>(m_height), 0);
 
    for (const Node_ptr& n : get_nodes()) {
        if (n->area() == 0)
            continue;
 
        for (auto& [_, p] : n->get_pixels()) {
            label_map[p.y * m_width + p.x] = n->id();
        }
    }
 
    constexpr int8_t dirs[8][2] {{1, 0}, {-1, 0},  {0, 1},  {0, -1},
                                 {1, 1}, {-1, -1}, {-1, 1}, {1, -1}};
 
    // 2. Iterate directly over the pixels of each node
    for (const Node_ptr& n : get_nodes()) {
        if (n->area() == 0)
            continue;
        int32_t val = n->id();
 
        for (auto& [_, p] : n->get_pixels()) {
            int x = p.x;
            int y = p.y;
 
            // Check 8 neighbors in the global map
            for (int k = 0; k < 8; ++k) {
                int nx = x + dirs[k][0];
                int ny = y + dirs[k][1];
 
                // Fast boundary check (replaces std::clamp)
                if (nx < 0 || nx >= m_width || ny < 0 || ny >= m_height)
                    continue;
 
                int32_t n_val = label_map[ny * m_width + nx];
 
                // Is it a neighbor? AND have we not processed this pairing yet?
                if (n_val != 0 && n_val != val && val < n_val) {
                    bool is_too_thin = false;
 
                    // Check around the neighbor pixel for a 3rd region (pinching)
                    for (int mk = 0; mk < 8; ++mk) {
                        int mx = nx + dirs[mk][0];
                        int my = ny + dirs[mk][1];
 
                        if (mx < 0 || mx >= m_width || my < 0 || my >= m_height)
                            continue;
 
                        int32_t m_val = label_map[my * m_width + mx];
 
                        if (m_val != 0 && m_val != val && m_val != n_val) {
                            is_too_thin = true;
                            break; // CRITICAL: Stop checking immediately once proven thin!
                        }
                    }
 
                    if (is_too_thin) {
                        // Give our pixel to the neighbor
                        Node_ptr neighbor_node =
                            m_nodes->at(m_node_ids[n_val]); // get_node_by_id(n_val); // Assuming
                                                            // you have this lookup
                        if (neighbor_node) {
                            neighbor_node->add_edge_pixel(XY {x, y});
                        }
                    } else {
                        // Take the neighbor's pixel
                        n->add_edge_pixel(XY {nx, ny});
                    }
                }
            }
        }
    }
}

size()

const size_t Graph::size ( )

inline

Definition at line 97 of file graph.h.

                               {
        return m_nodes->size();
    }

Member Data Documentation

m_height

int Graph::m_height

protected

Definition at line 35 of file graph.h.

m_node_ids

std::unordered_map<int32_t, int32_t> Graph::m_node_ids

protected

Definition at line 37 of file graph.h.

m_nodes

std::unique_ptr<std::vector<Node_ptr> > Graph::m_nodes

protected

Definition at line 36 of file graph.h.

m_width

int Graph::m_width

protected

Definition at line 35 of file graph.h.

---

The documentation for this class was generated from the following files:

• include/internal/graph.h
• src/internal/graph.cpp