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Diffstat (limited to '.venv/lib/python3.12/site-packages/networkx/algorithms/planar_drawing.py')
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diff --git a/.venv/lib/python3.12/site-packages/networkx/algorithms/planar_drawing.py b/.venv/lib/python3.12/site-packages/networkx/algorithms/planar_drawing.py new file mode 100644 index 00000000..ea25809b --- /dev/null +++ b/.venv/lib/python3.12/site-packages/networkx/algorithms/planar_drawing.py @@ -0,0 +1,464 @@ +from collections import defaultdict + +import networkx as nx + +__all__ = ["combinatorial_embedding_to_pos"] + + +def combinatorial_embedding_to_pos(embedding, fully_triangulate=False): + """Assigns every node a (x, y) position based on the given embedding + + The algorithm iteratively inserts nodes of the input graph in a certain + order and rearranges previously inserted nodes so that the planar drawing + stays valid. This is done efficiently by only maintaining relative + positions during the node placements and calculating the absolute positions + at the end. For more information see [1]_. + + Parameters + ---------- + embedding : nx.PlanarEmbedding + This defines the order of the edges + + fully_triangulate : bool + If set to True the algorithm adds edges to a copy of the input + embedding and makes it chordal. + + Returns + ------- + pos : dict + Maps each node to a tuple that defines the (x, y) position + + References + ---------- + .. [1] M. Chrobak and T.H. Payne: + A Linear-time Algorithm for Drawing a Planar Graph on a Grid 1989 + http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.51.6677 + + """ + if len(embedding.nodes()) < 4: + # Position the node in any triangle + default_positions = [(0, 0), (2, 0), (1, 1)] + pos = {} + for i, v in enumerate(embedding.nodes()): + pos[v] = default_positions[i] + return pos + + embedding, outer_face = triangulate_embedding(embedding, fully_triangulate) + + # The following dicts map a node to another node + # If a node is not in the key set it means that the node is not yet in G_k + # If a node maps to None then the corresponding subtree does not exist + left_t_child = {} + right_t_child = {} + + # The following dicts map a node to an integer + delta_x = {} + y_coordinate = {} + + node_list = get_canonical_ordering(embedding, outer_face) + + # 1. Phase: Compute relative positions + + # Initialization + v1, v2, v3 = node_list[0][0], node_list[1][0], node_list[2][0] + + delta_x[v1] = 0 + y_coordinate[v1] = 0 + right_t_child[v1] = v3 + left_t_child[v1] = None + + delta_x[v2] = 1 + y_coordinate[v2] = 0 + right_t_child[v2] = None + left_t_child[v2] = None + + delta_x[v3] = 1 + y_coordinate[v3] = 1 + right_t_child[v3] = v2 + left_t_child[v3] = None + + for k in range(3, len(node_list)): + vk, contour_nbrs = node_list[k] + wp = contour_nbrs[0] + wp1 = contour_nbrs[1] + wq = contour_nbrs[-1] + wq1 = contour_nbrs[-2] + adds_mult_tri = len(contour_nbrs) > 2 + + # Stretch gaps: + delta_x[wp1] += 1 + delta_x[wq] += 1 + + delta_x_wp_wq = sum(delta_x[x] for x in contour_nbrs[1:]) + + # Adjust offsets + delta_x[vk] = (-y_coordinate[wp] + delta_x_wp_wq + y_coordinate[wq]) // 2 + y_coordinate[vk] = (y_coordinate[wp] + delta_x_wp_wq + y_coordinate[wq]) // 2 + delta_x[wq] = delta_x_wp_wq - delta_x[vk] + if adds_mult_tri: + delta_x[wp1] -= delta_x[vk] + + # Install v_k: + right_t_child[wp] = vk + right_t_child[vk] = wq + if adds_mult_tri: + left_t_child[vk] = wp1 + right_t_child[wq1] = None + else: + left_t_child[vk] = None + + # 2. Phase: Set absolute positions + pos = {} + pos[v1] = (0, y_coordinate[v1]) + remaining_nodes = [v1] + while remaining_nodes: + parent_node = remaining_nodes.pop() + + # Calculate position for left child + set_position( + parent_node, left_t_child, remaining_nodes, delta_x, y_coordinate, pos + ) + # Calculate position for right child + set_position( + parent_node, right_t_child, remaining_nodes, delta_x, y_coordinate, pos + ) + return pos + + +def set_position(parent, tree, remaining_nodes, delta_x, y_coordinate, pos): + """Helper method to calculate the absolute position of nodes.""" + child = tree[parent] + parent_node_x = pos[parent][0] + if child is not None: + # Calculate pos of child + child_x = parent_node_x + delta_x[child] + pos[child] = (child_x, y_coordinate[child]) + # Remember to calculate pos of its children + remaining_nodes.append(child) + + +def get_canonical_ordering(embedding, outer_face): + """Returns a canonical ordering of the nodes + + The canonical ordering of nodes (v1, ..., vn) must fulfill the following + conditions: + (See Lemma 1 in [2]_) + + - For the subgraph G_k of the input graph induced by v1, ..., vk it holds: + - 2-connected + - internally triangulated + - the edge (v1, v2) is part of the outer face + - For a node v(k+1) the following holds: + - The node v(k+1) is part of the outer face of G_k + - It has at least two neighbors in G_k + - All neighbors of v(k+1) in G_k lie consecutively on the outer face of + G_k (excluding the edge (v1, v2)). + + The algorithm used here starts with G_n (containing all nodes). It first + selects the nodes v1 and v2. And then tries to find the order of the other + nodes by checking which node can be removed in order to fulfill the + conditions mentioned above. This is done by calculating the number of + chords of nodes on the outer face. For more information see [1]_. + + Parameters + ---------- + embedding : nx.PlanarEmbedding + The embedding must be triangulated + outer_face : list + The nodes on the outer face of the graph + + Returns + ------- + ordering : list + A list of tuples `(vk, wp_wq)`. Here `vk` is the node at this position + in the canonical ordering. The element `wp_wq` is a list of nodes that + make up the outer face of G_k. + + References + ---------- + .. [1] Steven Chaplick. + Canonical Orders of Planar Graphs and (some of) Their Applications 2015 + https://wuecampus2.uni-wuerzburg.de/moodle/pluginfile.php/545727/mod_resource/content/0/vg-ss15-vl03-canonical-orders-druckversion.pdf + .. [2] M. Chrobak and T.H. Payne: + A Linear-time Algorithm for Drawing a Planar Graph on a Grid 1989 + http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.51.6677 + + """ + v1 = outer_face[0] + v2 = outer_face[1] + chords = defaultdict(int) # Maps nodes to the number of their chords + marked_nodes = set() + ready_to_pick = set(outer_face) + + # Initialize outer_face_ccw_nbr (do not include v1 -> v2) + outer_face_ccw_nbr = {} + prev_nbr = v2 + for idx in range(2, len(outer_face)): + outer_face_ccw_nbr[prev_nbr] = outer_face[idx] + prev_nbr = outer_face[idx] + outer_face_ccw_nbr[prev_nbr] = v1 + + # Initialize outer_face_cw_nbr (do not include v2 -> v1) + outer_face_cw_nbr = {} + prev_nbr = v1 + for idx in range(len(outer_face) - 1, 0, -1): + outer_face_cw_nbr[prev_nbr] = outer_face[idx] + prev_nbr = outer_face[idx] + + def is_outer_face_nbr(x, y): + if x not in outer_face_ccw_nbr: + return outer_face_cw_nbr[x] == y + if x not in outer_face_cw_nbr: + return outer_face_ccw_nbr[x] == y + return outer_face_ccw_nbr[x] == y or outer_face_cw_nbr[x] == y + + def is_on_outer_face(x): + return x not in marked_nodes and (x in outer_face_ccw_nbr or x == v1) + + # Initialize number of chords + for v in outer_face: + for nbr in embedding.neighbors_cw_order(v): + if is_on_outer_face(nbr) and not is_outer_face_nbr(v, nbr): + chords[v] += 1 + ready_to_pick.discard(v) + + # Initialize canonical_ordering + canonical_ordering = [None] * len(embedding.nodes()) + canonical_ordering[0] = (v1, []) + canonical_ordering[1] = (v2, []) + ready_to_pick.discard(v1) + ready_to_pick.discard(v2) + + for k in range(len(embedding.nodes()) - 1, 1, -1): + # 1. Pick v from ready_to_pick + v = ready_to_pick.pop() + marked_nodes.add(v) + + # v has exactly two neighbors on the outer face (wp and wq) + wp = None + wq = None + # Iterate over neighbors of v to find wp and wq + nbr_iterator = iter(embedding.neighbors_cw_order(v)) + while True: + nbr = next(nbr_iterator) + if nbr in marked_nodes: + # Only consider nodes that are not yet removed + continue + if is_on_outer_face(nbr): + # nbr is either wp or wq + if nbr == v1: + wp = v1 + elif nbr == v2: + wq = v2 + else: + if outer_face_cw_nbr[nbr] == v: + # nbr is wp + wp = nbr + else: + # nbr is wq + wq = nbr + if wp is not None and wq is not None: + # We don't need to iterate any further + break + + # Obtain new nodes on outer face (neighbors of v from wp to wq) + wp_wq = [wp] + nbr = wp + while nbr != wq: + # Get next neighbor (clockwise on the outer face) + next_nbr = embedding[v][nbr]["ccw"] + wp_wq.append(next_nbr) + # Update outer face + outer_face_cw_nbr[nbr] = next_nbr + outer_face_ccw_nbr[next_nbr] = nbr + # Move to next neighbor of v + nbr = next_nbr + + if len(wp_wq) == 2: + # There was a chord between wp and wq, decrease number of chords + chords[wp] -= 1 + if chords[wp] == 0: + ready_to_pick.add(wp) + chords[wq] -= 1 + if chords[wq] == 0: + ready_to_pick.add(wq) + else: + # Update all chords involving w_(p+1) to w_(q-1) + new_face_nodes = set(wp_wq[1:-1]) + for w in new_face_nodes: + # If we do not find a chord for w later we can pick it next + ready_to_pick.add(w) + for nbr in embedding.neighbors_cw_order(w): + if is_on_outer_face(nbr) and not is_outer_face_nbr(w, nbr): + # There is a chord involving w + chords[w] += 1 + ready_to_pick.discard(w) + if nbr not in new_face_nodes: + # Also increase chord for the neighbor + # We only iterator over new_face_nodes + chords[nbr] += 1 + ready_to_pick.discard(nbr) + # Set the canonical ordering node and the list of contour neighbors + canonical_ordering[k] = (v, wp_wq) + + return canonical_ordering + + +def triangulate_face(embedding, v1, v2): + """Triangulates the face given by half edge (v, w) + + Parameters + ---------- + embedding : nx.PlanarEmbedding + v1 : node + The half-edge (v1, v2) belongs to the face that gets triangulated + v2 : node + """ + _, v3 = embedding.next_face_half_edge(v1, v2) + _, v4 = embedding.next_face_half_edge(v2, v3) + if v1 in (v2, v3): + # The component has less than 3 nodes + return + while v1 != v4: + # Add edge if not already present on other side + if embedding.has_edge(v1, v3): + # Cannot triangulate at this position + v1, v2, v3 = v2, v3, v4 + else: + # Add edge for triangulation + embedding.add_half_edge(v1, v3, ccw=v2) + embedding.add_half_edge(v3, v1, cw=v2) + v1, v2, v3 = v1, v3, v4 + # Get next node + _, v4 = embedding.next_face_half_edge(v2, v3) + + +def triangulate_embedding(embedding, fully_triangulate=True): + """Triangulates the embedding. + + Traverses faces of the embedding and adds edges to a copy of the + embedding to triangulate it. + The method also ensures that the resulting graph is 2-connected by adding + edges if the same vertex is contained twice on a path around a face. + + Parameters + ---------- + embedding : nx.PlanarEmbedding + The input graph must contain at least 3 nodes. + + fully_triangulate : bool + If set to False the face with the most nodes is chooses as outer face. + This outer face does not get triangulated. + + Returns + ------- + (embedding, outer_face) : (nx.PlanarEmbedding, list) tuple + The element `embedding` is a new embedding containing all edges from + the input embedding and the additional edges to triangulate the graph. + The element `outer_face` is a list of nodes that lie on the outer face. + If the graph is fully triangulated these are three arbitrary connected + nodes. + + """ + if len(embedding.nodes) <= 1: + return embedding, list(embedding.nodes) + embedding = nx.PlanarEmbedding(embedding) + + # Get a list with a node for each connected component + component_nodes = [next(iter(x)) for x in nx.connected_components(embedding)] + + # 1. Make graph a single component (add edge between components) + for i in range(len(component_nodes) - 1): + v1 = component_nodes[i] + v2 = component_nodes[i + 1] + embedding.connect_components(v1, v2) + + # 2. Calculate faces, ensure 2-connectedness and determine outer face + outer_face = [] # A face with the most number of nodes + face_list = [] + edges_visited = set() # Used to keep track of already visited faces + for v in embedding.nodes(): + for w in embedding.neighbors_cw_order(v): + new_face = make_bi_connected(embedding, v, w, edges_visited) + if new_face: + # Found a new face + face_list.append(new_face) + if len(new_face) > len(outer_face): + # The face is a candidate to be the outer face + outer_face = new_face + + # 3. Triangulate (internal) faces + for face in face_list: + if face is not outer_face or fully_triangulate: + # Triangulate this face + triangulate_face(embedding, face[0], face[1]) + + if fully_triangulate: + v1 = outer_face[0] + v2 = outer_face[1] + v3 = embedding[v2][v1]["ccw"] + outer_face = [v1, v2, v3] + + return embedding, outer_face + + +def make_bi_connected(embedding, starting_node, outgoing_node, edges_counted): + """Triangulate a face and make it 2-connected + + This method also adds all edges on the face to `edges_counted`. + + Parameters + ---------- + embedding: nx.PlanarEmbedding + The embedding that defines the faces + starting_node : node + A node on the face + outgoing_node : node + A node such that the half edge (starting_node, outgoing_node) belongs + to the face + edges_counted: set + Set of all half-edges that belong to a face that have been visited + + Returns + ------- + face_nodes: list + A list of all nodes at the border of this face + """ + + # Check if the face has already been calculated + if (starting_node, outgoing_node) in edges_counted: + # This face was already counted + return [] + edges_counted.add((starting_node, outgoing_node)) + + # Add all edges to edges_counted which have this face to their left + v1 = starting_node + v2 = outgoing_node + face_list = [starting_node] # List of nodes around the face + face_set = set(face_list) # Set for faster queries + _, v3 = embedding.next_face_half_edge(v1, v2) + + # Move the nodes v1, v2, v3 around the face: + while v2 != starting_node or v3 != outgoing_node: + if v1 == v2: + raise nx.NetworkXException("Invalid half-edge") + # cycle is not completed yet + if v2 in face_set: + # v2 encountered twice: Add edge to ensure 2-connectedness + embedding.add_half_edge(v1, v3, ccw=v2) + embedding.add_half_edge(v3, v1, cw=v2) + edges_counted.add((v2, v3)) + edges_counted.add((v3, v1)) + v2 = v1 + else: + face_set.add(v2) + face_list.append(v2) + + # set next edge + v1 = v2 + v2, v3 = embedding.next_face_half_edge(v2, v3) + + # remember that this edge has been counted + edges_counted.add((v1, v2)) + + return face_list |