2 * Everything that needs the Boost Graph Library and C++ templates etc.
3 * (and what a crazy set of stuff that all is)
10 #include <boost/config.hpp>
11 #include <boost/iterator/iterator_facade.hpp>
12 #include <boost/graph/graph_traits.hpp>
13 #include <boost/graph/graph_concepts.hpp>
14 #include <boost/graph/dijkstra_shortest_paths.hpp>
15 #include <boost/graph/properties.hpp>
16 #include <boost/iterator/counting_iterator.hpp>
17 #include <boost/iterator/iterator_categories.hpp>
25 * edge descriptor f = 00 | e | y | x
28 * e is 0..5. The edge is edge e out of vertex (x,y).
30 * BGL expects an undirected graph's edges to have two descriptors
31 * each, one in each direction (otherwise e would be just 0..2).
35 * We use BGL's implementation of Dijkstra's single source shortest
36 * paths. We really want all pairs shortest paths, so Johnson All
37 * Pairs Shortest Paths would seem sensible. But actually Johnson's
38 * algorithm is just a wrapper around Dijkstra's; the extra
39 * functionality is just to deal with -ve edge weights, which we don't
40 * have. So we can use Dijkstra directly and save some cpu (and some
41 * code: we don't have to supply all of the machinery needed for
42 * Johnson's invocation of Bellman-Ford). The overall time cost is
43 * O(VE log V); I think the space used is O(E).
46 #define VMASK (YMASK|XMASK)
47 #define ESHIFT (YBITS+XBITS)
49 class Graph { }; // this is a dummy as our graph has no actual representation
51 using namespace boost;
54 * We iterate over edges in the following order:
61 * #4/ #5\ and finally #6 is V6
64 * This ordering permits the order-4 nodes at the strip's edge
65 * to have a contiguous edge iterator values. The iterator
66 * starts at #0 which is edge 2 (see mgraph.h), or #2 (edge 3).
68 static const int oei_edge_delta[V6]=
69 /* 0 1 2 3 4 5 initial e
70 * #3 #1 #0 #2 #4 #5 initial ix
71 * #4 #2 #1 #3 #5 #6 next ix
74 4<<ESHIFT, 2<<ESHIFT, -1<<ESHIFT,
75 -3<<ESHIFT, 1<<ESHIFT, (V6-5)<<ESHIFT
78 class OutEdgeIterator :
79 public iterator_facade<
87 //printf("incrementing f=%03x..",f);
88 f += oei_edge_delta[f>>ESHIFT];
91 bool equal(OutEdgeIterator const& other) const { return f == other.f; }
92 int const& dereference() const { return f; }
94 OutEdgeIterator(int _f) : f(_f) { }
95 OutEdgeIterator(int v, int e) : f(e<<ESHIFT | v) {
96 //printf("constructed v=%x e=%x f=%03x\n",v,e,f);
99 static int voe_min(int _v) { return (_v & YMASK) ? 2 : 3; }
100 static int voe_max(int _v) { return (~_v & YMASK) ? V6 : 4; }
101 static int voe_degree(int _v) { return (_v & YMASK | ~_v & YMASK) ? 4 : V6; }
104 typedef counting_iterator<int> VertexIterator;
107 // We make Graph a model of various BGL Graph concepts.
108 // This mainly means that graph_traits<Graph> has lots of stuff.
110 // First, some definitions used later:
112 struct layout_graph_traversal_category :
113 public virtual incidence_graph_tag,
114 public virtual vertex_list_graph_tag,
115 public virtual edge_list_graph_tag { };
117 struct graph_traits<Graph> {
119 typedef int vertex_descriptor; /* vertex number, -1 => none */
120 typedef int edge_descriptor; /* see above */
121 typedef undirected_tag directed_category;
122 typedef disallow_parallel_edge_tag edge_parallel_category;
123 typedef layout_graph_traversal_category traversal_category;
125 // Concept IncidenceGraph:
126 typedef OutEdgeIterator out_edge_iterator;
127 typedef unsigned degree_size_type;
129 // Concept VertexListGraph:
130 typedef VertexIterator vertex_iterator;
131 typedef unsigned vertices_size_type;
135 inline int null_vertex() { return -1; }
137 // Concept IncidenceGraph:
138 inline int source(int f, const Graph&) { return f&VMASK; }
139 inline int target(int f, const Graph&) { return EDGE_END2(f&VMASK, f>>ESHIFT); }
140 inline std::pair<OutEdgeIterator,OutEdgeIterator>
141 out_edges(int v, const Graph&) {
142 return std::make_pair(OutEdgeIterator(v, OutEdgeIterator::voe_min(v)),
143 OutEdgeIterator(v, OutEdgeIterator::voe_max(v)));
145 inline unsigned out_degree(int v, const Graph&) {
146 return OutEdgeIterator::voe_degree(v);
149 // Concept VertexListGraph:
150 inline std::pair<VertexIterator,VertexIterator> vertices(const Graph&) {
151 return std::make_pair(VertexIterator(0), VertexIterator(N));
153 inline unsigned num_vertices(const Graph&) { return N; }
156 static void single_source_shortest_paths(int v1,
157 const double edge_weights[/*f*/],
158 double vertex_distances[/*v*/]) {
161 dijkstra_shortest_paths(g, v1,
162 weight_map(edge_weights).
163 vertex_index_map(identity_property_map()).
164 distance_map(vertex_distances));
167 double graph_layout_cost(const Vertices v, const double vertex_areas[N]) {
168 /* For each (vi,vj) computes shortest path s_ij = |vi..vj|
169 * along edges, and actual distance d_ij = |vi-vj|.
171 * We will also use the `vertex areas': for each vertex vi the
172 * vertex area a_vi is the mean area of the incident triangles.
173 * This is computed elsewhere.
175 * Energy contribution is proportional to
178 * a a . d . [ (s/d) - 1 ]
181 * (In practice we compute d^2+epsilon and use it for the
182 * divisions, to avoid division by zero.)
184 static const double d2_epsilon= 1e-6;
186 double edge_weights[N*V6], vertex_distances[N], total_cost=0;
192 edge_weights[f]= NAN)
193 edge_weights[f]= hypotD(v[v1], v[v2]);
196 double a1= vertex_areas[v1];
197 single_source_shortest_paths(v1, edge_weights, vertex_distances);
199 double a2= vertex_areas[v2];
200 double d2= hypotD2plus(v[v1],v[v2], d2_epsilon);
201 double sd= vertex_distances[v2] / d2;
203 total_cost += a1*a2 * (sd2 - 1) / (d2*d2);