LIBPACK(3)

NAME
libpack - support for connected components

SYNOPSIS

#include <graphviz/pack.h>
typedef enum { l_clust, l_node, l_graph} pack_mode;
typedef struct {
    unsigned int margin;
    boolean      doSplines;
    pack_mode    mode;
    boolean*     fixed;
} pack_info;
point*     putGraphs (int, Agraph_t**, Agraph_t*, pack_info*);
int        shiftGraphs (int, Agraph_t**, point*, Agraph_t*, int);
int        packGraphs (int, Agraph_t**, Agraph_t*, pack_info*);
int        packSubgraphs (int, Agraph_t**, Agraph_t*, pack_info*);
pack_mode  getPackMode (Agraph_t*, pack_mode dflt);
int        getPack (Agraph_t*, int, int);
int        isConnected (Agraph_t*);
Agraph_t** ccomps (Agraph_t*, int*, char*);
Agraph_t** pccomps (Agraph_t*, int*, char*, boolean*);
int        nodeInduce (Agraph_t*);

DESCRIPTION
libpack supports the use of connected components in the context of laying out graphs using other graphviz libraries. One set of functions can be used to take a single graph and break it apart into connected components. A complementary set of functions takes a collection of graphs (not necessarily components of a single graph) which have been laid out separately, and packs them together moderately tightly. The packing is done using the polyomino algorithm of K. Freivalds et al. As this library is meant to be used with libcommon, it relies on the Agraphinfo_t, Agnodeinfo_t and Agedgeinfo_t used in that library. The specific dependencies are given below in the function descriptions.

  Creating components

  Agraph_t** ccomps (Agraph_t* g, int* cnt, char* pfx)
The function ccomps takes a graph g and returns an array of pointers to subgraphs of g which are its connected components. cnt is set to the number of components. If pfx is non-NULL, it is used as a prefix for the names of the subgraphs; otherwise, the string ``_cc_'' is used. Note that the subgraphs only contain the relevant nodes, not any corresponding edges. Depending on the use, this allows the caller to retrieve edge information from the root graph.

The array returned is obtained from malloc and must be freed by the caller. The function relies on the mark field in Agnodeinfo_t.

  Agraph_t** pccomps (Agraph_t* g, int* cnt, char* pfx, boolean* pinned)
This is identical to ccomps except that is puts all pinned nodes in the first component returned. In addition, if pinned is non-NULL, it is set to true if pinned nodes are found and false otherwise.

  int nodeInduce (Agraph_t* g)
This function takes a subgraph g and finds all edges in its root graph both of whose endpoints are in g. It returns the number of such edges and, if this edge is not already in the subgraph, it is added.

  int isConnected (Agraph_t* g)
This function returns non-zero if the graph g is connected.

  Packing components

  point* putGraphs (int ng, Agraph_t** gs, Agraph_t* root, pack_info ip)
putGraphs packs together a collection of laid out graphs into a single layout which avoids any overlap. It takes as input ng graphs gs. For each graph, it is assumed that all the nodes have been positioned using pos, and that the xsize and ysize fields have been set. The packing is done using the polyomino-based algorithm of Freivalds et al. This allows for a fairly tight packing, in which a convex part of one graph might be inserted into the concave part of another.

If root is non-NULL, it is taken as the root graph of the subgraphs gs and is used to find the edges. Otherwise, putGraphs uses the edges found in each graph gs[i].

The granularity of the polyominoes used depends on the value of ip->mode. If this is l_node, a polyomino is constructed to approximate the nodes and edges. If this is l_clust, the polyomino treats top-level clusters as single rectangles, unioned with the polyominoes for the remaining nodes and edges. If the value is l_graph, the polyomino for a graph is a single rectangle corresponding to the bounding box of the graph.

If ip->doSplines is true, the function uses the spline information in the spl field of an edge, if it exists. Otherwise, the algorithm represents an edge as a straight line segment connecting node centers.

The parameter ip->margin specifies a boundary of margin points to be allowed around each node. It must be non-negative.

The parameter ip->fixed, if non-null, should point to an array of ng booleans. If ip->fixed[i] is true, graph gs[i] should be left at its original position. The packing will first first place all of the fixed graphs, then fill in the with the remaining graphs.

The function returns an array of points which can be used as the origin of the bounding box of each graph. If the graphs are translated to these positions, none of the graph components will overlap. The array returned is obtained from malloc and must be freed by the caller. If any problem occurs, putGraphs returns NULL. As a side-effect, at its start, putGraphs sets the bb of each graph to reflect its initial layout. Note that putGraphs does not do any translation or change the input graphs in any other way than setting the bb.

This function uses the bb field in Agraphinfo_t, the pos, xsize and ysize fields in nodehinfo_t and the spl field in Aedgeinfo_t.

  int shiftGraphs (int ng, Agraph_t** gs, point* ps, Agraph_t* root, int doSplines)
The function shiftGraphs takes ng graphs gs and a similar number of points ps and translates each graph so that the lower left corner of the bounding box of graph gs[i] is at point ps[i]. To do this, it assumes the bb field in Agraphinfo_t accurately reflects the current graph layout. The graph is repositioned by translating the pos field of each node appropriately.

If doSplines is non-zero, the function also translates the coord field of each node and the splines coordinates of each edge, if they have been calculated. In addition, edge labels are repositioned. If root is non-NULL, it is taken as the root graph of the graphs in gs and is used to find the edges. Otherwise, the function uses the edges found in each graph gs[i].

It returns 0 on success. Note also that the bounding boxes of all graphs are left unmodified.

This function uses the bb field in Agraphinfo_t, the pos and coord fields in nodehinfo_t and the spl field in Aedgeinfo_t.

  int packGraphs (int ng, Agraph_t** gs, Agraph_t* root, pack_info* ip)
This function takes ng subgraphs gs of a root graph root and calls putGraphs with the given arguments to generate a packing of the subgraphs. If successful, it then invokes shiftGraphs to apply the new positions. It returns 0 on success.

  int packSubgraphs (int ng, Agraph_t** gs, Agraph_t* root, pack_info* ip)
This function simply calls packGraphs with the given arguments, and then recomputes the bounding box of the root graph.

  Utility functions
The library provides several functions which can be used to tailor the packing based on graph attributes.

  pack_mode getPackMode (Agraph_t* g, pack_mode dflt)
This function returns a pack_mode associated with g. If the graph attribute "packmode" is "cluster", it returns l_clust; for "graph", it returns l_graph; for "node", it returns l_node; otherwise, it returns dflt.

  int getPack (Agraph_t* g, int not_def, int dflt)
This function queries the graph attribute "pack". If this is defined as a non-negative integer, the integer is returned; if it is defined as "true", the value dflt is returned; otherwise, the value not_def is returned.

SEE ALSO
dot(1), neato(1), twopi(1), libgraph(3)
K. Freivalds et al., "Disconnected Graph Layout and the Polyomino Packing Approach", GD0'01, LNCS 2265, pp. 378-391.

BUGS
The packing does not take into account edge or graph labels.

AUTHORS
Emden Gansner (erg@research.att.com).