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Layout Engines
 1: dot
 2: neato
 3: fdp
 4: sfdp
 5: circo
 6: twopi
 7: nop
 8: nop2
 9: osage
 10: patchwork
 11: Writing Layout Plugins
1  dot
dot
is the default tool to use if edges have directionality.
The layout algorithm aims edges in the same direction (top to bottom, or left to right) and then attempts to avoid edge crossings and reduce edge length.
 PDF Manual
 User Guide (caveat: not current with latest features of Graphviz)
 Browse code
Attributes for dot features
 clusterrank – Mode used for handling clusters. Valid on: Graphs.
 compound – If true, allow edges between clusters. Valid on: Graphs.
 constraint – If false, the edge is not used in ranking the nodes. Valid on: Edges.
 group – Name for a group of nodes, for bundling edges avoiding crossings.. Valid on: Nodes.
 lhead – Logical head of an edge. Valid on: Edges.
 ltail – Logical tail of an edge. Valid on: Edges.
 mclimit – Scale factor for mincross (mc) edge crossing minimiser parameters. Valid on: Graphs.
 minlen – Minimum edge length (rank difference between head and tail). Valid on: Edges.
 newrank – Whether to use a single global ranking, ignoring clusters. Valid on: Graphs.
 nslimit – Sets number of iterations in network simplex applications. Valid on: Graphs.
 nslimit1 – Sets number of iterations in network simplex applications. Valid on: Graphs.
 ordering – Constrains the lefttoright ordering of node edges.. Valid on: Graphs, Nodes.
 rank – Rank constraints on the nodes in a subgraph. Valid on: Subgraphs.
 rankdir – Sets direction of graph layout. Valid on: Graphs.
 ranksep – Specifies separation between ranks. Valid on: Graphs.
 remincross – If there are multiple clusters, whether to run edge crossing minimization a second time.. Valid on: Graphs.

samehead
–
Edges with the same head and the same
samehead
value are aimed at the same point on the head. Valid on: Edges. 
sametail
–
Edges with the same tail and the same
sametail
value are aimed at the same point on the tail.. Valid on: Edges.  searchsize – During network simplex, the maximum number of edges with negative cut values to search when looking for an edge with minimum cut value.. Valid on: Graphs.
 showboxes – Print guide boxes for debugging. Valid on: Edges, Nodes, Graphs.
 TBbalance – Which rank to move floating (loose) nodes to. Valid on: Graphs.
2  neato
neato
is a reasonable default tool to use for undirected graphs that aren't
too large (about 100 nodes), when you don't know anything else about the graph.
neato
attempts to minimize a global energy function, which is equivalent to
statistical multidimensional scaling.
The solution is achieved using stress majorization^{1}, though the older
KamadaKawai algorithm^{2}, using steepest descent, is also available,
by switching mode
.
 PDF Manual
 User Guide (caveat: not current with latest features of Graphviz)
 Browse code
 Gallery
Attributes for neato features
 Damping – Factor damping force motions.. Valid on: Graphs.
 defaultdist – The distance between nodes in separate connected components. Valid on: Graphs.
 dim – Set the number of dimensions used for the layout. Valid on: Graphs.
 dimen – Set the number of dimensions used for rendering. Valid on: Graphs.
 diredgeconstraints – Whether to constrain most edges to point downwards. Valid on: Graphs.
 epsilon – Terminating condition. Valid on: Graphs.
 esep – Margin used around polygons for purposes of spline edge routing. Valid on: Graphs.
 inputscale – Scales the input positions to convert between length units. Valid on: Graphs.
 len – Preferred edge length, in inches. Valid on: Edges.
 levelsgap – strictness of neato level constraints. Valid on: Graphs.
 maxiter – Sets the number of iterations used. Valid on: Graphs.
 mode – Technique for optimizing the layout. Valid on: Graphs.
 model – Specifies how the distance matrix is computed for the input graph. Valid on: Graphs.
 normalize – normalizes coordinates of final layout. Valid on: Graphs.
 notranslate – Whether to avoid translating layout to the origin point. Valid on: Graphs.
 overlap – Determines if and how node overlaps should be removed. Valid on: Graphs.
 overlap_scaling – Scale layout by factor, to reduce node overlap.. Valid on: Graphs.
 pin – Keeps the node at the node's given input position. Valid on: Nodes.
 pos – Position of node, or spline control points. Valid on: Edges, Nodes.
 scale – Scales layout by the given factor after the initial layout. Valid on: Graphs.
 sep – Margin to leave around nodes when removing node overlap. Valid on: Graphs.
 start – Parameter used to determine the initial layout of nodes. Valid on: Graphs.
 voro_margin – Tuning margin of Voronoi technique. Valid on: Graphs.

Gansner, E.R., Koren, Y., North, S. (2005). Graph Drawing by Stress Majorization. In: Pach, J. (eds) Graph Drawing. GD 2004. Lecture Notes in Computer Science, vol 3383. Springer, Berlin, Heidelberg. ↩︎

Tomihisa Kamada, Satoru Kawai, An algorithm for drawing general undirected graphs, Information Processing Letters, Volume 31, Issue 1, 1989, Pages 715. ↩︎
3  fdp
"spring model" layouts similar to those of neato, but does this by reducing forces rather than working with energy.
fdp
implements the FruchtermanReingold heuristic^{1} including a multigrid solver
that handles larger graphs and clustered undirected graphs.
Attributes for fdp features
 dim – Set the number of dimensions used for the layout. Valid on: Graphs.
 dimen – Set the number of dimensions used for rendering. Valid on: Graphs.
 inputscale – Scales the input positions to convert between length units. Valid on: Graphs.
 K – Spring constant used in virtual physical model. Valid on: Graphs, Clusters.
 len – Preferred edge length, in inches. Valid on: Edges.
 maxiter – Sets the number of iterations used. Valid on: Graphs.
 normalize – normalizes coordinates of final layout. Valid on: Graphs.
 overlap_scaling – Scale layout by factor, to reduce node overlap.. Valid on: Graphs.
 pin – Keeps the node at the node's given input position. Valid on: Nodes.
 pos – Position of node, or spline control points. Valid on: Edges, Nodes.
 sep – Margin to leave around nodes when removing node overlap. Valid on: Graphs.
 start – Parameter used to determine the initial layout of nodes. Valid on: Graphs.
4  sfdp
sfdp
is a fast, multilevel, forcedirected algorithm that efficiently layouts large graphs, outlined in "Efficient and High Quality ForceDircted Graph Drawing"^{1}.
Multiscale version of the fdp
layout, for the layout of large graphs.
Attributes for sfdp features
 beautify – Whether to draw leaf nodes uniformly in a circle around the root node in sfdp.. Valid on: Graphs.
 dim – Set the number of dimensions used for the layout. Valid on: Graphs.
 dimen – Set the number of dimensions used for rendering. Valid on: Graphs.
 K – Spring constant used in virtual physical model. Valid on: Graphs, Clusters.

label_scheme
–
Whether to treat a node whose name has the form
edgelabel*
as a special node representing an edge label.. Valid on: Graphs.  levels – Number of levels allowed in the multilevel scheme. Valid on: Graphs.
 normalize – normalizes coordinates of final layout. Valid on: Graphs.
 overlap_scaling – Scale layout by factor, to reduce node overlap.. Valid on: Graphs.
 overlap_shrink – Whether the overlap removal algorithm should perform a compression pass to reduce the size of the layout. Valid on: Graphs.
 quadtree – Quadtree scheme to use. Valid on: Graphs.
 repulsiveforce – The power of the repulsive force used in an extended FruchtermanReingold. Valid on: Graphs.
 rotation – Rotates the final layout counterclockwise by the specified number of degrees. Valid on: Graphs.
 smoothing – Specifies a postprocessing step used to smooth out an uneven distribution of nodes.. Valid on: Graphs.
 start – Parameter used to determine the initial layout of nodes. Valid on: Graphs.
 voro_margin – Tuning margin of Voronoi technique. Valid on: Graphs.
5  circo
After Six and Tollis 1999^{1}^{2}, Kauffman and Wiese 2002^{3}.
This is suitable for certain diagrams of multiple cyclic structures, such as certain telecommunications networks.
Attributes for circo features
 mindist – Specifies the minimum separation between all nodes. Valid on: Graphs.
 root – Specifies nodes to be used as the center of the layout. Valid on: Graphs, Nodes.
 normalize – normalizes coordinates of final layout. Valid on: Graphs.
 oneblock – Whether to draw circo graphs around one circle.. Valid on: Graphs.
 overlap_scaling – Scale layout by factor, to reduce node overlap.. Valid on: Graphs.
 voro_margin – Tuning margin of Voronoi technique. Valid on: Graphs.

Six J.M., Tollis I.G. (1999) A Framework for Circular Drawings of Networks. In: Kratochvíyl J. (eds) Graph Drawing. GD 1999. Lecture Notes in Computer Science, vol 1731. Springer, Berlin, Heidelberg. ↩︎

Six J.M., Tollis I.G. (1999) Circular Drawings of Biconnected Graphs. In: Goodrich M.T., McGeoch C.C. (eds) Algorithm Engineering and Experimentation. ALENEX 1999. Lecture Notes in Computer Science, vol 1619. Springer, Berlin, Heidelberg. ↩︎

Michael Kaufmann, Roland Wiese (2002) Embedding Vertices at Points: Few Bends suffice for Planar Graphs. In: Journal of Graph Algorithms and Applications. vol. 6, no. 1, pp. 115–129 ↩︎
6  twopi
After Graham Wills 1997^{1}.
Nodes are placed on concentric circles depending their distance from a given root node.
You can set the root node, or let twopi
do it.
Attributes for twopi features
 normalize – normalizes coordinates of final layout. Valid on: Graphs.
 overlap_scaling – Scale layout by factor, to reduce node overlap.. Valid on: Graphs.
 ranksep – Specifies separation between ranks. Valid on: Graphs.
 root – Specifies nodes to be used as the center of the layout. Valid on: Graphs, Nodes.
 voro_margin – Tuning margin of Voronoi technique. Valid on: Graphs.
 weight – Weight of edge. Valid on: Edges.
7  nop
nop1
.Prints input graphs in prettyprinted (canonical) form.
Example, indenting the input:
$ echo 'digraph { a > b; c>d; }'  nop
digraph {
a > b;
c > d;
}
nop
also deduplicates node specifications:
$ echo 'digraph { a; a [label="A"]; a [color=blue]; }'  nop
digraph {
a [color=blue,
label=A];
}
nop p
produces no output, just checks the input for valid DOT language.
For example, this valid graph produces no output:
$ echo 'digraph {}'  nop p
But this syntax error (missing }
) exits with status code 1
and prints error
message:
$ echo 'digraph {'  nop p
Error: <stdin>: syntax error in line 2
8  nop2
Invoke equivalently as:
neato n2
dot Knop2
Assumes positions already specified in the input with the pos
attribute.
This performs an optional adjustment to remove nodenode overlap, computes edge layouts, and emites the graphs.
9  osage
As input, osage
takes any graph in the dot format.
osage
draws the graph recursively. At each level, there will be a collection of
nodes and a collection of cluster subgraphs. The internals of each cluster
subgraph are laid out, then the cluster subgraphs and nodes at the current
level are positioned relative to each other, treating each cluster subgraph as
a node.
At each level, the nodes and cluster subgraphs are viewed as rectangles to be
packed together. At present, edges are ignored during packing. Packing is done
using the standard packing functions. In particular, the graph attributes
pack
and packmode
control the layout. Each graph and cluster can
specify its own values for these attributes. Remember also that a cluster
inherits its attribute values from its parent graph.
After all nodes and clusters, edges are routed based on the value of the
splines
attribute.
Example:
Source of the example:
graph {
layout=osage
subgraph cluster_0 {
label="composite cluster";
subgraph cluster_1 {
label="the first cluster";
C
L
U
S
T
E
R
}
subgraph cluster_2 {
label="the second\ncluster";
a
b
c
d
}
1
2
}
3
4
5
}
10  patchwork
Each cluster is given an area based on the areas specified by the clusters and
nodes it contains. The areas of nodes and empty clusters can be specified by
the area
attribute. The default area
is 1.
The root graph is laid out as a square. Then, recursively, the region of a cluster or graph is partitioned among its toplevel nodes and clusters, with each given a roughly square subregion with its specified area.
Example: Australian Coins, area proportional to value
Source of the example:
graph {
layout=patchwork
node [style=filled]
"$2" [area=200 fillcolor=gold]
"$1" [area=100 fillcolor=gold]
"50c" [area= 50 fillcolor=silver]
"20c" [area= 20 fillcolor=silver]
"10c" [area= 10 fillcolor=silver]
"5c" [area= 5 fillcolor=silver]
}
Attributes for patchwork features
 area – Indicates the preferred area for a node or empty cluster. Valid on: Nodes, Clusters.
11  Writing Layout Plugins
To create a new layout plugin called xxx
, you first need
to provide two functions: xxx_layout
and xxx_cleanup
. The
semantics of these are described below.
Layout
void xxx_layout(Agraph_t * g)
Initialize the graph.

If the algorithm will use the common edge routing code, it should call
setEdgeType (g, ...);
. 
For each node, call
common_init_node
andgv_nodesize
. 
If the algorithm will use
spline_edges()
to route the edges, the node coordinates need to be stored inND_pos
, so this should be allocated here. This, and the two calls mentioned above, are all handled by a call toneato_init_node()
. 
For each edge, call
common_init_edge
. 
The algorithm should allocate whatever other data structures it needs. This can involve fields in the
A*info_t
fields. In addition, each of these fields contains avoid* alg;
subfield that the algorithm can use the store additional data. Once we move to cgraph, this will all be replaced with algorithm specific records. 
Layout the graph. When finished, each node should have its coordinates stored in points in
ND_coord_i(n)
, each edge should have its layout described inED_spl(e)
. (N.B. As of version 2.21,ND_coord_i
has been replaced byND_coord
, which are now floating point coordinates.)
To add edges, there are 3 functions available:
spline_edges1 (Agraph_t*, int edgeType)
Assumes the node coordinates are stored inND_coord_i
, and thatGD_bb
is set. For each edge, this function constructs the appropriate data and stores it inED_spl
.spline_edges0 (Agraph_t*)
Assumes the node coordinates are stored inND_pos
, and thatGD_bb
is set. This function uses the ratio attribute if set, copies the values inND_pos
toND_coord_i
(converting from inches to points); and calls spline_edges1 using the edge type specified bysetEdgeType()
.spline_edges (Agraph_t*)
Assumes the node coordinates are stored inND_pos
. This function calculates the bounding box of g and stores it inGD_bb
, then callsspline_edges0()
.
If the algorithm only works with connected components, the code can
use the pack library to get components, lay them out individually, and
pack them together based on user specifications. A typical schema is
given below. One can look at the code for twopi
, circo
, neato
or fdp
for more detailed examples.
Agraph_t **ccs;
Agraph_t *sg;
Agnode_t *c = NULL;
int ncc;
int i;
ccs = ccomps(g, &ncc, 0);
if (ncc == 1) {
/* layout nodes of g */
adjustNodes(g); /* if you need to remove overlaps */
spline_edges(g); /* generic edge routing code */
} else {
pack_info pinfo;
pack_mode pmode = getPackMode(g, l_node);
for (i = 0; i < ncc; i++) {
sg = ccs[i];
/* layout sg */
adjustNodes(sg); /* if you need to remove overlaps */
}
spline_edges(g); /* generic edge routing */
/* initialize packing info, e.g. */
pinfo.margin = getPack(g, CL_OFFSET, CL_OFFSET);
pinfo.doSplines = 1;
pinfo.mode = pmode;
pinfo.fixed = 0;
packSubgraphs(ncc, ccs, g, &pinfo);
}
for (i = 0; i < ncc; i++) {
agdelete(g, ccs[i]);
}
free(ccs);
Be careful in laying of subgraphs if you rely on attributes that have only been set in the root graph. With connected components, edges can be added with each component, before packing (as above) or after the components have been packed (see circo).
It is good to check for trivial cases where the graph has 0 or 1 nodes, or no edges.
At the end of xxx_layout
, call
dotneato_postprocess(g);
The following template will work in most cases, ignoring the problems of handling disconnected graphs and removing node overlaps:
static void
xxx_init_node(node_t * n)
{
neato_init_node(n);
/* add algorithmspecific data, if desired */
}
static void
xxx_init_edge(edge_t * e)
{
common_init_edge(e);
/* add algorithmspecific data, if desired */
}
static void
xxx_init_node_edge(graph_t * g)
{
node_t *n;
edge_t *e;
for (n = agfstnode(g); n; n = agnxtnode(g, n)) {
xxx_init_node(n);
}
for (n = agfstnode(g); n; n = agnxtnode(g, n)) {
for (e = agfstout(g, n); e; e = agnxtout(g, e)){
xxx_init_edge(e);
}
}
}
void
xxx_layout (Agraph_t* g)
{
xxx_init_node_edge(g);
/* Set ND_pos(n) for each node n */
spline_edges(g);
dotneato_postprocess(g);
}
Cleanup
void xxx_cleanup(Agraph_t * g)
Free up any resources allocated in the layout.
Finish with calls to gv_cleanup_node
and gv_cleanup_edge
for
each node and edge. This cleans up splines labels, ND_pos
, shapes
and 0's out the A*info_t
, so these have to occur last, but could be
part of explicit xxx_cleanup_node
and xxx_cleanup_edge
, if desired.
At the end, you should do:
if (g != g>root) memset(&(g>u), 0, sizeof(Agraphinfo_t));
This is necessary for the graph to be laid out again, as the layout code assumes this structure is clean.
libgvc
does a final cleanup to the root graph, freeing any drawing,
freeing its label, and zeroing out Agraphinfo_t
of the root graph.
The following template will work in most cases:
static void xxx_cleanup_graph(Agraph_t * g)
{
/* Free any algorithmspecific data attached to the graph */
if (g != g>root) memset(&(g>u), 0, sizeof(Agraphinfo_t));
}
static void xxx_cleanup_edge (Agedge_t* e)
{
/* Free any algorithmspecific data attached to the edge */
gv_cleanup_edge(e);
}
static void xxx_cleanup_node (Agnode_t* n)
{
/* Free any algorithmspecific data attached to the node */
gv_cleanup_node(e);
}
void xxx_cleanup(Agraph_t * g)
{
Agnode_t *n;
Agedge_t *e;
for (n = agfstnode(g); n; n = agnxtnode(g, n)) {
for (e = agfstout(g, n); e; e = agnxtout(g, e)) {
xxx_cleanup_edge(e);
}
xxx_cleanup_node(n);
}
xxx_cleanup_graph(g);
}
Most layouts use auxiliary routines similar to neato
, so
the entry points can be added in plugin/neato_layout
.
Add to gvlayout_neato_layout.c
:
gvlayout_engine_t xxxgen_engine = {
xxx_layout,
xxx_cleanup,
};
and the line
{LAYOUT_XXX, "xxx", 0, &xxxgen_engine, &neatogen_features},
to gvlayout_neato_types
and a new emum LAYOUT_XXX
to layout_type
in that file.
The above allows the new layout to piggyback on top of the neato
plugin, but requires rebuilding the plugin. In general, a user
can (and probably should) build a layout plugin totally separately.
To do this, after writing xxx_layout
and xxx_cleanup
, it is necessary to:

Add the types and data structures:
typedef enum { LAYOUT_XXX } layout_type; static gvlayout_features_t xxxgen_features = { 0 }; gvlayout_engine_t xxxgen_engine = { xxx_layout, xxx_cleanup, }; static gvplugin_installed_t gvlayout_xxx_types[] = { {LAYOUT_XXX, "xxx", 0, &xxxgen_engine, &xxxgen_features}, {0, NULL, 0, NULL, NULL} }; static gvplugin_api_t apis[] = { {API_layout, &gvlayout_xxx_types}, {(api_t)0, 0}, }; gvplugin_library_t gvplugin_xxx_layout_LTX_library = { "xxx_layout", apis };

Combine all of this into a dynamic library whose name contains the string
gvplugin_
and install the library in the same directory as the other Graphviz plugins. For example, on Linux systems, the dot layout plugin is in the librarylibgvplugin_dot_layout.so
. 
Run
dot c
to regenerate the config file.
NOTES:
 Additional layouts can be added as extra lines in
gvlayout_xxx_types
.  Obviously, most of the names and strings can be arbitrary. One
constraint is that external identifier for the
gvplugin_library_t
type must end in_LTX_library
. In addition, the stringxxx
in each entry ofgvlayout_xxx_types
is the name used to identify the layout algorithm, so needs to be distinct from any other layout name.  The features of a layout algorithm are currently limited to a
flag of bits, and the only flag supported is
LAYOUT_USES_RANKDIR
, which enables the layout to therankdir
attribute.
Changes need to be made to any applications that statically know about layout algorithms.
Automake Configuration
If you want to integrate your code into the Graphviz software and use its build system, follow the instructions below. You can certainly build and install your plugin using your own build software.
 Put your software in
lib/xxxgen
, and added the hooks describe above intogvlayout_neato_layout.c
 In
lib/xxxgen
, provide aMakefile.am
(based on a simple example likelib/fdpgen/Makefile.am
)  In
lib/Makefile.am
, addxxxgen
toSUBDIRS
 In
configure.ac
, addlib/xxxgen/Makefile
toAC_CONFIG_FILES
.  In
lib/plugin/neato_layout/Makefile.am
, insert$(top_builddir)/lib/xxxgen/libxxxgen_C.la
inlibgvplugin_neato_layout_C_la_LIBADD
.  Remember to run
autogen.sh
because on its ownconfigure
can guess wrong.
This also assumes you have a good version of the various automake tools on your system.