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Graphviz plugin for Trac 1.4 and later

Project description


The graphviz wiki processor is a plugin for Trac that allows the the dynamic generation of diagrams by the various graphviz programs. The text of a wiki page can contain the source text for graphviz and the web browser will show the resulting image.

Simple Example

A simple example would be:

digraph G {Hello->World->Graphviz->Rules}

There are also several additional examples available in the examples directory. They can be loaded into a Trac installation by the examples/ program. Once loaded, navigate to the wiki/GraphvizExamples page to access the examples.

Usage Details

The graphviz wiki processor supports all 5 graphviz drawing programs: dot, neato, twopi, circo and fdp. By default, the dot program is used to generate the images.

The different programs can be invoked using one of these:


The supported image formats are: png (default), gif, jpg, svg and svgz. The format can be specified using a “/format” modifier, in the hashbang, as shown below:


Platform Specific Requirements


On FreeBSD systems, installing the x11-fonts/urwfonts package will provide the fonts needed for graphviz to correctly generate images.

Optional requirements

To allow antialiasing of PNG images produced by graphviz, you need to have rsvg, the librsvg rasterizer, installed on your system. It can be downloaded from <>. Note that rsvg is not available for Windows.

Installation via Source

The installation of the graphviz plugin from source is done by creating a Python egg distribution file and copying the .egg file to the Trac plugins directory. Detailed information on Python eggs can be found at: In addition, the Easy Install package is required to create Python eggs. See for more information on using and installing Easy Install.

Download the source code for the graphviz plugin from or checkout the source from the trac hacks subversion repository at:

Change to the graphvizplugin/0.11 directory and run:

python bdist_egg

This will generate a python egg in the dist directory. Copy the egg file into the trac/plugins directory and follow the Configuration steps outlined below.

Installation via Egg



Once the graphviz plugin has been installed either via source or via a python egg, some changes to the conf/trac.ini file must be done before it can be used.

As for any plugin, if you did a global installation (as opposed to simply dropping the .egg in the plugins folder of your Trac environment), you first need to enable it:

graphviz.* = enabled

A new section called [graphviz] should be added to the trac.ini file with these fields:

cache_dir       - The directory that will be used to cache the
                  generated images. That directory must exist,
                  unless you keep the default 'gvcache' value,
                  in which case the plugin is allowed to create
                  the folder inside the Trac environment.

cmd_path        - Full path to the directory where the graphviz
                  programs are located. If not specified, the
                  default is /usr/bin on Linux, c:\Program
                  Files\ATT\Graphviz\bin on Windows and
                  /usr/local/bin on FreeBSD 6.

out_format      - Graph output format. Valid formats are: png, jpg,
                  svg, svgz, gif. If not specified, the default is
                  png. This setting can be overrided on a per-graph

processor       - Graphviz default processor. Valid processors
                  are: dot, neato, twopi, fdp, circo. If not
                  specified, the default is dot. This setting can
                  be overrided on a per-graph basis.

                  GraphvizMacro will verify that the default
                  processor is installed and will not work if it
                  is missing. All other processors are optional.
                  If any of the other processors are missing, a
                  warning message will be sent to the trac log and
                  GraphvizMacro will continue to work.

png_antialias   - If this entry exists in the configuration file,
                  then PNG outputs will be antialiased.

rsvg_path       - Full path to the rsvg program (including the filename).
                  The default is `<cmd_path>/rsvg`.

default_*       - These settings define the default graph, node and
                  edge attributes. They must be written as:
                        default_TYPE_ATTRIBUTE = VALUE
                  where TYPE      is one of graph, node, edge
                        ATTRIBUTE is a valid graphviz attribute
                        VALUE     is the attribute value.
                    eg: default_edge_fontname = "Andale Mono"
                        default_graph_fontsize = 10

cache_manager   - If this entry exists in the configuration file,
                  then the cache management logic will be invoked
                  and the cache_max_size, cache_min_size,
                  cache_max_count and cache_min_count must be

cache_max_size  - The maximum size in bytes that the cache should
                  consume. This is the high watermark for disk space

cache_min_size  - When cleaning out the cache, remove files until
                  this size in bytes is used by the cache. This is
                  the low watermark for disk space used.

cache_max_count - The maximum number of files that the cache should
                  contain. This is the high watermark for the
                  directory entry count.

The cache_dir directory must exist and the trac server must have read and write access.

The cache manager is an attempt at keeping the cache directory under control. This is experimental code that may cause more problems than it fixes. The cache manager will be invoked only if a new graphviz image is to be produced. If the image can be loaded from the cache, then the cache manager shouldn’t need to run. This should minimize the I/O performance impact on the trac server. When the cache manager determines that it should clean up the cache, it will delete files based on the file access time. The files that were least accessed will be deleted first.

Configuration Example

Here is a sample graphviz section:

cache_dir = /tmp/trac/htdocs/graphviz
png_antialias = true
default_graph_fontname = "Andale Mono"
default_graph_fontsize = 10

Here is a sample graphviz section that activates the cache manager:

cache_dir = /tmp/trac/htdocs/graphviz
png_antialias = true
default_graph_fontname = "Andale Mono"
default_graph_fontsize = 10
cache_manager = yes
cache_max_size = 10000000
cache_min_size = 5000000
cache_max_count = 2000
cache_min_count = 1500

The cache manager is turned on since there is an entry in the graphviz section called cache_manager. The value doesn’t matter. To turn off the cache manager, simply comment out the cache_manager entry.

When the size of all the files in the cache directory exceeds 10,000,000 bytes or the number of files in the cache directory exceeds 2,000, then files are deleted until the size is less than 5,000,000 bytes and the number of files is less than 1,500.

Here’s the same example but for Windows systems:

[graphviz] cache_dir = C:\projects\plugins\env\trac\htdocs\graphviz
cache_manager = yes
cache_max_size = 10000000
cache_min_size = 5000000
cache_max_count = 2000
cache_min_count = 1500

Notice that the png_antialias, rsvg_path, default_graph_fontname and default_graph_fontsize are not defined. This is because rsvg is not available on Windows and these options are not used.


I’d like to extend my thanks to following people:

  • Kilian Cavalotti for

    • the code to allow the output format to be specified system wide and per diagram.

    • work on the code to expand Trac wiki links within Graphviz diagrams.

  • Alec Thomas for creating Trac Hacks ( and providing hosting for the Graphviz module.

  • Emmanuel Blot for the swift kick in the butt to get the 0.9 - 0.10 releated bug fixes resolved ;-)

$Id: README.rst 17774 2020-05-28 16:25:13Z rjollos $

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