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<h2>How to write a Scribus Plugin</h2>
<h3>Preface</h3>
<p>This article shows you how to write plugins for Scribus. Plugins are
libraries that are loaded into the main application at run-time. Plugins can
extend and to an extent modify the behavior of the application without having
to edit and recompile the core application. They are useful for adding extra tools,
extra import and export functions, and for various more advanced uses.</p>
<p>This document assumes some basic knowledge of C++. You're assumed to know
what a header file is, how include files work, know about classes an
inheritance, and have some general familiarity with the language. Some
familiarity with Qt - mainly QString and QObject - will also help. Issues like
virtual and pure virtual functions, "extern C" declarations, the details of
memory management, etc are glossed over and avoided in this document. You don't
have to know about them, but it'll help you follow what's going on better if
you do.</p>
<p>We're not going to try to explain the details of how the Scribus plugin
system works here. This is just about how to write a plugin. The documentation
in the <code>scplugin.h</code> and <code>pluginmanager.h</code> help explain
how the system works.</p>
<p>For any reasonable plugin idea, you will receive encouragement and assistance from the Scribus Team.
As rule, we do not do a lot of planning or development discussion by e-mail, but by <a href="irc.html">IRC</a>. Probably 99% of
the planning and project discussions take place there. You will find #scribus usually lively during parts of each day. The team is mostly resident in Europe, so Central European Time evenings is when it is busiest. </p>
<h3>Where do I find Scribus Plugins?</h3>
<p>Scribus ships with a number of standard plug-ins. These will be installed
along with the Scribus program and its other files. On UNIX, plug-ins will be
installed in the same prefix as the main app. In Mac OS X they're included in
the .app bundle. If you want to know what these plug-ins do, the easiest way to
find out is to to fire up Scribus and go into <code>Edit->Preferences</code>
and click on the "plugins" icon. From there you will see a list of what
plug-ins are installed, what type of plug-in they are, and where the files
are.</p>
<p>In addition to the plug-ins shipped as standard with Scribus, it is possible
to build and install plug-ins you obtain from elsewhere, or to write and add
your own.</p>
<h3>Before you start coding</h3>
<p>Let's suppose you've got a great idea to improve Scribus and you cannot wait
to start writing some excellent C++ code. <b>Hold on for just a few minutes</b>
and read this section; you might save yourself some time and trouble.</p>
<h4>Important</h4>
<p>Maybe you are at the edge of "reinventing the wheel" - that is, writing
something you don't have to because someone else has already done it. You
should probably join the mailing-list and post about your idea, or join the
<code>#scribus</code> channel on <code>irc.freenode.net</code>. Your topic will
be discussed and you will probably get some help and ideas from the developers
and from other users. As Scribus is freely licensed, you're welcome to work
on your own, but at least an introductory chat on IRC, or a mail to the
mailing list may save hours of work and head banging. We want to make
writing plug-ins as painless as possible for those who're interested.
<h4>Compatability</h4>
<p>Scribus does not have a fixed C++ API for plugins to use. Releases are not
binary compatible, and unstable versions frequently break source compatibility.
Source compatibility is not currently guaranteed even across stable releases
if changes are required to fix a problem. We hope to improve this so we can
provide a stable C++ API for external code in the future. For now, if possible
you should try to bundle the core of your plugin's functionality into a
separate module that knows as little about the innards of Scribus as
possible.</p>
<p>This document covers implementing a plugin for Scribus 1.3.x. It is
dramatically different to what was required for the 1.2.x series. Future
changes should be smaller.</p>
<h3>Quick Start</h3>
<p>It's not too hard to jump in and start writing a plugin. The documentation
below describes the implementation of a plugin in some detail, with references
to places where you can find out more if you need it. A "plugin template" is
provided for your use, so if you like you can get started by making a copy of
that and getting hacking. Some basic instructions are included in the file, and
if you get confused you can refer back to this document.</p>
<p>We'll build the plugin as a part of Scribus. That's the easiest way to get
started, though you'll probably want to start distributing it separately later
on (see later). To start work on an Action plugin:</p>
<p>We use <a href="http://cmake.org">CMake</a>, as support for autotools has been
deprecated and moving forward it will be the only one used in 1.3.5+</p>
<ul>
<li>Copy <code>scribus/plugins/myplugin</code>
to <code>scribus/plugins/pluginname</code>
(where "pluginname" is what you want to call your plugin).
pluginname must be a valid C identifier - I suggest
sticking to nothing but lower case characters.</li>
<li>Edit <code>scribus/plugins/CmakeLists.txt</code> and add
"pluginname" to it by adding the subdirectory to the others. This tells Scribus's build
system to compile your plugin.</li>
<li>rename all the files in <code>scribus/plugins/pluginname/</code>
from <code>myplugin</code> to <code>pluginname</code>, eg
<code>myplugin.h</code> to <code>pluginname.h</code>.
</li>
<li>rename <code>myplugin</code> wherever it appears in the files to
<code>pluginname</code>, e.g. <code>myplugin_getPluginAPIVersion()</code>
to <code>pluginname_getPluginAPIVersion()</code>. Do the same for
<code>MyPlugin</code> and <code>MYPLUGIN</code>. On UNIX, you can use this
command:<br/>
<code>sed -i -e "s/myplugin/pluginname/g" -e "s/MyPlugin/PluginName/g" -e "s/MYPLUGIN/PLUGINNAME/g" myplugin*</code><br/>
(all on one line, run from <code>scribus/plugins/pluginname/</code>).
</li>
</ul>
<p>You're now ready to start work on your plug-in. First, you need to fill
out some information about your plug-in in <code>pluginname.cpp</code>:</p>
<ul>
<li>In <code>PluginName::languageChange()</code>:
<ul>
<li>Change <code>m_actionInfo.text</code> to the text of the menu item
you want to trigger your plugin.</li>
<li>Change <code>m_actionInfo.menu</code> to the name of the menu you
want the menu item to go in. See <b><i>FIXME where????
FIXME</i></b> for a list of menu names.</li>
<li>If you want your plugin to have a keyboard shortcut, uncomment
<code>m_actionInfo.keySequence</code> and set it to your preferred
shortcut. The example there should show you how that works.</li>
</ul>
</li>
<li>Change the name in <code>PluginName::fullTrName()</code>
to the name of your plugin as you want it to appear in the Help->About Plugins dialog
box and in the Plugin Manager pane in the preferences.</li>
<li>If you want your plugin to have information such as author info and a
description when the user looks at it in Help->About Plugins, fill out
as much as you want of the about info by assigning members of
<code>about</code>. You can see what information can be provided by looking
at the definition of <code>AboutData</code> in
<code>scplugin.h</code>.</li>
</ul>
<p>You've finished setting up the plugin, and can now start programming. Your
code should go in <code>pluginnameimpl.cpp</code> and
<code>pluginnameimpl.h</code>. The existing code should display a message
dialog box.</p>
<p>To compile the plugin, you can simply re-run <code>cmake with your usual options. </code>,
and <code>make</code> in the top-level Scribus directory. You may need to remove CmakeCache.txt,
but this is becoming a rarer necessity in newer versions of CMake.
When the compile completes, run <code>make install</code> and fire up Scribus.
Your plugin should now appear in the plugin manager (in the preferences), and
should have a menu item. If you press the menu item, a dialog box should appear.</p>
<h3>Building plugins outside the Scribus tree</h3>
<h4>Quick and dirty using QMake</h4>
<p><strong>Warning</strong></p>
<li>Beware - a qmake project easy to use but isn't necessarily the most standard
way to distribute software on the Linux platform. Scribus runs natively on Linux/Unix, MacOSX, OS/2 and
Windows. This process is an example
only for development. When you create your bug-free functional package then
make time to prepare a full featured distributon as described in the next section.</li>
<li>Let's compile it, but it isn't so easy as typing in <code>gcc
myplugin.cpp</code> ;). One easy way to build it - Qt qmake (because some
people really really hate autoconf and automake in their complexity. We've been know to
call it worse things more than once. ). Note: you
will need to create an empty <code>config.h</code> file before running these
steps</li>
<li>On Linux or OSX systems where Qt3 and Qt4 are installed parallel, you may need to
provide the full path: e.g. <code>/usr/lib/Qt4/qmake</code></li>
<blockquote><table width="100%" border="1" bgcolor="#eeeeee"><tr><td border="0">
<pre>
$qmake -project
</pre>
</td></tr></table></blockquote>
<p>Now the project file is created and we'll make just a few changes into it.</p>
<blockquote><table width="100%" border="1" bgcolor="#eeeeee"><tr><td border="0">
<pre>
######################################################################
# Automatically generated by qmake (1.06c) Sun Dec 14 13:32:11 2003
######################################################################
#change TEMPLATE = app. We aren't working on application just plugin
TEMPLATE = lib
INCLUDEPATH += .
#As working with Scribus, we need Scribus includes too.
INCLUDEPATH += /home/subzero/devel/Scribus/include/Scribus/
#And Scribus have to use freetype2.
#So we should link it too. Use paths returned from
##freetype-config --cflags and --libs
INCLUDEPATH += /usr/include/freetype2
LIBS += -lfreetype -lz
# Input
#create empty config.h file
HEADERS += myplugin.h config.h
SOURCES += myplugin.cpp
</pre>
</td></tr></table></blockquote>
<p>After these changes you're ready to compile</p>
<blockquote><table width="100%" border="1" bgcolor="#eeeeee"><tr><td border="0">
<pre>
$qmake
$make
</pre>
</td></tr></table></blockquote>
<p>Running Qmake creates the Makefile and by running make you compile your
plugin.</p>
<p>Then just copy *so* files into Scribus plugin directory and run Scribus.
You'll see "Do Nothing Plugin" in the Extras menu.</p>
<p>It is clear that you have to use some other way to distribute your
source code to others - some use autogenerated qmake pro files, other use
the autoconf/automake combination.</p>
<h4>Distribute it! (a.k.a. Compile it! 2nd edition)</h4>
<p>Qmake is user frendly and useful for rapid development, but traditionally there has been
one standard way to compile/distribute software for Linux, *BSD etc. - autoconf
and automake. Lets call these two programs by the automagic acronym in the
following text.</p>
<p>To use automagic successfully you'll need chalk drawn to the north
oriented pentagram on the floor (Carrefour, 2€), red-black daemonic
dress (Hugo Boss, 2000€) and a sacrificed penguin on the home altar
(one hour of fear in your local zoo). Err, only joking.. dont harm any
nice little penguins, you wont need to. We strongly prefer the simpler and
easier to use CMake build system.</p>
<p>Download the <code>donothingplugin-1.0.tar.gz</code> example from
http://docs.scribus.net, unpack it and browse it.</p>
<h3>Learning More</h3>
<p>To go on from here, you should probably read <code>scplugin.h</code> and ensure
you understand that. There is an explanation of the way the plugin system works
in more detail <a href="WHERE">here</a>. Above all else, though, you'll learn how
to get things done by reading the other plugins and the core Scribus code.</p>
<h4>Storing your plugin's preferences:</h4>
<p>Scribus provides a preferences api for plugin writers to store data between
Scribus launches. There are two types of storage formats available: key-value
pairs and tables.</p>
<p>First you will need to get the <code>PrefsContext</code> object for your
plugin. Then you can query <code>PrefsContext</code> to get the value for a
specific key or you can ask for a <code>PrefsTable</code> by it's name. Here is
a short example using key-value pairs.</p>
<pre>
#include <prefsfile.h>
#include <prefscontext.h>
extern PrefsFile* prefsFile;
PrefsContext *myPluginPrefs = prefsFile->getPluginContext("MyPlugin");
// default value -1 will be used if "i" doesn't already exist
int i = myPluginPrefs->getInt("i");
// default value "dog" will be used if "s" doesn't already exist
QString s = myPluginPrefs->get("s", "dog");
myPluginPrefs->set("i", 221);
myPluginPrefs->set("s", "cat");
</pre>
<h4>Scribus Object Model</h4>
<p>Scribus's source code is lightly documented. There is a significant
effort to correct this, but given the size of the codebase it's taking
quite some time. Please do try to follow what's going on based on the
header files and the code. If you're unable to sort it out, feel free to
drop in on IRC or ask on the mailing list, and someone may well be able to
help you. Try to be patient - we're not always on IRC or available, and it
can take time to answer a message if everybody's busy.</p>
<p>If you feel like improving the documentation or fixing the doxygen api
docs generation, the praise will be endless.</p>
<p>One important thing to understand is that the core Scribus application
can be accessed via the static global pointer <code>ScApp</code>, declared
in <code>scribus.h</code>. Confusingly, this is a QMainWindow subclass.
You can also get to the QApplication subclass used as <code>ScQApp</code>
from <code>scribusapp.h</code>.</p>
<p>Some major subsystems are singleton classes that are accessible via
ClassName::instance() . Examples include <code>PluginManager</code>,
<code>ScPaths</code>, and growing numbers of others. The advantage
of this is that you can interact with these classes without having to
delve into the guts of ScApp.</p>
<h3>Plugin related links</h3>
<a href="http://doc.trolltech.com/">Qt documentation from Trolltech</a><br />
<a href="http://doc.trolltech.com/3.3/qmake-manual.html">QMake documentation from Trolltech</a><br />
<!--<a href="http://www.murrayc.com/learning/linux/automake/automake.shtml">Automake/autoconf example</a>--><br />
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