Enigma2 Plugins Design Information

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enigma2 plugins
===============

Enigma2 plugins are always written in python. If you really have to call
C/C++ functions from your code, you can supply a python module with it,
implementing your functions.

Let's write a plugin. We call it "OurSmallTest", and it should be a test
plugin. Thus we choose "DemoPlugins" as a category. The category is just to
organize plugins in the filesystem.

The simplest plugin looks like the following:

Plugins/DemoPlugins/OurSmallTest/plugin.py:

"from Plugins.Plugin import PluginDescriptor

def main(session, **kwargs):
print "Hello world!"

def Plugins(**kwargs):
return PluginDescriptor(
name="Our Small Test",
description="plugin to test some capabilities",
where = PluginDescriptor.WHERE_PLUGINMENU,
fnc=main)"

Basically, you're writing a "python module", which is called
Plugins.DemoPlugins.OurSmallTest.plugin. This corresponds to the
Plugins/DemoPlugins/OurSmallTest/plugin.py file.

This module must define a single function called "Plugins". The functions is
called for every Plugin, and should return (a list of)
PluginDescriptor-Objects. A PluginDescriptor is a simple object, holding the
Plugin's name, description, picture etc., and an entry point.

In the first line, we import that class. It's contained in a module called
Plugins.Plugin.

At the end, we define the "Plugins"-Functions. As said, it returns a
constructed PluginDescriptor-object (in fact it can return either one or a
list of descriptors, here it returns exactly one). We use keyword arguments
to supply the Plugin's information, like the name, the descripttion etc.

We also supply an entry point, called "fnc". It's set to the "main"
function, which is defined before. Our entry point is called with a number
of arguments, depending on where the plugin was launched from. In this case,
it's a "session" argument. You need the session argument if you want to do
graphical output. A session basically connects to "user". There is always
one sessions which corresponds to the main screen output, but there can also
be other sessions, which yet have to be implemented. (A possible example is a
networked remote session.) If you don't need that argument, just ignore it.

A plugin can decide where it wants to be displayed. A possible example is
the plugin menu out of the main menu. In the "where" argument to the
descriptor, you can supply one (or a list of) "WHERE_"-identifiers. We use
WHERE_PLUGINMENU. There will be other ones, for example for the blue button,
or specific other menus.

Now, if you copy this plugin in-place, it should be listed in the plugin
browser in the main menu. You can press "ok" on the plugin, and the "main"
function, which was specified as the plugin's entry point, is executed.

If you want to open a graphical screen, you might want the entry point to
look like:

def main(session):
session.open(MyScreen)

with MyScreen being a GUI screen.

About the **kwargs:
This somewhat special syntax (in fact the name 'kwargs' is arbitrary, but
stands for "keyword arguments") collects all addition keyword arguments
(i.e. named parameters). For example. the Plugins()-call gets a "path"
parameter, and probably more in the future. You must ignore all additional
keywords which you don't need!

skins
=====

Generally, you can include the skin in your Screens by having a static (or
non-static, if you really want) variable "skin", for example:

class OurSmallTestScreen(Screen):
skin = "<skin>...</skin>"
def __init__(self, session):
Screen.__init__(self, session)
...

However, users can override the skin from their skin.xml. Note that the
Screen's name (unless you override this, which is possible) is used for
determining which skin is used. Thus, if you're choosing generic skin names
like "TheScreen", it's likely to cause namespace clashes.

Thus, please use skin names (i.e. Screen-names, unless you're overriding the
skin name) which are unique enough to not clash. In doubt, prepend the
pluginname like in our example.

autostarting plugins
====================

you can configure your plugin to automatically start on enigma startup, and
end on shutdown.

you just have to use "WHERE_AUTOSTART". your entry point must (fnc) look
like:

def autostartEntry(raeson, **kwargs):
if reason == 0: # startup
print "startup"
elif reason == 1:
print "shutdown"

autostart plugins should always be configurable, and should default to an
OFF state!

Configuration
=============

Speaking about configuration, plugins must live in

config.plugins.<PluginName>

and nowhere else!

You are, however, free to change settings which are already existing. If you

Dependencies
============

Plugin dependencies (one plugin requires another plugin) should generally be
avoided, but are possible. If there are dependencies, the .ipk file must
list them.

If possible, make them optional. If your plugin doesn't support one feature
because another plugin isn't installed, that's fine (but should be noted in
the docs).

Categories
==========

Currently defined categories are:

* DemoPlugins: Plugins fore pure demonstration purposes
* Extensions: User interface extensions
* SystemPlugins: Hardware specific plugins

Plugin Names
============

A plugin name:
- should always start with a Uppercase letter,
- must not start with the word "Dream",
- nor end with "Plugin",
- should be unique even across Categories,
- must be understandable by english speaking people,
(unless it's a geographically restricted plugin)
- is not user changeable (that is, the user is not allowed to rename the
plugin directory)