[maemo-developers] [maemo-developers] Hildon UI Development News

[From: Lucas Rocha]

Hi all,

I've posted this in my blog but I want to make sure everyone interested
read this. 

As you probably (don't) know, we, from the Hildon UI Framework team,
have been working hard in the new code for the next releases of Maemo
(The "don't" is because even though the development happens in a public
repository, sometimes we're not very good in communicating about what
we're doing). Now, the heavy development work of maemo-af-desktop[1] is
taking place in a separate branch called hildon-desktop[2] (the new name
of maemo-af-desktop).

Our main goals for the next releases is flexibility, scalability,
maintainability and developer-friendliness. The code of
"maemo-af-desktop" received a lot of improvements for the N800 and Bora
release (As you with a N800 in hands have probably noticed!) but still
it has some serious problems. The layout of the UI is hardcoded (is was
done for a specific display with specific resolution) and the plugin
infrastructure is fragmented and (kind of) duplicated for each UI
component (Home, Statusbar and Tasknavigator). Also, the plugin API is
not very developer-friendly because it doesn't take full advantage of
the GNOME Platform[3] knowlegde that developers interested in Maemo
already have (this is my personal opinion). So, what are we doing to
target those issues? Let's see!

++ Separating the generic parts from the specific ones ++

We detached the "generic" parts of the UI into a library called
libhildondesktop[4] This lib has things like different kinds of panels,
a generic widget for Home, and interfaces for different kinds of desktop
items that will reside in the panels and Home. The window management
code has been put into a library called libhildonwm[5] which is intented
for very specific cases where the developer need some control over the
windows behavior. For example, libhildonwm is used by application
switcher to show the list of active windows in the Task Navigator panel.

So, what does this mean? This means that out future UI will be just a
specific application of libhildondesktop and libhildonwm for a specific
device. In hildon-desktop branch, we're about to finish the UI (based on
libhildondesktop and libhildowm, of course) that reproduces exactly what
you have in N800. Also, it's good to remark that this aproach makes it
easier/faster to prototype different UIs and increase the hacking
possibilities for the UI! Yay!

++ New plugin system ++

We now have a common plugin system for all UI components. The new plugin
system is based on plugin loaders. Each type of plugin loader is
reponsible for loading desktop items from different "sources". For
example, we have a plugin loader that loads (Task Navigator, Statubar
and Home) plugins written with the current plugin API (To keep backwards
compatibility). However, we'll have a new GTypeModule-based[6] API for
developing desktop plugins so obviously we have a plugin loader for this
kind of plugin too. This aproach give us flexibility enough to even have
plugins written in different programming languages. We already have a
Python plugin loader and the bindings for libhildondesktop (libhildonwm
bindings yet to come).

Plugin loaders can be dynamically loaded without needing to rebuild
hildon-desktop. We did this way because in the case of plugin loaders
for plugins written in programming languages other than C, we cannot
ensure that the runtime requirements will be available in the device by
default. For example, the Python loader resides in a different module
together with the libhildondesktop bindings so that in the future, if
you want to add support for Python desktop plugins, you just need to
install the bindings, the Python loader and Python debian packages.
That's it! The hildon-desktop Python support code[7] is available, of
course. We've written some really dummy example plugins[8] with the new
API and Python API just to give a taste of what is coming.

++ Contribute! ++

Any suggestions, comments, ideas, construtive critics and (specially!)
patches are welcome. Get the code from Maemo repository and play, brake,
adapt, change, etc. If you want to use the latest pre-built packages,
you can always use Sardine[9].

++ Important note! ++

This is unstable-under-heavy-development code. You should not rely on
this code for anything. At this moment, hildon-desktop should only be
used by courageous developers who want to contribute/use the very latest
UI framework stuff.

Cheers!

--lucasr

[1] 
https://stage.maemo.org/svn/maemo/projects/haf/trunk/maemo-af-desktop

[2] 
https://stage.maemo.org/svn/maemo/projects/haf/branches/maemo-af-desktop/hildon-desktop/

[3]
http://developer.gnome.org/doc/guides/platform-overview/platform-overview.html

[4]
https://stage.maemo.org/svn/maemo/projects/haf/branches/maemo-af-desktop/hildon-desktop/libhildondesktop

[5]
https://stage.maemo.org/svn/maemo/projects/haf/branches/maemo-af-desktop/hildon-desktop/libhildonwm

[6]
http://developer.gnome.org/doc/API/2.0/gobject/GTypeModule.html

[7]
https://stage.maemo.org/svn/maemo/projects/haf/branches/maemo-af-desktop/python-hildondesktop/

[8]
https://stage.maemo.org/svn/maemo/projects/haf/branches/maemo-af-desktop/example-plugins/

[9]
http://sardine.garage.maemo.org/