Specifying thumbnailers as a service

Philip Van Hoof spam at pvanhoof.be
Fri Aug 29 02:25:03 PDT 2008

Hi there,

Not only filemanagers want to request the creation of a thumbnail. For
example desktop search engines like Strigi and Tracker want to schedule
the creation of thumbnails for certain of the contents that they find,
ahead of time (not sure about Strigi, as one of Tracker's developers
myself I'm sure about Tracker).

This is why we would like to have a desktop wide DBus API for requesting
the creation of a thumbnail. Not just a specification about how to store
the thumbnails and where you can find them [1], but also a method to
request thumbnails.

We want to reuse the infrastructure that is available.

We want to request the creation of a thumbnail for rather a lot of items
so this API would have to accept a an array of paths to thumbnail-able
items. When finished it would return an array of paths to the

For example (this is glib-dbus XML api)

<node name="/">
  <interface name="org.freedesktop.Thumbnailer">  
    <method name="Create">
      <annotation name="org.freedesktop.DBus.GLib.Async" value="true"/>
      <arg type="as" name="uris" direction="in" />
      <arg type="i" name="size_x" direction="in" />
      <arg type="i" name="size_y" direction="in" />
      <arg type="as" name="thumbnails" direction="out" />
    <method name="Move">
      <annotation name="org.freedesktop.DBus.GLib.Async" value="true"/>
      <arg type="as" name="from_uris" direction="in" />
      <arg type="as" name="to_uris" direction="in" />
    <method name="Delete">
      <annotation name="org.freedesktop.DBus.GLib.Async" value="true"/>
      <arg type="as" name="uris" direction="in" />

Nobody does something for no reason. Our own reason for wanting this is
to have a platform wide thumbnailer for the Maemo platform and we want
it aligned with upstream projects.

A thumbnail service on a mobile platform is not going to have the same
requirements as a thumbnail service on a KDE or a GNOME platform. It's
my opinion that although the requirements are going to be different, the
API for requesting the creation of a thumbnail isn't.

Therefore, and this is a strong opinion of me:

We make it more easy for our application developers if we cooperate on a
DBus standard at the level of freedesktop.org, instead of each having
our own client APIs for this.

We can help with the work on patches for Nautilus and Konqueror.

ps. Filemanagers could either become the providers of these DBus APIs,
this is probably the most easy change, or if the architecture is chosen
to offshore this functionality to a daemon they could be adapted to
consume the DBus API instead.

My proposal is *not* about having one great thumbnailer. If different
teams want to compete on a thumbnailer implementation, then they must
compete and that way drive innovation. This proposal is about the DBus
API only for it (to see if we can reach an agreement on that).


--- footnotes
[1] http://jens.triq.net/thumbnail-spec/index.html

Philip Van Hoof, freelance software developer
home: me at pvanhoof dot be 
gnome: pvanhoof at gnome dot org 

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