DBus service for screenshots.

[Emmanuele Bassi]

Hi;

On 24 September 2015 at 23:25, Boudhayan Gupta <bgupta at kde.org> wrote:
> Hi,
>
> In December we'll be releasing a new screenshot app for KDE. We've
> implemented a generic DBus interface for this app, and I'm posting
> this to the dbus mailing list as others may be interested in this idea
> and may want to implement it in their own desktop environments.
>
> The service we've implemented is called org.freedesktop.Screenshot
> (we're using the freedesktop namespace because we truly want the
> service to be DE or platform agnostic).

Commendable spirit, but that's not how it works — we've been bitten by
this in the past already. Please, use org.kde.* for your DBus
interfaces, and *then* propose a org.freedesktop.* interface up for
discussion. Otherwise you'll have to start versioning your own methods
because any shared interface will likely not map to what you expose
right now.

Implementing multiple interfaces is easy; breaking them because you
proposed them for discussion *after* release is going to be painful
for everybody.

> The XML definition of the
> interface is available here:
> https://raw.githubusercontent.com/KDE/spectacle/master/dbus/org.freedesktop.Screenshot.xml
>
> You'll notice that we define 4 different types of screenshots that can
> be taken, and a StartAgent method. The StartAgent method should just
> start the application GUI, the other 4 methods should take the
> appropriate shot, save the image in a default location, and quit.

StartAgent would show the UI? Why? That can be done with a simple hot
key, or via DBus activation of a service, instead of asking a service
to spawn another service. For instance, if I want to show a dialog to
save the screenshot I just took, the gnome-screenshot tool is what I
will launch. There's another consideration that applies to Wayland:
applications like GIMP (or Krita) may ask the compositor to take a
screenshot; this means that the UI is already running, and it most
definitely is not something that should be spawned by the compositor
itself in reply to a DBus method call. If you want to keep the
StartAgent method then it's probably good to ensure in the
documentation that the method is not mandatory.

The API is also missing the ability to take a screenshot of an area.
For reference, this is the DBus interface that GNOME Shell provides:
https://git.gnome.org/browse/gnome-shell/tree/data/org.gnome.Shell.Screenshot.xml

GNOME Shell also has an equivalent screencast API, which may be
interesting to standardise alongside the screenshot one.

Ciao,
 Emmanuele.

-- 
https://www.bassi.io
[@] ebassi [@gmail.com]