[maemo-developers] window focus and screen lock events

[From: Hämäläinen Kimmo]

On Sat, 2010-10-30 at 10:50 +0200, ext lukash wrote:
> Hi all,
> 
> there was a discussion some time ago about suspending (pausing) an
> application when it loses focus or the screen is locked. I am now
> trying to do just that. I gathered that I need to handle a GTK signal
> for window focus and a DBus message for the screen lock. But searching
> further I haven't found much information...
> 
> I must be looking in the wrong place for the GTK signal documentation.
> The DBus message I could probably figure out, but I thought I'd ask
> first for pointers to any existing examples or a good documentation
> someone might have? (I have zero knowledge of both GTK and DBus...)

Here is a command line utility that prints the currently focused window
based on X protocol messages:
http://meego.gitorious.org/meegotouch/meegotouch-compositor/trees/master/tests/focus-tracker

Notice that just stopping applications that don't have focus would break
things like playing music in the background. Some applications are also
multi-process, such as the browser (engine + UI process).  Also, in the
case of e.g. XEmbed, the focused window is not the application window
but a special, separate focus window.

Finally, if you have an application with a dialog, the dialog can have
the input focus (temporarily) but the main application window not.  Now
if you stop the application, you'll have a jammed application in the
foreground as result.

It is better to only consider windows that are stacked behind the
hildon-desktop's TYPE_DESKTOP window.  XQueryTree() gives you the window
stack.  There is also _NET_WM_CLIENT_LIST_STACKING root window property,
which could be easier to use.

-Kimmo

> 
> Thanks in advance
> lukash
> 
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