[maemo-developers] Optimal battery life considerations in apps

[From: Henrik Hedberg]

Andrew Flegg wrote 09.07.2009 00:29:

 >     2) Stop updating the screen when your app isn't in the
 >        foreground.
 >
 > (1) is trivial to implement. (2) is trickier (there's
 > hildon_program_is_topmost() and hildon_window_is_topmost(), but
 > polling to discover when you're topmost again is hideous).

    You are raising a very important question. Actually, 
hildon_program_is_topmost() and hildon_window_is_topmost() are not 
enough, because a desktop widget (HDHomePluginItem) is not a Hildon 
Window, but inherited from GtkWindow. Thus, there is also need for 
hildon_gtk_window_is_topmost(GtkWindow*);

 >     2) In Fremantle, there's a compositing window manager. On a
 >        desktop this means you never receive an "expose" event
 >        since your window is always exposed on an off-screen
 >        buffer. What is the best way of implementing (2) in
 >        Maemo 5?

    There is a standard X event for that: XVisibilityEvent. The X server 
(and a window manager) can keep window contents cached (backing store) 
and decide not to send exposure events, but my interpretation is that if 
it is not sending visibility events it is broken (and it is currently as 
I showed in my earlier post).

    There is no need to reinvent the wheel. We could just hope that 
Nokia fixes the issue - in a standard way. The main advantage of using 
Linux also in mobile devices is that developers can use their earlier 
knowledge and code from desktop world (UI is a different thing, 
naturally). Maemo is going to dangerous direction if more and more 
things are done differently. I really do not hope that.

    BR,

    Henrik

-- 
    Henrik Hedberg  -  http://www.henrikhedberg.net/