DBus server for keyboard layouts

[Lubos Lunak]

On Friday 05 of October 2007, Sergey Udaltsov wrote:
> >  How exactly should that work when switching between applications?
>
> There can be 3 scenarios:
> 1. If you switch to the "classic" app (which does not support
> "context-driven" layouts), there are no changes:

 I think "classic app" is somewhat misleading here ... how about "the vast 
majority of apps" ? It rather changes what's written below.

>   - if DE/WM implements "layout per window" mode, each application
> "remembers" its layout.
>   - otherwise the layout is preserved on switching

 Which I expect would be so annoying that keyboard switcher would have to 
implement the layout per window feature.

> 2. If the app supports "context-driven" layouts, the layout would be
> changed depending on where you caret would be put to, immediately
> after switch.

 Given the asynchronous nature of the desktop, this part of your proposal is 
prone to race conditions. Imagine:
- two apps running, app A has support, app B is "classic", as you say
- keyboard switcher (let me call it kxkb for short) has layout per window 
switching
- B is active
1) user switches to A
2) kxkb saves B's active layout and switches layout to A's remembered layout
3) A asks kxkb to switch to layout matching the active part of the document
4) user switches back to B
5) kxkb saves A's layout and switches the layout to the one it saved for B

 As far as I can see, there are several race conditions:
- 2 vs 3, i.e. A asks kxkb for the change before kxkb notices changed active 
window, thus changing saved layout for B
- 3 vs 4+5, i.e. A takes a while to activate and asks kxkb to change layout 
after kxkb has already switched back for B, again setting wrong layout for B

 Maybe there are more, but these two are enough and they're both realistic. I 
think you cannot just have apps say "switch (the global layout) to layout 
XYZ". A possible solution I see is e.g. instead having setLayoutForWindow( 
window_id, layout ).

> > I don't
> > think people would like it if their global keyboard layout changed
> > "randomly" just because they happen to have a multi-language document
> > open in a text editor.
>
> Of course, this all should be optional behavior - like per-window
> layout settings in GNOME these days. But I think many people would
> actually like that idea - it would save some keypresses in situations
> where necessary layout is obvious.

-- 
Lubos Lunak
KDE developer
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