Complex text input in Plasma

[Martin Gräßlin]

Am 2017-04-06 19:16, schrieb Eike Hein:
> Hi,
> 
> In the aftermath of D5301, Martin asked to compile a document on the
> requirements for complex text input in Plasma, especially with the
> opportunities provided by the Wayland transition. It makes sense to
> share this document with all of you, to

Thanks for the nice write down.

> * KWin is smart enough to do cool things like switch keyboard
>   layouts automatically per virtual desktop or even window

that's actually also a feature of the keyboard daemon we have on X11. 
Only on wayland KWin takes care of it.

> = The situation on Wayland =
> 
> Currently, only ibus works on Wayland. Input method popups are not
> positioned correctly, but otherwise things work. The situation is
> just as good or bad as on X11.

Sharing a bit more about state of Wayland:

There is the text-input protocol which KWin supports and uses for 
virtual keyboard. This means we already have the possibility to do 
things like text input, text prediction, cursor moving, styling hints 
(not yet implemented as virt keyboard doesn't support it), etc. etc. out 
of the box with Qt applications. We know whether the application 
supports it. We know the position of the text field and much more. For 
those interested: relevant code is in KWin/virtualkeyboard.cpp

Ideally we would build up on this. We must not (!) specify an input 
plugin for Qt apps as that would break the virtual keyboard. And even if 
others give up on convergence I still think it's important to support it 
and have it as a target.

So for input methods KWin would have to provide the UI interaction. Of 
course I do not want to rebuild such a stack but would prefer to be able 
to hook into an existing - I hope that's possible. Maybe a similar 
approach as to how virtual keyboard works: kwin just emulates to the 
qtvirtualkeyboard like if it were in application. So maybe KWin could 
load one of the plugins and interact with them as a proxy for the 
application and just forward the result through the text input 
interface.

What I could imagine is that we start with emoji support. Might sound 
weird but is a simplified use case to just "play" with it and 
experiment. We could setup a global shortcut (like the one in GNOME), 
pop up a UI with the emoji selection and go through the text input 
protocol to send the emoji into the application.

Unfortunately text input in Wayland is weird as there are two competing 
protocol versions and Qt has one of them. There is the zwp_text_input_v1 
which is part of Wayland-protocols and zwp_text_input_v2 which is part 
of Qt. It is not upstreamed, but uses upstream naming conventions. Which 
will result in a horrible mess once upstream introduces a 
zwp_text_input_v2. KWin supports both versions at the same time, but it 
makes everything more complex and we currently can only assume that it 
works correctly with Qt apps. The GTK version we support on Wayland 
neither supports v1 nor v2. For the newer GTK versions which we do not 
support yet I do not know. Also it leaves out Xwayland application but 
there a bridge to one of the existing X11 solutions is thinkable.

Cheers
Martin