(IBus) IME integration

Hi,

As I tried to use touchscreen input in a tablet computer installed GNOME, I filed an issue to IBus that they probably need to implement protocols for touchscreen input keyboard:

https://github.com/ibus/ibus/issues/2114

I would like to see the following implementations:

• Ability to switch to IME-specified keyboard
  • One IME can have multiple layouts, for example Japanese can have Romaji layout, full keyboard Kana layout, and flicking numpad Kana layout (which is common on the phones).
  • Depending on the protocols, the text on the keyboard and the scancode can be different, or we can consider decoupling the concept of physical keyboards and feed the IME the input we want.
• Change keyboard according to IME-specified mode (Katakana/Hiragana for example)
• Display one-line candidates (because consonant- or stroke-based inputs can have multiple choices, and most IMEs are about choosing the correct words with dictionary or machine learning) above the keyboard area, and is expandable if needed.
• [Optional] Handwriting input (which I don't see popular open source implementations...)

I see the keyboard protocol proposal, but I am wondering how would that display IME-provided candidates according to the protocol.

Or, alternatively we can let IME OSK taking over squeekboard, making us able to switch betweek OSKs