[Feature Request] UserInterface string / CJK input method (IME) support

[ExMikuPro]

Feature Proposal: String / CJK Input Method Extension for UserInterface functions

Hi, first of all thank you for the amazing library — it's been a pleasure to work with on STM32 projects.

Current Limitation

The existing u8g2_UserInterfaceInputValue only supports numeric input (uint8, 0–255). There is currently no built-in way to input arbitrary strings or CJK (e.g. Chinese) characters through the user interface API.

Proposal

I'd like to propose adding a string input method extension, tentatively named u8g2_UserInterfaceInputString, that follows the same style as the existing UserInterface functions.

The rough idea:

• Pinyin → CJK input with a candidate selection bar
• ASCII / numeric fallback modes
• Dictionary stored either in internal Flash (compiled-in const array, ~40–80 KB, selectable tiers) or external SPI Flash (via a user-provided read callback, keeping the core hardware-agnostic)
• A small soft keyboard rendered using existing u8g2 draw primitives
• User-supplied font pointer for CJK candidate rendering (no hardcoded font dependency)

Questions Before I Start

Before writing any code I wanted to check:

1. Is this something you'd consider merging, or is it outside the intended scope of u8g2?
2. Do you have a preference on the dictionary backend (internal Flash only, or also external Flash via callback)?
3. Is there a Flash/RAM budget you'd like the feature to stay within?
4. Would you prefer a blocking API (consistent with existing UserInterface functions) or a non-blocking state-machine style?

Happy to start small — for example a first PR with only ASCII string input and no CJK, then build on top of that.

Thanks for your time!

[olikraus]

Those user interface functions had been written only as a little bit of a demo code.

A more advanced user interface has been added with the MUI sub lib for u8g2. Especially it contains kind of a text input: https://github.com/olikraus/u8g2/wiki/muiref#character-input

Basically the MUI char input function could be extended to CJK, but i don't know whether it makes sense to cycle through >1000 chars. So maybe a different input concept is required for CJK.

MUI in general is a none-blocking UI (unlike the u8g2 user interface function), so in general MUI should be preferred.

U8g2 itself should stay as a core graphics lib, high level functionality like more complex UI widget could be added to MUI.
If you provide field processing functions (MUIF) which fit to the naming convention of MUI, then I could imagine to accept merge requests here.

Another option is to check out existing arduino libraries: https://github.com/neu-rah/ArduinoMenu
Maybe those libs already support CJK out of the box.