Develop an simple input method

<languages > This is a step-by-step instruction for writing a Fcitx 5 input method. The same instruction can be used for developing other types of addons, just input method engine is the most complex ones.

Understand the file structure for a Fcitx shared library addon

Fcitx 5 provides a extensible framework for adding new addon types, but shared library support is built in and is the base of all other addon types. So we will only cover shared library addon in this document.

[fcitx install prefix]
|
|- share/fcitx5
|  |
|  |- addons/[addon name].conf
|  |- inputmethod/[input method name 1].conf
|  |  ...
|  |- inputmethod/[input method name n].conf
|
|- lib/fcitx5
   |
   |- [library name].so

Above is the file structure for an input method addon. For other types of addons, files under inputmethod/ is not needed. The file name of [addon name].conf matters and will be used to uniquely reference this specific addon. Fcitx also follows XDG directory standard, so the files under XDG_DATA_DIR/fcitx5 will also be checked. Similarly, file name of configuration file under inputmethod/ also matters and will be the unique name of a certain input method.

Example of [addon name].conf

[Addon]
Name[ca]=Pinyin
Name[da]=Pinyin
Name[de]=Pinyin
Name[he]=פיניין:
Name[ko]=병음
Name[ru]=Пиньинь
Name[zh_CN]=拼音
Name=Pinyin
Category=InputMethod
Version=5.0.8
Library=pinyin
Type=SharedLibrary
OnDemand=True
Configurable=True

[Addon/Dependencies]
0=punctuation

[Addon/OptionalDependencies]
0=fullwidth
1=quickphrase
2=cloudpinyin
3=notifications
4=spell
5=pinyinhelper
6=chttrans
7=imeapi

Example of [input method name].conf

[InputMethod]
Name[ca]=Pinyin
Name[da]=Pinyin
Name[de]=Pinyin
Name[he]=פיניין:
Name[ko]=병음
Name[ru]=Пиньинь
Name[zh_CN]=拼音
Name=Pinyin
Icon=fcitx-pinyin
Label=拼
LangCode=zh_CN
Addon=pinyin
Configurable=True

The file is in a ini-like format, with certain fcitx specific extensions and rules. It also supports XDG Desktop file style I18N for translation.

Use CMake build system

It is your own freedom to pick whatever build system you would d like to use, as long as you produce the correct files. Fcitx 5 provides lots of support with CMake, so using CMake would be the most convenient way to build a Fcitx project. In this document, we will only cover using CMake as build system.

A quick start: Quwei

Quwei input method is an input method that basically allow you type the digit of GB2312 and produce the Chinese Character that matches this code. It used to be supported by Fcitx 4, but not included by Fcitx 5 anymore. Though it is hard to use, it can serve as a good example on how to implement a simple input method for Fcitx 5.