Add One Key Keyboard Layout Switcher mod

[Anixx]

This mod allows switching keyboard layouts with a single key press instead of a two-key combination. It includes settings for various keys and methods for layout switching.

Changelog

If this pull request updates an existing mod, describe the changes below:

• Changelog item 1...
• Changelog item 2...

Mod authorship

If this pull request introduces a new mod, please complete the section below.

This mod was created by:

• • The submitter, without AI assistance
• • The submitter, with AI assistance
• • Claude
• • ChatGPT
• • Gemini
• • Another AI (please specify):
• • Other (please specify):

Please select the options that best apply. Your selection does not affect the acceptance criteria, but it helps reviewers understand the context of the code and provide relevant feedback.

[Anixx]

I re-submit the request because in the previous one I messed up with files (changed the wrong one).

The automated review was addressed, but switching the method from sending keys to pure API does not work in all programs. So, I keep the sending the sey combination method.

[m417z]

Submission review

Note: This review was done by Claude, and then refined manually. Due to the amount of submissions, doing a fully manual review for each pull request is no longer feasible. Thank you for understanding.

Please address the following issues. The items in the collapsed sections are optional, so it's your call whether to address them.

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• The Sleep(100) runs on the hook-owning thread. Because the WH_KEYBOARD_LL callback and the WM_SWITCH_LAYOUT handler share the same thread's message loop, while SendLayoutSwitch sleeps the low-level hook isn't being serviced, so keystrokes during that ~100 ms window may be delayed or pass through (the system applies LowLevelHooksTimeout). This also disappears with the WM_INPUTLANGCHANGEREQUEST approach.

Optional improvements

Minor polish — none of this affects users, so it's your call.

• Redundant unhook in Wh_ModUninit. The worker thread already calls UnhookWindowsHookEx when it receives WM_QUIT and exits its loop, so the UnhookWindowsHookEx(g_hook) at the top of Wh_ModUninit is redundant and races with the worker thread on the non-atomic g_hook (the NULL guard makes it benign, but it's unnecessary). You can just post WM_QUIT and WaitForSingleObject for the thread to do the cleanup. If you keep an explicit teardown, prefer a bounded wait (e.g. WaitForSingleObject(g_thread, 1000)) over INFINITE, as caps-ime-switcher does.
• RAII for the string setting. WindhawkUtils::StringSetting (from windhawk_utils.h) replaces the manual Wh_GetStringSetting + Wh_FreeStringSetting pair in LoadSettings.
• memset(s_keyDown, 0, ...) in Wh_ModUninit is unnecessary — the array is a zero-initialized global and is re-created fresh each time the mod is loaded.

Functionality notes

Non-critical observations about the feature behavior itself.

• The enableRightAlt: true default consumes AltGr. On many international layouts (German, Polish, Portuguese, etc.) the Right Alt key is AltGr, used to type @, €, ł, @, accented characters, and so on. Because an enabled key is fully blocked on both down and up, defaulting enableRightAlt to true breaks AltGr text entry out of the box for exactly the multi-layout users this mod targets. Consider defaulting it to false (Menu / Right Win are safer always-on defaults).
• Both mode performs two different operations. Ctrl+Shift and Alt+Shift are bound to two distinct Windows actions (switch keyboard layout vs. switch input language); if a user has both hotkeys enabled, Both triggers two switches in a row (with the Sleep(100) between), which can land back on the original layout or skip one. Switching via WM_INPUTLANGCHANGEREQUEST (item 2) sidesteps this entirely.
• An enabled key loses all its other functions. This is inherent to "single key = switch", but worth documenting: enabling Left Alt disables Alt+Tab / Alt+F4 / menu mnemonics on that key, and enabling Menu disables the context-menu key. Users may not anticipate it.