qmk_firmware/docs/feature_unicode.md
James Young 1646c0f26c
2021 May 29 Breaking Changes Update (#13034)
* Add Per Key functionality for AutoShift (#11536)

* LED Matrix: Reactive effect buffers & advanced indicators (#12588)

* [Keyboard] kint36: switch to sym_eager_pk debouncing (#12626)

* [Keyboard] kint2pp: reduce input latency by ≈10ms (#12625)

* LED Matrix: Split (#12633)

* [CI] Format code according to conventions (#12650)

* feat: infinite timeout for leader key (#6580)

* feat: implement leader_no_timeout logic

* docs(leader_key): infinite leader timeout docs

* Format code according to conventions (#12680)

* Update ADC driver for STM32F1xx, STM32F3xx, STM32F4xx (#12403)

* Fix default ADC_RESOLUTION for ADCv3 (and ADCv4)

Recent ChibiOS update removed ADC_CFGR1_RES_10BIT from the ADCv3 headers
(that macro should not have been there, because ADCv3 has CFGR instead of
CFGR1).  Fix the default value for ADC_RESOLUTION to use ADC_CFGR_RES_10BITS
if it is defined (that name is used for ADCv3 and ADCv4).

* Update ADC docs to match the actually used resolution

ADC driver for ChibiOS actually uses the 10-bit resolution by default
(probably to match AVR); fix the documentation accordingly.  Also add
both ADC_CFGR_RES_10BITS and ADC_CFGR1_RES_10BIT constants (these names
differ according to the ADC implementation in the particular MCU).

* Fix pinToMux() for B12 and B13 on STM32F3xx

Testing on STM32F303CCT6 revealed that the ADC mux values for B12 and
B13 pins were wrong.

* Add support for all possible analog pins on STM32F1xx

Added ADC mux values for pins A0...A7, B0, B1, C0...C5 on STM32F1xx
(they are the same at least for STM32F103x8 and larger F103 devices, and
also F102, F105, F107 families).  Actually tested on STM32F103C8T6
(therefore pins C0...C5 were not tested).

Pins F6...F10, which are present on STM32F103x[C-G] in 144-pin packages,
cannot be supported at the moment, because those pins are connected only
to ADC3, but the ChibiOS ADC driver for STM32F1xx supports only ADC1.

* Add support for all possible analog pins on STM32F4xx

Added ADC mux values for pins A0...A7, B0, B1, C0...C5 and optionally
F3...F10 (if STM32_ADC_USE_ADC3 is enabled).  These mux values are
apparently the same for all F4xx devices, except some smaller devices may
not have ADC3.

Actually tested on STM32F401CCU6, STM32F401CEU6, STM32F411CEU6 (using
various WeAct “Blackpill” boards); only pins A0...A7, B0, B1 were tested.

Pins F3...F10 are inside `#if STM32_ADC_USE_ADC3` because some devices
which don't have ADC3 also don't have the GPIOF port, therefore the code
which refers to Fx pins does not compile.

* Fix STM32F3xx ADC mux table in documentation

The ADC driver documentation had some errors in the mux table for STM32F3xx.
Fix this table to match the datasheet and the actual code (mux settings for
B12 and B13 were also tested on a real STM32F303CCT6 chip).

* Add STM32F1xx ADC pins to the documentation

* Add STM32F4xx ADC pins to the documentation

* Add initial support for tinyuf2 bootloader (when hosted on F411 blackpill) (#12600)

* Add support for jumping to tinyuf2 bootloader. Adds blackpill UF2 example.

* Update flashing.md

* Update chconf.h

* Update config.h

* Update halconf.h

* Update mcuconf.h

* eeprom driver: Refactor where eeprom driver initialisation (and EEPROM emulation initialisation) occurs to make it non-target-specific. (#12671)

* Add support for MCU = STM32F446 (#12619)

* Add support for MCU = STM32F446

* Update platforms/chibios/GENERIC_STM32_F446XE/configs/config.h

* Restore mcuconf.h to the one used by RT-STM32F446RE-NUCLEO64

* stm32f446: update mcuconf.h and board.h for 16MHz operation, with USB enabled, and other peripherals disabled.

* Format code according to conventions (#12682)

* Format code according to conventions (#12687)

* Add STM32L433 and L443 support (#12063)

* initial L433 commit

* change to XC

* fix L433

* disable all peripherals

* update system and peripheral clocks

* 433 change

* use its own board  files

* revert its own board files

* l433 specific change

* fix stm32l432xx define

* remove duplicate #define

* fix bootloader jump

* move to L443xx and add i2c2, spi2, usart3 to mcuconf.h

* move to L443

* move to L443

* fix sdmmc in mcuconf.h

* include STM32L443

* add L443

* Include L443 in compatible microcontrollers

* Include L443 in compatible microcontrollers

* Update config bootloader jump description

* Update ChibiOS define reasoning

* Update quantum/mcu_selection.mk

* fix git conflict

* Updated Function96 with V2 files and removed chconf.h and halconf.h (#12613)

* Fix bad PR merge for #6580. (#12721)

* Change RGB/LED Matrix to use a simple define for USB suspend (#12697)

* [CI] Format code according to conventions (#12731)

* Fixing transport's led/rgb matrix suspend state logic (#12770)

* [CI] Format code according to conventions (#12772)

* Fix comment parsing (#12750)

* Added OLED fade out support (#12086)

* fix some references to bin/qmk that slipped in (#12832)

* Resolve a number of warnings in `qmk generate-api` (#12833)

* New command: qmk console (#12828)

* stash poc

* stash

* tidy up implementation

* Tidy up slightly for review

* Tidy up slightly for review

* Bodge environment to make tests pass

* Refactor away from asyncio due to windows issues

* Filter devices

* align vid/pid printing

* Add hidapi to the installers

* start preparing for multiple hid_listeners

* udev rules for hid_listen

* refactor to move closer to end state

* very basic implementation of the threaded model

* refactor how vid/pid/index are supplied and parsed

* windows improvements

* read the report directly when usage page isn't available

* add per-device colors, the choice to show names or numbers, and refactor

* add timestamps

* Add support for showing bootloaders

* tweak the color for bootloaders

* Align bootloader disconnect with connect color

* add support for showing all bootloaders

* fix the pyusb check

* tweaks

* fix exception

* hide a stack trace behind -v

* add --no-bootloaders option

* add documentation for qmk console

* Apply suggestions from code review

* pyformat

* clean up and flesh out KNOWN_BOOTLOADERS

* Remove pointless SERIAL_LINK_ENABLE rules (#12846)

* Make Swap Hands use PROGMEM (#12284)

This converts the array that the Swap Hands feature uses to use PROGMEM,
and to read from that array, as such. Since this array never changes at
runtime, there is no reason to keep it in memory. Especially for AVR
boards, as memory is a precious resource.

* Fix another bin/qmk reference (#12856)

* [Keymap] Turn OLED off on suspend in soundmonster keymap (#10419)

* Fixup build errors on `develop` branch. (#12723)

* LED Matrix: Effects! (#12651)

* Fix syntax error when compiling for ARM (#12866)

* Remove KEYMAP and LAYOUT_kc (#12160)

* alias KEYMAP to LAYOUT

* remove KEYMAP and LAYOUT_kc

* Add setup, clone, and env to the list of commands we allow even with broken modules (#12868)

* Rename `point_t` -> `led_point_t` (#12864)

* [Keyboard] updated a vendor name / fixed minor keymap issues (#12881)

* Add missing LED Matrix suspend code to suspend.c (#12878)

* LED Matrix: Documentation (#12685)

* Deprecate `send_unicode_hex_string()` (#12602)

* Fix spelling mistake regarding LED Matrix in split_common. (#12888)

* [Keymap] Fix QWERTY/DVORAK status output for kzar keymap (#12895)

* Use milc.subcommand.config instead of qmk.cli.config (#12915)

* Use milc.subcommand.config instead

* pyformat

* remove the config test

* Add function to allow repeated blinking of one layer (#12237)

* Implement function rgblight_blink_layer_repeat to allow repeated blinking of one layer at a time

* Update doc

* Rework rgblight blinking according to requested change

* optimize storage

* Fixup housekeeping from being invoked twice per loop. (#12933)

* matrix: wait for row signal to go HIGH for every row (#12945)

I noticed this discrepancy (last row of the matrix treated differently than the
others) when optimizing the input latency of my keyboard controller, see also
https://michael.stapelberg.ch/posts/2021-05-08-keyboard-input-latency-qmk-kinesis/

Before this commit, when tuning the delays I noticed ghost key presses when
pressing the F2 key, which is on the last row of the keyboard matrix: the
dead_grave key, which is on the first row of the keyboard matrix, would be
incorrectly detected as pressed.

After this commit, all keyboard matrix rows are interpreted correctly.

I suspect that my setup is more susceptible to this nuance than others because I
use GPIO_INPUT_PIN_DELAY=0 and hence don’t have another delay that might mask
the problem.

* ensure we do not conflict with existing keymap aliases (#12976)

* Add support for up to 4 IS31FL3733 drivers (#12342)

* Convert Encoder callbacks to be boolean functions (#12805)

* [Keyboard] Fix Terrazzo build failure (#12977)

* Do not hard set config in CPTC files (#11864)

* [Keyboard] Corne - Remove legacy revision support (#12226)

* [Keymap] Update to Drashna keymap and user code (based on develop) (#12936)

* Add Full-duplex serial driver for ARM boards (#9842)

* Document LED_MATRIX_FRAMEBUFFER_EFFECTS (#12987)

* Backlight: add defines for default level and breathing state (#12560)

* Add dire message about LUFA mass storage bootloader (#13014)

* [Keyboard] Remove redundant legacy and common headers for crkbd (#13023)

Was causing compiler errors on some systems.

* Fix keyboards/keymaps for boolean encoder callback changes (#12985)

* `backlight.c`: include `eeprom.h` (#13024)

* Add changelog for 2021-05-29 Breaking Changes merge (#12939)

* Add ChangeLog for 2021-05-29 Breaking Changes Merge: initial version

* Add recent develop changes

* Sort recent develop changes

* Remove sections for ChibiOS changes per tzarc

No ChibiOS changes this round.

* Add and sort recent develop changes

* add notes about keyboard moves/deletions

* import changelog for PR 12172

Documents the change to BOOTMAGIC_ENABLE.

* update section headings

* re-sort changelog

* add additional note regarding Bootmagic changes

* remove changelog timestamp

* update dates in main Breaking Changes docs

* fix broken section anchors in previous changelogs

* add link to backlight/eeprom patch to changelog

* highlight some more changes

* link PRs from section headers

* Restore standard readme

* run: qmk cformat --core-only
2021-05-29 14:38:50 -07:00

19 KiB
Raw Blame History

Unicode Support

Unicode characters can be input straight from your keyboard! There are some limitations, however.

In order to enable Unicode support on your keyboard, you will need to do the following:

  1. Choose one of three supported Unicode implementations: Basic Unicode, Unicode Map, UCIS.
  2. Find which input mode is the best match for your operating system and setup.
  3. Set the appropriate input mode (or modes) in your configuration.
  4. Add Unicode keycodes to your keymap.

1. Methods :id=methods

QMK supports three different methods for enabling Unicode input and adding Unicode characters to your keymap. Each has its pros and cons in terms of flexibility and ease of use. Choose the one that best fits your use case.

The Basic method should be enough for most users. However, if you need a wider range of supported characters (including emoji, rare symbols etc.), you should use Unicode Map.


1.1. Basic Unicode :id=basic-unicode

The easiest to use method, albeit somewhat limited. It stores Unicode characters as keycodes in the keymap itself, so it only supports code points up to 0x7FFF. This covers characters for most modern languages (including East Asian), as well as symbols, but it doesn't cover emoji.

Add the following to your rules.mk:

UNICODE_ENABLE = yes

Then add UC(c) keycodes to your keymap, where c is the code point of the desired character (preferably in hexadecimal, up to 4 digits long). For example, UC(0x40B) will output Ћ, and UC(0x30C4) will output .


1.2. Unicode Map :id=unicode-map

In addition to standard character ranges, this method also covers emoji, ancient scripts, rare symbols etc. In fact, all possible code points (up to 0x10FFFF) are supported. Here, Unicode characters are stored in a separate mapping table. You need to maintain a unicode_map array in your keymap file, which may contain at most 16384 entries.

Add the following to your rules.mk:

UNICODEMAP_ENABLE = yes

Then add X(i) keycodes to your keymap, where i is the desired character's index in the mapping table. This can be a numeric value, but it's recommended to keep the indices in an enum and access them by name.

enum unicode_names {
    BANG,
    IRONY,
    SNEK
};

const uint32_t PROGMEM unicode_map[] = {
    [BANG]  = 0x203D,  // ‽
    [IRONY] = 0x2E2E,  // ⸮
    [SNEK]  = 0x1F40D, // 🐍
};

Then you can use X(BANG), X(SNEK) etc. in your keymap.

Lower and Upper Case

Characters often come in lower and upper case pairs, such as å and Å. To make inputting these characters easier, you can use XP(i, j) in your keymap, where i and j are the mapping table indices of the lower and upper case character, respectively. If you're holding down Shift or have Caps Lock turned on when you press the key, the second (upper case) character will be inserted; otherwise, the first (lower case) version will appear.

This is most useful when creating a keymap for an international layout with special characters. Instead of having to put the lower and upper case versions of a character on separate keys, you can have them both on the same key by using XP(). This helps blend Unicode keys in with regular alphas.

Due to keycode size constraints, i and j can each only refer to one of the first 128 characters in your unicode_map. In other words, 0 ≤ i ≤ 127 and 0 ≤ j ≤ 127. This is enough for most use cases, but if you'd like to customize the index calculation, you can override the unicodemap_index() function. This also allows you to, say, check Ctrl instead of Shift/Caps.


1.3. UCIS :id=ucis

This method also supports all possible code points. As with the Unicode Map method, you need to maintain a mapping table in your keymap file. However, there are no built-in keycodes for this feature — you have to create a custom keycode or function that invokes this functionality.

Add the following to your rules.mk:

UCIS_ENABLE = yes

Then define a table like this in your keymap file:

const qk_ucis_symbol_t ucis_symbol_table[] = UCIS_TABLE(
    UCIS_SYM("poop", 0x1F4A9),                // 💩
    UCIS_SYM("rofl", 0x1F923),                // 🤣
    UCIS_SYM("cuba", 0x1F1E8, 0x1F1FA),       // 🇨🇺
    UCIS_SYM("look", 0x0CA0, 0x005F, 0x0CA0)  // ಠ_ಠ
);

By default, each table entry may be up to 3 code points long. This number can be changed by adding #define UCIS_MAX_CODE_POINTS n to your config.h file.

To use UCIS input, call qk_ucis_start(). Then, type the mnemonic for the character (such as "rofl") and hit Space, Enter or Esc. QMK should erase the "rofl" text and insert the laughing emoji.

Customization

There are several functions that you can define in your keymap to customize the functionality of this feature.

  • void qk_ucis_start_user(void) This runs when you call the "start" function, and can be used to provide feedback. By default, it types out a keyboard emoji.
  • void qk_ucis_success(uint8_t symbol_index) This runs when the input has matched something and has completed. By default, it doesn't do anything.
  • void qk_ucis_symbol_fallback (void) This runs when the input doesn't match anything. By default, it falls back to trying that input as a Unicode code.

You can find the default implementations of these functions in process_ucis.c.

2. Input Modes :id=input-modes

Unicode input in QMK works by inputting a sequence of characters to the OS, sort of like a macro. Unfortunately, the way this is done differs for each platform. Specifically, each platform requires a different combination of keys to trigger Unicode input. Therefore, a corresponding input mode has to be set in QMK.

The following input modes are available:

  • UC_MAC: macOS built-in Unicode hex input. Supports code points up to 0x10FFFF (all possible code points).

    To enable, go to System Preferences > Keyboard > Input Sources, add Unicode Hex Input to the list (it's under Other), then activate it from the input dropdown in the Menu Bar. By default, this mode uses the left Option key (KC_LALT) for Unicode input, but this can be changed by defining UNICODE_KEY_MAC with a different keycode.

    !> Using the Unicode Hex Input input source may disable some Option-based shortcuts, such as Option+Left and Option+Right.

    !> UC_OSX is a deprecated alias of UC_MAC that will be removed in future versions of QMK. All new keymaps should use UC_MAC.

  • UC_LNX: Linux built-in IBus Unicode input. Supports code points up to 0x10FFFF (all possible code points).

    Enabled by default and works almost anywhere on IBus-enabled distros. Without IBus, this mode works under GTK apps, but rarely anywhere else. By default, this mode uses Ctrl+Shift+U (LCTL(LSFT(KC_U))) to start Unicode input, but this can be changed by defining UNICODE_KEY_LNX with a different keycode. This might be required for IBus versions ≥1.5.15, where Ctrl+Shift+U behavior is consolidated into Ctrl+Shift+E.

    Users who wish support in non-GTK apps without IBus may need to resort to a more indirect method, such as creating a custom keyboard layout (more on this method).

  • UC_WIN: (not recommended) Windows built-in hex numpad Unicode input. Supports code points up to 0xFFFF.

    To enable, create a registry key under HKEY_CURRENT_USER\Control Panel\Input Method of type REG_SZ called EnableHexNumpad and set its value to 1. This can be done from the Command Prompt by running reg add "HKCU\Control Panel\Input Method" -v EnableHexNumpad -t REG_SZ -d 1 with administrator privileges. Reboot afterwards. This mode is not recommended because of reliability and compatibility issues; use the UC_WINC mode instead.

  • UC_BSD: (non implemented) Unicode input under BSD. Not implemented at this time. If you're a BSD user and want to help add support for it, please open an issue on GitHub.

  • UC_WINC: Windows Unicode input using WinCompose. As of v0.9.0, supports code points up to 0x10FFFF (all possible code points).

    To enable, install the latest release. Once installed, WinCompose will automatically run on startup. This mode works reliably under all version of Windows supported by the app. By default, this mode uses right Alt (KC_RALT) as the Compose key, but this can be changed in the WinCompose settings and by defining UNICODE_KEY_WINC with a different keycode.

3. Setting the Input Mode :id=setting-the-input-mode

To set your desired input mode, add the following define to your config.h:

#define UNICODE_SELECTED_MODES UC_LNX

This example sets the board's default input mode to UC_LNX. You can replace this with UC_MAC, UC_WINC, or any of the other modes listed above. The board will automatically use the selected mode on startup, unless you manually switch to another mode (see below).

You can also select multiple input modes, which allows you to easily cycle through them using the UC_MOD/UC_RMOD keycodes.

#define UNICODE_SELECTED_MODES UC_MAC, UC_LNX, UC_WINC

Note that the values are separated by commas. The board will remember the last used input mode and will continue using it on next power-up. You can disable this and force it to always start with the first mode in the list by adding #define UNICODE_CYCLE_PERSIST false to your config.h.

Keycodes

You can switch the input mode at any time by using the following keycodes. Adding these to your keymap allows you to quickly switch to a specific input mode, including modes not listed in UNICODE_SELECTED_MODES.

Keycode Alias Input Mode Description
UNICODE_MODE_FORWARD UC_MOD Next in list Cycle through selected modes, reverse direction when Shift is held
UNICODE_MODE_REVERSE UC_RMOD Prev in list Cycle through selected modes in reverse, forward direction when Shift is held
UNICODE_MODE_MAC UC_M_MA UC_MAC Switch to macOS input
UNICODE_MODE_LNX UC_M_LN UC_LNX Switch to Linux input
UNICODE_MODE_WIN UC_M_WI UC_WIN Switch to Windows input
UNICODE_MODE_BSD UC_M_BS UC_BSD Switch to BSD input (not implemented)
UNICODE_MODE_WINC UC_M_WC UC_WINC Switch to Windows input using WinCompose

You can also switch the input mode by calling set_unicode_input_mode(x) in your code, where x is one of the above input mode constants (e.g. UC_LNX).

?> Using UNICODE_SELECTED_MODES is preferable to calling set_unicode_input_mode() in matrix_init_user() or similar functions, since it's better integrated into the Unicode system and has the added benefit of avoiding unnecessary writes to EEPROM.

Audio Feedback

If you have the Audio feature enabled on the board, you can set melodies to be played when you press the above keys. That way you can have some audio feedback when switching input modes.

For instance, you can add these definitions to your config.h file:

#define UNICODE_SONG_MAC  AUDIO_ON_SOUND
#define UNICODE_SONG_LNX  UNICODE_LINUX
#define UNICODE_SONG_BSD  TERMINAL_SOUND
#define UNICODE_SONG_WIN  UNICODE_WINDOWS
#define UNICODE_SONG_WINC UNICODE_WINDOWS

Additional Customization

Because Unicode is a large and versatile feature, there are a number of options you can customize to make it work better on your system.

Start and Finish Input Functions

The functions for starting and finishing Unicode input on your platform can be overridden locally. Possible uses include customizing input mode behavior if you don't use the default keys, or adding extra visual/audio feedback to Unicode input.

  • void unicode_input_start(void) This sends the initial sequence that tells your platform to enter Unicode input mode. For example, it holds the left Alt key followed by Num+ on Windows, and presses the UNICODE_KEY_LNX combination (default: Ctrl+Shift+U) on Linux.
  • void unicode_input_finish(void) This is called to exit Unicode input mode, for example by pressing Space or releasing the Alt key.

You can find the default implementations of these functions in process_unicode_common.c.

Input Key Configuration

You can customize the keys used to trigger Unicode input for macOS, Linux and WinCompose by adding corresponding defines to your config.h. The default values match the platforms' default settings, so you shouldn't need to change this unless Unicode input isn't working, or you want to use a different key (e.g. in order to free up left or right Alt).

Define Type Default Example
UNICODE_KEY_MAC uint8_t KC_LALT #define UNICODE_KEY_MAC KC_RALT
UNICODE_KEY_LNX uint16_t LCTL(LSFT(KC_U)) #define UNICODE_KEY_LNX LCTL(LSFT(KC_E))
UNICODE_KEY_WINC uint8_t KC_RALT #define UNICODE_KEY_WINC KC_RGUI

Sending Unicode Strings

QMK provides several functions that allow you to send Unicode input to the host programmatically:

send_unicode_string()

This function is much like send_string(), but it allows you to input UTF-8 characters directly. It supports all code points, provided the selected input mode also supports it. Make sure your keymap.c file is formatted using UTF-8 encoding.

send_unicode_string("(ノಠ痊ಠ)ノ彡┻━┻");

Example uses include sending Unicode strings when a key is pressed, as described in Macros.

send_unicode_hex_string() (Deprecated)

Similar to send_unicode_string(), but the characters are represented by their Unicode code points, written in hexadecimal and separated by spaces. For example, the table flip above would be achieved with:

send_unicode_hex_string("0028 30CE 0CA0 75CA 0CA0 0029 30CE 5F61 253B 2501 253B");

An easy way to convert your Unicode string to this format is to use this site and take the result in the "Hex/UTF-32" section.

Additional Language Support

In quantum/keymap_extras, you'll see various language files — these work the same way as the ones for alternative layouts such as Colemak or BÉPO. When you include one of these language headers, you gain access to keycodes specific to that language / national layout. Such keycodes are defined by a 2-letter country/language code, followed by an underscore and a 4-letter abbreviation of the character to which the key corresponds. For example, including keymap_french.h and using FR_UGRV in your keymap will output ù when typed on a system with a native French AZERTY layout.

If the primary system layout you use on your machine is different from US ANSI, using these language-specific keycodes can help your QMK keymaps better match what will actually be output on the screen. However, keep in mind that these keycodes are just aliases for the corresponding default US keycodes under the hood, and that the HID protocol used by keyboards is itself inherently based on US ANSI.

International Characters on Windows

AutoHotkey

The method does not require Unicode support in the keyboard itself but instead depends on AutoHotkey running in the background.

First you need to select a modifier combination that is not in use by any of your programs. Ctrl+Alt+Win is not used very widely and should therefore be perfect for this. There is a macro defined for a mod-tab combo LCAG_T. Add this mod-tab combo to a key on your keyboard, e.g.: LCAG_T(KC_TAB). This makes the key behave like a tab key if pressed and released immediately but changes it to the modifier if used with another key.

In the default script of AutoHotkey you can define custom hotkeys.

<^<!<#a::Send, ä
<^<!<#<+a::Send, Ä

The hotkeys above are for the combination CtrlAltGui and CtrlAltGuiShift plus the letter a. AutoHotkey inserts the Text right of Send, when this combination is pressed.

US International

If you enable the US International layout on the system, it will use punctuation to accent the characters. For instance, typing "`a" will result in à. You can find details on how to enable this here.

Software keyboard layout on Linux :id=custom-linux-layout

This method does not require Unicode support on the keyboard itself but instead uses a custom keyboard layout for Xorg. This is how special characters are inserted by regular keyboards. This does not require IBus and works in practically all software. Help on creating a custom layout can be found here, here and here. An example of how you could edit the us layout to gain 🤣 on RALT(KC_R):

Edit the keyboard layout file /usr/share/X11/xkb/symbols/us.

Inside xkb_symbols "basic" {, add include "level3(ralt_switch)".

Find the line defining the R key and add an entry to the list, making it look like this:

key <AD04> {	[	  r,	R, U1F923		]	};

Save the file and run the command setxkbmap us to reload the layout.

You can define one custom character for key defined in the layout, and another if you populate the fourth layer. Additional layers up to 8th are also possible.

This method is specific to the computer on which you set the custom layout. The custom keys will be available only when Xorg is running. To avoid accidents, you should always reload the layout using setxkbmap, otherwise an invalid layout could prevent you from logging into your system, locking you out.