qmk_firmware/quantum/process_keycode/process_unicode.c

#include "process_unicode.h"

static uint8_t input_mode;

uint16_t hex_to_keycode(uint8_t hex)
{
  if (hex == 0x0) {
    return KC_0;
  } else if (hex < 0xA) {
    return KC_1 + (hex - 0x1);
  } else {
    return KC_A + (hex - 0xA);
  }
}

void set_unicode_mode(uint8_t os_target)
{
  input_mode = os_target;
}

bool process_unicode(uint16_t keycode, keyrecord_t *record) {
  if (keycode > QK_UNICODE && record->event.pressed) {
    uint16_t unicode = keycode & 0x7FFF;
    switch(input_mode) {
      case UC_OSX:
        register_code(KC_LALT);
        break;
      case UC_LNX:
        register_code(KC_LCTL);
        register_code(KC_LSFT);
        register_code(KC_U);
        unregister_code(KC_U);
        break;
      case UC_WIN:
        register_code(KC_LALT);
        register_code(KC_PPLS);
        unregister_code(KC_PPLS);
        break;
    }
    for(int i = 3; i >= 0; i--) {
        uint8_t digit = ((unicode >> (i*4)) & 0xF);
        register_code(hex_to_keycode(digit));
        unregister_code(hex_to_keycode(digit));
    }
    switch(input_mode) {
      case UC_OSX:
      case UC_WIN:
        unregister_code(KC_LALT);
        break;
      case UC_LNX:
        unregister_code(KC_LCTL);
        unregister_code(KC_LSFT);
        break;
    }
  }
  return true;
}