custom_shift_keys.c

// Copyright 2021-2024 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

/**
 * @file custom_shift_keys.c
 * @brief Custom Shift Keys implementation
 *
 * For full documentation, see
 * <https://getreuer.info/posts/keyboards/custom-shift-keys>
 */

#include "custom_shift_keys.h"

#if !defined(IS_QK_MOD_TAP)
// Attempt to detect out-of-date QMK installation, which would fail with
// implicit-function-declaration errors in the code below.
#error "custom_shift_keys: QMK version is too old to build. Please update QMK."
#else

bool process_custom_shift_keys(uint16_t keycode, keyrecord_t *record) {
  static uint16_t registered_keycode = KC_NO;

  // If a custom shift key is registered, then this event is either releasing
  // it or manipulating another key at the same time. Either way, we release
  // the currently registered key.
  if (registered_keycode != KC_NO) {
    unregister_code16(registered_keycode);
    registered_keycode = KC_NO;
  }

  if (record->event.pressed) {  // Press event.
    const uint8_t saved_mods = get_mods();
#ifndef NO_ACTION_ONESHOT
    const uint8_t mods = saved_mods | get_weak_mods() | get_oneshot_mods();
#else
    const uint8_t mods = saved_mods | get_weak_mods();
#endif  // NO_ACTION_ONESHOT
#if CUSTOM_SHIFT_KEYS_LAYER_MASK != 0
    const uint8_t layer = read_source_layers_cache(record->event.key);
#endif  // CUSTOM_SHIFT_KEYS_LAYER_MASK
    if ((mods & MOD_MASK_SHIFT) != 0  // Shift is held.
#if CUSTOM_SHIFT_KEYS_NEGMODS != 0
        // Nothing in CUSTOM_SHIFT_KEYS_NEGMODS is held.
        && (mods & (CUSTOM_SHIFT_KEYS_NEGMODS)) == 0
#endif  // CUSTOM_SHIFT_KEYS_NEGMODS != 0
#if CUSTOM_SHIFT_KEYS_LAYER_MASK != 0
        // Pressed key is on a layer appearing in the layer mask.
        && ((1 << layer) & (CUSTOM_SHIFT_KEYS_LAYER_MASK)) != 0
#endif  // CUSTOM_SHIFT_KEYS_LAYER_MASK
          ) {
      // Continue default handling if this is a tap-hold key being held.
      if ((IS_QK_MOD_TAP(keycode) || IS_QK_LAYER_TAP(keycode)) &&
          record->tap.count == 0) {
        return true;
      }

      // Search for a custom shift key whose keycode is `keycode`.
      for (int i = 0; i < NUM_CUSTOM_SHIFT_KEYS; ++i) {
        if (keycode == custom_shift_keys[i].keycode) {
          registered_keycode = custom_shift_keys[i].shifted_keycode;
          if (IS_QK_MODS(registered_keycode) &&  // Should keycode be shifted?
              (QK_MODS_GET_MODS(registered_keycode) & MOD_LSFT) != 0) {
            register_code16(registered_keycode);  // If so, press it directly.
          } else {
            // Otherwise cancel shift mods, press the key, and restore mods.
            del_weak_mods(MOD_MASK_SHIFT);
#ifndef NO_ACTION_ONESHOT
            del_oneshot_mods(MOD_MASK_SHIFT);
#endif  // NO_ACTION_ONESHOT
            unregister_mods(MOD_MASK_SHIFT);
            register_code16(registered_keycode);
            set_mods(saved_mods);
          }
          return false;
        }
      }
    }
  }

  return true;  // Continue with default handling.
}

#endif  // version check