qmk_firmware/quantum/process_keycode/process_key_lock.c

/* Copyright 2017 Fredric Silberberg
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include "inttypes.h"
#include "stdint.h"
#include "process_key_lock.h"

#define SHIFT(shift) (((uint64_t)1) << (shift))
#define GET_KEY_ARRAY(code) (((code) < 0x40) ? key_state[0] : \
                             ((code) < 0x80) ? key_state[1] : \
                             ((code) < 0xC0) ? key_state[2] : key_state[3])
#define GET_CODE_INDEX(code) (((code) < 0x40) ? (code) : \
                              ((code) < 0x80) ? (code) - 0x40 : \
                              ((code) < 0xC0) ? (code) - 0x80 : (code) - 0xC0)
#define KEY_STATE(code)  (GET_KEY_ARRAY(code) & SHIFT(GET_CODE_INDEX(code))) == SHIFT(GET_CODE_INDEX(code))
#define SET_KEY_ARRAY_STATE(code, val) do { \
    switch (code) { \
        case 0x00 ... 0x3F: \
            key_state[0] = (val); \
            break; \
        case 0x40 ... 0x7F: \
            key_state[1] = (val); \
            break; \
        case 0x80 ... 0xBF: \
            key_state[2] = (val); \
            break; \
        case 0xC0 ... 0xFF: \
            key_state[3] = (val); \
            break; \
    } \
} while(0)
#define SET_KEY_STATE(code) SET_KEY_ARRAY_STATE(code, (GET_KEY_ARRAY(code) | SHIFT(GET_CODE_INDEX(code))))
#define UNSET_KEY_STATE(code) SET_KEY_ARRAY_STATE(code, (GET_KEY_ARRAY(code)) & ~(SHIFT(GET_CODE_INDEX(code))))
#define IS_STANDARD_KEYCODE(code) ((code) <= 0xFF)

// Locked key state. This is an array of 256 bits, one for each of the standard keys supported qmk.
uint64_t key_state[4] = { 0x0, 0x0, 0x0, 0x0 };
bool watching = false;

bool process_key_lock(uint16_t keycode, keyrecord_t *record) {
    // We start by categorizing the keypress event. In the event of a down
    // event, there are several possibilities:
    // 1. The key is not being locked, and we are not watching for new keys.
    //    In this case, we bail immediately. This is the common case for down events.
    // 2. The key was locked, and we need to unlock it. In this case, we will
    //    reset the state in our map and return false. When the user releases the
    //    key, the up event will no longer be masked and the OS will observe the
    //    released key.
    // 3. KC_LOCK was just pressed. In this case, we set up the state machine
    //    to watch for the next key down event, and finish processing
    // 4. The keycode is below 0xFF, and we are watching for new keys. In this case,
    //    we will send the key down event to the os, and set the key_state for that
    //    key to mask the up event.
    // 5. The keycode is above 0xFF, and we're wathing for new keys. In this case,
    //    the user pressed a key that we cannot "lock", as it's a series of keys,
    //    or a macro invocation, or a layer transition, or a custom-defined key, or
    //    or some other arbitrary code. In this case, we bail immediately, reset
    //    our watch state, and return true.
    //
    // In the event of an up event, there are these possibilities:
    // 1. The key is not being locked. In this case, we return true and bail
    //    immediately. This is the common case.
    // 2. The key is being locked. In this case, we will mask the up event
    //    by returning false, so the OS never sees that the key was released
    //    until the user pressed the key again.
    if (record->event.pressed) {
        // Non-standard keycode, reset and return
        if (!(IS_STANDARD_KEYCODE(keycode) || keycode == KC_LOCK)) {
            watching = false;
            return true;
        }

        // If we're already watching, turn off the watch.
        if (keycode == KC_LOCK) {
            watching = !watching;
            return false;
        }
        
        if (IS_STANDARD_KEYCODE(keycode)) {
            // We check watching first. This is so that in the following scenario, we continue to
            // hold the key: KC_LOCK, KC_F, KC_LOCK, KC_F
            // If we checked in reverse order, we'd end up holding the key pressed after the second
            // KC_F press is registered, when the user likely meant to hold F
            if (watching) {
                watching = false;
                SET_KEY_STATE(keycode);
                // Let the standard keymap send the keycode down event. The up event will be masked.
                return true;
            }
            
            if (KEY_STATE(keycode)) {
                UNSET_KEY_STATE(keycode);
                // The key is already held, stop this process. The up event will be sent when the user
                // releases the key.
                return false;
            }
        }
        
        // Either the key isn't a standard key, or we need to send the down event. Continue standard
        // processing
        return true;
    } else {
        // Stop processing if it's a standard key and we're masking up.
        return !(IS_STANDARD_KEYCODE(keycode) && KEY_STATE(keycode));
    }
}