[Core] Add Layer Lock feature (#23430)

Co-authored-by: Daniel <1767914+iamdanielv@users.noreply.github.com>
Co-authored-by: Pascal Getreuer <getreuer@google.com>
Co-authored-by: Pascal Getreuer <50221757+getreuer@users.noreply.github.com>

quantum/keyboard.c

@@ -140,6 +140,9 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #ifdef OS_DETECTION_ENABLE
 #    include "os_detection.h"
 #endif
+#if defined(LAYER_LOCK_ENABLE) && LAYER_LOCK_IDLE_TIMEOUT > 0
+#    include "layer_lock.h"
+#endif // LAYER_LOCK_ENABLE
 
 static uint32_t last_input_modification_time = 0;
 uint32_t        last_input_activity_time(void) {
@@ -655,6 +658,10 @@ void quantum_task(void) {
 #ifdef SECURE_ENABLE
     secure_task();
 #endif
+
+#if defined(LAYER_LOCK_ENABLE) && LAYER_LOCK_IDLE_TIMEOUT > 0
+    layer_lock_task();
+#endif
 }
 
 /** \brief Main task that is repeatedly called as fast as possible. */

quantum/keycodes.h

@@ -759,6 +759,7 @@ enum qk_keycode_defines {
     QK_TRI_LAYER_UPPER = 0x7C78,
     QK_REPEAT_KEY = 0x7C79,
     QK_ALT_REPEAT_KEY = 0x7C7A,
+    QK_LAYER_LOCK = 0x7C7B,
     QK_KB_0 = 0x7E00,
     QK_KB_1 = 0x7E01,
     QK_KB_2 = 0x7E02,
@@ -1445,6 +1446,7 @@ enum qk_keycode_defines {
     TL_UPPR    = QK_TRI_LAYER_UPPER,
     QK_REP     = QK_REPEAT_KEY,
     QK_AREP    = QK_ALT_REPEAT_KEY,
+    QK_LLCK    = QK_LAYER_LOCK,
 };
 
 // Range Helpers
@@ -1501,7 +1503,7 @@ enum qk_keycode_defines {
 #define IS_UNDERGLOW_KEYCODE(code) ((code) >= QK_UNDERGLOW_TOGGLE && (code) <= QK_UNDERGLOW_SPEED_DOWN)
 #define IS_RGB_KEYCODE(code) ((code) >= RGB_MODE_PLAIN && (code) <= RGB_MODE_TWINKLE)
 #define IS_RGB_MATRIX_KEYCODE(code) ((code) >= QK_RGB_MATRIX_ON && (code) <= QK_RGB_MATRIX_SPEED_DOWN)
-#define IS_QUANTUM_KEYCODE(code) ((code) >= QK_BOOTLOADER && (code) <= QK_ALT_REPEAT_KEY)
+#define IS_QUANTUM_KEYCODE(code) ((code) >= QK_BOOTLOADER && (code) <= QK_LAYER_LOCK)
 #define IS_KB_KEYCODE(code) ((code) >= QK_KB_0 && (code) <= QK_KB_31)
 #define IS_USER_KEYCODE(code) ((code) >= QK_USER_0 && (code) <= QK_USER_31)
 
@@ -1527,6 +1529,6 @@ enum qk_keycode_defines {
 #define UNDERGLOW_KEYCODE_RANGE             QK_UNDERGLOW_TOGGLE ... QK_UNDERGLOW_SPEED_DOWN
 #define RGB_KEYCODE_RANGE                   RGB_MODE_PLAIN ... RGB_MODE_TWINKLE
 #define RGB_MATRIX_KEYCODE_RANGE            QK_RGB_MATRIX_ON ... QK_RGB_MATRIX_SPEED_DOWN
-#define QUANTUM_KEYCODE_RANGE               QK_BOOTLOADER ... QK_ALT_REPEAT_KEY
+#define QUANTUM_KEYCODE_RANGE               QK_BOOTLOADER ... QK_LAYER_LOCK
 #define KB_KEYCODE_RANGE                    QK_KB_0 ... QK_KB_31
 #define USER_KEYCODE_RANGE                  QK_USER_0 ... QK_USER_31

quantum/layer_lock.c

@@ -0,0 +1,81 @@
+// Copyright 2022-2023 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.
+
+#include "layer_lock.h"
+#include "quantum_keycodes.h"
+
+#ifndef NO_ACTION_LAYER
+// The current lock state. The kth bit is on if layer k is locked.
+layer_state_t locked_layers = 0;
+
+// Layer Lock timer to disable layer lock after X seconds inactivity
+#    if defined(LAYER_LOCK_IDLE_TIMEOUT) && LAYER_LOCK_IDLE_TIMEOUT > 0
+uint32_t layer_lock_timer = 0;
+
+void layer_lock_task(void) {
+    if (locked_layers && timer_elapsed32(layer_lock_timer) > LAYER_LOCK_IDLE_TIMEOUT) {
+        layer_lock_all_off();
+        layer_lock_timer = timer_read32();
+    }
+}
+#    endif // LAYER_LOCK_IDLE_TIMEOUT > 0
+
+bool is_layer_locked(uint8_t layer) {
+    return locked_layers & ((layer_state_t)1 << layer);
+}
+
+void layer_lock_invert(uint8_t layer) {
+    const layer_state_t mask = (layer_state_t)1 << layer;
+    if ((locked_layers & mask) == 0) { // Layer is being locked.
+#    ifndef NO_ACTION_ONESHOT
+        if (layer == get_oneshot_layer()) {
+            reset_oneshot_layer(); // Reset so that OSL doesn't turn layer off.
+        }
+#    endif // NO_ACTION_ONESHOT
+        layer_on(layer);
+#    if defined(LAYER_LOCK_IDLE_TIMEOUT) && LAYER_LOCK_IDLE_TIMEOUT > 0
+        layer_lock_timer = timer_read32();
+#    endif   // LAYER_LOCK_IDLE_TIMEOUT > 0
+    } else { // Layer is being unlocked.
+        layer_off(layer);
+    }
+    layer_lock_set_kb(locked_layers ^= mask);
+}
+
+// Implement layer_lock_on/off by deferring to layer_lock_invert.
+void layer_lock_on(uint8_t layer) {
+    if (!is_layer_locked(layer)) {
+        layer_lock_invert(layer);
+    }
+}
+
+void layer_lock_off(uint8_t layer) {
+    if (is_layer_locked(layer)) {
+        layer_lock_invert(layer);
+    }
+}
+
+void layer_lock_all_off(void) {
+    layer_and(~locked_layers);
+    locked_layers = 0;
+    layer_lock_set_kb(locked_layers);
+}
+
+__attribute__((weak)) bool layer_lock_set_kb(layer_state_t locked_layers) {
+    return layer_lock_set_user(locked_layers);
+}
+__attribute__((weak)) bool layer_lock_set_user(layer_state_t locked_layers) {
+    return true;
+}
+#endif // NO_ACTION_LAYER

quantum/layer_lock.h

@@ -0,0 +1,135 @@
+// Copyright 2022-2023 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 layer_lock.h
+ * @brief Layer Lock, a key to stay in the current layer.
+ *
+ * Overview
+ * --------
+ *
+ * Layers are often accessed by holding a button, e.g. with a momentary layer
+ * switch `MO(layer)` or layer tap `LT(layer, key)` key. But you may sometimes
+ * want to "lock" or "toggle" the layer so that it stays on without having to
+ * hold down a button. One way to do that is with a tap-toggle `TT` layer key,
+ * but here is an alternative.
+ *
+ * This library implements a "Layer Lock key". When tapped, it "locks" the
+ * highest layer to stay active, assuming the layer was activated by one of the
+ * following keys:
+ *
+ *  * `MO(layer)` momentary layer switch
+ *  * `LT(layer, key)` layer tap
+ *  * `OSL(layer)` one-shot layer
+ *  * `TT(layer)` layer tap toggle
+ *  * `LM(layer, mod)` layer-mod key (the layer is locked, but not the mods)
+ *
+ * Tapping the Layer Lock key again unlocks and turns off the layer.
+ *
+ * @note When a layer is "locked", other layer keys such as `TO(layer)` or
+ * manually calling `layer_off(layer)` will override and unlock the layer.
+ *
+ * Configuration
+ * -------------
+ *
+ * Optionally, a timeout may be defined so that Layer Lock disables
+ * automatically if not keys are pressed for `LAYER_LOCK_IDLE_TIMEOUT`
+ * milliseconds. Define `LAYER_LOCK_IDLE_TIMEOUT` in your config.h, for instance
+ *
+ *     #define LAYER_LOCK_IDLE_TIMEOUT 60000  // Turn off after 60 seconds.
+ *
+ * and call `layer_lock_task()` from your `matrix_scan_user()` in keymap.c:
+ *
+ *     void matrix_scan_user(void) {
+ *       layer_lock_task();
+ *       // Other tasks...
+ *     }
+ *
+ * For full documentation, see
+ * <https://getreuer.info/posts/keyboards/layer-lock>
+ */
+
+#pragma once
+
+#include <stdint.h>
+#include <stdbool.h>
+#include "action_layer.h"
+#include "action_util.h"
+
+/**
+ * Handler function for Layer Lock.
+ *
+ * In your keymap, define a custom keycode to use for Layer Lock. Then handle
+ * Layer Lock from your `process_record_user` function by calling
+ * `process_layer_lock`, passing your custom keycode for the `lock_keycode` arg:
+ *
+ *     #include "features/layer_lock.h"
+ *
+ *     bool process_record_user(uint16_t keycode, keyrecord_t* record) {
+ *       if (!process_layer_lock(keycode, record, LLOCK)) { return false; }
+ *       // Your macros ...
+ *
+ *       return true;
+ *     }
+ */
+
+#ifndef NO_ACTION_LAYER
+/** Returns true if `layer` is currently locked. */
+bool is_layer_locked(uint8_t layer);
+
+/** Locks and turns on `layer`. */
+void layer_lock_on(uint8_t layer);
+
+/** Unlocks and turns off `layer`. */
+void layer_lock_off(uint8_t layer);
+
+/** Unlocks and turns off all locked layers. */
+void layer_lock_all_off(void);
+
+/** Toggles whether `layer` is locked. */
+void layer_lock_invert(uint8_t layer);
+
+/**
+ * Optional callback that gets called when a layer is locked or unlocked.
+ *
+ * This is useful to represent the current lock state, e.g. by setting an LED or
+ * playing a sound. In your keymap, define
+ *
+ *     void layer_lock_set_user(layer_state_t locked_layers) {
+ *       // Do something like `set_led(is_layer_locked(NAV));`
+ *     }
+ *
+ * @param locked_layers Bitfield in which the kth bit represents whether the
+ *                      kth layer is on.
+ */
+bool layer_lock_set_kb(layer_state_t locked_layers);
+bool layer_lock_set_user(layer_state_t locked_layers);
+
+void layer_lock_task(void);
+#else  // NO_ACTION_LAYER
+static inline bool is_layer_locked(uint8_t layer) {
+    return false;
+}
+static inline void layer_lock_on(uint8_t layer) {}
+static inline void layer_lock_off(uint8_t layer) {}
+static inline void layer_lock_all_off(void) {}
+static inline void layer_lock_invert(uint8_t layer) {}
+static inline bool layer_lock_set_kb(layer_state_t locked_layers) {
+    return true;
+}
+static inline bool layer_lock_set_user(layer_state_t locked_layers) {
+    return true;
+}
+static inline void layer_lock_task(void) {}
+#endif // NO_ACTION_LAYER

quantum/process_keycode/process_layer_lock.c

@@ -0,0 +1,95 @@
+// Copyright 2022-2023 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 layer_lock.c
+ * @brief Layer Lock implementation
+ *
+ * For full documentation, see
+ * <https://getreuer.info/posts/keyboards/layer-lock>
+ */
+
+#include "layer_lock.h"
+#include "process_layer_lock.h"
+#include "quantum_keycodes.h"
+#include "action_util.h"
+
+// The current lock state. The kth bit is on if layer k is locked.
+extern layer_state_t locked_layers;
+#if defined(LAYER_LOCK_IDLE_TIMEOUT) && LAYER_LOCK_IDLE_TIMEOUT > 0
+extern uint32_t layer_lock_timer;
+#endif
+
+// Handles an event on an `MO` or `TT` layer switch key.
+static bool handle_mo_or_tt(uint8_t layer, keyrecord_t* record) {
+    if (is_layer_locked(layer)) {
+        if (record->event.pressed) { // On press, unlock the layer.
+            layer_lock_invert(layer);
+        }
+        return false; // Skip default handling.
+    }
+    return true;
+}
+
+bool process_layer_lock(uint16_t keycode, keyrecord_t* record) {
+#ifndef NO_ACTION_LAYER
+#    if defined(LAYER_LOCK_IDLE_TIMEOUT) && LAYER_LOCK_IDLE_TIMEOUT > 0
+    layer_lock_timer = timer_read32();
+#    endif // LAYER_LOCK_IDLE_TIMEOUT > 0
+
+    // The intention is that locked layers remain on. If something outside of
+    // this feature turned any locked layers off, unlock them.
+    if ((locked_layers & ~layer_state) != 0) {
+        layer_lock_set_kb(locked_layers &= layer_state);
+    }
+
+    if (keycode == QK_LAYER_LOCK) {
+        if (record->event.pressed) { // The layer lock key was pressed.
+            layer_lock_invert(get_highest_layer(layer_state));
+        }
+        return false;
+    }
+
+    switch (keycode) {
+        case QK_MOMENTARY ... QK_MOMENTARY_MAX: // `MO(layer)` keys.
+            return handle_mo_or_tt(QK_MOMENTARY_GET_LAYER(keycode), record);
+
+        case QK_LAYER_TAP_TOGGLE ... QK_LAYER_TAP_TOGGLE_MAX: // `TT(layer)`.
+            return handle_mo_or_tt(QK_LAYER_TAP_TOGGLE_GET_LAYER(keycode), record);
+
+        case QK_LAYER_MOD ... QK_LAYER_MOD_MAX: { // `LM(layer, mod)`.
+            uint8_t layer = QK_LAYER_MOD_GET_LAYER(keycode);
+            if (is_layer_locked(layer)) {
+                if (record->event.pressed) { // On press, unlock the layer.
+                    layer_lock_invert(layer);
+                } else { // On release, clear the mods.
+                    clear_mods();
+                    send_keyboard_report();
+                }
+                return false; // Skip default handling.
+            }
+        } break;
+
+#    ifndef NO_ACTION_TAPPING
+        case QK_LAYER_TAP ... QK_LAYER_TAP_MAX: // `LT(layer, key)` keys.
+            if (record->tap.count == 0 && !record->event.pressed && is_layer_locked(QK_LAYER_TAP_GET_LAYER(keycode))) {
+                // Release event on a held layer-tap key where the layer is locked.
+                return false; // Skip default handling so that layer stays on.
+            }
+            break;
+#    endif // NO_ACTION_TAPPING
+    }
+#endif // NO_ACTION_LAYER
+    return true;
+}

quantum/process_keycode/process_layer_lock.h

@@ -0,0 +1,69 @@
+// Copyright 2022-2023 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 layer_lock.h
+ * @brief Layer Lock, a key to stay in the current layer.
+ *
+ * Overview
+ * --------
+ *
+ * Layers are often accessed by holding a button, e.g. with a momentary layer
+ * switch `MO(layer)` or layer tap `LT(layer, key)` key. But you may sometimes
+ * want to "lock" or "toggle" the layer so that it stays on without having to
+ * hold down a button. One way to do that is with a tap-toggle `TT` layer key,
+ * but here is an alternative.
+ *
+ * This library implements a "Layer Lock key". When tapped, it "locks" the
+ * highest layer to stay active, assuming the layer was activated by one of the
+ * following keys:
+ *
+ *  * `MO(layer)` momentary layer switch
+ *  * `LT(layer, key)` layer tap
+ *  * `OSL(layer)` one-shot layer
+ *  * `TT(layer)` layer tap toggle
+ *  * `LM(layer, mod)` layer-mod key (the layer is locked, but not the mods)
+ *
+ * Tapping the Layer Lock key again unlocks and turns off the layer.
+ *
+ * @note When a layer is "locked", other layer keys such as `TO(layer)` or
+ * manually calling `layer_off(layer)` will override and unlock the layer.
+ *
+ * Configuration
+ * -------------
+ *
+ * Optionally, a timeout may be defined so that Layer Lock disables
+ * automatically if not keys are pressed for `LAYER_LOCK_IDLE_TIMEOUT`
+ * milliseconds. Define `LAYER_LOCK_IDLE_TIMEOUT` in your config.h, for instance
+ *
+ *     #define LAYER_LOCK_IDLE_TIMEOUT 60000  // Turn off after 60 seconds.
+ *
+ * and call `layer_lock_task()` from your `matrix_scan_user()` in keymap.c:
+ *
+ *     void matrix_scan_user(void) {
+ *       layer_lock_task();
+ *       // Other tasks...
+ *     }
+ *
+ * For full documentation, see
+ * <https://getreuer.info/posts/keyboards/layer-lock>
+ */
+
+#pragma once
+
+#include <stdint.h>
+#include <stdbool.h>
+#include "action.h"
+
+bool process_layer_lock(uint16_t keycode, keyrecord_t* record);

quantum/quantum.c

@@ -76,6 +76,10 @@
 #    include "process_unicode_common.h"
 #endif
 
+#ifdef LAYER_LOCK_ENABLE
+#    include "process_layer_lock.h"
+#endif // LAYER_LOCK_ENABLE
+
 #ifdef AUDIO_ENABLE
 #    ifndef GOODBYE_SONG
 #        define GOODBYE_SONG SONG(GOODBYE_SOUND)
@@ -400,6 +404,9 @@ bool process_record_quantum(keyrecord_t *record) {
 #ifdef TRI_LAYER_ENABLE
             process_tri_layer(keycode, record) &&
 #endif
+#ifdef LAYER_LOCK_ENABLE
+            process_layer_lock(keycode, record) &&
+#endif
 #ifdef BLUETOOTH_ENABLE
             process_connection(keycode, record) &&
 #endif

quantum/quantum.h

@@ -240,6 +240,10 @@ extern layer_state_t layer_state;
 #    include "os_detection.h"
 #endif
 
+#ifdef LAYER_LOCK_ENABLE
+#    include "layer_lock.h"
+#endif // LAYER_LOCK_ENABLE
+
 void set_single_default_layer(uint8_t default_layer);
 void set_single_persistent_default_layer(uint8_t default_layer);