layers: Add a MoveToLayer(n) key

While `ShiftToLayer` and `LockLayer` activate the given layer, and keep all
others active as well, `MoveToLayer` activates the given layer, and deactivates
all others. This allows one to have discrete layers that stand on their own,
without any other layers interfering.

Basically, this is a different way to work with layers, a less powerful, but
also simpler one.

Fixes #564.

Signed-off-by: Gergely Nagy <algernon@keyboard.io>

src/kaleidoscope/key_defs_keymaps.h

@@ -20,7 +20,9 @@
 
 #include "kaleidoscope_internal/deprecations.h"
 
-static const uint8_t LAYER_SHIFT_OFFSET = 42;
+static const uint8_t LAYER_OP_OFFSET = 42;
+static const uint8_t LAYER_SHIFT_OFFSET = LAYER_OP_OFFSET;
+static const uint8_t LAYER_MOVE_OFFSET = LAYER_SHIFT_OFFSET + LAYER_OP_OFFSET;;
 
 #define KEYMAP_0     0
 #define KEYMAP_1     1
@@ -68,3 +70,10 @@ static const uint8_t LAYER_SHIFT_OFFSET = 42;
  * value declared previously.
  */
 #define ShiftToLayer(n) Key(n + LAYER_SHIFT_OFFSET, KEY_FLAGS | SYNTHETIC | SWITCH_TO_KEYMAP)
+
+/** Move to layer `n`.
+ *
+ * Moving to a layer disables all other layers. Unlike locking and shifting to,
+ * this is a one-way operation.
+ */
+#define MoveToLayer(n) Key(n + LAYER_MOVE_OFFSET, KEY_FLAGS | SYNTHETIC | SWITCH_TO_KEYMAP)

src/kaleidoscope/layers.cpp

@@ -45,7 +45,11 @@ uint8_t Layer_::active_layers_[Runtime.device().numKeys()];
 Layer_::GetKeyFunction Layer_::getKey = &Layer_::getKeyFromPROGMEM;
 
 void Layer_::handleKeymapKeyswitchEvent(Key keymapEntry, uint8_t keyState) {
-  if (keymapEntry.getKeyCode() >= LAYER_SHIFT_OFFSET) {
+  if (keymapEntry.getKeyCode() >= LAYER_MOVE_OFFSET) {
+    if (keyToggledOn(keyState)) {
+      move(keymapEntry.getKeyCode() - LAYER_MOVE_OFFSET);
+    }
+  } else if (keymapEntry.getKeyCode() >= LAYER_SHIFT_OFFSET) {
     uint8_t target = keymapEntry.getKeyCode() - LAYER_SHIFT_OFFSET;
 
     switch (target) {