Add one-hand support.

This adds an action, `ACTION_SWAP_HANDS`, that swaps the the keys on the keyboard across a keymap-defined hemisphere in order to support one-hand typing without requiring a separate one-handed layer. See updated `doc/keymap.md` for more information.

1 files changed, 18 insertions, 0 deletions

diff --git a/tmk_core/common/action.h b/tmk_core/common/action.h
index e8aa12a7c..b9bdfe642 100644
--- a/tmk_core/common/action.h
+++ b/tmk_core/common/action.h
@@ -65,6 +65,24 @@ bool process_record_quantum(keyrecord_t *record);
 #if !defined(NO_ACTION_LAYER) && defined(PREVENT_STUCK_MODIFIERS)
 extern bool disable_action_cache;
 #endif
+
+/* Code for handling one-handed key modifiers. */
+#ifdef ONEHAND_ENABLE
+extern bool swap_hands;
+extern const keypos_t hand_swap_config[MATRIX_ROWS][MATRIX_COLS];
+#if (MATRIX_COLS <= 8)
+typedef  uint8_t    swap_state_row_t;
+#elif (MATRIX_COLS <= 16)
+typedef  uint16_t   swap_state_row_t;
+#elif (MATRIX_COLS <= 32)
+typedef  uint32_t   swap_state_row_t;
+#else
+#error "MATRIX_COLS: invalid value"
+#endif
+
+void process_hand_swap(keyevent_t *record);
+#endif
+
 void process_record_nocache(keyrecord_t *record);
 void process_record(keyrecord_t *record);
 void process_action(keyrecord_t *record, action_t action);