tap-dance: Support for holding keys

With this change, tap dance will now store the pressed state of the
tap-dance key, and allow one to make an action sooner, while the key is
still held, and only unregister when the key is released.

The registration must happen in the `on_dance_finished` callback, while
unregistering goes to `on_reset`. The surrounding code makes sure not to
call either multiple times.

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>

quantum/process_keycode/process_tap_dance.c

@@ -73,10 +73,14 @@ bool process_tap_dance(uint16_t keycode, keyrecord_t *record) {
     process_tap_dance_action_on_each_tap (qk_tap_dance_state.keycode);
     if (qk_tap_dance_state.keycode && qk_tap_dance_state.keycode != keycode) {
       process_tap_dance_action_on_dance_finished (qk_tap_dance_state.keycode);
+    } else if (qk_tap_dance_state.active && qk_tap_dance_state.pressed) {
+      reset_tap_dance (&qk_tap_dance_state);
     } else {
       r = false;
     }
 
+    qk_tap_dance_state.active = true;
+    qk_tap_dance_state.pressed = record->event.pressed;
     if (record->event.pressed) {
       qk_tap_dance_state.keycode = keycode;
       qk_tap_dance_state.timer = timer_read ();
@@ -90,6 +94,7 @@ bool process_tap_dance(uint16_t keycode, keyrecord_t *record) {
       process_tap_dance_action_on_each_tap (qk_tap_dance_state.keycode);
       process_tap_dance_action_on_dance_finished (qk_tap_dance_state.keycode);
       reset_tap_dance (&qk_tap_dance_state);
+      qk_tap_dance_state.active = false;
     }
     break;
   }
@@ -98,7 +103,7 @@ bool process_tap_dance(uint16_t keycode, keyrecord_t *record) {
 }
 
 void matrix_scan_tap_dance () {
-  if (qk_tap_dance_state.keycode && timer_elapsed (qk_tap_dance_state.timer) > TAPPING_TERM) {
+  if (qk_tap_dance_state.active && timer_elapsed (qk_tap_dance_state.timer) > TAPPING_TERM) {
     // if we are here, the tap dance was timed out
     process_tap_dance_action_on_dance_finished (qk_tap_dance_state.keycode);
     reset_tap_dance (&qk_tap_dance_state);
@@ -109,6 +114,9 @@ void reset_tap_dance (qk_tap_dance_state_t *state) {
   uint16_t idx = state->keycode - QK_TAP_DANCE;
   qk_tap_dance_action_t action;
 
+  if (state->pressed)
+    return;
+
   action = tap_dance_actions[idx];
   switch (action.type) {
   case QK_TAP_DANCE_TYPE_FN:
@@ -123,4 +131,5 @@ void reset_tap_dance (qk_tap_dance_state_t *state) {
 
   state->keycode = 0;
   state->count = 0;
+  state->active = false;
 }

quantum/process_keycode/process_tap_dance.h

@@ -11,6 +11,8 @@ typedef struct
   uint8_t count;
   uint16_t keycode;
   uint16_t timer;
+  bool active:1;
+  bool pressed:1;
 } qk_tap_dance_state_t;
 
 #define TD(n) (QK_TAP_DANCE + n)