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Tap Dance: A Single Key Can Do 3, 5, or 100 Different Things

Introduction

Hit the semicolon key once, send a semicolon. Hit it twice, rapidly -- send a colon. Hit it three times, and your keyboard's LEDs do a wild dance. That's just one example of what Tap Dance can do. It's one of the nicest community-contributed features in the firmware, conceived and created by algernon in #451. Here's how algernon describes the feature:

With this feature one can specify keys that behave differently, based on the amount of times they have been tapped, and when interrupted, they get handled before the interrupter.

Explanatory Comparison with ACTION_FUNCTION_TAP

ACTION_FUNCTION_TAP can offer similar functionality to Tap Dance, but it's worth noting some important differences. To do this, let's explore a certain setup! We want one key to send Space on single-tap, but Enter on double-tap.

With ACTION_FUNCTION_TAP, it is quite a rain-dance to set this up, and has the problem that when the sequence is interrupted, the interrupting key will be sent first. Thus, SPC a will result in a SPC being sent, if SPC and a are both typed within TAPPING_TERM. With the Tap Dance feature, that'll come out correctly as SPC a (even if both SPC and a are typed within the TAPPING_TERM.

To achieve this correct handling of interrupts, the implementation of Tap Dance hooks into two parts of the system: process_record_quantum(), and the matrix scan. These two parts are explained below, but for now the point to note is that we need the latter to be able to time out a tap sequence even when a key is not being pressed. That way, SPC alone will time out and register after TAPPING_TERM time.

How to Use Tap Dance

But enough of the generalities; lets look at how to actually use Tap Dance!

First, you will need TAP_DANCE_ENABLE=yes in your rules.mk, because the feature is disabled by default. This adds a little less than 1k to the firmware size.

Optionally, you might want to set a custom TAPPING_TERM time by adding something like this in you config.h:

#define TAPPING_TERM 175

The TAPPING_TERM time is the maximum time allowed between taps of your Tap Dance key, and is measured in milliseconds. For example, if you used the above #define statement and set up a Tap Dance key that sends Space on single-tap and Enter on double-tap, then this key will send ENT only if you tap this key twice in less than 175ms. If you tap the key, wait more than 175ms, and tap the key again you'll end up sending SPC SPC instead.

Next, you will want to define some tap-dance keys, which is easiest to do with the TD() macro, that - similar to F() - takes a number, which will later be used as an index into the tap_dance_actions array.

After this, you'll want to use the tap_dance_actions array to specify what actions shall be taken when a tap-dance key is in action. Currently, there are five possible options:

  • ACTION_TAP_DANCE_DOUBLE(kc1, kc2): Sends the kc1 keycode when tapped once, kc2 otherwise. When the key is held, the appropriate keycode is registered: kc1 when pressed and held, kc2 when tapped once, then pressed and held.
  • ACTION_TAP_DANCE_DUAL_ROLE(kc, layer): Sends the kc keycode when tapped once, or moves to layer. (this functions like the TO layer keycode).
  • ACTION_TAP_DANCE_FN(fn): Calls the specified function - defined in the user keymap - with the final tap count of the tap dance action.
  • ACTION_TAP_DANCE_FN_ADVANCED(on_each_tap_fn, on_dance_finished_fn, on_dance_reset_fn): Calls the first specified function - defined in the user keymap - on every tap, the second function when the dance action finishes (like the previous option), and the last function when the tap dance action resets.
  • ACTION_TAP_DANCE_FN_ADVANCED_TIME(on_each_tap_fn, on_dance_finished_fn, on_dance_reset_fn, tap_specific_tapping_term): This functions identically to the ACTION_TAP_DANCE_FN_ADVANCED function, but uses a custom tapping term for it, instead of the predefined TAPPING_TERM.

The first option is enough for a lot of cases, that just want dual roles. For example, ACTION_TAP_DANCE_DOUBLE(KC_SPC, KC_ENT) will result in Space being sent on single-tap, Enter otherwise.

!> Keep in mind that only basic keycodes are supported here. Custom keycodes are not supported.

Similar to the first option, the second option is good for simple layer-switching cases.

For more complicated cases, use the third or fourth options (examples of each are listed below).

Finally, the fifth option is particularly useful if your non-Tap-Dance keys start behaving weirdly after adding the code for your Tap Dance keys. The likely problem is that you changed the TAPPING_TERM time to make your Tap Dance keys easier for you to use, and that this has changed the way your other keys handle interrupts.

Implementation Details

Well, that's the bulk of it! You should now be able to work through the examples below, and to develop your own Tap Dance functionality. But if you want a deeper understanding of what's going on behind the scenes, then read on for the explanation of how it all works!

The main entry point is process_tap_dance(), called from process_record_quantum(), which is run for every keypress, and our handler gets to run early. This function checks whether the key pressed is a tap-dance key. If it is not, and a tap-dance was in action, we handle that first, and enqueue the newly pressed key. If it is a tap-dance key, then we check if it is the same as the already active one (if there's one active, that is). If it is not, we fire off the old one first, then register the new one. If it was the same, we increment the counter and reset the timer.

This means that you have TAPPING_TERM time to tap the key again; you do not have to input all the taps within a single TAPPING_TERM timeframe. This allows for longer tap counts, with minimal impact on responsiveness.

Our next stop is matrix_scan_tap_dance(). This handles the timeout of tap-dance keys.

For the sake of flexibility, tap-dance actions can be either a pair of keycodes, or a user function. The latter allows one to handle higher tap counts, or do extra things, like blink the LEDs, fiddle with the backlighting, and so on. This is accomplished by using an union, and some clever macros.

Examples

Simple Example

Here's a simple example for a single definition:

  1. In your rules.mk, add TAP_DANCE_ENABLE = yes
  2. In your config.h (which you can copy from qmk_firmware/keyboards/planck/config.h to your keymap directory), add #define TAPPING_TERM 200
  3. In your keymap.c file, define the variables and definitions, then add to your keymap:
//Tap Dance Declarations
enum {
  TD_ESC_CAPS = 0
};

//Tap Dance Definitions
qk_tap_dance_action_t tap_dance_actions[] = {
  //Tap once for Esc, twice for Caps Lock
  [TD_ESC_CAPS]  = ACTION_TAP_DANCE_DOUBLE(KC_ESC, KC_CAPS)
// Other declarations would go here, separated by commas, if you have them
};

//In Layer declaration, add tap dance item in place of a key code
TD(TD_ESC_CAPS)

Complex Examples

This section details several complex tap dance examples. All the enums used in the examples are declared like this:

// Enums defined for all examples:
enum {
 CT_SE = 0,
 CT_CLN,
 CT_EGG,
 CT_FLSH,
 X_TAP_DANCE
};

Example 1: Send : on Single Tap, ; on Double Tap

void dance_cln_finished (qk_tap_dance_state_t *state, void *user_data) {
  if (state->count == 1) {
    register_code (KC_RSFT);
    register_code (KC_SCLN);
  } else {
    register_code (KC_SCLN);
  }
}

void dance_cln_reset (qk_tap_dance_state_t *state, void *user_data) {
  if (state->count == 1) {
    unregister_code (KC_RSFT);
    unregister_code (KC_SCLN);
  } else {
    unregister_code (KC_SCLN);
  }
}

//All tap dance functions would go here. Only showing this one.
qk_tap_dance_action_t tap_dance_actions[] = {
 [CT_CLN] = ACTION_TAP_DANCE_FN_ADVANCED (NULL, dance_cln_finished, dance_cln_reset)
};

Example 2: Send "Safety Dance!" After 100 Taps

void dance_egg (qk_tap_dance_state_t *state, void *user_data) {
  if (state->count >= 100) {
    SEND_STRING ("Safety dance!");
    reset_tap_dance (state);
  }
}

qk_tap_dance_action_t tap_dance_actions[] = {
 [CT_EGG] = ACTION_TAP_DANCE_FN (dance_egg)
};

Example 3: Turn LED Lights On Then Off, One at a Time

// on each tap, light up one led, from right to left
// on the forth tap, turn them off from right to left
void dance_flsh_each(qk_tap_dance_state_t *state, void *user_data) {
  switch (state->count) {
  case 1:
    ergodox_right_led_3_on();
    break;
  case 2:
    ergodox_right_led_2_on();
    break;
  case 3:
    ergodox_right_led_1_on();
    break;
  case 4:
    ergodox_right_led_3_off();
    _delay_ms(50);
    ergodox_right_led_2_off();
    _delay_ms(50);
    ergodox_right_led_1_off();
  }
}

// on the fourth tap, set the keyboard on flash state
void dance_flsh_finished(qk_tap_dance_state_t *state, void *user_data) {
  if (state->count >= 4) {
    reset_keyboard();
    reset_tap_dance(state);
  }
}

// if the flash state didn't happen, then turn off LEDs, left to right
void dance_flsh_reset(qk_tap_dance_state_t *state, void *user_data) {
  ergodox_right_led_1_off();
  _delay_ms(50);
  ergodox_right_led_2_off();
  _delay_ms(50);
  ergodox_right_led_3_off();
}

//All tap dances now put together. Example 3 is "CT_FLASH"
qk_tap_dance_action_t tap_dance_actions[] = {
  [CT_SE]  = ACTION_TAP_DANCE_DOUBLE (KC_SPC, KC_ENT)
 ,[CT_CLN] = ACTION_TAP_DANCE_FN_ADVANCED (NULL, dance_cln_finished, dance_cln_reset)
 ,[CT_EGG] = ACTION_TAP_DANCE_FN (dance_egg)
 ,[CT_FLSH] = ACTION_TAP_DANCE_FN_ADVANCED (dance_flsh_each, dance_flsh_finished, dance_flsh_reset)
};

Example 4: 'Quad Function Tap-Dance'

By DanielGGordon

Allow one key to have 4 (or more) functions, depending on number of presses, and if the key is held or tapped. Below is a specific example:

  • Tap = Send x
  • Hold = Send Control
  • Double Tap = Send Escape
  • Double Tap and Hold = Send Alt

Setup

You will need a few things that can be used for 'Quad Function Tap-Dance'.

You'll need to add these to the top of your keymap.c file, before your keymap.

typedef struct {
  bool is_press_action;
  int state;
} tap;

enum {
  SINGLE_TAP = 1,
  SINGLE_HOLD = 2,
  DOUBLE_TAP = 3,
  DOUBLE_HOLD = 4,
  DOUBLE_SINGLE_TAP = 5, //send two single taps
  TRIPLE_TAP = 6,
  TRIPLE_HOLD = 7
};

//Tap dance enums
enum {
  X_CTL = 0,
  SOME_OTHER_DANCE
};

int cur_dance (qk_tap_dance_state_t *state);

//for the x tap dance. Put it here so it can be used in any keymap
void x_finished (qk_tap_dance_state_t *state, void *user_data);
void x_reset (qk_tap_dance_state_t *state, void *user_data);

Now, at the bottom of your keymap.c file, you'll need to add the following:

/* Return an integer that corresponds to what kind of tap dance should be executed.
 *
 * How to figure out tap dance state: interrupted and pressed.
 *
 * Interrupted: If the state of a dance dance is "interrupted", that means that another key has been hit
 *  under the tapping term. This is typically indicitive that you are trying to "tap" the key.
 *
 * Pressed: Whether or not the key is still being pressed. If this value is true, that means the tapping term
 *  has ended, but the key is still being pressed down. This generally means the key is being "held".
 *
 * One thing that is currenlty not possible with qmk software in regards to tap dance is to mimic the "permissive hold"
 *  feature. In general, advanced tap dances do not work well if they are used with commonly typed letters.
 *  For example "A". Tap dances are best used on non-letter keys that are not hit while typing letters.
 *
 * Good places to put an advanced tap dance:
 *  z,q,x,j,k,v,b, any function key, home/end, comma, semi-colon
 *
 * Criteria for "good placement" of a tap dance key:
 *  Not a key that is hit frequently in a sentence
 *  Not a key that is used frequently to double tap, for example 'tab' is often double tapped in a terminal, or
 *    in a web form. So 'tab' would be a poor choice for a tap dance.
 *  Letters used in common words as a double. For example 'p' in 'pepper'. If a tap dance function existed on the
 *    letter 'p', the word 'pepper' would be quite frustating to type.
 *
 * For the third point, there does exist the 'DOUBLE_SINGLE_TAP', however this is not fully tested
 *
 */
int cur_dance (qk_tap_dance_state_t *state) {
  if (state->count == 1) {
    if (state->interrupted || !state->pressed)  return SINGLE_TAP;
    //key has not been interrupted, but they key is still held. Means you want to send a 'HOLD'.
    else return SINGLE_HOLD;
  }
  else if (state->count == 2) {
    /*
     * DOUBLE_SINGLE_TAP is to distinguish between typing "pepper", and actually wanting a double tap
     * action when hitting 'pp'. Suggested use case for this return value is when you want to send two
     * keystrokes of the key, and not the 'double tap' action/macro.
    */
    if (state->interrupted) return DOUBLE_SINGLE_TAP;
    else if (state->pressed) return DOUBLE_HOLD;
    else return DOUBLE_TAP;
  }
  //Assumes no one is trying to type the same letter three times (at least not quickly).
  //If your tap dance key is 'KC_W', and you want to type "www." quickly - then you will need to add
  //an exception here to return a 'TRIPLE_SINGLE_TAP', and define that enum just like 'DOUBLE_SINGLE_TAP'
  if (state->count == 3) {
    if (state->interrupted || !state->pressed)  return TRIPLE_TAP;
    else return TRIPLE_HOLD;
  }
  else return 8; //magic number. At some point this method will expand to work for more presses
}

//instanalize an instance of 'tap' for the 'x' tap dance.
static tap xtap_state = {
  .is_press_action = true,
  .state = 0
};

void x_finished (qk_tap_dance_state_t *state, void *user_data) {
  xtap_state.state = cur_dance(state);
  switch (xtap_state.state) {
    case SINGLE_TAP: register_code(KC_X); break;
    case SINGLE_HOLD: register_code(KC_LCTRL); break;
    case DOUBLE_TAP: register_code(KC_ESC); break;
    case DOUBLE_HOLD: register_code(KC_LALT); break;
    case DOUBLE_SINGLE_TAP: register_code(KC_X); unregister_code(KC_X); register_code(KC_X);
    //Last case is for fast typing. Assuming your key is `f`:
    //For example, when typing the word `buffer`, and you want to make sure that you send `ff` and not `Esc`.
    //In order to type `ff` when typing fast, the next character will have to be hit within the `TAPPING_TERM`, which by default is 200ms.
  }
}

void x_reset (qk_tap_dance_state_t *state, void *user_data) {
  switch (xtap_state.state) {
    case SINGLE_TAP: unregister_code(KC_X); break;
    case SINGLE_HOLD: unregister_code(KC_LCTRL); break;
    case DOUBLE_TAP: unregister_code(KC_ESC); break;
    case DOUBLE_HOLD: unregister_code(KC_LALT);
    case DOUBLE_SINGLE_TAP: unregister_code(KC_X);
  }
  xtap_state.state = 0;
}

qk_tap_dance_action_t tap_dance_actions[] = {
  [X_CTL]     = ACTION_TAP_DANCE_FN_ADVANCED(NULL,x_finished, x_reset)
};

And then simply use TD(X_CTL) anywhere in your keymap.

If you want to implement this in your userspace, then you may want to check out how DanielGGordon has implemented this in their userspace.

Example 5: Using tap dance for advanced mod-tap and layer-tap keys

Tap dance can be used to emulate MT() and LT() behavior when the tapped code is not a basic keycode. This is useful to send tapped keycodes that normally require Shift, such as parentheses or curly braces—or other modified keycodes, such as Control + X.

Below your layers and custom keycodes, add the following:

// tapdance keycodes
enum td_keycodes {
  ALT_LP // Our example key: `LALT` when held, `(` when tapped. Add additional keycodes for each tapdance.
};

// define a type containing as many tapdance states as you need
typedef enum {
  SINGLE_TAP,
  SINGLE_HOLD,
  DOUBLE_SINGLE_TAP
} td_state_t;

// create a global instance of the tapdance state type
static td_state_t td_state;

// declare your tapdance functions:

// function to determine the current tapdance state
int cur_dance (qk_tap_dance_state_t *state);

// `finished` and `reset` functions for each tapdance keycode
void altlp_finished (qk_tap_dance_state_t *state, void *user_data);
void altlp_reset (qk_tap_dance_state_t *state, void *user_data);

Below your LAYOUT, define each of the tapdance functions:

// determine the tapdance state to return
int cur_dance (qk_tap_dance_state_t *state) {
  if (state->count == 1) {
    if (state->interrupted || !state->pressed) { return SINGLE_TAP; }
    else { return SINGLE_HOLD; }
  }
  if (state->count == 2) { return DOUBLE_SINGLE_TAP; }
  else { return 3; } // any number higher than the maximum state value you return above
}
 
// handle the possible states for each tapdance keycode you define:

void altlp_finished (qk_tap_dance_state_t *state, void *user_data) {
  td_state = cur_dance(state);
  switch (td_state) {
    case SINGLE_TAP:
      register_code16(KC_LPRN);
      break;
    case SINGLE_HOLD:
      register_mods(MOD_BIT(KC_LALT)); // for a layer-tap key, use `layer_on(_MY_LAYER)` here
      break;
    case DOUBLE_SINGLE_TAP: // allow nesting of 2 parens `((` within tapping term
      tap_code16(KC_LPRN);
      register_code16(KC_LPRN);
  }
}

void altlp_reset (qk_tap_dance_state_t *state, void *user_data) {
  switch (td_state) {
    case SINGLE_TAP:
      unregister_code16(KC_LPRN);
      break;
    case SINGLE_HOLD:
      unregister_mods(MOD_BIT(KC_LALT)); // for a layer-tap key, use `layer_off(_MY_LAYER)` here
      break;
    case DOUBLE_SINGLE_TAP:
      unregister_code16(KC_LPRN);
  }
}

// define `ACTION_TAP_DANCE_FN_ADVANCED()` for each tapdance keycode, passing in `finished` and `reset` functions
qk_tap_dance_action_t tap_dance_actions[] = {
  [ALT_LP] = ACTION_TAP_DANCE_FN_ADVANCED(NULL, altlp_finished, altlp_reset)
};

Wrap each tapdance keycode in TD() when including it in your keymap, e.g. TD(ALT_LP).

Example 6: Using tap dance for momentary-layer-switch and layer-toggle keys

Tap Dance can be used to mimic MO(layer) and TG(layer) functionality. For this example, we will set up a key to function as KC_QUOT on single-tap, as MO(_MY_LAYER) on single-hold, and TG(_MY_LAYER) on double-tap.

The first step is to include the following code towards the beginning of your keymap.c:

typedef struct {
  bool is_press_action;
  int state;
} tap;

//Define a type for as many tap dance states as you need
enum {
  SINGLE_TAP = 1,
  SINGLE_HOLD = 2,
  DOUBLE_TAP = 3
};

enum {
  QUOT_LAYR = 0     //Our custom tap dance key; add any other tap dance keys to this enum 
};

//Declare the functions to be used with your tap dance key(s)

//Function associated with all tap dances
int cur_dance (qk_tap_dance_state_t *state);

//Functions associated with individual tap dances
void ql_finished (qk_tap_dance_state_t *state, void *user_data);
void ql_reset (qk_tap_dance_state_t *state, void *user_data);

//Declare variable to track which layer is active
int active_layer;

The above code is similar to that used in previous examples. The one point to note is that you need to declare a variable to keep track of what layer is currently the active layer. We'll see why shortly.

Towards the bottom of your keymap.c, include the following code:

//Update active_layer
uint32_t layer_state_set_user(uint32_t state) {
  switch (biton32(state)) {
    case 1:
      active_layer = 1;
      break;
    case 2:
      active_layer = 2;
      break;
    case 3:
      active_layer = 3;
      break;
    default:
      active_layer = 0;
      break;
  }
  return state;
}

//Determine the current tap dance state
int cur_dance (qk_tap_dance_state_t *state) {
  if (state->count == 1) {
    if (!state->pressed) {return SINGLE_TAP;}
    else return SINGLE_HOLD;
  } else if (state->count == 2) {return DOUBLE_TAP;}
  else return 8;
}

//Initialize tap structure associated with example tap dance key
static tap ql_tap_state = {
  .is_press_action = true,
  .state = 0
};

//Functions that control what our tap dance key does
void ql_finished (qk_tap_dance_state_t *state, void *user_data) {
  ql_tap_state.state = cur_dance(state);
  switch (ql_tap_state.state) {
    case SINGLE_TAP: tap_code(KC_QUOT); break;
    case SINGLE_HOLD: layer_on(_MY_LAYER); break;
    case DOUBLE_TAP: 
      if (active_layer==_MY_LAYER) {layer_off(_MY_LAYER);}
      else layer_on(_MY_LAYER);
  }
}

void ql_reset (qk_tap_dance_state_t *state, void *user_data) {
  if (ql_tap_state.state==SINGLE_HOLD) {layer_off(_MY_LAYER);}
  ql_tap_state.state = 0;
}

//Associate our tap dance key with its functionality
qk_tap_dance_action_t tap_dance_actions[] = {
  [QUOT_LAYR] = ACTION_TAP_DANCE_FN_ADVANCED_TIME(NULL, ql_finished, ql_reset, 275)
};

The is where the real logic of our tap dance key gets worked out. Since layer_state_set_user() is called on any layer switch, we use it to update active_layer. Our example is assuming that your keymap.c includes 4 layers, so adjust the switch statement here to fit your actual number of layers.

The use of cur_dance() and ql_tap_state mirrors the above examples.

The case:SINGLE_TAP in ql_finished is similar to the above examples. The case:SINGLE_HOLD works in conjunction with ql_reset() to switch to _MY_LAYER while the tap dance key is held, and to switch away from _MY_LAYER when the key is released. This mirrors the use of MO(_MY_LAYER). The case:DOUBLE_TAP works by checking whether _MY_LAYER is the active layer, and toggling it on or off accordingly. This mirrors the use of TG(_MY_LAYER).

tap_dance_actions[] works similar to the above examples. Note that I used ACTION_TAP_DANCE_FN_ADVANCED_TIME() instead of ACTION_TAP_DANCE_FN_ADVANCED(). This is because I like my TAPPING_TERM to be short (~175ms) for my non-tap-dance keys but find that this is too quick for me to reliably complete tap dance actions - thus the increased time of 275ms here.

Finally, to get this tap dance key working, be sure to include TD(QUOT_LAYR) in your keymaps[].