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](https://github.com/algernon) in [#451](https://github.com/qmk/qmk_firmware/pull/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.
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.
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_LAYER_MOVE(kc, layer)`: Sends the `kc` keycode when tapped once, or moves to `layer`. (this functions like the `TO` layer keycode).
* This is the same as `ACTION_TAP_DANCE_DUAL_ROLE`, but renamed to something that is clearer about its functionality. Both names will work.
*`ACTION_TAP_DANCE_LAYER_TOGGLE(kc, layer)`: Sends the `kc` keycode when tapped once, or toggles the state of `layer`. (this functions like the `TG` layer keycode).
*`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.
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.
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.
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](https://github.com/qmk/qmk_firmware/tree/master/users/gordon) 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:
```c
// 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
### 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`:
The above code is similar to that used in previous examples. The one point to note is that we need to be able to check which layers are active at any time so we can toggle them if needed. To do this we use the `layer_state_is( layer )` function which returns `true` if the given `layer` is active.
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[]`.
