Akela-Leader

Leader keys are a kind of key where when they are tapped, all following keys are swallowed, until the plugin finds a matching sequence in the dictionary, it times out, or fails to find any possibilities. When a sequence is found, the corresponding action is executed, but the processing still continues. If any key is pressed that is not the continuation of the existing sequence, processing aborts, and the key is handled normally.

This behaviour is best described with an example. Suppose we want a behaviour where LEAD u starts unicode input mode, and LEAD u h e a r t should result in a heart symbol being input, and we want LEAD u 0 0 e 9 SPC to input é, and any other hex code that follows LEAD u, should be handled as-is, and passed to the host. Obviously, we can't have all of this in a dictionary.

So we put LEAD u and LEAD u h e a r t in the dictionary only. The first will start unicode input mode, the second will type in the magic sequence that results in the symbol, and then aborts the leader sequence processing. With this setup, if we type LEAD u 0, then LEAD u will be handled first, and start unicode input mode. Then, at the 0, the plugin notices it is not part of any sequence, so aborts leader processing, and passes the key on as-is, and it ends up being sent to the host. Thus, we covered all the cases of our scenario!

Using the plugin

To use the plugin, one needs to include the header, implement some actions, create a dictionary, and configure the provided Leader object to use the dictionary:

#include <Akela-Leader.h>

static void leaderA (void) {
  Serial.println ("leaderA");
}

static void leaderTX (void) {
  Serial.println ("leaderTX");
}

static const Akela::Leader::dictionary_t leaderDictionary PROGMEM = LEADER_DICT
  (
    {LEADER_SEQ (LEAD (0), Key_A), leaderA},
    {LEADER_SEQ (LEAD (0), Key_T, Key_X), leaderTX}
  );

void setup () {
  Serial.begin (9600);

  Leader.configure (leaderDictionary);

  Keyboardio.setup (KEYMAP_SIZE);
  Keyboardio.use (&Leader, NULL);
}

The dictionary is made up of a list of keys, and an action callback. Using the LEADER_DICT and LEADER_SEQ helpers is recommended. The dictionary must be marked PROGMEM!

Note that we need to use the Leader object before any other that adds or changes key behaviour! Failing to do so may result in unpredictable behaviour.

Plugin methods

The plugin provides the Leader object, with the following methods:

.configure(dictionary)

Tells Leader to use the specified dictionary. The dictionary is an array of Akela::Leader::dictionary_t elements. Each element is made up of two elements, the first being a list of keys, the second an action to perform when the sequence is found.

.reset()

Finishes the leader sequence processing. This is best called from actions that are final actions, where one does not wish to continue the leader sequence further in the hopes of finding a longer match.

Further reading

Starting from the example is the recommended way of getting started with the plugin.