Add support for Key Overrides

[rrotter]

Key Overrides in QMK allow remapping a key based upon which mods the user is holding. This allows, for example, switching the shift layer to produce different symbols, or swapping a base key with its shifted variant.

Docs for QMK implementation

[xs5871]

Could be done with combos. We're missing some knobs for combos anyway and I'm currently working on making this possible as a side effect.

[kilipan]

I've written this for my own usage, maybe someone more versed in python object orientation and kmk's internal logic could refactor it into something like a module? (in an oop-implementation you'd also probably get rid of the need for a global variable)

from kmk.keys import KC, make_key


mods_before_modmorph = set()
def modmorph(names = {'DUMMY_KEY',}, default_kc = KC.NO, morphed_kc = KC.NO, triggers = {KC.LSHIFT, KC.RSHIFT}):
    def _pressed(key, state, KC, *args, **kwargs):
        global mods_before_modmorph
        mods_before_modmorph = triggers.intersection(state.keys_pressed)
        # if a trigger is held, morph key
        if mods_before_modmorph:
            state._send_hid()
            for mod_kc in mods_before_modmorph:
                # discard triggering mods so morphed key is unaffected by them
                state.keys_pressed.discard(mod_kc)
            state.keys_pressed.add(morphed_kc)
            state.hid_pending = True
            return state
        # else return default keycode
        state.keys_pressed.add(default_kc)
        state.hid_pending = True
        return state
    def _released(key, state, KC, *args, **kwargs):
        if {morphed_kc,}.intersection(state.keys_pressed):
            state.keys_pressed.discard(morphed_kc)
            for mod_kc in mods_before_modmorph:
                # re-add previously discarded shift so normal typing isn't impacted
                state.keys_pressed.add(mod_kc)
        else:
            state.keys_pressed.discard(default_kc)
        state.hid_pending = True
        return state
    modmorph_key = make_key(names=names, on_press=_pressed,
                            on_release=_released)
    return modmorph_key

Define a mod morph / key override for e.g. a comma/semicolon key like this:

modmorph({'CSEM', 'COMMA_SEMICOLON'}, KC.COMMA, KC.SEMICOLON)

Then simply use the chosen keycode (here: KC.CSEM or KC.COMMA_SEMICOLON) in your keymap.

[Edits: Improve clarity]

[ShreddingGuitars]

Came across this thread while looking for a way to add custom behaviour on certain keys while holding shift. Based on the Generally Recommended section of the Keys docs and the way overrides are handled for KC.GESC, I wrote the code below, which seems to work fine for me.

class CustomShiftKey(Key):
    def __init__(self, key, shift_key):
        self.key = key
        self.shift_key = shift_key

    def on_press(self, keyboard, coord_int=None):
        SHIFT_TRIGGERS = {KC.LSFT, KC.RSFT}
        
        if SHIFT_TRIGGERS.intersection(keyboard.keys_pressed):
            keyboard._send_hid()
            keyboard.keys_pressed.add(self.shift_key)
            keyboard.hid_pending = True
            return keyboard
        
        keyboard.keys_pressed.add(self.key)
        keyboard.hid_pending = True
        return keyboard
        

    def on_release(self, keyboard, coord_int=None):
        keyboard.keys_pressed.discard(self.key)
        keyboard.keys_pressed.discard(self.shift_key)
        keyboard.hid_pending = True
        return keyboard


KC_LPAK = CustomShiftKey(KC.LPRN, KC.LABK)  # '(', or '<' while holding shift

[xs5871]

KC.GESC, shifted ANSII keys, and similar all have naive implementations that do not take anything else that happens while you type into account. They are known to be buggy and will produce occasional undesired output.