MacOS alt (fn+option) keycode

[calvn]

I've been trying to find the keycode for the alt key press (fn+option), but could not find it in the docs,, GH issues, or internet forums. KC_LALT acts as option on MacOS, but I would like to have a key mapped for alt. There's an open discussion in #2179 with regards to the fn key, but it seems that mapping the fn key is not recommended so there's no straightforward way to register that key press.

Wondering if there's a keycode for it that's documented elsewhere, and if not what would be the best approach to map that to my keymap?

[egla89]

fn + option does nothing on a Mac. Alt is just written on top of it to ensure compatibility with non MacOS software.

Since the 1990s, "alt" typically appears on the key, as well, for use as an Alt key with non-Mac software, such as Unix and Windows programs

[calvn]

They appear to register different escape sequences through key combinations:

fn+option + up: ^[[5~
option + up: ^[[1;5A

I currently can't do the former in my external keyboard.

[egla89]

were do you see those? Even MacOS itself shows me no difference

[egla89]

option + up is just up on my mac
fn + up = page up
fn + option + up = page up

Go to system preferences -> keyboard -> Input Sources -> show input in menu bar and then "Show keyboard viewer"

[calvn]

You can see the escape sequence of your input in the terminal if you do ctrl+v and then perform the keypress combo.

[egla89]

can you confirm that

fn + option + up

has a different result than

fn + up

?

[calvn]

Yes, they are different. Over the terminal fn + up simply scrolls up the terminal. fn + option + up is mapped to a command on my zsh config, which is the escape sequence for ^[[5~.

In the keyboard viewer, you can also see the difference if you keep option held and then press fn a couple of times to see that a few keys are different -- namely the arrow keys, enter, and backspace.

[egla89]

well if you mapped command to a shortcut that obviously explains it.

[calvn]

This is regardless of what I mapped on zsh (it's an escape sequence to command, not a keypress to escape sequence mapping). I could have an empty zsh config, or not be using zsh at all for this matter, and the above still stands. The actual keypress registers differently.

[skullydazed]

@calvn I think if you press Alt+Page Up on your external keyboard you will get the same result as Fn+Alt+Up on your laptop. Can you give that a try?

[calvn]

@skullydazed I don't have the page up keycode mapped. I'll flash a new keymap with that on it later today and give it a try. Thanks for the suggestion :)

[calvn]

From the looks of the icons in the keyboard viewer it seems that the addition of fn turns those different keys into map to KC_DEL, KC_HOME, KC_END, KC_PGUP, KC_PGDN, and KC_PENT, so that's promising.

[calvn]

@skullydazed That was it! Doing a Alt+Page Up and Alt+Page Down sends ^[[5~ and ^[[6~ respectively.