More on input

I’ve written about input before (here and here), and more recently, Carlos and myself gave a Guadec talk about input-related topics (slides). In those writings, I have explained how dead keys work, and how you can type

<dead_acute> A

to produce an Á character.

But input is full of surprises, and I’ve just learned about an alternative to dead keys that is worth presenting here.


First lets recap what happens when you send the <dead_acute> A sequence to GTK.

We receive the first key event and notice that it is a dead key, so we stash it in what we call the preedit, and wait for the next event.  When the next key arrives, and it represents a letter (more precisely, is in one of the Unicode categories Ll, Lu, Lt, Lm or Lo), we look up the Unicode combining mark matching the dead_acute, which is U+301 COMBINING ACUTE ACCENT, and then we flip the sequence around. So the text that gets committed is

A <combining acute>

The reason that we have to flip things around is that combining marks go after the base character, while dead keys go before.

This works, but it is a bit unintuitive for writing multi-accented characters. You have to think about the accents you want to apply from top to bottom, since they get applied backwards. For example to create an  with an acute accent on top, you type

<dead_acute> <dead_circumflex> A

which then gets flipped around and ends up as:

A <combinining circumflex> <combining acute>

A better way

To me, it feels much more natural to specify the accents in that order:

  1. give me an A
  2. then put a ^ on top
  3. and then put an ´ on top

The good news is: we can do just that! Keyboard layouts can use any Unicode character as keysyms, so we can just use the combining marks directly, without the detour through dead keys.

For example, the “English (US,  Intl, AltGr Unicode combining)” layout contains keys for combining marks. A slight hurdle to using this layout is that it does not show up in the GNOME Settings keyboard panel by default. You have to run

gsettings set org.gnome.desktop.input-sources show-all-sources true

to make it show up.

The combining marks in this layout are placed in a “3rd level”. To use them, you need to set up a “3rd level chooser” key. In the keyboard panel, this is called the “Alternative Characters Key”. A common choice is the right Alt key.

After all these preparations, you can now type A Alt+^ Alt+’ to get an   with an   ́ on top. Neat!