WIP: per-output default column width

[balsoft]

Add a way to set the default column width per-output.

This is useful when there are multiple outputs with wildly different
aspect ratios, such as one vertical and one horizontal; with this change,
one can set the default width to 1.0 on a vertical one and 0.5 on the
horizontal one, making niri much more usable.

I'm making this draft just to see if a change like this would be accepted;

If there's a chance, I'll add some tests, documentation, and maybe think about
the priorities of various defaults a bit more.

[YaLTeR]

Hey, so I wanted to do this generally, by adding a layout {} section to the output: #401 It's quite a bit more work than just adding 1 setting unfortunately. But I don't want to add a config option that will be obviously obsoleted later.

I'm not sure what's the best way to proceed. You could of course change this PR to add this one option but inside layout {} so it would naturally extend into the full thing when we get to it. But also maybe we should just wait and do the full Layout config right away?

[balsoft]

Hey, so I wanted to do this generally, by adding a layout {} section to the output: #401 It's quite a bit more work than just adding 1 setting unfortunately. But I don't want to add a config option that will be obviously obsoleted later.

Ah, I missed this one.

I'm not sure what's the best way to proceed. You could of course change this PR to add this one option but inside layout {} so it would naturally extend into the full thing when we get to it. But also maybe we should just wait and do the full Layout config right away?

I'd be happy to have this in Niri so that I can avoid maintaining this patch. However I also see why it would be less than ideal to have a partial implementation that would probably be ripped out eventually.

I might first try to just implement the per-output Layout configuration myself to see how hard it would be, and if it's too much work I'll update this PR to have a layout section and leave it to your own judgement.