wayland: fix vertical resize

[christoph-heinrich]

The first implementation is really ugly, so I tried it a different way. I'm not sure it's actually preferable over the first attempt, so I made it a separate commit to compare.

[Dudemanguy]

The second commit was more along the lines of what I was thinking but you should choose based on which dimension has the larger absolute value difference since both can change.

Edit: possible third approach just popped in to my head. Maybe just MPSWAP it, do the calculation and then MPSWAP it back?

[christoph-heinrich]

The MPSWAP variant isn't bad. Not as dense as before, but might be easier to understand.
One can make an argument for inverting the condition, but that's purely up to taste.

[Dudemanguy]

Looks reasonable enough.

[Dudemanguy]

Now that I actually tested this (on sway). It unexpectedly doesn't work at all and regresses resizing in the horizontal direction even. I presume this worked for you on plasma so that is weird. We'll need a different approach (no good ideas atm).

[christoph-heinrich]

When resizing vertically or horizontally I can only make the window bigger, but when resizing both (corner with border) I can also make it smaller 😕. I'm pretty sure that used to work, maybe the change to MPSWAP broke it somehow 🤷. I'll look into it later.

[christoph-heinrich]

This is a surprisingly difficult problem to solve... seemingly impossible really.
I'll make it a draft for now and if I ever come up with some genius idea of how to make this work well for all kinds of resizing without having the window jump around or anything, I'll open it up again.

[christoph-heinrich]

I think I found a way to make it behave how it should by keeping track of the kind of resize in the wayland state.
Don't worry about how terrible the code is for now, I'll try to clean it up once it works how it should.
Can you please test if this behaves correctly?

Edit: I already found a bug where after a diagonal resize it sometimes doesn't let the window get smaller in a vertical resize, but when trying again it works. It probably doesn't reliably reset the resize state.

[Dudemanguy]

Succeeded by #11420 instead.