How to make an autocommand run for closing a window?

Question

There is a (moderately complicated) way to make an autocommand that only runs when windows are created, but I want to have one for when they are removed as well.

The reason is that whenever a window is created or removed I'd like to run a function I wrote which calculates window heights and re-assigns them into the open windows.

It's mainly about efficient allocation of screen space (tiling). When you remove a window, or add one, any small files may get stretched out into the average height and then it is a pain to shrink them down again.

I don't know that there's a way to embed on this site, so here is gfy link.

https://gfycat.com/UnrulyLikelyDrever

The 9 line file at the bottom ends up taking up half the space once the middle window is closed.

My routine automates it a bit so it works sort of like a tiling window system, but since vimscript is missing some API that would make things nicer it is somewhat slow to run (as I have to use wincmd j/k to move around a bunch inside the function). Therefore I'd like to trigger this only when necessary, which means only when creating or removing entire windows (not upon entry to or exiting focus from them).

Indeed the linked solution for a window open autocommand doesn't even work properly, as I'd really need to have it run after the buffer has loaded (to know the number of lines in the buffer), but I am willing to accept a half-baked solution at this stage.

So the point is I need some autocommands that effectively let me find out when window reflow has occurred. Since there's clearly no WindowReflowed autocommand for this I am looking for some hacks.

Answer 1

You could listen to WinEnter and then compare winnr('$') result to the previous one you could have memorized for the current tab.

If the number increases, it means "new window", a decrease will mean "a window has been closed"

Answer 2

Perhaps the WinClosed event can help (merged in Vim 8.2.3591 and Neovim 0.5).

Answer 3

I didn't quite understand the functionality you are trying to implement, but I'll try to help anyway.

It's an inefficient way, but you can run your function every time you enter a new window, using the WinEnter event.
You will obviously run your function a lot more than needed, but it will also run it when a split is being opened or closed. If you aren't doing anything too heavy, you won't notice it running every time you enter a new split.

For example, this command will resize all the splits to be equal every time you open/close a split or move to a different split:

au WinEnter * normal ^W=

note that ^W is actually Ctrl-w, inserted by pressing Ctrl-v and then Ctrl-w.