Set 'scrolloff' to a fraction based on terminal size

smart_scrolloff.vim

" Reimplementation of https://github.com/tonymajestro/smart-scrolloff.nvim
" Place in `~/.vim/plugin/`
"
" Note that the value is based on `&lines`, which is the global number of
" lines available to Vim. If you'd like to scale scrolloff based on window
" size, you could use `line('w$') - line('w0')`. In that case, you'd update
" `&l:scrolloff`, the window-local option.
"
" See `:help 'scrolloff'`, `:help 'lines'`, and `:help getpos()` for more
" details.

if !exists('g:scrolloff_fraction')
  " Set to 0 to disable. Change value and resize any window to update the
  " global `scrolloff` value.
  let g:scrolloff_fraction = 0.2
endif

augroup smart_scrolloff
  autocmd!

  autocmd BufRead,BufNewFile,WinResized *
        \ if g:scrolloff_fraction > 0 |
        \   let &scrolloff = float2nr(floor(&lines * g:scrolloff_fraction)) |
        \ endif
augroup END

This works great. I've only added BufRead and BufNewFile in the list of events so that it kicks-in without having to resize first (e.g. toggle really quick a filelist, quickfix or something):

-  autocmd WinResized *
+  autocmd BufRead,BufNewFile,WinResized *

@vladimiroff Yeah, I think I did the same while testing, I kept this event, because that's the one used in the original project, but I'll update it for usefulness' sake