How to automatically change the background color of the active split?

Question

I use several splits (windows). To quickly identify the splits that has the focus I would like Vim to auromatically adapt the background color of the active split.

Is there a way to do so?

Is it possible to have a different definition of the highlighting group Normal depending if the split (window) is active or not?

Answer 1

You can use :h wincolor for this: https://asciinema.org/a/od7Eh6sVZdw9r65vUrtctZ0PC

Change non-active windows background:

hi DimNormal guibg=#203040

augroup ActiveWin | au!
    au WinEnter * setl wincolor=
    au WinLeave * setl wincolor=DimNormal
augroup END

Of course, you can do the opposite -- change active window background:

hi NormalActive guibg=#203040

augroup ActiveWin | au!
    au WinEnter * setl wincolor=NormalActive
    au WinLeave * setl wincolor=
augroup END

Answer 2

Another useful mapping (which I have on <leader><leader><leader>, or 3 spaces for me) is to "blink" the current cursor location in an obvious way:

" ~/.vim/autoload/bk.vim
function bk#cursor#blink(time) abort
  call bk#cursor#hl_on()
  let time_in_ms = float2nr(a:time * 1000)
  if has('timers')
    let _ = timer_start(time_in_ms, {_ -> bk#cursor#hl_off()})
  else
    exec 'sleep'  time_in_ms  'm'
    call bk#cursor#hl_off()
  endif
endfunction

function bk#cursor#hl_on() abort
  set cursorline cursorcolumn
  redraw
endfunction

function bk#cursor#hl_off() abort
  set nocursorline nocursorcolumn
  redraw
endfunction

Along with

nnoremap <leader><leader><leader> :call bk#cursor#blink(0.2)<enter>

(Adjust timing as needed.)

Answer 3

Here is a small variation from the solution of @Maxim that seems more robust:

hi DimNormal guibg=#203040

augroup ActiveWin | au!
    au WinEnter,BufEnter * setl wincolor=
    au WinLeave,BufLeave * setl wincolor=DimNormal
augroup END