OSC11 query caches response until client is changed

[Baspar]

Issue description

Following commit a41a927, the OSC 11 sequence correctly returns the background color, but doesn't reflect any change in background color until client is detached/attached

How to reproduce:

~/osc11.bash

#!/usr/bin/env bash
read -rs -d \\ -p $'\e]11;?\e\\' BG
echo "$BG" \
    | xxd -c 64 \
    | grep -o -E "rgb:.{4}/.{4}/.{4}"

1. Clean existing tmux tmux kill-server
2. Start a new session tmux new
3. bash ~/osc11.bash => rgb:fbfb/f1f1/c8c8
4. Update the background from the terminal (In my case, Change from OS light mode to dark mode)
5. bash ~/osc11.bash => rgb:fbfb/f1f1/c8c8 Still shows the previous background color
6. Detach session C-b d
7. Re-attach tmux attach
8. bash ~/osc11.bash => rgb:2020/2020/2020 Shows the new background color

Required information

• tmux version: tmux next-3.4 @ 0eb5d25
• Platform: Darwin arm
• $TERM inside tmux: xterm-256color
• $TERM outside tmux: xterm-256color
• Terminal: Wezterm

[nicm]

There is no mechanism for the terminal to tell tmux the colour has changed and polling for the background colour would be silly. If you change the background colour outside tmux you need to detach and reattach.

[Baspar]

Isn't a41a927 simply relaying the OSC11 ? request to the terminal in case the default background colour isn't set ?
In which case, it should print the updated background in step 5., since that's how it behaves when I run those steps outside of Tmux

[nicm]

Good point, but no, it doesn't, it reads the default value on attach and uses that if you haven't set a background inside tmux.

[Baspar]

Then it explains the behavior indeed.
Is there any plan to add that functionality (If it's possible to implement), or would you be open to a PR for it ?

[nicm]

I would accept a PR but I don't know how easy it would be, it might be fiddly to do (there isn't a way for it to wait for a reply before sending the response).

[vimpostor]

polling for the background colour would be silly

Zellij queries for the bg/fg colour on every SIGWINCH (in addition to on attach), see: zellij-org/zellij#1358

Maybe this could help here, but it looks like not many terminals send SIGWINCH when their colorscheme changes (I only know of iTerm that does this, but it might be something worth implementing in other terminal emulators).

Edit: On second thought, SIGWINCH may be triggered multiple times per second on a real window resize. Repeatedly polling for fg/bg colors could cause performance problems.

[nicm]

Try this please which will do it on WINCH but at most once every 30 seconds: tmux-fgbg-winch.diff.txt

[vimpostor]

@nicm I can confirm the patch is working.

Tested with starting vim inside tmux (which sets background according to OSC11 response), as well as with a manual printf '\e]11;?\a'.

The only problem with this implementation is that tmux may miss a colorscheme change, if the user resizes the window and then changes the colorscheme within the next 30 seconds. But still, it's better than nothing.

[nicm]

Great, I have applied this to OpenBSD now, it will be in GitHub later. Thanks!

[github-actions]

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