TUI: detect background color #5027

joshtriplett · 2016-07-11T10:39:27Z

(Also reported as a vim issue, though I have more hope of a fix here.)

Vim's automatic background color detection works in GUI mode, but not in a terminal.

On any xterm-compatible terminal, vim could detect the background color via terminal escapes (documented in http://invisible-island.net/xterm/ctlseqs/ctlseqs.html) and use that to automatically detect whether to use bg=dark or bg=light (by default or with :set bg&).

To detect the background color:

Include `\e]11;?\a' during terminal initialization.
Asynchronously, when processing input, watch for the escape sequence \e]11;COLOR\a (or equivalent using OSC instead of \e] for the escape, and ST or \e\\ instead of \a for the terminator, which the existing terminal escape sequence handling probably already handles). If the COLOR portion matches rgb:RRRR/GGGG/BBBB where R, G, and B are hex digits, then compute the luminance of the RGB color and classify it as light/dark accordingly. Note that the color components may have anywhere from one to four hex digits, and require scaling accordingly as values out of 4, 8, 12, or 16 bits.

joshtriplett · 2016-07-11T10:45:51Z

Apparently vim already includes support for this, though neovim does not. Search for rbg_status in vim to find the implementation.

It looks like the terminal input handling drastically changed in neovim, making this hard to directly port over. I attached a WIP commit providing an implementation of this for neovim. It almost works: the background detection works perfectly, as does the setting of the default (so set bg& picks up the right default based on the terminal background), but the call to set_option_value to set the current background sometimes (but not always) causes a SIGABRT deep in init_highlight, while processing /usr/share/nvim/runtime/syntax/syncolor.vim. I haven't yet figured out why, and I'd appreciate some help debugging this.

justinmk · 2016-07-13T05:16:27Z

The TUI runs on a separate thread. Most likely that is the cause of the segfault.

but the call to set_option_value to set the current background sometimes (but not always) causes a SIGABRT deep in init_highlight

This is because init_highlight evaluates vimscript, which must always be done only on the main thread. See inline comment for how to avoid this.

justinmk · 2016-07-13T05:16:35Z

src/nvim/tui/input.c

+      if (!option_was_set((char_u *)"bg")) {
+        set_option_value((char_u *)"bg", 0, (char_u *)bgvalue, 0);
+      }
+    }


Try putting this block in a function e.g. set_bg_color_deferred, then schedule it on the main thread like this

loop_schedule(&main_loop, event_create(1, set_bg_color_deferred, ...));

Sure enough, that was the problem. New version momentarily.

joshtriplett · 2016-07-13T06:32:48Z

Just pushed a new version, which now works reliably thanks to @justinmk's advice about running on the main loop.

justinmk · 2016-07-13T06:53:05Z

LGTM. Is there a termcode to set the background? It could be used to feed("\027[...") in tui_spec.lua, to set up a test. Otherwise I can't think of a way to test it, it might be too much trouble. But tests help ASan and coverity.

joshtriplett · 2016-07-13T07:41:37Z

Is there a termcode to set the background?

Yes, the same code the terminal writes back to the application: \x1b]rgb:RRRR/GGGG/BBBB\a. However, note that this would change the background of the running terminal. (And the test itself would only work in a terminal, so it might not work on a CI bot.)

It could be used to feed("\027[...") in tui_spec.lua, to set up a test. Otherwise I can't think of a way to test it, it might be too much trouble. But tests help ASan and coverity.

Looking at tui_spec.lua, it seems possible to add tests for this: just feed the terminal the escape sequences for various colors, followed by :set bg, and see if it has the right background color.

joshtriplett · 2016-07-13T10:10:56Z

I'm not sure why varying subsets of the tests fail on some platforms, while some of the tests pass. I don't know what would cause spurious test failures.

Is it a race condition to send the control sequence that will change the background, followed by echo &background? Could the background remain unset through the echo?

joshtriplett · 2016-07-13T10:11:04Z

One interesting caveat about this change: setting the background causes a redraw, which dismisses the vim intro message. So if you run on a terminal that supports background color detection, and you don't already have set shortmess+=I, this will cause that message to immediately disappear.

oni-link · 2016-07-24T08:38:23Z

src/nvim/tui/input.c

+      } else if (isxdigit(c)) {
+        if (component < 3 && rgb_max[component] != 0xffff) {
+          uint16_t digit = (uint16_t)((c >= '0' && c <= '9')
+                                      ? c - '0' : 10 + tolower(c) - 'a');


hex2nr() in charset.h could be used here.

Thanks; done.

xterm-compatible terminals support reporting their configured colors back to the application. Use this to obtain the current background color, compute its luminance to classify it as light or dark, and set 'bg' accordingly. Also set the default for 'bg', so that `:set bg&` will revert to that detected default.

oni-link · 2016-07-24T09:30:26Z

src/nvim/tui/input.c

+      } else if (bad) {
+        // ignore
+      } else if (c == '/') {
+        if (component < 3) {


Is the sequence not already bad if we see three '/'? Should bad be set?

justinmk · 2016-10-10T11:48:42Z

@joshtriplett Any comment on @oni-link's question? And could you rebase this?

justinmk · 2019-02-17T14:04:14Z

Merged in #9509

justinmk added the tui label Jul 9, 2016

justinmk added this to the todo milestone Jul 9, 2016

justinmk reviewed Jul 13, 2016
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joshtriplett force-pushed the terminal-background branch from c29dd00 to 50030e8 Compare July 13, 2016 06:31

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justinmk modified the milestones: 0.2, todo Jul 13, 2016

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oni-link reviewed Jul 24, 2016
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joshtriplett added 2 commits July 24, 2016 01:56

Add tests for terminal background detection

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joshtriplett force-pushed the terminal-background branch from 0a30531 to 5372d9a Compare July 24, 2016 08:56

oni-link reviewed Jul 24, 2016
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justinmk modified the milestones: 0.2, 0.3 Oct 31, 2016

justinmk mentioned this pull request Jan 15, 2019

Default colorscheme using bright colours #9455

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justinmk modified the milestones: 0.6, 0.4 Jan 16, 2019

justinmk added a commit to justinmk/neovim that referenced this pull request Jan 16, 2019

Merge neovim#5027 'TUI: detect background color'

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justinmk mentioned this pull request Jan 16, 2019

TUI: detect background color #9509

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justinmk added a commit to justinmk/neovim that referenced this pull request Jan 16, 2019

Merge neovim#5027 'TUI: detect background color'

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justinmk added a commit to justinmk/neovim that referenced this pull request Jan 17, 2019

Merge neovim#5027 'TUI: detect background color'

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justinmk added a commit to justinmk/neovim that referenced this pull request Jan 17, 2019

Merge neovim#5027 'TUI: detect background color'

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justinmk changed the title ~~Background color detection for terminals~~ TUI: detect background color Jan 28, 2019

justinmk added a commit to justinmk/neovim that referenced this pull request Feb 17, 2019

Merge neovim#5027 'TUI: detect background color'

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justinmk added a commit to justinmk/neovim that referenced this pull request Feb 17, 2019

Merge neovim#5027 'TUI: detect background color'

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justinmk closed this Feb 17, 2019

gavocanov mentioned this pull request Feb 24, 2019

feature request: query background color kovidgoyal/kitty#1417

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blueyed mentioned this pull request Dec 20, 2019

TUI: bg color response consumed as user input (inserts "g", "0000/2b2b/3636^G") #11393

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khu-md mentioned this pull request Sep 28, 2020

Neovim struggles with detecting light vs dark terminal background color within tmux #13000

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will mentioned this pull request Aug 17, 2021

TUI: re-detect background color on SIGWINCH #15411

Closed

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