True color support

[XVilka]

Supporting truecolour means that you can display 16 milion
different colours at the same time.

Truecolour escape codes doesn't use a colour palete. They just specify the
colour itself.

Here's a test case:

printf "\x1b[38;2;255;100;0mTRUECOLOR\x1b[0m\n"

• or https://raw.githubusercontent.com/JohnMorales/dotfiles/master/colors/24-bit-color.sh
• or http://github.com/robertknight/konsole/tree/master/tests/color-spaces.pl
• or https://git.gnome.org/browse/vte/tree/perf/img.sh?h=vte-0-36
• or just run this:

awk 'BEGIN{
    s="/\\/\\/\\/\\/\\"; s=s s s s s s s s;
    for (colnum = 0; colnum<77; colnum++) {
        r = 255-(colnum*255/76);
        g = (colnum*510/76);
        b = (colnum*255/76);
        if (g>255) g = 510-g;
        printf "\033[48;2;%d;%d;%dm", r,g,b;
        printf "\033[38;2;%d;%d;%dm", 255-r,255-g,255-b;
        printf "%s\033[0m", substr(s,colnum+1,1);
    }
    printf "\n";
}'

Keep in mind that it is possible to use both ';' and ':' as parameters delimiter.

According to Wikipedia[1], this is only supported by xterm and konsole.

[1] https://en.wikipedia.org/wiki/ANSI_color

Currently, there is no support for the 24-bit colour descriptions in the terminfo/termcap database and utilites.
See the discussion thread here: https://lists.gnu.org/archive/html/bug-ncurses/2013-10/msg00007.html

Detection

There's no reliable way, and ncurses/terminfo's maintainer expressed he has no intent on introducing support. S-Lang author added a check for $COLORTERM containing either "truecolor" or "24bit" (case sensitive). In turn, VTE, Konsole and iTerm2 set this variable to "truecolor" (it's been there in VTE for a while, it's relatively new and maybe still git-only in Konsole and iTerm2).

This is obviously not a reliable method, and is not forwarded via sudo, ssh etc. However, whenever it errs, it errs on the safe side: does not advertise support whereas it's actually supported. App developers can freely choose to check for this same variable, or introduce their own method (e.g. an option in their config file), whichever matches better the overall design of the given app. Checking $COLORTERM is recommended though, since that would lead to a more unique desktop experience where the user has to set one variable only and it takes effect across all the apps, rather than something separately for each app.

Here are terminals discussions:

Now supporting truecolour

• st (from suckless) [delimeter: semicolon] - http://lists.suckless.org/dev/1307/16688.html
• konsole [delimeter: colon, semicolon] - https://bugs.kde.org/show_bug.cgi?id=107487
• iterm2 [delimeter: colon, semicolon] - since v3 version
• qterminal [delimeter: semicolon] - Colons support in RGB definition lxqt/qterminal#78
• alacritty [delimeter: semicolon] - written in Rust
• kitty [delimeter: semicolon] - uses OpenGL
• cool-retro-term [delimeter: semicolon]
• Black Screen [delimeter: semicolon] - crossplatform, HTML/CSS/JS-based
• Hyper.app [delimeter: semicolon] - crossplatform, HTML/CSS/JS-based (Electron)
• Tera Term [delimeter: colon, semicolon] - Windows platform
• ConEmu [delimeter: semicolon] - Windows platform
• FinalTerm [delimeter: semicolon] - abandoned, iTerm2 borrowing it's ideas and features.
• MacTerm [delimeter: semicolon] - Mac OS X platform
• mintty [delimeter: semicolon] Cygwin and MSYS/MSYS2 since commit mintty/mintty@43f0ed8 (2.0.1 release) - Windows platform
• Windows 10 bash console, since Windows Insiders build 14931
• all libvte based terminals (since 0.36 version) [delimeter: colon, semilocon] - https://bugzilla.gnome.org/show_bug.cgi?id=704449
  • libvte-based Gnome Terminal
  • libvte-based sakura
  • libvte-based xfce4-terminal - since 0.6.90 release, if compiled with GTK+3
  • libvte-based Terminator - since 1.90 release
  • libvte-based Terminix - written in D. Similar user interface as for Terminator.
  • libvte-based Lilyterm - since commit Tetralet/LilyTerm@72536e7
  • libvte-based ROXTerm
  • libvte-based evilvte - no release yet, version from git https://github.com/caleb-/evilvte
  • libvte-based Termit
  • libvte-based Termite
  • libvte-based Tilda
  • libvte-based tinyterm
  • libvte-based Pantheon Terminal
  • libvte-based lxterminal - with --enable-gtk3 configure flag.
  • libvte-based mlterm - with --with-gtk=3.0 configure flag

But there are bunch of libvte-based terminals for GTK2 so they are listed in the another section.

Also, while this one is not exactly a terminal, but a terminal replayer, it still worth mentioning:

• asciinema player: https://github.com/asciinema/asciinema-player

Parsing ANSI colour sequences, but approximating them to 256 palette

• xterm (though doing it wrong: "it uses nearest colour in RGB colour space, with a usualfalse assumption about orthogonal axes")
• urxvt aka rxvt-unicode - since Revision 1.570 http://lists.schmorp.de/pipermail/rxvt-unicode/2016q2/002261.html
• linux console (since v3.16): torvalds/linux@cec5b2a

Note about colour differences: a) RGB axes are not orthogonal, so you cannot use sqrt(R^2+G^2+B^2) formula, b) for colour differences there is more correct (but much more complex) CIEDE2000 formula (which may easily blow up performance if used blindly) [2].

[2] neovim/neovim#793 (comment)

Terminal multiplexers

• tmux - starting from version 2.2 (support since 427b820...)
• screen - has support in 'master' branch, need to be enabled (see 'truecolor' option)
• pymux - tmux clone in pure Python (to enable truecolour run pymux with --truecolor option)
• dvtm - not yet supporting True Colour Add support for true color martanne/dvtm#10

NOT supporting truecolour

• Terminology (Enlightenment) - https://phab.enlightenment.org/T746
• mrxvt (looks abandoned) - https://sourceforge.net/p/materm/feature-requests/41/
• aterm (looks abandoned) - https://sourceforge.net/p/aterm/feature-requests/23/
• fbcon (from linux kernel) - https://bugzilla.kernel.org/show_bug.cgi?id=79551
• FreeBSD console - https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=191652
• yaft framebuffer terminal - RGB SGR sequences support (truecolor) uobikiemukot/yaft#12
• PuTTY (patched version [3] {xterm-like approximation to 256 colors} and [4] {real true colors} available) - Windows platform
• libvte and GTK2 - based:
  • libvte-based GTKTerm2
  • libvte-based stjerm (looks abandoned) - GTK3 and lbvte >= 0.3x support stjerm/stjerm#39

[3] You can download patched version here https://github.com/rdebath/PuTTY

[4] You can download patched version here https://github.com/halcy/PuTTY

Here are another console programs discussions:

Supporting True Colour:

• mc - since 682a5.... See also ticket #3724 for truecolor themes.
• irssi - since PR #48
• neovim - since commit 8dd415e887923f99ab5daaeba9f0303e173dd1aa; need to set termguicolors to enable true color.
• vim - (from 7.4.1770) since commit 8a633e3427b47286869aa4b96f2bfc1fe65b25cd; need to set termguicolors to enable true color.
• emacs - since commit e463e57..., require custom terminfo
• elinks - configure.in:1410 (./configure --enable-true-color)
• s-lang library - (since pre2.3.1-35, for 64bit systems)
• timg - Terminal Image Viewer
• tv - tool to quickly view high-resolution multi-band imagery directly in terminal
• mpv - video player with support of console-only output (since mpv-player/mpv@dd02369)
• radare2 - reverse engineering franework; since be46b9... commit.

Not supporting True Colour:

• mutt - http://dev.mutt.org/trac/ticket/3674
• neomutt - Neomutt true colors support neomutt/neomutt#85
• ncurses library - https://lists.gnu.org/archive/html/bug-ncurses/2013-10/msg00007.html
• termbox library - 24 bit colors support (true colors) nsf/termbox#37
• mcabber - https://bitbucket.org/McKael/mcabber-crew/issue/126/support-for-true-color-16-millions-colors
• tig - Support for True Color (16 millions colors) jonas/tig#227
• joe - https://sourceforge.net/p/joe-editor/patches/116/

[lmorg]

True colour means your users cannot define the colour palette which means if they use a while background (like xterm on Linux and most of the OS X terms do) then the text will be hard to read vs those with black backgrounds.

As it is this package already suffers from that problem - I suspect it's using 256 colours? - which makes it completely unusable for me.

[AXGKl]

finally found some time to work on it a little, especially the config mechanics. will consider both extremes.