TERM "*-direct" values are not recognized as True Color-capable

[mc-butler]

Important

This issue was migrated from Trac:

Origin	https://midnight-commander.org/ticket/4137
Reporter	RogueScholar (admin@….net)
Keywords	truecolor, terminfo, color

Using latest versions of Konsole and Yakuake terminal emulators with True Color (24-bit or Direct RGB) color support announced via the pair of environment variables:

 TERM=konsole-direct
 COLORTERM=truecolor

With MC configured to use either 256-color or 16M-color skins reports on invocation that the terminal is capable of only basic 16-color palettes and has reverted to the default skin accordingly. Prepending 'TERM=konsole-256color' to the invocation while leaving the COLORTERM variable set as before provides the expected behavior, with skins of all color bit-depths able to be set and subsequently displaying as designed. A test with TERM set to the more generic 'xterm-direct' value produced the same results as 'konsole-direct' where MC does not recognize direct RGB colors. This leads me to conclude that MC lacks recognition for the "-direct" values for TERM which were implemented in S-Lang 2.3.1 built with ncurses >=6.1.

System info

• Operating System: Kubuntu 20.10
• KDE Plasma Version: 5.20.0
• KDE Frameworks Version: 5.76.0
• Qt Version: 5.15.0
• Kernel Version: 5.8.0-23-generic
• OS Type: 64-bit

Hardware

• Model: Lenovo ThinkPad T420s
• Processor: Intel® Core™ i7-2620M CPU @ 2.70GHz
• Memory: 8 GiB of RAM
• Graphics Processor: NVS 4200M/PCIe/SSE2

Relevant Software Versions

• libncursesw6: 6.2
• libslang2: 2.3.2 (built using unicode-data 13.0.0)
• konsole: 20.08.2
• yakuake: 20.08.1

Debugging command output

$ LC_MESSAGES=C mc -V
GNU Midnight Commander 4.8.25-55-g5bf714b

Built with GLib 2.64.2

Built with S-Lang 2.3.2 with terminfo database

With builtin Editor and Aspell support

With subshell support as default

With support for background operations

With mouse support on xterm and Linux console

With support for X11 events

With internationalization support

With multiple codepages support

With ext2fs attributes support

Virtual File Systems:

cpiofs, tarfs, sfs, extfs, ftpfs, sftpfs, fish

Data types:

char: 8; int: 32; long: 64; void *: 64; size_t: 64; off_t: 64;
$ mc --configure-options
'--build=x86_64-linux-gnu' '--prefix=/usr' '--includedir=${prefix}/include'

'--mandir=${prefix}/share/man' '--infodir=${prefix}/share/info'

'--sysconfdir=/etc' '--localstatedir=/var' '--libexecdir=/usr/lib'

'--srcdir=.' '--disable-maintainer-mode' '--disable-dependency-tracking'

'--disable-silent-rules' '--with-x' '--with-screen=slang' '--enable-aspell'

'--disable-rpath' '--disable-static' 'build_alias=x86_64-linux-gnu'

'CFLAGS=-g -O2 -fdebug-prefix-map=/build/mc-4.8.25~git20201017=.

-fstack-protector-strong -Wformat -Werror=format-security'

'LDFLAGS=-Wl,-Bsymbolic-functions -Wl,-z,relro'

'CPPFLAGS=-Wdate-time -D_FORTIFY_SOURCE=2'

[mc-butler]

Changed by andrew_b (@aborodin) on Oct 20, 2020 at 13:01 UTC (comment 1)

• Component changed from mc-core to mc-tty

[mc-butler]

Changed by andrew_b (@aborodin) on Oct 20, 2020 at 13:24 UTC (comment 2)

Is ncurses-term package installed?

[mc-butler]

Changed by RogueScholar (admin@….net) on Oct 21, 2020 at 4:16 UTC (comment 2.3)

Replying to andrew_b:

Is ncurses-term package installed?

Indeed it is, sorry for having neglected to include it in my report. It and ncurses-base are both installed, matching set with libncursesw6, all version 6.2.

[egmontkob]

*-direct terminfo entries are about as broken as they could be.

mc checks for the number of colors the terminfo entry claims to support, as well as the widespread practice of $COLORTERM (((which is so stupid to exist outside of terminfo, there should be a good way to denote that inside terminfo, but that's what we have))), and based on that it decides whether to allow or reject 256-color or truecolor skins. This logic could easily be adjusted to recognize *-direct entries.

But the question is: Will it work? Can mc be adjusted to make them work?

• Would the bright variants of the basic 8 colors work?
• Would the extended 256 colors (the newly added 6x6x6 color cube and the 24-color grayscale ramp) work?
• Would truecolors #000000 .. #000007 work?

Because *-direct terminfo is so broken by design that it's unable to describe any of these three.

Would these work in ncurses? Given that it's developed by the same person who came up with this *-direct nonsense, I pretty much doubt it, although I haven't tested.

Would these work in slang? I have no idea. It could if slang knows some hardwired escape sequences rather than taking them from terminfo (just as it does now for truecolors if terminfo only describes 256).

[egmontkob]

Just go to know, thanks to #4821 / PR #4822 that there exist xterm-direct16 and xterm-direct256 terminfo entries.

These do support compatibility with the older 16-color or 256-color modes.

In turn, they chop off a larger part of the 256x256x256 truecolor cube. E.g. with xterm-direct256, colors #000000 .. #0000FF (i.e. where R==0 and G==0) are inaccessible.