Re: [PATCH iproute2-next v2] color: default to dark color theme

[Phil Sutter <phil@nwl.cc>]

On Fri, Mar 14, 2025 at 06:12:37PM +0100, Phil Sutter wrote:
> On Thu, Mar 13, 2025 at 09:30:35AM -0700, Stephen Hemminger wrote:
> > On Thu, 13 Mar 2025 13:05:19 +0100
> > Phil Sutter <phil@nwl.cc> wrote:
> > 
> > > On Thu, Mar 13, 2025 at 12:41:54PM +0100, Matteo Croce wrote:
> > > > Il giorno gio 13 mar 2025 alle ore 12:28 Phil Sutter <phil@nwl.cc> ha scritto:  
> > > > >
> > > > > On Mon, Mar 10, 2025 at 02:12:16PM -0700, Stephen Hemminger wrote:  
> > > > > > On Mon, 10 Mar 2025 21:36:09 +0100
> > > > > > Matteo Croce <technoboy85@gmail.com> wrote:
> > > > > >  
> > > > > > > From: Matteo Croce <teknoraver@meta.com>
> > > > > > >
> > > > > > > The majority of Linux terminals are using a dark background.
> > > > > > > iproute2 tries to detect the color theme via the `COLORFGBG` environment
> > > > > > > variable, and defaults to light background if not set.
> > > > > > >  
> > > > > >
> > > > > > This is not true. The default gnome terminal color palette is not dark.  
> > > > >
> > > > > ACK. Ever since that famous movie I stick to the real(TM) programmer
> > > > > colors of green on black[1], but about half of all the blue pill takers
> > > > > probably don't.
> > > > >  
> > > > > > > Change the default behaviour to dark background, and while at it change
> > > > > > > the current logic which assumes that the color code is a single digit.
> > > > > > >
> > > > > > > Signed-off-by: Matteo Croce <teknoraver@meta.com>  
> > > > > >
> > > > > > The code was added to follow the conventions of other Linux packages.
> > > > > > Probably best to do something smarter (like util-linux) or more exactly
> > > > > > follow what systemd or vim are doing.  
> > > > >
> > > > > I can't recall a single system on which I didn't have to 'set bg=dark'
> > > > > in .vimrc explicitly, so this makes me curious: Could you name a
> > > > > concrete example of working auto color adjustment to given terminal
> > > > > background?
> > > > >
> > > > > Looking at vim-9.1.0794 source code, I see:
> > > > >
> > > > > |     char_u *
> > > > > | term_bg_default(void)
> > > > > | {
> > > > > | #if defined(MSWIN)
> > > > > |     // DOS console is nearly always black
> > > > > |     return (char_u *)"dark";
> > > > > | #else
> > > > > |     char_u      *p;
> > > > > |
> > > > > |     if (STRCMP(T_NAME, "linux") == 0
> > > > > |             || STRCMP(T_NAME, "screen.linux") == 0
> > > > > |             || STRNCMP(T_NAME, "cygwin", 6) == 0
> > > > > |             || STRNCMP(T_NAME, "putty", 5) == 0
> > > > > |             || ((p = mch_getenv((char_u *)"COLORFGBG")) != NULL
> > > > > |                 && (p = vim_strrchr(p, ';')) != NULL
> > > > > |                 && ((p[1] >= '0' && p[1] <= '6') || p[1] == '8')
> > > > > |                 && p[2] == NUL))
> > > > > |         return (char_u *)"dark";
> > > > > |     return (char_u *)"light";
> > > > > | #endif
> > > > > | }
> > > > >
> > > > > So apart from a little guesswork based on terminal names, this does the
> > > > > same as iproute currently (in his commit 54eab4c79a608 implementing
> > > > > set_color_palette(), Petr Vorel even admitted where he had copied the
> > > > > code from). No hidden gems to be found in vim sources, at least!
> > > > >
> > > > > Cheers, Phil
> > > > >
> > > > > [1] And have the screen rotated 90 degrees to make it more realistic,
> > > > >     but that's off topic.  
> > > > 
> > > > I think that we could use the OSC command 11 to query the color:
> > > > 
> > > > # black background
> > > > $ echo -ne '\e]11;?\a'
> > > > 11;rgb:0000/0000/0000
> > > > 
> > > > # white background
> > > > $ echo -ne '\e]11;?\a'
> > > > 11;rgb:ffff/ffff/ffff  
> > > 
> > > Maybe a better technique than checking $COLORFGBG. Note that:
> > > 
> > > - This may return rgba and a transparency value
> > > - In 'xterm -bg green', it returns '11;rgb:0000/ffff/0000'
> > > 
> > > So the value may not be as clear as in the above cases.
> > > 
> > > Cheers, Phil
> > 
> > Rather than hard coding color palettes it would be better to use some
> > form of environment or config file to allow user to choose.
> 
> I think we have that already. Quoting from ip(8):
> 
>  -c[color][={always|auto|never}
>     [...]
>     Used color palette can be influenced by COLORFGBG environment
>     variable (see ENVIRONMENT).
>  [...]
>  ENVIRONMENT
>     COLORFGBG
>       If set, it’s value is used for detection whether background is
>       dark or light and use contrast colors for it.
> 
>       COLORFGBG  environment  variable  usually contains either two or
>       three values separated by semicolons; we want the last value in
>       either case. If this value is 0-6 or 8, chose colors suitable for
>       dark background:
> 
>       COLORFGBG=";0" ip -c a

Assuming not every terminal sets $COLORFGBG, I guess what Matteo
suggests should aid as a fallback for those cases. This would retain the
existing behaviour wrt. COLORFGBG but improve the situation when
user/terminal don't provide this hint.

Cheers, Phil