Re: 't_Co' is always set to 256 if 'nocompatible' is set

On 04/11/13 00:55, fechnedu@gmail.com wrote:
>> When you set Vim to be not-compatible, it checks the returned info from
>> xterm to figure out the number of supported colors. So your xterm
>> probably actually supports 256 colors, right?
>
> Yes, the xterm I'm using supports 256 colors. I actually switched my
> operating system recently, so thats probably the reason I didn't experienced
> this before (can't remember how many colors xterm supported there).
>
> I set TERM to 'xterm-16color' because I want all programs (and especially Vim)
> to use only 16 colors.
>
> Anyway, it seems like I have to hardcode 't_Co' in my vimrc which is quite ugly.
> Or can I somehow force Vim to use the appropriate terminfo entry instead?
>
The colours Vim uses depend on its colorscheme. If you don't set any,
you get the default colours, which use only the 16 color codes
compatible with any color depth (or maybe even 16 foreground and 8
background colours; there are still some consoles in use today which
don't go higher than that). Most programs displaying on the console do
the same; many even use only black & white, possibly with underline if
available (on some consoles, underlining becomes blue color).

To display more than 16 colours on a console in Vim, you need a
colorscheme which defines highlights with ctermfg= and/or ctermbg=
values higher than 15, and those who do may assume that the user knows
hat he's doing, and not check that t_Co is high enough (they could test
if they wanted to).

So I think your fears are unfounded. If you don't set any colorscheme,
or if you choose one that supports 16-color consoles, Vim won't use
more. Of course, gvim uses all 2^24 (or 16777216) colors available on
modern color graphic displays.

However, even so, you can force Vim to ignore the t_Co value returned by
the xterm, as follows (untested):

:autocmd TermResponse * set t_Co=16
or even
:au TermResponse * if &term ~= '^xterm-\=16'
\ | set t_Co=16 | endif

This will be triggered only when the response comes back from the xterm,
thus not on any other terminals. The condition in the if clause means:
if 'term' starts with "xterm16" or "xterm-16". The single quotes are
essential in order to pass the backslash as-is to the regex engine.

I'm writing this second example on two lines with \ line continuation
for legibility, but note that continuation lines are not supported in
'compatible' mode. If this is a concern, you may prefer to write
everything on one long line.


Best regards,
Tony.
--
More are taken in by hope than by cunning.
-- Vauvenargues

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