Re: How does vim choose a color that is not in the terminals color palette?

On Thu, Jun 15, 2017 at 1:17 PM, S. Jacobi <sjacobi@mailueberfall.de> wrote:
> On Wed, 14 Jun 2017 17:54:50 -0700 (PDT)
> Tony Mechelynck <antoine.mechelynck@gmail.com> wrote:
>
>> On Thursday, June 15, 2017 at 2:35:39 AM UTC+2, S. Jacobi wrote:
>> > I am using termite as my terminal emulator, which advertises 256
>> > colors support via terminfo. I only defined 20 colors: fg, fg_bold,
>> > bg, cursor and the 16 colors in their normal and bright variants.
>> > I do not use a vim colorscheme, just the terminal colors. In some
>> > shell scripts I see colors that I have not defined and which are
>> > not affected if I change my color palette. So my question is: How
>> > are those colors determined and how can I change them?
>> >
>> > How to reproduce:
>> > 1) set t_Co=256 in vimrc (if it is set to 16 those "new" colors do
>> > not appear)
>> > 2) I set all 16 colors in my termite config file to #ff0000 (to
>> > oberserve the changes)
>> > 3) Minimal shell script:
>> > #/bin/bash
>> > $testvar=1
>> > cd dir
>> > ./command --help
>> > 4) $testvar is in cyan, --help is in some pinkish color
>> >
>> > I haven't tested setting all 256 colors in my config file to red, if
>> > this affects those two cases I found.
>> >
>> > Kind regards
>>
>> First, check that Vim knows that yout terminal allows 256 colors:
>>
>> :set t_Co?
>>
>> The answer should be
>>
>> t_Co=256
>>
>> If it isn't, and you know that your current console _does_ support
>> 256 colors, you can set it. Even in your vimrc if you know how to
>> identify that terminal (as opposed to a dumb 16-color text console)
>> at startup, e.g. from its 'term' value.
>>
>> Then, if you don't want to bother to identify where (at which
>> ordinal) in the terminal palette a certain pink or green or whichever
>> color is found, I recommend to use gui-like settings in the cterm.
>> There are two ways to do that:
>>
>> a) (easiest)
>> if has('termguicolors')
>> set termguicolors
>> endif
>>
>> b) to use guifg= guibg= in the cterm even with a gui-enabled Vim not
>> compiled with +termguicolors, you could also take advantage of the
>> CSApprox plugin, see
>> http://vim.wikia.com/wiki/Using_GUI_color_settings_in_a_terminal#Solution_2:_the_CSApprox_plugin
>>
>>
>> Best regards,
>> Tony.
>>
>
> Thanks for your answer. Me setting t_Co=256 in my vimrc was just
> keeping this line for testing purposes. If t_Co is not set at all, it
> is set automatically to 256 because this is what termite adertises via
> terminfo. I can manually force it to 16 so the "extra" colors are not
> used.
> My vim was not compiled with the termguicolors feature, so I don't know
> if b) applies here, too.

The CSApprox plugin was written before the +termguicolors feature was
even invented. It applies regardless of its presence, in any Vim
version which can remember GUI highlight settings while running in the
console. I tried to find out which Vim version this means but failed.
If when running Vim in a console and setting both (gui= guibg= guifg=
guisp= ) and (cterm= ctermfg= ctermbg= ) parts of the :highlight
command they are both remembered, then you should be all right.

> But I am actually interested in the internals. Is there a way to find
> the color index without manually checking color16 to color 255? Or
> even a comprehensive list of all uses of colorX with X > 15? No vim
> color scheme is used.

From the CSApprox plugin help:
[...]
Also, there are at least three different 256-color palettes in use. Nearly
all terminals use an xterm-compatible palette, so most users need not concern
themselves with this, with only two exceptions: Eterm uses a slightly
different palette, and older Konsole (pre KDE 2.2.0) used a third palette.
CSApprox has no reliable way to tell which palette your terminal uses, so it
makes some educated guesses:
[...]

There is also a "colortest" plugin, see ":help colortest.vim" — but by
default it will display the basic bg & fg colors by setting special
highlight groups to them. Vim cannot define anywhere near 16777216²,
or even 256², highlight groups at the same time so it is not possible
to get a list of all possible combinations displayed. IIUC the 256
colors are subdivided in 3 categories:
- Colors 0 to 0x0F are the colors used by 16-color terminals
- 216 (i.e. 6³) positions are used for the so-called "safe" colors,
i.e. those of the 16777216 for which the red, green and blue settings
are each (separately) a multiple of 0x33, namely one of {0x00, 0x33,
0x66, 0x99, 0xCC, 0xFF} for red, one of the same list for green and
one of the same list for blue.
- The rest (24 positions) are additional greyscale values.

Best regards,
Tony.

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