Re: Question about setal in terminfo db

[Thomas Dickey]

On Sat, Mar 19, 2022 at 05:11:37PM -0400, Robert Lange wrote:
> On Sat, Mar 19, 2022 at 04:10:09PM -0400, Thomas Dickey wrote:
> > On Sat, Mar 19, 2022 at 01:05:04PM -0400, Robert Lange via Bug reports for 
> > ncurses, the GNU implementation of curses wrote:
> > > I have a concern about the terminfo definition for setal, particularly 
> > > for tmux, but also in the other places it appears.
> > > 
> > > The definition I'm looking at in tmux-direct is:
> > > 
> > > setal=\E[%?%p1%{8}%<%t5%p1%d%e58:2::%p1%{65536}%/%d:%p1
> > >       %{256}%/%{255}%&%d:%p1%{255}%&%d%;m
> > > 
> > > This is clearly patterned after the setaf and setab definitions for 
> > > direct addressed color, in which the parameter value less than 8 
> > > generates something like '\E[31m' and anything greater than 8 generates 
> > > an RGB value. However, for setal, I don't think this makes sense, as SGR 
> > > 50-57 don't refer to the primary terminal colors, but to other (generally 
> > > unimplemented) terminal features.
> > > 
> > > I *think* the definition for setal should be simply:
> > > 
> > > setal=\E[58:2::%p1%{65536}%/%d:%p1%{256}%/%{255}%&%d:%p1
> > >       %{255}%&%dm
> > > 
> > > I've tested this on tmux 3.2a and it works.  When I pass in a parameter 
> > > less
> > > than 8, the underline color becomes the corresponding primary terminal 
> > > color,
> > > so I assume that the underlying terminal (libvte 0.54.2 in my case) has 
> > > some
> > > built-in logic to handle colors #000000-#000007 specially.  Specifying 
> > > colors
> > 
> > I recall some comment about that, but since there's no documentation for VTE
> > aside from its source-code, that's an unimportant implementation detail.
> > 
> > git says the feature was added in 0.51.2 (December 2017).
> > 
> > Its developers decided to refer to this as "deco" (apparently to use
> > the same number of characters as "fore" (foreground) and "back" 
> > (background).
> > 
> > > greater than or equal to 8 work exactly as expected, using the RGB value.
> > > (I've also double-checked this using a libvte 0.54.2-based terminal 
> > > without
> > > tmux, with the same results.)
> > > 
> > > I don't have a copy of mintty handy, so I can't yet verify how that 
> > > handles
> > > setal, but I'd be surprised if '\E[51m' is the correct code for red
> > > underline, given that their own documentation says it's supposed to be an
> > > emoji style selector.
> > 
> > hmm - mintty doesn't have a terminfo file in its sources.
> > Reading the source-code... there's nothing that would handle 50-57 
> > specially,
> > and I don't see any commits in the git which would do that.
> 
> I got the info about emoji style selectors from:
> 
> https://github.com/mintty/mintty/wiki/Tips#text-attributes-and-rendering
> 
> But if there's nothing in the source about that, then I guess it's
> just a planned feature...
> 
> > commit ee62f9006b4a14b5f71bf450e235fe63f3fba210
> > Author: mintty <mintty@users.noreply.github.com>
> > Date:   Tue Apr 17 23:31:26 2018 +0200
> > 
> >    SGR 58/59 text attributes for underline colour
> > 
> > (about 6 months after the corresponding changes in VTE).
> > 
> > agreeing, that's an error here:
> > # 2019-06-08
> > #   + add mintty, mintty-direct (Thomas Wolff)
> > 
> > tmux-direct came from here:
> > 
> > https://github.com/tmux/tmux/issues/2370
> > 
> > and while Nicholas commented that (this detail) was incorrect,
> > 
> > https://github.com/tmux/tmux/issues/2370#issuecomment-688158151
> > 
> > neither he nor I noticed that the updated patch did not fix it.
> > 
> > > (That leads me to another point, which is that vte (at least 0.54.2 and
> > > later) supports setal, so I'd like to add that to vte-256color and
> > > vte-direct, but we can handle that in a separate thread if preferable.)
> > 
> > it seems simple enough - I'm only working on terminfo today, will add/amend
> 
> One other feature that I noticed that vte supported that was missing
> in the terminfo entry was 'blink=\E[5m'. Not sure if there's a reason
> that got left out (a lot of hate for blink in some quarters) or if it
> just got missed b/c vte doesn't really document their terminal.

I overlooked it.  The git log says this was added in December 2017.

I recall some earlier comments (probably in a bug report, though
some use other forums for venting) by the developers saying that they
did not intend adding blink.

Best practice for terminal developers is to provide in their sources
a terminal description which uses the supported features (keeping
in mind that terminfo doesn't cover _all_ of the control sequences).

Presumably the developers test _their_ terminal description, and
it helps with documenting things.

In (real life) practice, a minority of terminal developers follow
best practice.  There's a lot of poor behavior in this area.

So... for these, I notice some feature while looking for something
else, or someone mentions it to me, or (probably more often than
not), it just gets ignored.

Now that I'm reminded, I can add that.  But do look at the output of

        infocmp -x xterm vte

to see a few other details where they're different.

-- 
Thomas E. Dickey <dickey@invisible-island.net>
https://invisible-island.net
ftp://ftp.invisible-island.net

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