Re: Issue using more than 255 color pairs

[Thomas Dickey]

On Sun, Jul 16, 2023 at 10:57:54AM -0400, Bill Gray wrote:
> On 7/16/23 04:35, Thomas Dickey wrote:
> 
> > Rather than using the SVr4-compatible "attron", if you were using a terminal
> > description with more than 256 colors (such as xterm-direct), then the 
> > X/Open
> > interfaces using cchar_t rather than chtype would help:
> > 
> >         int attr_get(attr_t *attrs, short *pair, void *opts);
> >         int wattr_get(WINDOW *win, attr_t *attrs, short *pair, void *opts);
> >         int attr_set(attr_t attrs, short pair, void *opts);
> >         int wattr_set(WINDOW *win, attr_t attrs, short pair, void *opts);
> 
>    And it's documented.  From :
> 
> https://invisible-island.net/ncurses/man/curs_attr.3x.html
> 
> "Color pair values can only be OR'd with attributes if the pair number is
> less than 256.  The alternate functions such as color_set can pass a color
> pair value directly."
> 
>    Looking a few lines above that paragraph reminded me of some things I've
> occasionally wondered about but never got around to asking.  From the same
> URL:
> 
>    "The XSI standard extended conformance level adds new highlights
> A_HORIZONTAL,  A_LEFT,  A_LOW,  A_RIGHT, A_TOP, A_VERTICAL (and
> corresponding WA_ macros for each).  As of August 2013, no known terminal
> provides these highlights."
> 
>    Does that mean "some terminal(s) once did provide these highlights, but
> they're all obsolete/missing as of August 2013"?  Or "Somebody might someday
> provide them,  but they haven't been yet"?

I could change the FAQ to say 2023 (no real difference).  If there's a
chance that something might change, I mention the month/year when I
write the comment.

There aren't a lot of places to look, though: the AT&T terminal database
stopped changing ~1995, while ncurses is still changing.

I've got snapshots of several old-Unix terminal databases, and aside
from some vendor-specific stuff (more flavors of HP and IBM terminals in
their respective HPUX and AIX databases), they're much the same.
 
>    Is there any difference intended between A_UNDERLINE and A_LOW?

I can only guess :-)
 
>    Is A_HORIZONAL basically 'strikeout'?  And what are A_VERTICAL and
> A_PROTECT supposed to be?

I can only guess :-)

In principle, someone could decide how they wanted to interpret it,
and write a terminal description using the capabilities (and then
create bug reports if ncurses doesn't handle it properly).
 
>    I'd think the intended display characteristics might have been described
> it the XSI Curses standard, Issue 4,  but I can't seem to find that on-line.

I link to it from the FAQ

https://invisible-island.net/ncurses/ncurses.faq.html#additional_reading

https://pubs.opengroup.org/onlinepubs/7908799/cursesix.html

but this doesn't give more insight:

https://pubs.opengroup.org/onlinepubs/7908799/xcurses/curses.h.html

(there are a few later revisions only available as PDFs)

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

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