|
NAME | SYNOPSIS | DESCRIPTION | PORTABILITY | SEE ALSO | AUTHORS | COLOPHON |
|
user_caps(5) File Formats Manual user_caps(5)
user_caps - user-defined terminfo capabilities
tic -x, infocmp -x
Background
Before ncurses 5.0, terminfo databases used a fixed repertoire of
terminal capabilities designed for the SVr2 terminal database in
1984, and extended in stages through SVr4 (1989), and standardized in
the Single Unix Specification beginning in 1995.
Most of the extensions in this fixed repertoire were additions to the
tables of boolean, numeric and string capabilities. Rather than
change the meaning of an existing capability, a new name was added.
The terminfo database uses a binary format; binary compatibility was
ensured by using a header which gave the number of items in the
tables for each type of capability. The standardization was
incomplete:
· The binary format itself is not described in the X/Open Curses
documentation. Only the source format is described.
Library developers rely upon the SVr4 documentation, and reverse-
engineering the compiled terminfo files to match the binary
format.
· Lacking a standard for the binary format, most implementations
copy the SVr2 binary format, which uses 16-bit signed integers,
and is limited to 4096-byte entries.
The format cannot represent very large numeric capabilities, nor
can it represent large numbers of special keyboard definitions.
· The tables of capability names differ between implementations.
Although they may provide all of the standard capability names,
the position in the tables differs because some features were
added as needed, while others were added (out of order) to comply
with X/Open Curses.
While ncurses' repertoire of predefined capabilities is closest
to Solaris, Solaris's terminfo database has a few differences
from the list published by X/Open Curses.
During the 1990s, some users were reluctant to use terminfo in spite
of its performance advantages over termcap:
· The fixed repertoire prevented users from adding features for
unanticipated terminal improvements (or required them to reuse
existing capabilities as a workaround).
· The limitation to 16-bit signed integers was also mentioned.
Because termcap stores everything as a string, it could represent
larger numbers.
Although termcap's extensibility was rarely used (it was never the
speaker who had actually used the feature), the criticism had a
point. ncurses 5.0 provided a way to detect nonstandard
capabilities, determine their type and optionally store and retrieve
them in a way which did not interfere with other applications. These
are referred to as user-defined capabilities because no modifications
to the toolset's predefined capability names are needed.
The ncurses utilities tic and infocmp have a command-line option “-x”
to control whether the nonstandard capabilities are stored or
retrieved. A library function use_extended_names is provided for the
same purpose.
When compiling a terminal database, if “-x” is set, tic will store a
user-defined capability if the capability name is not one of the
predefined names.
Because ncurses provides a termcap library interface, these user-
defined capabilities may be visible to termcap applications:
· The termcap interface (like all implementations of termcap)
requires that the capability names are 2-characters.
When the capability is simple enough for use in a termcap
application, it is provided as a 2-character name.
· There are other user-defined capabilities which refer to features
not usable in termcap, e.g., parameterized strings that use more
than two parameters or use more than the trivial expression
support provided by termcap. For these, the terminfo database
should have only capability names with 3 or more characters.
· Some terminals can send distinct strings for special keys
(cursor-, keypad- or function-keys) depending on modifier keys
(shift, control, etc.). While terminfo and termcap have a set of
60 predefined function-key names, to which a series of keys can
be assigned, that is insufficient for more than a dozen keys
multiplied by more than a couple of modifier combinations. The
ncurses database uses a convention based on xterm to provide
extended special-key names.
Fitting that into termcap's limitation of 2-character names would
be pointless. These extended keys are available only with
terminfo.
Recognized capabilities
The ncurses library uses the user-definable capabilities. While the
terminfo database may have other extensions, ncurses makes explicit
checks for these:
AX boolean, asserts that the terminal interprets SGR 39 and SGR 49
by resetting the foreground and background color, respectively,
to the default.
This is a feature recognized by the screen program as well.
E3 string, tells how to clear the terminal's scrollback buffer.
When present, the clear(1) program sends this before clearing
the terminal.
The command “tput clear” does the same thing.
RGB
boolean, number or string, to assert that the set_a_foreground
and set_a_background capabilities correspond to direct colors,
using an RGB (red/green/blue) convention. This capability
allows the color_content function to return appropriate values
without requiring the application to initialize colors using
init_color.
The capability type determines the values which ncurses sees:
boolean
implies that the number of bits for red, green and blue are
the same. Using the maximum number of colors, ncurses adds
two, divides that sum by three, and assigns the result to
red, green and blue in that order.
If the number of bits needed for the number of colors is not
a multiple of three, the blue (and green) components lose in
comparison to red.
number
tells ncurses what result to add to red, green and blue. If
ncurses runs out of bits, blue (and green) lose just as in
the boolean case.
string
explicitly list the number of bits used for red, green and
blue components as a slash-separated list of decimal
integers.
U8 boolean, asserts that ncurses must use Unicode values for line-
drawing characters, and that it should ignore the alternate
character set capabilities when the locale uses UTF-8 encoding.
For more information, see the discussion of NCURSES_NO_UTF8_ACS
in ncurses(3X).
Set this capability to a nonzero value to enable it.
XM string, override ncurses's built-in string which
enables/disables xterm mouse mode.
Extended key-definitions
Several terminals provide the ability to send distinct strings for
combinations of modified special keys. There is no standard for what
those keys can send.
Since 1999, xterm has supported shift, control, alt, and meta
modifiers which produce distinct special-key strings. In a terminal
description, ncurses has no special knowledge of the modifiers used.
Applications can use the naming convention established for xterm to
find these special keys in the terminal description.
Starting with the curses convention that key names begin with “k” and
that shifted special keys are an uppercase name, ncurses' terminal
database defines these names to which a suffix is added:
Name Description
───────────────────────────────────────────────────────────────
kDC special form of kdch1 (delete character)
kDN special form of kcud1 (cursor down)
kEND special form of kend (End)
kHOM special form of khome (Home)
kLFT special form of kcub1 (cursor-left or cursor-back)
kNXT special form of knext (Next, or Page-Down)
kPRV special form of kprev (Prev, or Page-Up)
kRIT special form of kcuf1 (cursor-right, or cursor-forward)
kUP special form of kcuu1 (cursor-up)
These are the suffixes used to denote the modifiers:
Value Description
──────────────────────────────────
2 Shift
3 Alt
4 Shift + Alt
5 Control
6 Shift + Control
7 Alt + Control
8 Shift + Alt + Control
9 Meta
10 Meta + Shift
11 Meta + Alt
12 Meta + Alt + Shift
13 Meta + Ctrl
14 Meta + Ctrl + Shift
15 Meta + Ctrl + Alt
16 Meta + Ctrl + Alt + Shift
None of these are predefined; terminal descriptions can refer to
names which ncurses will allocate at runtime to key-codes. To use
these keys in an ncurses program, an application could do this:
· using a list of extended key names, ask tigetstr(3X) for their
values, and
· given the list of values, ask key_defined(3X) for the key-code
which would be returned for those keys by wgetch(3X).
The “-x” extension feature of tic and infocmp has been adopted in
NetBSD curses. That implementation stores user-defined capabilities,
but makes no use of these capabilities itself.
tic(1), infocmp(1).
Thomas E. Dickey
beginning with ncurses 5.0 (1999)
This page is part of the ncurses (new curses) project. Information
about the project can be found at
⟨https://www.gnu.org/software/ncurses/ncurses.html⟩. If you have a
bug report for this manual page, send it to
bug-ncurses-request@gnu.org. This page was obtained from the
project's upstream Git mirror of the CVS repository
⟨git://ncurses.scripts.mit.edu/ncurses.git⟩ on 2018-02-02. (At that
time, the date of the most recent commit that was found in the repos‐
itory was 2018-01-30.) If you discover any rendering problems in
this HTML version of the page, or you believe there is a better or
more up-to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not part
of the original manual page), send a mail to man-pages@man7.org
user_caps(5)
Pages that refer to this page: ncurses(3x), terminfo(5)
|
HTML rendering created 2018-02-02 by Michael Kerrisk, author of The Linux Programming Interface, maintainer of the Linux man-pages project. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH.
|
|