Ubuntu Manpage: notcurses - TUI library for modern terminal emulators

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Provided by: libnotcurses-core-dev_3.0.6+dfsg.1-1_amd64

NAME

       notcurses - TUI library for modern terminal emulators

SYNOPSIS

       #include <notcurses/notcurses.h> or #include <notcurses/notcurses-core.h>

       -lnotcurses-core -lnotcurses or -lnotcurses-core

DESCRIPTION

Notcurses builds atop the terminfo(5) abstraction layer to provide reasonably portable vivid character
displays. It is an intellectual descendant of ncurses(3NCURSES), but goes beyond that library (and the
X/Open Curses API it implements).

A program wishing to use Notcurses will need to link it, ideally using the output of pkg-config --libs
notcurses (see pkg-config(1)). It is advised to compile with the output of pkg-config --cflags
notcurses. If using CMake, a support file is provided, and can be accessed as Notcurses (see cmake(1)).
If multimedia capabilities are not needed, it is possible to link against a minimal Notcurses using pkg-
config --libs notcurses-core.

notcurses_init(3) can then be used to initialize a Notcurses instance for a given FILE* (usually stdout,
usually attached to a terminal).

The alternate screen
Many terminals provide an "alternate screen" with its own contents, no scrollback buffer, and no
scrolling. Entering the alternate screen replaces the current visible contents wholesale, as does
returning to the regular screen. Notcurses refers to the alternate screen's semantics as "TUI mode", and
the regular screen's semantics as "CLI mode". It is possible to swap between the two modes at runtime
using notcurses_leave_alternate_screen(3) and notcurses_enter_alternate_screen(3). Notcurses will enter
TUI mode by default on startup; to prevent this, use NCOPTION_NO_ALTERNATE_SCREEN as described in
notcurses_init(3). On program exit, Notcurses will always return to the regular screen, independent of
the screen being used on program start.

Construction
Before calling into Notcurses—and usually as one of the first calls of the program—be sure to call
setlocale with an appropriate UTF-8 LC_ALL locale. It is usually appropriate to use setlocale(LC_ALL,
""), relying on the user to properly set the LANG environment variable. Notcurses will refuse to start
if nl_langinfo(3) doesn't indicate UTF-8 or ANSI_X3.4-1968 (aka US-ASCII). Be aware that capabilities
are substantially reduced in ASCII.

notcurses_init(3) accepts a struct notcurses_options allowing fine-grained control of Notcurses behavior,
including signal handlers, alternative screens, and overriding the TERM environment variable. A terminfo
entry appropriate for the actual terminal must be available.

ncdirect_init(3) makes available a restricted subset of Notcurses functionality. This subset is intended
to be interleaved with user-generated output, and is limited to coloring and styling. Direct mode is
documented in notcurses_direct(3).

Only one context can be active in a process at a time, whether direct mode (struct ncdirect) or rendered
mode (struct notcurses).

Output
All output is performed on struct ncplanes (see Ncplanes below). Output is not visible until explicitly
rendered via notcurses_render(3). Information on drawing functions is available at notcurses_output(3).

Input
Notcurses supports input from keyboards (via stdin) and pointing devices (via a broker such as GPM, X, or
Wayland). Input is delivered as 32-bit Unicode code points. Synthesized events such as mouse button
presses and arrow keys are mapped into Unicode's Supplementary Private Use Area-B
(https://unicode.org/charts/PDF/U100000.pdf). Information on input is available at notcurses_input(3).
The included tool notcurses-input(1) can be used to test input decoding.

Ncpiles
A given notcurses context is made up of one or more piles. Piles provide distinct rendering contexts: a
thread can be rendering or mutating one pile, while another thread concurrently renders or mutates
another pile. A pile is made up of planes, totally ordered on a z-axis. In addition to the z-ordering,
the planes of a pile are bound in a forest (a set of directed, acyclic graphs). Those planes which are
not bound to some other plane constitute the root planes of a pile. A pile is destroyed when all its
planes are destroyed, or moved to other piles. Since the standard plane (see below) always exists, and
cannot be moved to another pile, one pile always exists, known as the standard pile.

Note that rasterizing a pile will replace all content within its margins.

For more information, see notcurses_pile(3).

Ncplanes
Following initialization, a single ncplane exists, the "standard plane" (see notcurses_stdplane(3)).
This plane cannot be destroyed nor manually resized, and is always exactly as large as the screen (if run
without a TTY, the "screen" is assumed to be 80x24 cells). Further ncplanes can be created with
ncplane_create(3). A total z-ordering always exists on the set of ncplanes, and new ncplanes are placed
at the top of the z-buffer. Ncplanes can be larger, smaller, or the same size as the physical screen,
and can be placed anywhere relative to it (including entirely off-screen). Ncplanes are made up of
nccells (see NcCells below). Information on ncplanes is available at notcurses_plane(3).

NcCells
nccells make up the framebuffers backing each ncplane, one cell per coordinate, one extended grapheme
cluster (see unicode(7)) per cell. An nccell consists of a gcluster (either a directly-encoded 7-bit
ASCII character (see ascii(7)), or a 25-bit index into the ncplane's egcpool), a set of attributes, and
two channels (one for the foreground, and one for the background—see notcurses_channels(3)). Information
on cells is available at notcurses_cell(3).

It is not usually necessary for users to interact directly with nccells. They are typically encountered
when retrieving data from ncplanes or the rendered scene (see e.g. ncplane_at_yx(3)), or to achieve peak
performance when a particular EGC is heavily reused within a plane.

Visuals
Bitmaps can be loaded from disk or memory, or even synthesized from the content of existing planes.
These are stored in ncvisual objects, described in notcurses_visual(3). Visuals can be rendered to
arbitrarily many planes using a variety of blitters, varying in their aspect ratios and resolution. If
the terminal supports a pixel protocol such as Sixel or Kitty, it is possible to render bitmaps at the
pixel level (as opposed to the cell level, using geometric glyphs). Otherwise, various Unicode-based
blitters are available to render bitmaps in the text paradigm.

Widgets
A few high-level widgets are included, all built atop ncplanes:

• notcurses_fds(3) for dumping file descriptors/subprocesses to a plane

• notcurses_menu(3) for menu bars at the top or bottom of the screen

• notcurses_multiselector(3) for selecting one or more items from a set

• notcurses_plot(3) for drawing histograms and lineplots

• notcurses_progbar(3) for drawing progress bars

• notcurses_reader(3) for free-form input data

• notcurses_reel(3) for hierarchal display of block-based data

• notcurses_tabbed(3) for tabbed interfaces

• notcurses_selector(3) for selecting one item from a set

• notcurses_tree(3) for hierarchal display of line-based data

Threads
Notcurses explicitly supports use in multithreaded environments, but it does not itself perform any
locking.

• Only one pile's rendered frame can be rasterized at a time, and it is not safe to concurrently render
that pile. It is safe to rasterize a frame while rendering some other pile.

• It is otherwise always safe to operate concurrently on distinct piles.

• It is not safe to render a pile while concurrently modifying that pile.

• It is safe to output to multiple distinct ncplanes at the same time, even within the same pile.

• It is safe to output to ncplanes while adding or deleting some other ncplane.

• It is not safe for multiple threads to output to the same ncplane.

• It is not safe to add, delete, or reorder ncplanes within a single pile from multiple threads.

Only one thread may call notcurses_get(3) or any other input-related thread at a time, but it is safe to
call for input while another thread renders.

Since multiple threads can concurrently manipulate distinct ncplanes, peak performance might require
dividing the screen into several planes, and manipulating them from multiple threads.

Destruction
Before exiting, notcurses_stop(3) should be called. In addition to freeing up resources, this is
necessary to restore the terminal to a state useful for the shell. By default, notcurses_init(3)
installs signal handlers to catch all signals which would normally terminate the process. The new
handlers will try to call notcurses_stop(3), and then propagate the received signal to the previous
action.

ENVIRONMENT VARIABLES

       The TERM environment variable ought be correctly defined.  It will be used to index into the  terminfo(5)
       database  by  way  of  setupterm(3NCURSES).   Notcurses will additionally use TERM_PROGRAM to distinguish
       certain terminals.

       If the COLORTERM environment variable is defined as "24bit" or "truecolor",  Notcurses  will  assume  the
       terminal capable of 24-bit RGB color, even in the absence of "RGB" or "Tc" capabilities in terminfo.

       If  the  NOTCURSES_LOGLEVEL environment variable is defined as a number between -1 and 8, inclusive, that
       will override any logging level specified in the struct notcurses_options provided to notcurses_init(3).

       The LOGNAME environment variable, if defined, will be used for notcurses_accountname(3).

NOTES

       When using the C++ wrappers, NCPP_EXCEPTIONS_PLEASE can be defined in order to turn  most  error  returns
       into exceptions.

AUTHORS

       nick black <nickblack@linux.com>.

                                                     v3.0.6                                         notcurses(3)