notcurses_init - Man Page

initialize a notcurses instance


#include <notcurses/notcurses.h>

#define NCOPTION_VERIFY_SIXEL        0x0002ull
#define NCOPTION_RETAIN_CURSOR       0x0010ull
#define NCOPTION_SUPPRESS_BANNERS    0x0020ull
#define NCOPTION_NO_FONT_CHANGES     0x0080ull

typedef enum {
  NCLOGLEVEL_SILENT,  // default. print nothing once fullscreen service begins
  NCLOGLEVEL_PANIC,   // print diagnostics immediately related to crashing
  NCLOGLEVEL_FATAL,   // we're hanging around, but we've had a horrible fault
  NCLOGLEVEL_ERROR,   // we can't keep doin' this, but we can do other things
  NCLOGLEVEL_WARNING, // you probably don't want what's happening to happen
  NCLOGLEVEL_INFO,    // "standard information"
  NCLOGLEVEL_VERBOSE, // "detailed information"
  NCLOGLEVEL_DEBUG,   // this is honestly a bit much
  NCLOGLEVEL_TRACE,   // there's probably a better way to do what you want
} ncloglevel_e;

typedef struct notcurses_options {
  const char* termtype;
  FILE* renderfp;
  ncloglevel_e loglevel;
  int margin_t, margin_r, margin_b, margin_l;
  uint64_t flags; // from NCOPTION_* bits
} notcurses_options;

int notcurses_lex_margins(const char* op, notcurses_options* opts);

void notcurses_version_components(int* major, int* minor, int* patch, int* tweak);

struct notcurses* notcurses_init(const notcurses_options* opts, FILE* fp);


notcurses_init prepares the terminal for cursor-addressable (multiline) mode. The FILE provided as fp must be writable and attached to a terminal, or NULL. If it is NULL, /dev/tty will be opened. The struct notcurses_option passed as opts controls behavior. Only one instance should be associated with a given terminal at a time, though it is no problem to have multiple instances in a given process.

On success, a pointer to a valid struct notcurses is returned. NULL is returned on failure. Before the process exits, notcurses_stop(3) should be called to reset the terminal and free up resources.

An appropriate terminfo(5) entry must exist for the terminal. This entry is usually selected using the value of the TERM environment variable (see getenv(3)), but a non-NULL value for termtype will override this. An invalid terminfo specification can lead to reduced performance, reduced display capabilities, and/or display errors. notcurses natively targets 24bpp/8bpc RGB color, and it is thus desirable to use a terminal with the rgb capability (e.g. xterm’s xterm-direct).

If the terminal advertises support for an “alternate screen” via the smcup terminfo capability, notcurses will employ it by default. This can be prevented by setting NCOPTION_NO_ALTERNATE_SCREEN in flags. Users tend to have strong opinions regarding the alternate screen, so it’s often useful to expose this via a command-line option.

notcurses furthermore hides the cursor by default, but NCOPTION_RETAIN_CURSOR can prevent this (the cursor can be dynamically enabled or disabled during execution via notcurses_cursor_enable(3) and notcurses_cursor_disable(3)).

notcurses_init typically emits some diagnostics at startup, including version information and some details of the configured terminal. This can be inhibited with NCOPTION_SUPPRESS_BANNERS. This will also inhibit the performance summary normally printed by notcurses_stop(3).

Notcurses can render to a subregion of the terminal by specifying desired margins on all four sides. By default, all margins are zero, and thus rendering will be performed on the entirety of the viewing area. This is orthogonal to use of the alternate screen; using the alternate screen plus margins will see the full screen cleared, followed by rendering to a subregion. Inhibiting the alternate screen plus margins will see rendering to a subregion, with the screen outside this region not cleared. This is the only means by which existing output can be undisturbed by notcurses. Margins are best-effort. Supplying any negative margin is an error. notcurses_lex_margins provides lexing a margin argument expression in one of two forms:

To allow future options without requiring redefinition of the structure, the flags field is only a partially-defined bitfield. Undefined bits must be zero. The following flags are defined:

Fatal signals

It is important to reset the terminal before exiting, whether terminating due to intended operation or a received signal. This is usually accomplished by explicitly calling notcurses_stop(3) during shutdown. For convenience, notcurses by default installs signal handlers for various signals typically resulting in process termination (see signal(7)). These signal handlers call notcurses_stop(3) for each struct notcurses in the process, and then propagate the signal to any previously-configured handler. These handlers are disabled upon entry to notcurses_stop(3).

To prevent signal handler registration, set no_quit_sighandlers to true. No means is provided to selectively register fatal signal handlers. If this is done, the caller ought be sure to effect similar functionality themselves.

Resize events

SIGWINCH (SIGnal WINdow CHange) is delivered to the process when the terminal is resized. The default action is to ignore it (SIG_IGN). notcurses installs a handler for this signal. The handler causes notcurses to update its idea of the terminal’s size using TIOCGWINSZ (see ioctl_tty(2)), and generates an NCKEY_RESIZE input event (see notcurses_input(3). This signal handler can be inhibited by setting NCOPTION_NO_WINCH_SIGHANDLER in flags. If this is done, the caller should probably watch for the signal, and invoke notcurses_refresh(3) or notcurses_render(3) upon its receipt.

A resize event does not invalidate any references returned earlier by notcurses. The content of any new screen area is undefined until the next call to notcurses_render(3). This is true even if an existing struct ncplane (see notcurses_plane(3)) overlaps the new area, since the signal could arrive while the ncplanes are being modified. Signal handlers are quite restricted as to what actions they can perform, so minimal work is performed in the handler proper.

Thus, in the absence of NCOPTION_NO_WINCH_SIGHANDLER, SIGWINCH results in:

  • interruption of some thread to process the signal
  • a TIOCGWINSZ ioctl to retrieve the new screen size
  • queuing of a NCKEY_RESIZE input event (if there is space in the queue)

Upon the next call to notcurses_render(3) or notcurses_refresh(3), the standard plane (see notcurses_stdplane(3)) will be resized to the new screen size. The next notcurses_render(3) call will function as expected across the new screen geometry.

Return Values

NULL is returned on failure. Otherwise, the return value points at a valid struct notcurses, which can be used until it is provided to notcurses_stop(3).

See Also

getenv(3), setlocale(3), termios(3), notcurses(3), notcurses_input(3), notcurses_plane(3), notcurses_refresh(3), notcurses_render(3), notcurses_stop(3), terminfo(5), signal(7)


nick black <>.

Referenced By

notcurses(3), notcurses_refresh(3), notcurses_stop(3).