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102 lines
5.1 KiB
Markdown
102 lines
5.1 KiB
Markdown
# Notcurses viz Curses/NCURSES
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The biggest difference, of course, is that Notcurses is neither an
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implementation of X/Open (aka XSI) Curses, nor part of SUS4-2018.
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## Differences from Curses
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The detailed differences between Notcurses and NCURSES (a high-quality, ubiquitous
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implementation of Curses) probably can't be fully enumerated, and if they
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could, no one would want to read them. With that said, some design decisions
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might surprise NCURSES programmers:
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* There is no distinct `PANEL` type. The z-buffer is a fundamental property,
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and all drawable surfaces are ordered along the z axis. There is no
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equivalent to `update_panels()`.
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* Scrolling is disabled by default, and cannot be globally enabled.
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* The Curses `cchar_t` has a fixed-size array of `wchar_t`. The Notcurses
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`cell` instead supports a UTF-8 encoded extended grapheme cluster of
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arbitrary length. The only supported encodings are ASCII via `ANSI_X3.4-1968`
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and Unicode via `UTF-8`.
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* The cursor is disabled by default, when supported (`civis` capability).
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* Echoing of input is disabled by default, and `cbreak` mode is used by default.
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* Colors are usually specified as 24 bits in 3 components (RGB). If necessary,
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these will be quantized for the actual terminal. There are no "color pairs",
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but indexed palettes are supported.
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* There is no distinct "pad" concept (these are NCURSES `WINDOW`s created with
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the `newpad()` function). All drawable surfaces can exceed the display size.
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* Multiple threads can freely call into Notcurses, so long as they're not
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accessing the same data. In particular, it is always safe to concurrently
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mutate different `ncplane`s in different threads.
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* NCURSES has thread-ignorant and thread-semi-safe versions, trace-enabled and
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traceless versions, and versions with and without support for wide characters.
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Notcurses is one library: no tracing, UTF-8, thread safety.
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* There is no `ESCDELAY` concept; Notcurses expects that all bytes of a
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keyboard escape sequence arrive at the same time. This improves latency
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and simplifies the API.
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* It is an error in NCURSES to print to the bottommost, rightmost coordinate of
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the screen when scrolling is disabled (because the cursor cannot be advanced).
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Failure to advance the cursor does not result in an error in Notcurses (but
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attempting to print at the cursor when it has been advanced off the plane *does*).
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* Notcurses has no support for soft labels (`slk_init()`, etc.), subwindows
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which share memory with their parents, nor the NCURSES tracing functionality
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(`trace(3NCURSES)`).
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* Notcurses doesn't implement any of the `curs_util(3x)` functions, including
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window serialization/deserialization via `putwin()`/`getwin()`.
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* Notcurses doesn't interact with `LINES` nor `COLUMNS` environment variables.
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## Adapting NCURSES programs
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Do you really want to do such a thing? NCURSES and the Curses API it implements
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are far more portable and better-tested than Notcurses is ever likely to be.
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Will your program really benefit from Notcurses's advanced features? If not,
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it's probably best left as it is.
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Otherwise, most NCURSES concepts have clear partners in Notcurses. Any functions
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making implicit use of `stdscr` ought be replaced with their explicit
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equivalents. `stdscr` ought then be replaced with the result of
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`notcurses_stdplane()` (the standard plane). `PANEL`s become `ncplane`s; the
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Panels API is otherwise pretty close. Anything writing a bare character will
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become a simple `cell`; multibyte or wide characters become complex `cell`s.
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Color no longer uses "color pairs". You can easily enough hack together a
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simple table mapping your colors to RGB values, and color pairs to foreground
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and background indices into said table. That'll work for the duration of a
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porting effort, certainly.
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I have adapted two large (~5k lines of C UI code each) programs from NCURSES to
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Notcurses, and found it a fairly painless process. It was helpful to introduce
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a shim layer, e.g. `compat_mvwprintw` for NCURSES's `mvwprintw`:
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```c
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static int
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compat_mvwprintw(struct ncplane* nc, int y, int x, const char* fmt, ...){
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va_list va;
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va_start(va, fmt);
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if(ncplane_vprintf_yx(nc, y, x, fmt, va) < 0){
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va_end(va);
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return ERR;
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}
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va_end(va);
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return OK;
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}
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```
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These are pretty obvious, implementation-wise.
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### Some details
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* `cbreak()`/`nocbreak()`/`echo()`/`noecho()`/`nl()`/`nonl()`: termios
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properties are not exposed as granularly by Notcurses. Rendered mode
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always enters cbreak mode. Direct mode enters cbreak mode by default,
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but `NCDIRECT_OPTION_INHIBIT_CBREAK` will inhibit this.
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* `raw()`/`noraw()`: The line discipline conversions (e.g. Ctrl+C) can be
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disabled at any time with `notcurses_linesigs_disable()`, and turned back on
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with `notcurses_linesigs_enable()`.
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* `keypad()`: The keypad is always enabled, if the `smkx`
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capability is advertised.
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* `halfdelay()`/`nodelay()`/`timeout()`/`wtimeout()`: No such global controls
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are supported. Use `notcurses_getc()` with a timeout if you want a timeout.
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Use `notcurses_getc_nblock()` if you want an immediate return.
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* `intrflush()`/`qiflush()`/`noqiflush()`: No such functionality is supported.
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* `typeahead()`: No such functionality is supported.
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