BTUI - Bruce's Text User Interface Library

BTUI is a minimal, embeddable single header file alternative to bloatware like ncurses. BTUI aims to be less than 1% the size of ncurses,^1 while also providing a better API for the programmer who is not afraid to roll up their sleeves and manage their own state. If you want a drop-in TUI library that lets you switch into TUI mode, write some strings to the screen with 24-bit color, and get user keypresses, then this is the library for you!

Footnote 1: Currently, BTUI is somewhere between 0.5% and 0.1% the size of ncurses, but even counting the number of lines of code in ncurses is hard.

Cleanup by Default

Once BTUI is enabled, you can manually disable TUI Mode (e.g. if you want to temporarily drop back to the regular shell). However, BTUI will always automatically put the terminal back in a normal state when your program exits, even in the event of a segfault or other blockable signal. BTUI can't do anything about unblockable signals like SIGKILL though, so don't use killall -9 myprog unless you want a gunked up terminal, just use kill myprog instead. If your terminal does get gunked up, you can always run the reset shell command to reset it.

Easy 24-bit Colors

BTUI supports 24-bit colors. It's dead easy, just btui_set_fg(bt, r, g, b) (foreground color) or btui_set_bg(bt, r, g, b) (background color). Try make rainbow to see a demo of 24-bit colors in action. This has been supported by most terminals for aeons, but most TUI applications still default to using the same 8 colors. It doesn't have to be that way! (Although you can still use those colors with btui_set_attributes(bt, BTUI_BG_RED | BTUI_FG_BLACK) and so forth.)

User Input

BTUI lets you get keyboard input for all keypress events handled by your terminal, including mouse clicking and dragging. Warning: BTUI also hooks in to Ctrl-c, Ctrl-d, Ctrl-z, and other keyboard events that normally have very specific behavior in terminal programs. If you want that specific behavior, then you'll have to implement it manually. The upside is that you're able to handle it gracefully and do whatever cleanup you want. If you want to provide Ctrl-z suspend functionality, you can use btui_suspend(bt).

Language Bindings

BTUI comes with bindings for C and Lua, with plans to add Python bindings.

C API

BTUI has the following C function definitions, as well as definitions for some constants, including terminal escape values and keycodes.

btui_t* btui_enable(void);
void btui_disable(btui_t *bt);
int btui_getkey(btui_t *bt, int timeout, int *mouse_x, int *mouse_y);
int btui_move_cursor(btui_t *bt, int x, int y);
char *btui_keyname(int key, char *buf);
int btui_keynamed(const char *name);
int btui_set_attributes(btui_t *bt, attr_t attrs);
int btui_set_fg(btui_t *bt, unsigned char r, unsigned char g, unsigned char b);
int btui_set_bg(btui_t *bt, unsigned char r, unsigned char g, unsigned char b);
int btui_set_fg_hex(btui_t *bt, int hex);
int btui_set_bg_hex(btui_t *bt, int hex);
#define btui_printf(bt, ...) fprintf((bt)->out, __VA_ARGS__)
#define btui_puts(bt, s) fputs(s, (bt)->out)
#define btui_flush(bt) fflush((bt)->out)
#define btui_clear_below(bt) fputs("\033[J", (bt)->out)
#define btui_clear_above(bt) fputs("\033[1J", (bt)->out)
#define btui_clear_screen(bt) fputs("\033[2J", (bt)->out)
#define btui_clear_right(bt) fputs("\033[K", (bt)->out)
#define btui_clear_left(bt) fputs("\033[1K", (bt)->out)
#define btui_clear_line(bt) fputs("\033[2K", (bt)->out)
#define btui_suspend(bt) kill(getpid(), SIGTSTP)

See C/test.c for example usage.

Lua API

The Lua library returns a function that takes one argument: a function that will be called with a BTUI object, which can be used to do TUI actions. Errors will be propagated out of the function, but the terminal will be cleaned up nicely before the error is printed. Here's a simple example program:

require("btui")(function(bt)
    -- Run this code within the TUI, using "bt" as the TUI object
    ...
end)

bt:enable() -- Enables btui (if previously disabled)
bt:disable() -- Disables btui
bt:withdisabled(fn) -- Calls "fn" with btui disabled, then re-enables btui
bt:getkey(timeout=-1) -- Returns a keypress (and optionally, mouse x and y coordinates). The optional timeout argument specifies how long, in tenths of a second, to wait for the next keypress.
bt:print() -- Print text to the terminal
bt:clear(type="screen") -- Clear the terminal. Options are: "screen", "right", "left", "above", "below", "line"
bt:flush() -- Flush the terminal output. Most operations do this anyways.
bt:move(x, y) -- Move the cursor to the given position. (0,0) is the top left corner.
-- R,G,B values are in the range [0.0, 1.0]:
bt:withfg(r,g,b, fn) -- Set the foreground color to (r,g,b), call fn, then reset the foreground color to default
bt:withbg(r,g,b, fn) -- Set the background color to (r,g,b), call fn, then reset the background color to default
bt:withattributes(attrs..., fn) -- Set the given attributes, call fn, then unset them
bt:setattributes(attrs...) -- Set the given attributes
bt:unsetattributes(attrs...) -- Unset the given attributes
bt:suspend() -- Suspend the current process and drop back into normal terminal mode
bt:width() -- Return the scren width
bt:height() -- Return the screen height

See Lua/test.lua for example usage.

Python API

Coming soon.

FAQ

Why not use ncurses? It's already installed almost everywhere!

Ncurses is pretty ubiquitous among amateur TUI developers, however it's a really messy paradigm to work with, and it comes with hundreds of thousands of lines of code bloat. There's also tons of compatibility problems across different versions of ncurses. Using ncurses is a headache, and writing a wrapper around ncurses just adds more bloat on top of a mountain of bloat. So, if you want to write a really nice TUI library for your language of choice, BTUI is a good option for a foundation to build off of. BTUI handles all the low-level C stuff like setting terminal attributes and interrupt handlers, but after that, it mostly just gets out of the way and lets you write the bytes you want, with just a few helper functions that make writing the right bytes easy.

Why not use termbox?

Termbox is an okay library, but its API is built around modifying terminal cells one-at-a-time using function calls. This approach has two major flaws: it's very bad for performance and it makes the API very awkward to use if you want to write strings to the screen. Termbox uses its own custom internal write-buffering to reduce write calls and help performance, but in my experience, there is still noticeable lag when doing large amounts of writes compared to just using plain ol' C fprintf() buffering.

Also, termbox is intended to be used as a system-installed library, but BTUI is much simpler to use: just drop the .h file into your project and #import "btui.h"!

License

BTUI is released under the MIT license. See LICENSE for details.