tcell

Tcell is a Go package that provides a cell based view for text terminals, like xterm. It was inspired by termbox, but includes many additional improvements.

Note	Work has begun on version 2.0 of Tcell. There are breaking changes (and more coming.) Version 1.x is available using the import github.com/gdamore/tcell. The new work in progress is available using master and github.com/gdamore/tcell/v2.

Examples

• proxima5 - space shooter (video)

• govisor - service management UI (screenshot)

• mouse demo - included mouse test (screenshot)

• gomatrix - converted from Termbox

• micro - lightweight text editor with syntax-highlighting and themes

• godu - simple golang utility helping to discover large files/folders.

• tview - rich interactive widgets for terminal UIs

• tui-go - UI library for terminal apps (deprecated)

• gomandelbrot - Mandelbrot!

• WTF- Personal information dashboard for your terminal

• browsh - A fully-modern text-based browser, rendering to TTY and browsers (video)

• go-life - Conway’s Game of Life.

• gowid - compositional widgets for terminal UIs, inspired by urwid

• termshark - a terminal UI for tshark, inspired by Wireshark, built on gowid

• go-tetris - Go Tetris with AI option

• fzf - A command-line fuzzy finder

• ascii-fluid - A terminal based ASCII fluid simulation controlled by webcam

• cbind - Provides key event encoding, decoding and handling

• tpong - The old-school Pong remade in terminal

• aerc - An email client for your terminal.

• tblogs - A terminal based development blogs reader

• spinc - An irssi inspired terminal chat application for Cisco Spark/WebEx

• gorss - A RSS/Atom feed reader for your terminal

• memoryalike - A game where you have to memorize runes and hit their respective keys

• lf - Terminal file manager

Pure Go Terminfo Database

Tcell includes a full parser and expander for terminfo capability strings, so that it can avoid hard coding escape strings for formatting. It also favors portability, and includes support for all POSIX systems.

The database is also flexible & extensible, and can modified by either running a program to build the entire database, or an entry for just a single terminal.

More Portable

Tcell is portable to a wide variety of systems. Tcell is believed to work with all of the systems officially supported by golang with the exception of nacl (which lacks any kind of a terminal interface). (Plan9 is not supported by Tcell, but it is experimental status only in golang.) Tcell is pure Go, without any need for CGO.

No Async IO

Tcell is able to operate without requiring SIGIO signals (unlike termbox), or asynchronous I/O, and can instead use standard Go file objects and Go routines. This means it should be safe, especially for use with programs that use exec, or otherwise need to manipulate the tty streams. This model is also much closer to idiomatic Go, leading to fewer surprises.

Rich Unicode & non-Unicode support

Tcell includes enhanced support for Unicode, including wide characters and combining characters, provided your terminal can support them. Note that Windows terminals generally don’t support the full Unicode repertoire.

It will also convert to and from Unicode locales, so that the program can work with UTF-8 internally, and get reasonable output in other locales. Tcell tries hard to convert to native characters on both input and output, and on output Tcell even makes use of the alternate character set to facilitate drawing certain characters.

More Function Keys

Tcell also has richer support for a larger number of special keys that some terminals can send.

Better Color Handling

Tcell will respect your terminal’s color space as specified within your terminfo entries, so that for example attempts to emit color sequences on VT100 terminals won’t result in unintended consequences.

In legacy Windows mode, Tcell supports 16 colors, bold, dim, and reverse, instead of just termbox’s 8 colors with reverse. (Note that there is some conflation with bold/dim and colors.) Modern Windows 10 can benefit from much richer colors however.

Tcell maps 16 colors down to 8, for terminals that need it. (The upper 8 colors are just brighter versions of the lower 8.)

Better Mouse Support

Tcell supports enhanced mouse tracking mode, so your application can receive regular mouse motion events, and wheel events, if your terminal supports it.

(Note: The Windows 10 Terminal application suffers from a flaw in this regard, and does not support mouse interaction. The stock Windows 10 console host fired up with cmd.exe or PowerShell works fine however.)

Termbox Compatibility

A compatibility layer for termbox is provided in the compat directory. To use it, try importing github.com/gdamore/tcell/termbox instead. Most termbox-go programs will probably work without further modification.

Working With Unicode

Internally Tcell uses UTF-8, just like Go. However, Tcell understands how to convert to and from other character sets, using the capabilities of the golang.org/x/text/encoding packages. Your application must supply them, as the full set of the most common ones bloats the program by about 2MB. If you’re lazy, and want them all anyway, see the encoding sub-directory.

Wide & Combining Characters

The SetContent() API takes a primary rune, and an optional list of combining runes. If any of the runes is a wide (East Asian) rune occupying two cells, then the library will skip output from the following cell, but care must be taken in the application to avoid explicitly attempting to set content in the next cell, otherwise the results are undefined. (Normally wide character is displayed, and the other character is not; do not depend on that behavior.)

Experience has shown that the vanilla Windows 8 console application does not support any of these characters properly, but at least some options like ConEmu do support Wide characters.

Colors

Tcell assumes the ANSI/XTerm color model, including the 256 color map that XTerm uses when it supports 256 colors. The terminfo guidance will be honored, with respect to the number of colors supported. Also, only terminals which expose ANSI style setaf and setab will support color; if you have a color terminal that only has setf and setb, please let me know; it wouldn’t be hard to add that if there is need.

24-bit Color

Tcell supports true color! (That is, if your terminal can support it, Tcell can accurately display 24-bit color.)

To use 24-bit color, you need to use a terminal that supports it. Modern xterm and similar teminal emulators can support this. As terminfo lacks any way to describe this capability, we fabricate the capability for terminals with names ending in *-truecolor. The stock distribution ships with a database that defines xterm-truecolor. To try it out, set your TERM variable to xterm-truecolor.

When using TrueColor, programs will display the colors that the programmer intended, overriding any “themes” you may have set in your terminal emulator. (For some cases, accurate color fidelity is more important than respecting themes. For other cases, such as typical text apps that only use a few colors, its more desirable to respect the themes that the user has established.)

If you find this undesirable, you can either use a TERM variable that lacks the TRUECOLOR setting, or set TCELL_TRUECOLOR=disable in your environment.

Performance

Reasonable attempts have been made to minimize sending data to terminals, avoiding repeated sequences or drawing the same cell on refresh updates.

Terminfo

(Not relevant for Windows users.)

The Terminfo implementation operates with two forms of database. The first is the built-in go database, which contains a number of real database entries that are compiled into the program directly. This should minimize calling out to database file searches.

The second is in the form of JSON files, that contain the same information, which can be located either by the $TCELLDB environment file, $HOME/.tcelldb, or is located in the Go source directory as database.json.

These files (both the Go and the JSON files) can be generated using the mkinfo.go program. If you need to regnerate the entire set for some reason, run the mkdatabase.sh file. The generation uses the infocmp(1) program on the system to collect the necessary information.

The mkinfo.go program can also be used to generate specific database entries for named terminals, in case your favorite terminal is missing. (If you find that this is the case, please let me know and I’ll try to add it!)

Tcell requires that the terminal support the cup mode of cursor addressing. Terminals without absolute cursor addressability are not supported. This is unlikely to be a problem; such terminals have not been mass produced since the early 1970s.

Mouse Support

Mouse support is detected via the kmous terminfo variable, however, enablement/disablement and decoding mouse events is done using hard coded sequences based on the XTerm X11 model. As of this writing all popular terminals with mouse tracking support this model. (Full terminfo support is not possible as terminfo sequences are not defined.)

On Windows, the mouse works normally.

Mouse wheel buttons on various terminals are known to work, but the support in terminal emulators, as well as support for various buttons and live mouse tracking, varies widely. Modern xterm, macOS Terminal, and iTerm all work well.

Testablity

There is a SimulationScreen, that can be used to simulate a real screen for automated testing. The supplied tests do this. The simulation contains event delivery, screen resizing support, and capabilities to inject events and examine “physical” screen contents.

Platforms

POSIX (Linux, FreeBSD, macOS, Solaris, etc.)

For mainstream systems with a suitably well defined system call interface to tty settings, everything works using pure Go.

For the remainder (right now means only Solaris/illumos) we use POSIX function calls to manage termios, which implies that CGO is required on those platforms.

Windows

Windows console mode applications are supported. Unfortunately mintty and other cygwin style applications are not supported.

Modern console applications like ConEmu, as well as the Windows 10 console itself, support all the good features (resize, mouse tracking, etc.)

I haven’t figured out how to cleanly resolve the dichotomy between cygwin style termios and the Windows Console API; it seems that perhaps nobody else has either. If anyone has suggestions, let me know! Really, if you’re using a Windows application, you should use the native Windows console or a fully compatible console implementation.

Plan9 and Native Client (Nacl)

The nacl and plan9 platforms won’t work, but compilation stubs are supplied for folks that want to include parts of this in software targetting those platforms. The Simulation screen works, but as Tcell doesn’t know how to allocate a real screen object on those platforms, NewScreen() will fail.

If anyone has wisdom about how to improve support for either of these, please let me know. PRs are especially welcome.

Commercial Support

Tcell is absolutely free, but if you want to obtain commercial, professional support, there are options.

	Tidelift subscriptions include support for Tcell, as well as many other open source packages.
	Staysail Systems offers direct support, and custom development around Tcell on an hourly basis.
	I also welcome donations at Patreon, if you just want to make a contribution.