tcell

Tcell is a work in progress (Gamma). Please use with caution; interfaces may change in before final release. That said, our confidence in Tcell's stability is increasing. If you would like to use it in your own application, it is recommended that you drop a message to garrett@damore.org before commitment.

Package tcell provides a cell based view for text terminals, like xterm. It was inspired by termbox, but differs from termbox in some important ways. It also adds substantial functionality beyond termbox.

Examples

• proxima5 - space shooter (video)
• govisor - service management UI (screenshot)
• mouse demo - screenshot - included mouse test
• gomatrix - converted from Termbox

Pure Go Terminfo Database

First, it 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, at the slight expense of needing cgo support for terminal initializations. (This may be corrected when Go provides standard support for terminal handling via termio ioctls on all POSIX platforms.) The database itself, while built using CGO, as well as the parser for it, is implemented in Pure Go.

The database is also flexible & extensibel, and can modified by either running a program to build the database, or hand editing of simple JSON files.

More Portable

Tcell is portable to a wider variety of systems. It relies on standard POSIX supported function calls (on POSIX platforms) for setting terminal modes, which leads to improved support for a broader array of platforms. This does come at the cost of requiring your code to be able to use CGO, but we believe that the vastly improved portability justifies this requirement. Note that the functions called are part of the standard C library, so there shouldn't be any additional external requirements beyond that required for every POSIX program.

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.

Richer Unicode & non-Unicode support

Tcell includes enhanced support for Unicode, include 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. We try 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

It 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 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.)

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.

Why not just patch termbox-go?

I started this project originally by submitting patches to the author of go-termbox, but due to some fundamental differences of opinion, I thought it might be simpler just to start from scratch. At this point, Tcell has far exceeded the capabilities of termbox.

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 at least.

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 relevent for Windows users.)

The Terminfo implementation operates with two forms of database. The first is the database.go file, 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 a JSON file, that contains 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 database.go and the database.json) file 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 terminfo routines on the system to populate the data files.

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. As a particular datum, MacOS X Terminal does not support Mouse events at all (as of MacOS 10.10, aka Yosemite.) The excellent iTerm application is fully supported, as is vanilla XTerm.

Mouse tracking with live tracking also varies widely. Current XTerm implementations, as well as current Screen and iTerm2, and Windows consoles, all support this quite nicely. On other platforms you might find that only mouse click and release events are reported, with no intervening motion events. It really depends on your terminal.

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

Systems (Linux, FreeBSD, MacOS, Solaris, etc.)

On POSIX systems, a POSIX termios implementation with /dev/tty is required. It also requires functional CGO to run. As of this writing, CGO is available on all POSIX Go 1.5 platforms.

Windows

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

Modern console applications like ConEmu 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 consule implementation. Hopefully the Windows 10 console is more functional in this regard.

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.