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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.

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NOTE: This is version 2 of Tcell. There are breaking changes relative to version 1. Version 1.x remains available using the import github.com/gdamore/tcell.

Tutorial

A brief, and still somewhat rough, tutorial is available.

Examples

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 be 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, and is pure Go, without any need for CGO. Tcell is believed to work with mainstream systems officially supported by golang.

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. 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. 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 2 MB. 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. Care must be taken in the application to avoid explicitly attempting to set content in the next cell, otherwise the results are undefined. (Normally the wide character is displayed, and the other character is not; do not depend on that behavior.)

Older terminal applications (especially on systems like Windows 8) lack support for advanced Unicode, and thus may not fare well.

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 submit a ticket.

24-bit Color

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

NOTE: Technically the approach of using 24-bit RGB values for color is more accurately described as "direct color", but most people use the term "true color". We follow the (inaccurate) common convention.

There are a few ways you can enable (or disable) true color.

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.)

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 a built-in database. This should satisfy most users. However, it can also (on systems with ncurses installed), dynamically parse the output from infocmp for terminals it does not already know about.

See the terminfo/ directory for more information about generating new entries for the built-in database.

Tcell requires that the terminal support the cup mode of cursor addressing. Ancient terminals without the ability to position the cursor directly 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. 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.

Bracketed Paste

Terminals that appear to support the XTerm mouse model also can support bracketed paste, for applications that opt-in. See EnablePaste() for details.

Testability

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.)

Everything works using pure Go on mainstream platforms. Some more esoteric platforms (e.g., AIX) may need to be added. Pull requests are welcome!

Windows

Windows console mode applications are supported.

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

WASM

WASM is supported, but needs additional setup detailed in README-wasm.

Plan9 and others

These platforms won't work, but compilation stubs are supplied for folks that want to include parts of this in software for 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 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.