= tcell


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|===
|_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.
a|[.right]
image::logos/tcell.png[float="right"]
|===

## Examples

* https://github.com/gdamore/proxima5[proxima5] - space shooter (https://youtu.be/jNxKTCmY_bQ[video])
* https://github.com/gdamore/govisor[govisor] - service management UI (http://2.bp.blogspot.com/--OsvnfzSNow/Vf7aqMw3zXI/AAAAAAAAARo/uOMtOvw4Sbg/s1600/Screen%2BShot%2B2015-09-20%2Bat%2B9.08.41%2BAM.png[screenshot])
* mouse demo - included mouse test (http://2.bp.blogspot.com/-fWvW5opT0es/VhIdItdKqJI/AAAAAAAAATE/7Ojc0L1SpB0/s1600/Screen%2BShot%2B2015-10-04%2Bat%2B11.47.13%2BPM.png[screenshot])
* https://github.com/gdamore/gomatrix[gomatrix] - converted from Termbox
* https://github.com/zyedidia/micro/[micro] - lightweight text editor with syntax-highlighting and themes
* https://github.com/viktomas/godu[godu] - simple golang utility helping to discover large files/folders.
* https://github.com/rivo/tview[tview] - rich interactive widgets for terminal UIs
* https://github.com/marcusolsson/tui-go[tui-go] - UI library for terminal apps (_deprecated_)
* https://github.com/rgm3/gomandelbrot[gomandelbrot] - Mandelbrot!
* https://github.com/senorprogrammer/wtf[WTF]- Personal information dashboard for your terminal
* https://github.com/browsh-org/browsh[browsh] - A fully-modern text-based browser, rendering to TTY and browsers (https://www.youtube.com/watch?v=HZq86XfBoRo[video])
* https://github.com/sachaos/go-life[go-life] - Conway's Game of Life.
* https://github.com/gcla/gowid[gowid] - compositional widgets for terminal UIs, inspired by urwid
* https://termshark.io[termshark] - a terminal UI for tshark, inspired by Wireshark, built on gowid
* https://github.com/MichaelS11/go-tetris[go-tetris] - Go Tetris with AI option
* https://github.com/junegunn/fzf[fzf] - A command-line fuzzy finder
* https://github.com/esimov/ascii-fluid[ascii-fluid] - A terminal based ASCII fluid simulation controlled by webcam
* https://gitlab.com/tslocum/cbind[cbind] - Provides key event encoding, decoding and handling
* https://github.com/spinzed/tpong[tpong] - The old-school Pong remade in terminal

## 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 relevent 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.

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|===
^.^|
image:logos/tidelift.png[100,100]
a|
https://tidelift.com/[Tidelift] subscriptions include support for _Tcell_, as well as many other open source packages.

^.^|
image:logos/staysail.png[100,100]
a|
mailto:info@staysail.tech[Staysail Systems, Inc.] offers direct support, and custom development around _Tcell_ on an hourly basis.

^.^|
image:logos/patreon.png[100,100]
a|I also welcome donations at https://www.patreon.com/gedamore/[Patreon], if you just want to make a contribution.
|===