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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.
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.
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.
Tcell is portable to a wider 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.) For all of these systems except Solaris/illumos, Tcell is pure Go, with no need for CGO.
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.
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. 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.
It also has richer support for a larger number of special keys that some terminals can send.
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.)
Tcell supports enhanced mouse tracking mode, so your application can receive regular mouse motion events, and wheel events, if your terminal supports it.
A compatibility layer for termbox is provided in the compat directory. To use it, try importing “git.parallelcoin.io/dev/tcell/termbox” instead. Most termbox-go programs will probably work without further modification.
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.
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.
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.
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.
Reasonable attempts have been made to minimize sending data to terminals, avoiding repeated sequences or drawing the same cell on refresh updates.
(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 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.
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.
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 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.
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.
This software is absolutely free, but if you want to obtain commercial support (giving prioritized access to the developer, etc. on an hourly rate), please drop a line to email@example.com
I also welcome donations at Patreon, if you just want to feel good about defraying development costs: https://www.patreon.com/gedamore