terminfo

[Tony L. Hansen]

It's been interesting watching the recent discussions about terminfo and
curses, asking about the why's and wherefores, etc. As one of the people who
has been involved in the evolution of terminfo and curses, I thought I'd
add a little bit of real information to the net bandwidth.

1) why was terminfo created?

I believe that the main reason terminfo was written to begin with was that
the expressibility of arithmetic within a character attribute was severely
limited. Using the termcap arithmetic operators, one just cannot express all
of the different types of calculations necessary to handle the numerous
types of terminals present and appearing out there. Termcap is certainly
capable of handling numerous terminals, but there are just as many which it
cannot handle.

Once the decision was made to change the arithmetic capabilities of the
database to something which was more reasonable and usable with any
terminal, it was decided that it would be best to break away from the old
format entirely, allowing further improvements.

The longer names permit more capabilities to be supported easily. Although
there do exist equivalent termcap names for each and every terminfo name
there is, quick, what does the termcap "Fr" or "%1" capabilities represent?
The terminfo names of "kf63" and "khlp" representing the function-key #63
and the Help function key are certainly more usable.

The free-form input format and longer names, however, make it considerably
harder (and slower) to interpret the input file. Consequently, the compiled,
binary format and structure representation of the entire set of capabilities
permits very fast access to all of the capabilities. Termcap uses an n^2
algorithm to access capabilities.

2) How do I manipulate the database to change an entry?

All systems should have the uncompiled source to the terminfo database as
well as the compiled format. If yours doesn't, then complain to the vendor.
If you still cannot get the source, then you will have to make use of the
other tools available.

Unfortunately, System V release 2 didn't come with any way of looking at the
binary files. It's for that reason that I wrote the infocmp program which
subsequently was

    o	made available in source format for all via the AT&T Toolchest
	at a very low cost

    o	added to System V release 3.0

There have also been similar programs posted to the net; untic is one.

In a similar vein, I wrote captoinfo to convert termcap entries into
terminfo source format. It also became available within the Toolchest and in
System V release 3.0. PD versions of this program have also appeared on the
net.

3) Why has terminfo changed over the past few years

All evolution to terminfo has been of two flavors:

    o	add new capabilities to more fully support different terminals
    o	add new arithmetic operations

This was all done in an upwardly compatible manner.

One should also be able to take a terminfo binary compiled on one release of
the system to another release of the same system. One should also be able to
take the binary from one system of one type and put it onto another system
of a different type, but there may be difficulties going from an 8-bit byte
machine to a 9-bit byte machine. If necessary, the binary file will be
scanned a byte at a time to collect the 16-bit integer values, as the format
is supposed to be completely portable no matter what the byte order of the
machine in use. There may have been some minor bugs in the SysVr2 version
preventing full support of this on some machines, but the intent was there
and works completely in SysVr3.

4) I want to access the alternate character set of the terminal

The terminfo capability "acsc" (alternate character set characters) defines
a complete map of the alt. character set. It was added in System V release
3.0. Curses has always supported A_ALTCHARSET as a bit map similar to
A_BOLD. Additional curses level support (added in SysVr3.0) for these
characters comes in the form of variables named ACS_* (like ACS_ULCORNER and
ACS_RTEE). Yes, these characters are automatically used by the box()
function.

5) I want to define my own capabilites

The user defined terminfo capabilities user0 to user9 were added in SysVr3.1.
You're free to do with these as you will.

6) I want to redefine things on the fly

For redefining the number of lines and columns, the most straight-forward
method is to use $LINES and $COLUMNS to override the values kept within the
database. The terminfo level routines look for these values. The
terminfo level routines may also look at a couple of ioctl values to
determine the size of the window, but these are less reliable when going
beyond the local machine's boundaries.

Redefining other capabilities is somewhat more complicated, but not
impossible. Those with a SysVr3.1 source licence should look at chgtinfo in
the curses directory. I don't know if or when chgtinfo will make it into the
mainline system. One would use it like this:

	TERMINFO=`chgtinfo xhp, smso=\E[3m, smul@,`
	export TERMINFO

This would create a temporary version of the current terminfo entry under
/usr/tmp using the given modifications.

7) How do I deal with supporting both termcap and terminfo versions of a
terminal?

I recommend that you maintain only the terminfo version, since it can
describe so much more about the terminal. Then use "infocmp -C" when
necessary to create the termcap version of the entry.

5) What has changed in curses?

Yes, the curses library has evolved somewhat since Mark Horton's original
rewrite, which appeared in System V release 2.

With System V release 3.0,

    o	considerable tuning to make it faster
    o	additional terminfo capabilities and arithmetic operations
    o	support for an alternate character set
    o	support for soft labels
    o	additional minor functions
    o	rewrite of the curses and terminfo manual pages
    o	rewrite of the chapter on curses and terminfo
	in the Programmer's Guide
    o	tput enhanced
	    "tput init" provides the initialization capabilities of tset
	    tput can provide parameters  to capabilities which require them
    o	infocmp added
    o	captoinfo added

With System V release 3.1,

    o	A rewrite of the insides of curses by K. Phong Vo.
	The result is considerably smaller, yet faster, than all earlier
	versions.
    o	many new functions
    o	internationalization: full support for 16-bit character sets and
	removal of the 8-bit dependencies. This was done in both a binary
	and source level compatible manner.
    o	additional terminfo capabilities

With System V release 3.2

    o	full support for color terminals

The other major players in these enhancements besides myself, Mark Horton
and K. Phong Vo, were Ernie Rice, Ephrayim Naiman and Sam Shteingart.

6) Some specific requests in the article to which this is a followup:

< Terminfo Wish List:

< Support for backtab as a keypad character (maybe even support for tab as a
< keypad character, not just ^I).

Added in SVr3.0. Many additional input keys became supported due to the
large number of terminals in use with word processing systems.

< Support for terminals which allow on screen labels to descibe function
< keys (ie something like lab_f* but allowing a string parameter instead of
< a cursor)

Added in SVr3.0. The curses level offers a set of routines named slk_* for
dealing with the "soft labels"

< Modify pkey_* to allow length of string instead of using just assuming a
< terminating character (eg support for length of string on stack, %l)

Added in SVr3.0 were full support of the additional sprintf() sequences. For
example, to print a string out as exactly 16 characters, one would use the
normal sprintf() sequence of:

	%16.16s

< Support sequences to control block mode applications.
< Ability to define re-definable character sets.

I don't think that these have been considered.

< Support colour as well as standard high-lighting modes.

Added in SVr3.2

< Ability to use line drawing character sets (eg a set of commands that will
< emit corners, vertical lines, horizontal lines etc.)

Added in SVr3.0. See above.

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I hope some of this information proves useful for someone.

					Tony Hansen
				att!pegasus!hansen, attmail!tony