Abusing `curses' WINDOW structure (long)

[Brett Galloway]

In article <7565 at sun.uucp> guy at sun.uucp (Guy Harris) writes:
>> I'm writing a program which uses the curses library, and need to
>> include a "print screen" type of utility.  Rather than reproducing
>> my display logic in order to print a text file image, I was thinking
>> of simply copying the screen from stdscr->_y directly into my textfile
>> (adding newlines where appropriate). ...
>> Now, my machine uses termcap, and this seems to work OK.  The question
>> is, is the WINDOW structure different in the terminfo implementation?
>> And if so, can the routine above be rewritten and made to work?
>
>"Abusing" is right!  Assuming you "know" what an unadvertised data structure
>of a package looks like is a great way to get into trouble.

One nit is that at least in 4.2 BSD the WINDOW structure IS advertised --
in appendix B of the document, Screen Updating and Cursor Movement
Optimization: A Library Package, by Kenneth Arnold.

Nonetheless, I do agree that use of the internals of WINDOW is
dangerous.  However, there are cases where such use is unavoidable.

I have a program in which a WINDOW is passed as an argument to a function
which needs to know the bounds of the window.  At least in 4.2BSD, I know
of no portable way to deduce that from the WINDOW structure, although the
fields are apparent enough.  Therefore, I used the _maxx and _maxy fields.
Further, the only portable way I know to get the current coordinates in a
window is to use getyx(win,y,x); but frequently one only wants one of the
coordinates and not both.  Getyx() forces the user to provide variables for
both coordinates, and then lint barks about a variable set but not used.
In short, curses (at least 4.2BSD) doesn't provide enough functionality
through macros to avoid nonportable uses.

More generally, I find curses well-named.  Even excluding the many bugs
that exist in the 4.2 BSD implementation, it does not provide sufficient
functionality, and it is virtually possible to extend its
functionality in a portable manner.  What I would like to see is someone
define and implement a new package similar to curses but more powerful.
This package should have a well-defined interface to the
underlying terminal driver library, allowing termcap and terminfo drivers
to be written for it, and even drivers for certain pc's.  It should also
have separate drivers for controlling system-dependent information, such
as the BSD job-control-dependent stuff in 4.2 BSD curses.  It
should provide a more coherent and general mechanism for performing
input through windows.  Finally, it should provide a rational method to
treat dynamic window resizing, which I understand occurs on at least one
system, SUN, and which can be expected to appear on others.

I don't understand why it would not be possible to take the display end of
one of the powerful, portable editors and turn it into a display package of
this sort.  If done right, the core of the package could be completely
portable across systems both unix and non-unix.  As such, the package could
become a de facto standard for video character display handling for the C
language.  Far too often people keep re-inventing this package for different
editors, even under unix systems (because curses isn't powerful or general
enough).

-- 
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Brett Galloway
{pesnta,twg,ios,qubix,turtlevax,tymix,vecpyr,certes,isi}!wjvax!brett