Re: termcap and DISPLAY weirdness

From: Thomas Dickey (dickey_at_saltmine.radix.net)
Date: 11/18/03 

Date: 18 Nov 2003 00:09:11 GMT

Chuck Dillon <cdillon@nimblegen.com> wrote:
> Joe Durusau wrote:
>>
>> It appears that the O.P. is trying to run software that "thinks" it
>> is operating a VT220, while it is really operating an Xterm. The
>> two are not compatible. It is possible that setting the TERM env.
>> variable to Xterm (or something similar, depending on the system),
>> might work. The bootom line is that VT220 line graphics are not
>> avialable
>> in an Xterm window, at least not on systems I have used.

> The latest xterm supports VT220 according to the manpage on linux for
> example. Given that Thomas Dickey, one of the authors of xterm and I
> believe the current maintainer, responded in the thread and didn't
> raise this issue seems to confirm that.

he appears to be using AIX - hence I'd assume he's using X11R5 or X11R6
xterm. But the area that he's talking about should behave the same in
any of those flavors. It's possible that he's using aixterm rather than
xterm - I haven't used that recently enough to recall pitfalls in setting
up line-drawing.

> Not to mention that the OP indicates that the xterm does emulate the
> VT220 when telnet is in the loop.

...which leads me to suspect that he's not got $TERM set as he states.

vt100/vt220 line-drawing maps characters using this string:

        acsc=``aaffggjjkkllmmnnooppqqrrssttuuvvwwxxyyzz{{||}}~~,

(it's pairs of characters - you see that they're identical since it's the
reference). In xterm's vt100 (or whatever) emulation, the glyphs shown
are from the font's 1-31 positions (normally nonprinting characters).

linux console (and a few related terminals) use this:

        acsc=+^P\,^Q-^X.^Y0\333`^Da\261f\370g\361h\260i\316j\331k\277l\332m\300n\305o~p\304q\304r\304s_t\303u\264v\301w\302x\263y\363z\362{\343|\330}\234~\376,

The odd \333, etc., are codes in the range 160-255. If the font is something
like ISO-8859-1 (common), some of those will be the a's with umlauts, etc.
Since I'm familiar with fonts that show characters like this, and none that
have similar characters in positions 1-31, it seems that the application is
trying to use a mapping such as the latter - which isn't what a vt220 or vt100
would do. 

-- 
Thomas E. Dickey
http://invisible-island.net
ftp://invisible-island.net