Path: utzoo!attcan!uunet!vsi!friedl
From: friedl@vsi.COM (Stephen J. Friedl)
Newsgroups: comp.bugs.sys5
Subject: Re: bug in pg on System V
Summary: all about bogus DEC autowrap
Keywords: pg autowrap no-newline
Message-ID: <1096@vsi.COM>
Date: 16 Apr 89 17:33:41 GMT
References: <4935@ingr.com> <464@b11.INGR.COM> <10038@smoke.BRL.MIL>
Organization: V-Systems, Inc. -- Santa Ana, CA
Lines: 37

In article <10038@smoke.BRL.MIL>, gwyn@smoke.BRL.MIL (Doug Gwyn) writes:
> The VT100's margin wrap feature is exceedingly baroque and does
> not match the model associated with termcap/terminfo "am" capability,
> which describes a simple immediately-wraparound feature (the VT100
> maintains internal state and defers wraparound until it thinks it
> should have been done, but it gets confused by certain character
> sequences).

VT100 deferred autowrap waits until it receives the 81st character
on a line before thinking about an autowrap.  If this character is
printable, wrap occurs before it is printed, but if the character is
a newline then it is only done once.

This "feature" lets you look at an 80-column card image without
getting the double spacing that immediate autowrap would cause.
Since many more of us read 80-column card images than use screen-
oriented editors, this is a good thing.

> VT100 termcap/terminfo descriptions should NOT specify "am" even if
> the margin wrap option of the terminal is enabled.

Some terminals (HDS, for instance) let you specify which kind of
autowrap you want to use, and System V terminfo (on the 3B2, at least)
lets you specify that this happens: look at "eat_newline_glitch" or
the capname "xenl".

We used to have all kinds of problems with our vt220-compatible
terminals, but when we set "xenl" and "am" together, it never messes
up anymore, except for all those bugs it puts in my C code :-).

     Steve

-- 
Stephen J. Friedl / V-Systems, Inc. / Santa Ana, CA / +1 714 545 6442 
3B2-kind-of-guy   / friedl@vsi.com  / {attmail, uunet, etc}!vsi!friedl

"I'm making a fashion statement: I'm saying I don't know how to dress." - me