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Re: lynx-dev UTF-8 display questions (was: Superscripts)

From: Klaus Weide
Subject: Re: lynx-dev UTF-8 display questions (was: Superscripts)
Date: Wed, 14 Jun 2000 11:00:01 -0500 (CDT)

On 14 Jun 2000, Sergei Pokrovsky wrote:
> >>>>> Klaus Weide writes:
> ...
>   Klaus> Now I remember I also had been seeing some display glitches
>   Klaus> of the sort you describe, which would only appear when color
>   Klaus> was turned off.  But I tried to reproduce that now, both with
>   Klaus> released 2.8.3 and my own current code, and utterly failed...
>   Klaus> A possible reason is that earlier I was testing with ncurses,
>   Klaus> while my current code is complied with slang (1.3.9, with a
>   Klaus> private fix that should not be necessary for 1.4.1).

In the meantime, I have found _another_ problem which I can see in
2.8.3rel.1 with slang 1.3.9.  This time, it appears to be a real bug in
the lynx code (as opposed to: imperfect workaround for UTF-8-unaware
display library).  Let me try to describe this, it's rather strange,
I wonder if you can reproduce it.
This does not depend on -show_cursor, -nocolor, or link numbering.
Your window size should be 80x25, lynx User Mode == Advanced.
Start lynx on, in
an xterm -u8 (with lynx's display character set as UTF-8, of course).
The area of interest is the first line (3rd line on screen), which
has four links. 
1.) Move around among those 4 links, everything should be fine.
    (State A)
2.) Invoke the (form-based) 'O'ptions page.  Then return to the
    previous document, ether with Left Arrow or by submitting some
    option change (it doesn't seem to make a difference).
3.) Now back in AL.html, move around among those 4 links.  This time,
    the horizontal position of the current link (other than the first)
    is consistently wrong, shifted to the left.  In addition, strange
    things appear on the statusline (may only be visible if Show Cursor
    is in effect).
    (State B)
State B persists if you visit other links, even on the 2nd screenful
(p2 of 37), or the last page of the document, or even (some?) other
documents.  Return to the first line to check.
State B turns back to sane state A upon visit to the _3rd_ screenful
of the AL.html document (p3 of 37).  The third screen line on that
screenful is a "Ruse:" with quite a few Cyrillic characters, which
I suppose is relevant for this mysterious cure.
All this is reapeatable.  Only the 'O'ptions page seems to have this
curious effect, and it has it every time.

I am working on a fix, or I may already have fixed it "accidentally"
in my own separate code (but without understanding what's really going
on), have to check.

> ,----
> | Lynx Version 2.8.4dev.2 (21 May 2000)
> | Built on solaris2.7 Jun 12 2000 14:10:24
> `----
> with slang 1.4.1 and your SITE_DEFS="-DSLANG_MBCS_HACK".  That's what

Ah, I had thought you had already given up on that one.

> I am using now (and it misbehaves with -nocolor, which I really don't
> need).
>   Klaus> Anyway, this was the sort of thing where I found that
>   Klaus> simplifying terminfo descriptions helped.  So if you are
> ...
> Excuse me, Klaus, but I cannot do it for you now.  I've spent a bit
> too much time playing with lynx, and now I have to attend some of my
> duties a bit.  Maybe some time later.

I am making another attempt below to convince you. :)

>   >> Well, if I launch lynx with -nocolor,
>   >> 
>   >> xterm -u8 \ -fn
>   >> -misc-fixed-medium-r-semicondensed--13-120-75-75-c-60-iso10646-1
>   >> \ -g x57 -e lynx -nocolor &
>   >> 
>   >> and open a page in UTF-8 or even in Latin-1, say
>   >> 
>   >>
>   >> 
>   >> then moving through the links (press a few Up arrows, then a few
>   >> Downs) creates strange phantom anchors at random spots, sometimes
>   >> beyond the end of line, sometimes overwriting some innocent plain
>   >> prose ...  And these phantoms are not washed away with ^R ... And
>   >> the WHEREIS-line spawns are rising trough the screen ...

> I load a page, ^E, do some Ups. When an Up brings me to the uppermost
> anchor, the screen image (including the WHEREIS line) drifts 3 lines

(This first confused me - I thought you meant something about the
WHEREIS ('/') command, but apparently you mean the title line.)

> up, leaving 3 blank underlined lines; the current anchor is
> duplicated, one in the old position below, filled and with the cursor
> at it, the other within the drifted text (as a passive link).  The
> active link can be followed; the other (shifted) anchors are dead. 

Ok, this does sound familiar, although I cannot reproduce it right now.
Especially the 3 or so blank lines looks familiar.  When I have seen
this, the effect was even worse when viewing a local directory listing
('g .') or a HTTP-server generated file listing IIRC, which became
completely unusable.

I think _this_ appears only with SLANG_MBCS_HACK and with automatic
margins on (plus some other conditions...).  For a quick check,
change the xterm's "Enable Auto Wraparound" setting when this
is happening (from xterm's Ctrl+mouse-2 menu).

>   >> No such horror without -nocolor.
>   Klaus> Well, so you don't really need a fix (I assume that you can
>   Klaus> just use -color), but I am still curious whether the
>   Klaus> "simplified terminfo" approach works for you.
> I really am not interested in the nocolor mode.  Sorry that I cannot

But now you have found another case... (-show_cursor, in another message)

> help you now (I can answer question and experiment, but I'd rather not
> risk to change any system parameters right now.)

I probably made it look much more complicated that it is, by giving too
many details.  So I won't repeat that mistake. :)
But really, making a customized terminfo description doesn't involve
changing any system parameters.  Everything can be done by a non-root
user, in a private directory like ~/.terminfo/, you would just be
generating one new file.  And if you give it a non-standard name (like
I do by appending "-nlm"), it can't interfere with anything unless
you explicitly set TERM to the new name.  The worst part is figuring
out how to call 'tic', which means looking at the man page.


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