LMTX, BIdi, full paragraph, and spurious empty line

* LMTX, BIdi, full paragraph, and spurious empty line
@ 2021-06-22  2:52 Rik Kabel
  2021-06-23 22:10 ` Hans Hagen
  0 siblings, 1 reply; 4+ messages in thread
From: Rik Kabel @ 2021-06-22  2:52 UTC (permalink / raw)
  To: ntg-context

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Hello all,

Last October Denis Maier complained about a spurious empty line 
generated with protrusion and bidi active and a full paragraph. (See 
https://www.mail-archive.com/ntg-context@ntg.nl/msg95916.html 
<https://www.mail-archive.com/ntg-context@ntg.nl/msg95916.html> or 
similar on your favorite mail archive.)

I have recreated the issue without involving protrusion. When a 
paragraph is very full and bidi is on, an extra line seems to be 
generated. Without bidi there is no extra line. This is quite sensitive, 
of course, to line width. I have probably 30 instances of it occurring 
in a tightly-set bibliography. I would assume that it may occur in any 
text, but have not noticed it in the body of my book.

I have created an example document that shows it. The problem disappears 
if bidi is turned off (comment out the first non-comment line) but of 
course then the RTL text is mis-set. In this example, the spurious line 
appears after the Walt Kelly entry.

This was tested under ConTeXt  ver: 2021.06.18 23:37 LMTX  fmt: 
2021.6.21, but is not a new problem with this version. /The problem does 
not occur with MKIV from the same installation./

    %% Demonstration of spurious line insertion on full paragraph with
    bidi active

    \setupdirections  [bidi=on,method=unicode]

    \definepapersize  [Testing]
                       [width=6.69in]
    \setuppapersize   [Testing]

    \setuplayout      [width=fit,
                        backspace=1.4in,
                        cutspace=1in,
                        leftmargin=0.65in,
                        rightmargin=0.65in]

    \setupwhitespace  [small]

    \setupbodyfont    [libertinus,11pt]

    \define\SetupBib{
       \spaceskip 0.7\interwordspace plus .5\interwordstretch minus
    \interwordshrink
       \definedelimitedtext
         [Exdent]
         [leftmargin=1em,
          indenting={yes,-1em},
          indentnext=yes]}

    \starttext
       \input jojomayer

       \input klein

       \blank[2*line]

       \SetupBib
       \startExdent

         Kelly, Cynthia C., ed. 2005. {\em Oppenheimer and the Manhattan
         Project: Insights into J.~Robert Oppenheimer, ‘Father of the
         Atomic Bomb’}. Singapore: World Scientific.

         Kelly, Walt. 1953. {\em The Pogo Papers}. New York, NY: Simon
         & Schuster.

         Kuhn, Thomas S. 1962. {\em The Structure of Scientific
         Revolutions}. Chicago, IL: University of Chicago Press.

         Weinreich, Max. 1945. “Der YIVO un di problemen fun undzer
         tsayt (דער ייִוואָ און די פּראָבלעמען פֿון אונדזער צײַט).”
         {\em YIVO Bleter} 25 (1): 3--18. The title is translated as
         {\em The YIVO and the problems of our time}, and also as
         {\em The YIVO faces the post-war world}.

       \stopExdent
    \stoptext

Of course, there could be some other mechanism at work here than bidi, 
but changing that clears the problem in this instance. (It may be the 
adjustment to spaceskip that I use to tighten up the text in the 
bibliography, and if it is, I welcome an alternative way to do that.)

-- 
Rik

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