[bug #60673] adjustment algorithm should disregard nonadjusted lines in its alternation pattern

[Dave]

URL:
  <https://savannah.gnu.org/bugs/?60673>

                 Summary: adjustment algorithm should disregard nonadjusted
lines in its alternation pattern
                 Project: GNU troff
            Submitted by: barx
            Submitted on: Tue 25 May 2021 10:47:19 PM CDT
                Category: Core
                Severity: 1 - Wish
              Item Group: New feature
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
         Planned Release: None

    _______________________________________________________

Details:

This was originally reported in a comment in bug #57836, but I now feel it's a
separate enough problem to merit its own bug report.

The text below, mostly unaltered from that previous report, characterizes this
as "grotty" behavior, but it turns out, as Branden explained in bug #60665,
that the relevant code is device independent; it's just that the
line-alternation pattern is effectively invisible in typeset output.


$ nroff tty | uniq
While  the  example  in  bug  57836's original report is somewhat
contrived and a bit of an edge case in real life, there turns out
to  be  a  more  innate  bug  in grotty's balancing algorithm. As
mentioned before (and easily observable), when grotty adds spaces
to  a  line  in  the  process  of justifying it, the algorithm it
utilizes adds spaces from opposite ends of each line. But when it
adds  this  space,  it  does  not take into account lines with no
adjustment at all required. Therefore if space only need be added
to  every  other  line  of  the text, all the space ends up being
added to the same end of the line, degrading the uniform grayness
of  the  output,  as  can  be  seen in this example. There is one
fairly simple way to address this: grotty shouldn't "count" lines
that  don't  need  to  be  adjusted; instead, it should apply the
alternation pattern only to those lines that do need adjustment.

$ cat tty
.nh
.ss 12 0
While the example in bug 57836's original report is somewhat
contrived and a bit of an edge case in real life, there turns out
to be a more innate bug in grotty's balancing algorithm. As
mentioned before (and easily observable), when grotty adds spaces
to a line in the process of justifying it, the algorithm it
utilizes adds spaces from opposite ends of each line. But when it
adds this space, it does not take into account lines with no
adjustment at all required. Therefore if space only need be added
to every other line of the text, all the space ends up being
added to the same end of the line, degrading the uniform grayness
of the output, as can be seen in this example. There is one
fairly simple way to address this: grotty shouldn't "count" lines
that don't need to be adjusted; instead, it should apply the
alternation pattern only to those lines that do need adjustment.
$


Here is the same paragraph adjusted by hand using the suggested change to the
algorithm.  The overall grayness does not change from one side of the column
to the other as it did before; it's much more pleasing to the eye, while being
no harder (or easier) to read.  (If you're reading this in an email client
that uses a proportional typeface, neither example will display properly. 
Look at them in the bug tracker.)


While  the  example  in  bug  57836's original report is somewhat
contrived and a bit of an edge case in real life, there turns out
to be a more innate  bug  in  grotty's  balancing  algorithm.  As
mentioned before (and easily observable), when grotty adds spaces
to  a  line  in  the  process  of justifying it, the algorithm it
utilizes adds spaces from opposite ends of each line. But when it
adds this space, it does not take  into  account  lines  with  no
adjustment at all required. Therefore if space only need be added
to  every  other  line  of  the text, all the space ends up being
added to the same end of the line, degrading the uniform grayness
of the output, as can be seen  in  this  example.  There  is  one
fairly simple way to address this: grotty shouldn't "count" lines
that  don't  need  to  be  adjusted; instead, it should apply the
alternation pattern only to those lines that do need adjustment.





    _______________________________________________________

Reply to this item at:

  <https://savannah.gnu.org/bugs/?60673>

_______________________________________________
  Message sent via Savannah
  https://savannah.gnu.org/