Re: Line wrap reconsidered

[Yuan Fu <casouri@gmail.com>]

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> On Jul 12, 2020, at 2:27 PM, Eli Zaretskii <eliz@gnu.org> wrote:
> 
>> From: Yuan Fu <casouri@gmail.com>
>> Date: Sun, 12 Jul 2020 13:25:03 -0400
>> Cc: Lars Ingebrigtsen <larsi@gnus.org>,
>> emacs-devel@gnu.org
>> 
>> I’m having a strange problem that when bidi-paragraph-direction is ‘left-to-right, Arabic characters wraps fine but Hebrew characters doesn’t. Is there anything special about Hebrew (or Arabic)?
> 
> Not enough information.  Is this with your changes?

Yes, this only happens with my patch. And that what puzzles me. Here I enabled white-space-mode, as you can see, the second line starts with whitespace. That means Emacs cannot find a wrap point in the Hebrew text and thus is not wrapping but simply continuing the Hebrew text.



As you might remember, in my patch the function it_can_wrap_after determines if we can set a warp point after a character. xdisp uses this function to determine if we can set a wrap point, then this function must be the culprit. It looks like this:

/* Return true if the current character allows wrapping after it.   */
static bool char_can_wrap_after (struct it *it)
{
  /* For CJK (LTR) text in RTL paragraph, EOL and BOL are flipped.  */
  bool kinsoku_can_wrap;
  if (it->glyph_row && it->glyph_row->reversed_p)
    kinsoku_can_wrap = IT_CHAR_HAS_CATEGORY (it, LINE_BREAKABLE)
      && !IT_CHAR_HAS_CATEGORY (it, NOT_AT_BOL);
  else
    kinsoku_can_wrap = IT_CHAR_HAS_CATEGORY (it, LINE_BREAKABLE)
      && !IT_CHAR_HAS_CATEGORY (it, NOT_AT_EOL);

  /* We used to only check for whitespace characters for wrapping,
     hence this macro.  Obviously you can wrap after a space or
     tab.  */
  return (IT_DISPLAYING_WHITESPACE (it) /* || kinsoku_can_wrap */);
}

Basically, we can wrap if this char is a whitespace character, or kinsoku says this char is wrap-able. Now, if I comment out the kinsoku part (the last line after ||), Hebrew can wrap normally. But the value of kinsoku_can_wrap shouldn’t matter since IT_DISPLAYING_WHITESPACE (it) should short circuit when we are at a whitespace character.

Any guess on where could be the problem?

Yuan


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