Re: Line wrap reconsidered

[Yuan Fu <casouri@gmail.com>]

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> On May 31, 2020, at 1:55 PM, Eli Zaretskii <eliz@gnu.org> wrote:
> 
>> From: Yuan Fu <casouri@gmail.com>
>> Date: Sun, 31 May 2020 13:39:56 -0400
>> Cc: Lars Ingebrigtsen <larsi@gnus.org>,
>> emacs-devel <emacs-devel@gnu.org>
>> 
>>>> I think I did jus that, i.e., if (may_wrap && char_can_wrap_before(it)).
>>> 
>>> Fundamentally, yes.  But having a complex condition
>>> 
>>>  if (FOO && BAR)
>>> 
>>> makes the code harder to read and understand, and thus makes logical
>>> errors easier, than a simple condition like
>>> 
>>>  if (FOOBAR == some_value)
>> 
>> In principle, yes, but I doubt the current logic can be simplified. Do you have some concrete example?
> 
> It was a suggestion.  Maybe it can't be done.  Let's see the code, and
> then we could try simplifying the logic.  The issue here is that
> IT_DISPLAYING_WHITESPACE is used in many places, and it is not easy to
> understand how to map that to 2 different conditions.  Making just one
> condition eliminates that problem and lowers the probability of
> introducing bugs.

Aye.

> 
>>> If bidi-paragraph-direction is right-to-left, then yes, they are
>>> reversed.  But not if the paragraph direction is left-to-right.
>> 
>> Then does bidi.c handle word wrapping when bidi-paragraph-direction is right-to-left? Paragraph 3.4 mentioned that “The accumulated widths of those glyphs (in logical order) are used to determine line breaks.”
> 
> No, it's in xdisp.c, the code that you are changing.  bidi.c just
> makes it so that the "next" character is the next one in the visual
> order, i.e. it replaces a simple increment of buffer position.


Thanks for your patience. Then how does xdisp.c (or bidi.c) know how much space to leave at the left edge, when the paragraph is right-to-left? For example, in the figure below, how does Emacs determine how much space to leave at the place where I marked with yellow highlighter? I assume the iterater starts from the left edge of the first line and bidi gives it a line with a white space stretch ? The comment says “On graphics terminals, there's a single stretch glyph of a suitably computed width.” Or does the iterator go from right to left?


Yuan


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