bug#27525: 25.1; Line wrapping of bidi paragraphs

[Itai Berli <itai.berli@gmail.com>]

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You sure put a lot of thought and effort into it. Thank you for that.

Now that I have downloaded the source code, I'd like to take a look at this
problem first hand. I'm not a programmer, not even an amateur one, but I
can sometimes make sense of the general gist of code when I read it, and
I'd like to take a look at the part of code that's responsible for the
present bug, maybe put a breakpoint here and there and give it a test run
to get a feel of how it works, and why it misses the mark when it comes to
line wrapping bidi paragraphs.

Could you please give me some pointers: what files should I look into, what
functions should I read, possibly even suggestions for where to put
breakpoints and which variables to watch. I'm not asking for a
comprehensive and detailed run down of this feature; just a starting
point(s). Every tip and suggestion will be welcome.

On Thu, Jul 20, 2017 at 2:09 PM, Eli Zaretskii <eliz@gnu.org> wrote:

> > Resent-Sender: help-debbugs@gnu.org
> > From: Itai Berli <itai.berli@gmail.com>
> > Date: Thu, 20 Jul 2017 10:01:33 +0300
> >
> > I see no reason to continue this discussion any further.
>
> Thank you.
>
> > One thing I'm curious about, though. What bidi features exist in Emacs,
> half of which the other editors don't
> > have? Which features were you referring to when you wrote that, thanks
> to them, "10 years later, Emacs still
> > shines among all the bidi-aware editors out there"?
>
>  . For starters, all the UBA features are fully supported, including
>    the directional isolates and bracket-matching (a.k.a. "BPA").
>  . Support for bidirectional display on both GUI and text-mode terminals.
>  . Both logical-order and visual-order cursor motion.
>  . Full support for Arabic shaping and other complex-script shaping
>    features in bidirectional text (e.g., Hebrew "nikkud").
>  . Bidi formatting controls are visible on screen, so users don't need
>    to guess why display looks like it does.
>  . Variables to control where paragraphs begin and end, for the
>    purposes of determining base paragraph direction.
>  . Variables to disable mirroring of parentheses due to bidi context,
>    and even disable bidi reordering entirely, if needed.
>  . Lisp functions that are necessary when writing bidi-aware
>    customizations and features:
>    . a function that returns base paragraph direction at point
>    . a function that returns resolved bidi levels for a line
>    . a function that takes a string and wraps it so that it could be
>      concatenated with other strings without fear of producing jumbled
>      display due to reordering (important for tabular display)
>    . a function to find characters whose directionality was overridden
>      by bidi controls (which could be used to maliciously dupe the
>      user to think a string is not what it really is)
>    . a function to return a substring of buffer text surrounded by
>      bidi controls that make sure its visual appearance will not
>      change when copied to a different portion of text
>
> And that is even before we consider Emacs-only features, which those
> other editors can only dream about, like mouse-highlight, display and
> overlay strings, invisible text, text alignment on display, etc. --
> all of which are bidi-aware in Emacs.
>

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