Re: Basic WYSIWYG printing in GNU Emacs (Arabic & Hebrew)

[Eli Zaretskii]

> From: Anand Tamariya <atamariya@gmail.com>
> Date: Wed, 11 Aug 2021 21:29:53 +0530
> Cc: emacs-devel@gnu.org
> 
>  > It uses following API to determine BIDI classification and processes 
> accordingly:
>  > (get-char-code-property (char-after from) 'bidi-class)
> 
>  Hmm... not sure this is enough, except in the simplest cases.  The
>  bidi-class of a character is just its basic attribute; application of
>  the full Unicode Bidirectional Algorithm can and does change the
>  effective attributes of some characters, before they are displayed.
> 
> Do you have some sample text for this use case? I can run a quick test.

You could try TUTORIAL.he, for example.

>  Is this test performed on each character or only at the beginning of a
>  visual line?
> 
> This happens at every point where the font changes. 

So if the entire buffer uses just a single font, like TUTORIAL.he
does, you do the test only once, at the first character of the buffer
text?  But that could produce incorrect results, because the text
further into the buffer could have both RTL and LTR paragraphs
intermixed, and the correct display will show each of these at their
correct base direction.  For example, most of the paragraphs in
TUTORIAL.he have right-to-left base direction, but the last paragraph,
with the Local Variables, is left-to-right, so its display starts at
the left edge of the window.