Re: [emacs-bidi] mirroring of glyphs

[Alex Schroeder]

"Eli Zaretskii" <address@hidden> writes:

>> From: Alex Schroeder <address@hidden>
>> Date: Sat, 17 Nov 2001 15:55:58 +0100
>> 
>> Perhaps you see something I am missing.  I list various
>> definitions of bidi-visual-to-logical, together with input, output,
>> and expected output.
>
> It's very hard to look at this without a few debugging aids.  One such
> tool that helps a lot is to print the input string with final resolved
> levels under every character.  Could you add such a feature and post
> the results with the problematic strings?

I have actually resigned myself to the inevitable.  It is not
possible.  I think Ehud already mentioned this in a previous post.

Anyway, here are some examples to illustrate this.  There are certain
logical representations which yield the same visual representation:

(string= (bidi-logical-to-visual "my CAR123")
         (bidi-logical-to-visual "my 123CAR"))
  => t

Therefore the reverse operation must only return one of the many
possible logical representations in order to be correct:

(bidi-visual-to-logical
 (bidi-logical-to-visual "my CAR123") 'L2R)
  => "my 123CAR"

The same is true for the one remaining problem test case from the PGBA
page:

(bidi-visual-to-logical "<123H/>shalom<123H>" 'R2L)
  => "<Hshalom<123</H123>"

What I didn't appreciate is that this is just one of the many possible
logical representations for the same string:

(bidi-logical-to-visual (bidi-visual-to-logical "<123H/>shalom<123H>" 'R2L))
  => "<123H/>shalom<123H>"

Therefore the current bidi implementation is as good as it gets.  :)


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