Re: [emacs-bidi] Suboptimal display-reordering in minibuffer

[Eli Zaretskii]

> Date: Wed, 30 Jun 2010 02:04:30 +0300
> From: Amit Aronovitch <address@hidden>
> Cc: "Martin J. Dürst" <address@hidden>, 
>       address@hidden
> 
> Please have a look at the following draft Israeli standard (by SII):
> http://db.tt/rc21Gd

Thanks for the reference.  I didn't find there anything new to me, but
it will certainly be useful to have all that handy when working on the
implementation of this for Emacs.

> > The important thing is to establish whether we need some
> > infrastructure in Emacs that is currently missing, because that would
> > need to be coded first, before any user-visible progress can be made.
> 
> I believe that the required infrastructure has a lot in common with the
> coloring (font-lock) system.

It's not that simple.  The way bidi reordering is designed and
implemented in Emacs, the reordering itself happens _before_ faces,
overlays, and other display features are considered.  The bidi
reordering engine is totally oblivious to text properties, overlays,
images, etc.; it just controls which character will be considered next
for delivering it to the display, and all the rest, i.e. calculation
of the face of that character, its display metrics, etc. -- all this
happens _after_ reordering, in code that calls the reordering engine.

What we need is a way of telling the reordering engine to reorder only
portions of buffer text.  This is the infrastructure I was thinking
about, because I don't think we have anything like that at this time.
And I'm not sure it is a good idea to base the implementation on text
properties or overlays, at least not text properties of the kind used
for fontification.