Re: "... the window start at a meaningless point within a line."

[Alan Mackenzie <acm@muc.de>]

On Fri, Oct 16, 2015 at 08:26:08PM +0300, Eli Zaretskii wrote:
> > Date: Fri, 16 Oct 2015 15:19:36 +0000
> > Cc: emacs-devel@gnu.org
> > From: Alan Mackenzie <acm@muc.de>

[ .... ]

> > I've no experience with bidi text, or even RTL text.  Could you cite me
> > an appropriate bidi or RTL file I could play around with, even though I
> > couldn't read it.  Would I need any special set up with (for example)
> > fonts, or input methods?  In fact, before asking you to answer these I
> > should read the fine manual first.

> Just turn on the 'hebrew' input method and start typing.

Wow!  That is, er,.. different!

[ .... ]

> > I see that `it' movements from "left to right" are going to move to
> > successively lower buffer positions, and this will give me trouble.

> No, it's much worse: when it moves, the screen coordinates increase
> monotonously, but buffer position does not.  The buffer position can
> go up for a while, then jump a head many places and start moving down,
> then jump again and go up, etc.  That's what I meant when I said the
> buffer position changes non-linearly with screen position.

Yes, I see what you mean, now.  I haven't tried out the Hebrew input
method with follow mode yet.  That should be interesting!

> > > As long as you use functions that move the iterator, you cannot safely
> > > assign one 'struct it' to another.  That's because the iterator object
> > > has a (mostly invisible) companion -- the bidi cache, which must be in
> > > sync with the contents of 'struct it'.

> > But surely each struct it has its own bidi cache, doesn't it?

> No, there's only one cache.

OK.

-- 
Alan Mackenzie (Nuremberg, Germany).