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

[Eli Zaretskii <eliz@gnu.org>]

> From: David Kastrup <dak@gnu.org>
> Cc: Alan Mackenzie <acm@muc.de>,  emacs-devel@gnu.org
> Date: Fri, 16 Oct 2015 22:46:57 +0200
> 
> > Just turn on the 'hebrew' input method and start typing.

> דוד doesn't look all that different from L2R text.

Yes, that's an example.  But this example is actually not what Alan
should look at, he should look at something like this:

  L2R paragraph with some דוד מלך ישראל R2L text.

The reason is that the iterator geometry is always L2R; screen lines
in an R2L paragraph are produced "behind the back" of the iterator
object.  So all the move_it_* functions think the line begins at the
left window margin, like the above example.

To see the non-linear change in buffer position with the screen
coordinates, use C-f to move through the above line.  C-f moves
forward in the strict logical order of buffer positions, so the
non-linear way the cursor moves on the screen will demonstrate the
problem, i.e. why it is wrong to compare buffer positions to decide
which character is to the left of which on the screen.