Re: move_it_vertically_backward question

[Po Lu]

Eli Zaretskii <eliz@gnu.org> writes:

> No, I meant to ask window-text-pixel-size to do that, by passing it a
> specially-formatted value of FROM (and possibly also TO).
>
> So let's teach window-text-pixel-size to be able to accept the FROM
> argument which says "N pixels above position POS".

I still don't believe that would be better than a separate primitive
(since it doesn't make sense to supply the width information to the
pixel scrolling code), and unfortunately I don't quite understand how
`window_text_pixel_size' works either: for instance, it seems to disable
the bidirectional reordering of text?  I also don't see why `it' is
saved into `it2' only to be restored before anything interesting is done
with `it'.

Correctly pixel-scrolling over bidirectional text will probably be a
very important feature for people working with RTL languages, but I'm
not sure how many of them are likely to use such a feature.

> That's not very efficient if PIX can be a large value.

Yes.  Maybe calling `move_it_vertically_backward' itself until a
suitable position is reached will be better, as I really don't want to
reinvent "move_it_vertically_backwards but slightly different".

Something like this:

  move_it_vertically_backward (&it, pix);

  while (-it.current_y < pix)
    {
      last_y = it.current_y;
      move_it_vertically_backward (&it, pix + it.current_y);

      if (it.current_y == last_y)
        break;
    }

Thanks.