Re: move_it_vertically_backward question

[Eli Zaretskii <eliz@gnu.org>]

> From: Po Lu <luangruo@yahoo.com>
> Cc: emacs-devel@gnu.org
> Date: Wed, 15 Dec 2021 18:28:50 +0800
> 
> Po Lu <luangruo@yahoo.com> writes:
> 
> > 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;
> >     }
> 
> BTW, if this will work, I'd like to install this primitive along with
> the modification to the precision scrolling code that makes use of it
> as-is, at least as a temporary solution to the performance issues until
> we can decide which primitive to move its functionality into.

I would like our primitives to be sufficiently general and generic to
justify their existence.  I'm not sure I understand what exactly would
you like to install, but the original code you posted is definitely
unfit for being a primitive (too specific to
pixel-scroll-precision-mode), and given the unfinished discussion of
whether window-text-pixel-size could do the job, I think it's very
probable that we are not yet ready to seriously talk about what should
be installed.

So I suggest to continue discussing window-text-pixel-size until we
understand completely your needs on the one hand, and what can be done
by extending window-text-pixel-size on the other hand.  Then we will
be able to make the decision.

Thanks.