Re: move_it_vertically_backward question

[Eli Zaretskii]

> From: Po Lu <luangruo@yahoo.com>
> Cc: emacs-devel@gnu.org
> Date: Thu, 16 Dec 2021 21:34:40 +0800
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > What would such a primitive be used for, except for your specific use
> > case?
> 
> I can't think of any offhand, but I can't think of any other use case
> for the modification to the `from' parameter of `window-text-pixel-size'
> either.

The difference is that window-text-pixel-size already exists, we just
extend it for another use case.

> > Since ascent+descent are the line height, I don't understand why this
> > would be useful.
> 
> In this case, we don't want the line height of the line up to TO
> (because window start might be inside a line, such as in Info buffers
> and when there is a line-prefix property).

Well, then this is equivalent to telling window-text-pixel-size to
stop at the visual left edge of a screen line, right?  That is,
interpret TO not as a literal buffer position, but as the visual
beginning of the line which shows position TO.