Re: Scrolling commands and skipping redisplay, was: Re: emacs rendering comparisson between emacs23 and emacs26.3

[Eli Zaretskii]

> Cc: address@hidden, address@hidden, address@hidden, address@hidden,
>  address@hidden
> From: Dmitry Gutov <address@hidden>
> Date: Mon, 20 Apr 2020 21:29:07 +0300
> 
> On 20.04.2020 21:19, Eli Zaretskii wrote:
> > Btw, "line" in this context is actually the amount of pixels equal to
> > the canonical line height, not a physical line.  When the display
> > engine counts "lines" for the purpose of comparison with the value of
> > scroll-conservatively, it actually counts pixels and then divides that
> > by the canonical line height, it doesn't count screen lines.  So if
> > some lines in the buffer are displayed taller than the default face,
> > you will see a lot of recentering regardless of what you do.
> 
> I wonder if this was a result of some feature request.

No.  Scrolling-related variables always worked this way, since Emacs
21.  You will see the same with scroll-margin, for example.

> Sounds unnecessarily complex, IMHO.

If you think about this for a while, you will realize that it's the
only sane way of doing that, in an editor that is required to handle
lines which can contain anything: small and large characters, images,
you name it.  Any other way, and you will have a myriad of special
conditions and complex decisions.