bug#63187: 30.0.50; Tail of longer lines painted after end of nearby lines on macOS

[Aaron Jensen]

On Sun, Apr 30, 2023 at 11:26 AM Eli Zaretskii <eliz@gnu.org> wrote:
>
> > From: Aaron Jensen <aaronjensen@gmail.com>
> > Date: Sun, 30 Apr 2023 10:57:35 -0400
> > Cc: luangruo@yahoo.com, 63187@debbugs.gnu.org
> >
> > For what it's worth, disabling it has had no discernible impact on
> > scroll performance on my machine (which is an M1)
>
> scrolling_window is not about scrolling.  It's a redisplay
> optimization that attempts to speed up redrawing a window by scrolling
> on display the stuff already shown, when that is deemed less costly
> than redrawing every screen line that has changed.

Ah, so is it used (for example) when you insert a newline in part of a
buffer? How might I reproduce a usage of it both so I can benchmark
and play around with it when it is enabled to see if I can trigger the
bug I'm seeing?