bug#42406: Mouse-wheel scrolling can be flickering

[Alan Third]

On Thu, Jul 30, 2020 at 12:30:27PM +0200, Konrad Podczeck wrote:
> Having taken a closer look, it seems to me now that what I called 
> "flickering" is the following:
> 
> Mouse-wheel scroll downwards, so that the cursor becomes positioned
> at the top row of the frame. Then release the mouse-wheel, but so
> that inertia scrolling continues for a short time. After the
> scrolling comes to rest, which is probably determined by the window
> manager, there is an extra movement, governed probably by Emacs, to
> make sure that it is not the case that only, say, half of a row is
> visible at the top of the frame. It seems to me that it is this
> extra movement which leads to what I called "flickering."

I'm afraid I don't follow. The NS port doesn't let you scroll by part
of a line by default. Are you using pixel-scroll-mode or similar?

If I use pixel-scroll-mode I can see some flickering of the mode line
after scrolling has ceased (as you say, when it rolls back or forth to
show a whole line), but only in Emacs 27, Emacs 28 is fine.

> For how to enable/disable "inertia scrolling, see
> 
> https://support.apple.com/en-nz/guide/mac-help/unac899/mac

Thanks, strangely I don't see what they describe there... My Mac must
have something odd going on... :/
-- 
Alan Third