Subject: Re: bug#35389: 27.0.50; [PATCH] Emacs on macOS sets mouse-wheel variables directly

From: Alan Third <[email-masked]>
Date: Sun, 12 May 2019 00:06:59 +0100

On Sat, May 11, 2019 at 09:12:13AM +0300, Eli Zaretskii wrote:
> 
> Could there be some internal variable, either in Lisp or in C, which
> we then would use in the default value, as some unit, instead of just
> number of wheel turns and number of lines?  Then we could set that
> internal variable to different values, but keep the customization the
> same in those internally-defined units.  I think that would be
> somewhat cleaner, if possible and reasonable, because we'd be able to
> document the customization in these units in a platform-independent
> way.

The big issue is that both macOS and Emacs accelerate the scroll rate,
and that results in uncontrollable scroll rates.

Looking through previous discussions (link provided in another email
in this thread) it appears there’s an unfortunate trade‐off to be made
in how we handle scrolling acceleration varying between mousewheels
and trackpads on macOS.

The built‐in macOS acceleration feels natural on both, the Emacs
acceleration feels very slow on trackpads.

> If that's impractical, then I guess we'll have to live with this
> inconsistency, although I personally consider it a slippery slope.  At
> the very least it should be documented, in NEWS if not in the manual.

It was documented in NEWS for Emacs 26.

I don’t recall if it was added to the manual. A thorough review of the
macOS section of the manual is on my todo list for before Emacs 27 is
released.
-- 
Alan Third