Re: XInput 2 support

[Eli Zaretskii <eliz@gnu.org>]

> From: Po Lu <luangruo@yahoo.com>
> Date: Sat, 16 Oct 2021 13:37:13 +0800
> 
> I hacked up support for handling XInput 2 events, though it hasn't
> undergone any serious testing yet.

Thanks.  Would people who have this installed try the patch and report
what they see?

> So the only advantage of this code over the existing Core Input code as
> of present would be not relying on a fragile environment variable
> (GDK_CORE_DEVICE_EVENTS) to work properly in GTK 3 builds.  Call me
> paranoid, but this variable reeks of something that the GTK developers
> will remove at some point in the future.  (AFAIK, it's already been
> removed in GTK 4).

Who or what will promise us that XInput 2 will not be removed by those
same developers?

> However, it paves the way for future support of high-resolution
> scrollwheels, multi-touch trackpad support, and much more.
> 
> Would this support be worth installing?  Thanks.

Much of the code seems to be just a copy of the existing code in
xterm.c, just with different events.  Would it be possible to
preprocess XInput 2 events into X events, and then call the existing
code, instead of copy/paste-ing it?

Also, do these changes have any effect on user-visible behavior, or on
how users must set up their systems or how they use Emacs?  If so,
there should be suitable changes to the documentation.