Re: Touchscreen support

[Eli Zaretskii <eliz@gnu.org>]

> From: Po Lu <luangruo@yahoo.com>
> Cc: larsi@gnus.org,  monnier@iro.umontreal.ca,  emacs-devel@gnu.org
> Date: Sun, 19 Dec 2021 17:38:30 +0800
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > Which higher-level gestures did you intend to support?  The MS-Windows
> > classification has this list:
> >
> >   . zoom
> >   . pan
> 
> What about being able to change the selection by dragging (not holding
> and then dragging) left and right?  That has no equivalent on GTK.

How is that different from "pan"?

> I don't think GTK has a public API for the pan gesture either, even
> though it's clearly supported by the built-in widgets.

So maybe we will have to construct that from other gestures on those
platforms.

> However, I think your classification is an otherwise reasonable list of
> gestures to support; how about we use the code in Lisp for platforms
> where low level events are reported (such as PGTK and X-Windows), while
> directly sending the high-level events on platforms where those aren't
> available?

I'm not opposed to having parts of this in Lisp, but I do want to see
the events placed in the normal Emacs input queue, which probably
means that Lisp will be called from C.  Not sure if such design will
make sense in practice, though.  But OTOH, having events coming in
from another source, not through the input queue read by
read_socket_hook, is a complication I'd very much prefer to avoid (if
it's even feasible).