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 17:24:14 +0800
> 
> > In any case, it makes no sense to me to "decompose" events that are
> > already composed into meaningful gestures.  We should be able to use
> > those higher-level abstractions when they are provided.
> 
> The difference is that those higher-level abstractions vary too much for
> us to abstract around usefully.  (The GTK one is also very painful, for
> unrelated reasons.)  I think that's why Mozilla Firefox and other
> cross-platform programs that have to handle touch events rely on their
> own machinery for this stuff opposed to the platform-provided one.

We'd need to try to find some scheme that provides equivalence between
the different abstractions.  I don't understand how could it be too
hard, since the gestures are very similar, if not identical.

Which higher-level gestures did you intend to support?  The MS-Windows
classification has this list:

  . zoom
  . pan
  . rotate
  . two-finger tap
  . press and tap

Which other gestures did you have in mind?

> We would have to limit ourselves to only handling tap events and only
> sending them when the finger is lifted, if we were to rely on the lowest
> common denominator of all those different abstractions.

I see no reason to limit ourselves to the lowest common denominator.