Re: Touchscreen support

[Po Lu]

Eli Zaretskii <eliz@gnu.org> writes:

> If you do it in Lisp, it will be hard to use on other platforms, where
> the higher-level abstractions are reported on the level of the
> window-system events.

[...]

> I don't think so, although I'm far from being an expert.  I see it
> provides the gesture-begin and gesture-end events, but not
> gesture-update; instead, the "cooked" gestures are provided which are
> already constructed from lower-level events.  The MS documentation
> clearly says:
>
>   Note Most applications should ignore the GID_BEGIN and GID_END
>   messages and pass them to DefWindowProc. These messages are used by
>   the default gesture handler. Application behavior is undefined when
>   the GID_BEGIN and GID_END messages are consumed by a third-party
>   application.
>
> So they advise against using the low-level events.

> 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 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.