libinput: Disable tap-and-drag

[Peter Hutterer]

On Sat, Jan 02, 2016 at 04:02:29AM +0000, Caibin Chen wrote:
> Hi,
> 
> I've been working on disabling tap-and-drag feature in libinput because I'm
> not used to it. The code is on my Github branch:
> https://github.com/tigersoldier/libinput/tree/wip/disable-tap-to-drag
> 
> The basic idea is adding a branch at STATE_TOUCHED + EVENT_RELEASE
> transition:
> 
>    STATE_TOUCHED
>          |
>          |
>    EVENT_RELEASE
>          |
>          |
>          v
> tap-and-drag enabled?  --- yes ---> (unchanged)
>          |
>          no
>          |
>          v
>     button press
>     button release
>          |
>          v
>     STATE_IDLE
> 
> Aside from disabling the feature, this reduces the tapping latency as well,
> because we don't have to wait for the timeout for STATE_IDLE to
> STATE_DRAGGING_OR_DOUBLE_TAP/STATE_IDLE transition.
> 
> What do you guys think? If this makes sense, I can work on the
> documentation and tests and send patches to the list.

thanks for doing this work. tbh, I'm not a big fan of having this as a
configuration option. IMO if you are using tapping as an interaction method
on the touchpad, having tap-and-drag available is the natural extension and
I don't see why we should disable it. Without it, a user would have to
physically click the touchpad and move with a second finger, despite
otherwise using tapping as the clicking interaction. That seems disjointed.
And while I can see that this is what some people do (I use tapping and
clicking interchangeable), I don't really want to provide/maintain/test
configuration options for this. sorry.

Cheers,
   Peter